Willi A. Kalender

Continuous computed tomographic (CT) scanning of organ volumes during a single breath hold was studied. The authors modified the table feed mechanism of a continuously rotating CT scanner to allow patient transport at low, but accurately controlled, speeds (0.1-11.0 mm/sec) during continuous 1-second scanning. An algorithm was designed to reconstruct artifact-free images for arbitrary table positions from the helical data by interpolating between adjacent scans. Section sensitivity profiles were enlarged; the section width for a 10-mm section and a speed of 10.0 mm/sec was increased by a factor of 1.3, compared with the nominal value. Clinical examples were presented for studies of lung nodules and studies enhanced with contrast medium. Major advantages are the possibility of continuous scanning of extended volumes within a breath-hold period and retrospective, arbitrary selection of anatomic levels.

Purpose To determine conversion factors for the new International Commission on Radiological Protection (ICRP) publication 103 recommendations for adult and pediatric patients and to compare the effective doses derived from Monte Carlo calculations with those derived from dose-length product (DLP) for different body regions and computed tomographic (CT) scanning protocols. Materials and Methods Effective dose values for the Oak Ridge National Laboratory phantom series, including phantoms for newborns; 1-, 5-, and 10-year-old children; and adults were determined by using Monte Carlo methods for a 64-section multidetector CT scanner. For each phantom, five anatomic regions (head, neck, chest, abdomen, and pelvis) were considered. Monte Carlo simulations were performed for spiral scanning protocols with different voltages. Effective dose was computed by using ICRP publication 60 and publication 103 recommendations. The calculated effective doses were compared with those derived from the DLP by using previously published conversion factors. Results In general, conversion factors determined on the basis of Monte Carlo calculations led to lower values for adults with both ICRP publications. Values up to 33% and 32% lower than previously published data were found for ICRP publication 60 and ICRP publication 103, respectively. For pediatric individuals, effective doses based on the Monte Carlo calculations were higher than those obtained from DLP and previously published conversion factors (eg, for chest CT scanning in 5-year-old children, an increase of about 76% would be expected). For children, a variation in conversion factors of up to 15% was observed when the tube voltage was varied. For adult individuals, no dependence on voltage was observed. Conclusion Conversion factors from DLP to effective dose should be specified separately for both sexes and should reflect the new ICRP recommendations. For pediatric patients, new conversion factors specific for the spectrum used should be established. © RSNA, 2010 Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100047/-/DC1

Multislice spiral computed tomography (MSCT) with retrospectively ECG-gated image reconstruction permits coronary artery visualization. We investigated the method's ability to identify high-grade coronary artery stenoses and occlusions.A total of 64 consecutive patients were studied by MSCT (4x1 mm cross-sections, 500-ms rotation, table feed 1.5 mm/rotation, intravenous contrast agent, retrospectively ECG-gated image reconstruction). All coronary arteries and side branches with a luminal diameter >/=2.0 mm were assessed concerning evaluability and the presence of high-grade stenoses (>70% diameter stenosis) or occlusions. Results were compared with quantitative coronary angiography. Of 256 coronary arteries (left main, left anterior descending, left circumflex and right coronary artery, including their respective side branches), 174 could be evaluated (68%). In 19 patients (30%), all arteries were evaluable. Artifacts caused by coronary motion were the most frequent reason for unevaluable arteries. Overall, 32 of 58 high-grade stenoses and occlusions were detected by MSCT (58%). In evaluable arteries, 32 of 35 lesions were detected, and the absence of stenosis was correctly identified in 117 of 139 arteries (sensitivity, 91%; specificity, 84%). If analysis was extended to all stenoses with >50% diameter reduction, sensitivity was 85% (40 of 47) and specificity was 76% (96 of 127).MSCT with retrospective ECG gating permits the detection of coronary artery stenoses with high accuracy if image quality is sufficient, but its clinical use may presently be limited due to degraded image quality in a substantial number of cases, mainly due to rapid coronary motion.

Iterative reconstruction (IR) methods have recently re-emerged in transmission x-ray computed tomography (CT). They were successfully used in the early years of CT, but given up when the amount of measured data increased because of the higher computational demands of IR compared to analytical methods. The availability of large computational capacities in normal workstations and the ongoing efforts towards lower doses in CT have changed the situation; IR has become a hot topic for all major vendors of clinical CT systems in the past 5 years. This review strives to provide information on IR methods and aims at interested physicists and physicians already active in the field of CT. We give an overview on the terminology used and an introduction to the most important algorithmic concepts including references for further reading. As a practical example, details on a model-based iterative reconstruction algorithm implemented on a modern graphics adapter (GPU) are presented, followed by application examples for several dedicated CT scanners in order to demonstrate the performance and potential of iterative reconstruction methods. Finally, some general thoughts regarding the advantages and disadvantages of IR methods as well as open points for research in this field are discussed.

A technique to reduce metallic implant artifacts on computed tomography scans is presented. The implant boundaries are determined semiautomatically; the missing projection data are replaced by linear interpolation. The complete procedure requires 1-2 minutes per scan. Images with greatly improved quality were obtained in the presence of surgical clips and pelvic implants; success is limited in highly structured regions, such as the facial skull.

X-ray computed tomography (CT), introduced into clinical practice in 1972, was the first of the modern slice-imaging modalities. To reconstruct images mathematically from measured data and to display and to archive them in digital form was a novelty then and is commonplace today. CT has shown a steady upward trend with respect to technology, performance and clinical use independent of predictions and expert assessments which forecast in the 1980s that it would be completely replaced by magnetic resonance imaging. CT not only survived but exhibited a true renaissance due to the introduction of spiral scanning which meant the transition from slice-by-slice imaging to true volume imaging. Complemented by the introduction of array detector technology in the 1990s, CT today allows imaging of whole organs or the whole body in 5 to 20 s with sub-millimetre isotropic resolution. This review of CT will proceed in chronological order focussing on technology, image quality and clinical applications. In its final part it will also briefly allude to novel uses of CT such as dual-source CT, C-arm flat-panel-detector CT and micro-CT. At present CT possibly exhibits a higher innovation rate than ever before. In consequence the topical and most recent developments will receive the greatest attention.

Background —We investigated the applicability and image quality of contrast-enhanced coronary artery visualization by multislice spiral CT using retrospective ECG gating. Methods and Results —Twenty-five patients in sinus rhythm (significant coronary artery stenoses ruled out by invasive angiography) were studied with a multislice spiral CT (Siemens SOMATOM Volume Zoom). In inspiration (mean breathhold, 37 seconds), a volume data set of the heart was acquired (intravenous contrast agent; 4×1-mm slice thickness; 500-ms rotation; table feed, 1.5 mm/360°). Simultaneous recording of the ECG permitted retrospective reconstruction of contiguous cross sections in intervals of 1 mm at any desired interval of the cardiac cycle. The mean duration of the image reconstruction window was 185 ms. Next to 3-dimensional reconstructions of the heart and coronary arteries, multiplanar reconstructions were rendered to determine the visualized length of the coronary arteries, the contrast-to-noise ratio, and the correlation of coronary artery diameters to quantitative coronary angiography. Conclusions —The coronary arteries could be visualized over long segments (left main, 9±4 mm; left anterior descending, 112±34 mm; left circumflex, 80±29 mm; right coronary artery, 116±33 mm). On average, 78±16% of these distances were visualized free of motion artifacts. The mean contrast-to-noise ratio was 9.3±3.3. Coronary artery diameters in multislice spiral CT showed close correlation to quantitative coronary angiography (CT, 3.3±1.0 mm; angiography, 3.2±0.9 mm; mean difference, 0.38 mm; r =0.86). Contrast-enhanced multislice spiral CT permits visualization of the coronary artery lumen. Further studies are necessary to determine whether image quality is sufficient to reliably detect coronary artery stenoses.

We report the evaluation of a prototype dual‐energy implementation using rapid kVp switching on a clinical computed tomographic scanner. The method employs prereconstruction basis material decomposition of the dual‐energy projection data. Each dual‐energy scan can be processed into conventional single‐kVp images, basis material density images, and monoenergetic images. Phantom studies were carried out to qualitatively and quantitatively evaluate and validate the approach.

System concepts System components Image reconstruction Spiral CT Multi-slice spiral CT Cone-beam CT Dynamic CT Quantitative CT Dual source CT Dual energy CT Flat detector CT Micro CT Image quality Spatial resolution Contrast Pixel noise Homogeneity Routine and special applications 3D displays Post-processing Quality assurance

Multi-detector computed tomography (CT) scanners, by virtue of their high temporal and spatial resolution, permit imaging of the coronary arteries. However, motion artifacts, especially in patients with higher heart rates, can impair image quality. We thus evaluated the performance of a new dual-source CT (DSCT) with a heart rate independent temporal resolution of 83 ms for the visualization of the coronary arteries in 14 consecutive patients.Fourteen patients (mean age 61 years, mean heart rate 71 min(-1)) were studied by DSCT. The system combines two arrays of an X-ray tube plus detector (64 slices) mounted on a single gantry at an angle of 90 degrees With a rotation speed of 330 ms, a temporal resolution of 83 ms (one-quarter rotation) can be achieved independent of heart rate. For data acquisition, intraveous contrast agent was injected at a rate of 5 ml/s. Images were reconstructed with 0.75 slice thickness and 0.5 mm increment. The data sets were evaluated concerning visibility of the coronary arteries and occurrence of motion artifact.Visualization of the coronary arteries was successful in all patients. Most frequently, image reconstruction at 70% of the cardiac cycle provided for optimal image quality (50% of patients). Of a total of 226 coronary artery segments, 222 (98%) were visualized free of motion artifact. In summary, DSCT constitutes a promising new concept for cardiac CT. High and heart rate independent temporal resolution permits imaging of the coronary arteries without motion artifacts in a substantially increased number of patients as compared to earlier scanner generations. Larger and appropriately designed studies will need to determine the method's accuracy for detection of coronary artery stenoses.

Purpose: To develop a consensus standard for quantification of coronary artery calcium (CAC). Materials and Methods: A standard for CAC quantification was developed by a multi-institutional, multimanufacturer international consortium of cardiac radiologists, medical physicists, and industry representatives. This report specifically describes the standardization of scan acquisition and reconstruction parameters, the use of patient size–specific tube current values to achieve a prescribed image noise, and the use of the calcium mass score to eliminate scanner- and patient size–based variations. An anthropomorphic phantom containing calibration inserts and additional phantom rings were used to simulate small, medium-size, and large patients. The three phantoms were scanned by using the recommended protocols for various computed tomography (CT) systems to determine the calibration factors that relate measured CT numbers to calcium hydroxyapatite density and to determine the tube current values that yield comparable noise values. Calculation of the calcium mass score was standardized, and the variance in Agatston, volume, and mass scores was compared among CT systems. Results: Use of the recommended scanning parameters resulted in similar noise for small, medium-size, and large phantoms with all multi–detector row CT scanners. Volume scores had greater interscanner variance than did Agatston and calcium mass scores. Use of a fixed calcium hydroxyapatite density threshold (100 mg/cm3), as compared with use of a fixed CT number threshold (130 HU), reduced interscanner variability in Agatston and calcium mass scores. With use of a density segmentation threshold, the calcium mass score had the smallest variance as a function of patient size. Conclusion: Standardized quantification of CAC yielded comparable image noise, spatial resolution, and mass scores among different patient sizes and different CT systems and facilitated reduced radiation dose for small and medium-size patients. © RSNA, 2007

Flat-panel detectors or, synonymously, flat detectors (FDs) have been developed for use in radiography and fluoroscopy with the defined goal to replace standard X-ray film, film-screen combinations and image intensifiers by an advanced sensor system. FD technology in comparison to X-ray film and image intensifiers offers higher dynamic range, dose reduction, fast digital readout and the possibility for dynamic acquisitions of image series, yet keeping to a compact design. It appeared logical to employ FD designs also for computed tomography (CT) imaging. Respective efforts date back a few years only, but FD-CT has meanwhile become widely accepted for interventional and intra-operative imaging using C-arm systems. FD-CT provides a very efficient way of combining two-dimensional (2D) radiographic or fluoroscopic and 3D CT imaging. In addition, FD technology made its way into a number of dedicated CT scanner developments, such as scanners for the maxillo-facial region or for micro-CT applications. This review focuses on technical and performance issues of FD technology and its full range of applications for CT imaging. A comparison with standard clinical CT is of primary interest. It reveals that FD-CT provides higher spatial resolution, but encompasses a number of disadvantages, such as lower dose efficiency, smaller field of view and lower temporal resolution. FD-CT is not aimed at challenging standard clinical CT as regards to the typical diagnostic examinations; but it has already proven unique for a number of dedicated CT applications, offering distinct practical advantages, above all the availability of immediate CT imaging in the interventional suite or the operating room.

This Special Report presents the consensus of the Summit on Management of Radiation Dose in Computed Tomography (CT) (held in February 2011), which brought together participants from academia, clinical practice, industry, and regulatory and funding agencies to identify the steps required to reduce the effective dose from routine CT examinations to less than 1 mSv. The most promising technologies and methods discussed at the summit include innovations and developments in x-ray sources; detectors; and image reconstruction, noise reduction, and postprocessing algorithms. Access to raw projection data and standard data sets for algorithm validation and optimization is a clear need, as is the need for new, clinically relevant metrics of image quality and diagnostic performance. Current commercially available techniques such as automatic exposure control, optimization of tube potential, beam-shaping filters, and dynamic z-axis collimators are important, and education to successfully implement these methods routinely is critically needed. Other methods that are just becoming widely available, such as iterative reconstruction, noise reduction, and postprocessing algorithms, will also have an important role. Together, these existing techniques can reduce dose by a factor of two to four. Technical advances that show considerable promise for additional dose reduction but are several years or more from commercial availability include compressed sensing, volume of interest and interior tomography techniques, and photon-counting detectors. This report offers a strategic roadmap for the CT user and research and manufacturer communities toward routinely achieving effective doses of less than 1 mSv, which is well below the average annual dose from naturally occurring sources of radiation.

Radiation dose in x-ray computed tomography (CT) has become a topic of high interest due to the increasing numbers of CT examinations performed worldwide. This review aims to present an overview of current concepts for both scanner output metrics and for patient dosimetry and will comment on their strengths and weaknesses. Controversial issues such as the appropriateness of the CT dose index (CTDI) are discussed in detail. A review of approaches to patient dose assessment presently in practice, of the dose levels encountered and options for further dose optimization are also given and discussed. Patient dose assessment remains a topic for further improvement and for international consensus. All approaches presently in use are based on Monte Carlo (MC) simulations. Estimates for effective dose are established, but they are crude and not patient-specific; organ dose estimates are rarely available. Patient- and organ-specific dose estimates can be provided with adequate accuracy and independent of CTDI phantom measurements by fast MC simulations. Such information, in particular on 3D dose distributions, is important and helpful in optimization efforts. Dose optimization has been performed very successfully in recent years and even resulted in applications with effective dose values of below 1 mSv. In general, a trend towards lower dose values based on technical innovations has to be acknowledged. Effective dose values are down to clearly below 10 mSv on average, and there are a number of applications such as cardiac and pediatric CT which are performed routinely below 1 mSv on modern equipment.

Theoretical considerations and simulation studies have led to the expectation that patient dose in CT (computed tomography) can be reduced significantly without a concomitant loss in image quality if tube current is modulated according to rotation angle-dependent x-ray attenuation. In this study, the simulation results presented in Part I were validated with phantoms. We used one cylindrical, two oval, and one elliptical phantom, available both as mathematical descriptions and in physical form, to mimic different parts of the human anatomy. Prototype hardware was available to control tube current on a commercial clinical CT scanner. The potential for dose reduction was evaluated for sinusoidal and attenuation-based current modulation for variable modulation amplitudes. Agreement between simulations and measured results was better than within 10%. Dose reduction values of 8%-56% were found depending on the phantom geometry and tube current modulation function. Attenuation-based tube current modulation consistently yielded higher reduction than fixed-shape sinusoidal modulation functions. For the shoulder phantom and 70% modulation amplitude, 44.6% dose reduction was measured as compared to 34.1% for sinusoidal modulation. A maximum of 56% was measured for the shoulder phantom including inserts. Specifying mAs reduction as an estimate for dose reduction proved to be a valid and conservative estimate; measured dose is reduced more strongly than the total mAs product both centrally and on average. First patient studies confirm the results of simulation and phantom studies. We conclude that attenuation-based online tube current control has great potential for reducing patient dose in CT and that it should be made generally available for clinical use.

Spiral computed tomography (CT) offers continuous volume scanning of complete organs or body sections within a single breath hold. Almost all image quality characteristics of spiral CT are identical to those of conventional section-by-section CT; however, there is a change in pixel noise values and degradation in the shape of the section sensitivity profiles (SSPs). Computer simulations, phantom measurements, and clinical studies were used in evaluating the SSP and noise characteristics of two new section-interpolation algorithms. The results were compared with standard CT and spiral CT data processed with the commonly employed linear section-interpolation algorithm. Degradation of SSP quality was insignificant for a table feed distance per 360 degrees revolution equal to the section thickness when the new algorithms were applied; noise values, however, increased. SSP width increased for table feed distances greater than the section width, the effect being less pronounced with the new algorithms. The value of these algorithms is primarily seen in the improved quality of multiplanar reformations and cine and three-dimensional displays.

Noninvasive Visualization of Coronary Arteries Using Contrast-Enhanced Multidetector CT: Influence of Heart Rate on Image Quality and Stenosis DetectionTom Giesler1, Ulrich Baum2, Dieter Ropers1, Stefan Ulzheimer3, Evelyn Wenkel2, Maria Mennicke1, Werner Bautz2, Willi A. Kalender3, Werner G. Daniel1 and Stephan Achenbach1Audio Available | Share

Tube current modulation governed by x-ray attenuation during CT (computed tomography) acquisition can lead to noise reduction which in turn can be used to achieve patient dose reduction without loss in image quality. The potential of this technique was investigated in simulation studies calculating both noise amplitude levels and noise distribution in CT images. The dependence of noise on the inodulation function, amplitude of modulation, shape and size of the object, and possible phase shift between attenuation and modulation function were examined. Both sinusoidal and attenuation-based control functions were used to modulate tube current. Noise reduction was calculated for both ideal systems and for real systems with limited modulation amplitude. Dose reductions up to 50% can be achieved depending on the phantom geometry and tube current modulation function. Attenuation-based tube current modulation yields substantially higher reduction than fixed-shape modulation functions. Optimal results are obtained when the current is modulated as a function of the square root of attenuation. A modulation amplitude of at least 90% should be available to exploit the potential of these techniques.

In modern computed tomography (CT) there is a strong desire to reduce patient dose and/or to improve image quality by increasing spatial resolution and decreasing image noise. These are conflicting demands since increasing resolution at a constant noise level or decreasing noise at a constant resolution level implies a higher demand on x-ray power and an increase of patient dose. X-ray tube power is limited due to technical reasons. We therefore developed a generalized multi-dimensional adaptive filtering approach that applies nonlinear filters in up to three dimensions in the raw data domain. This new method differs from approaches in the literature since our nonlinear filters are applied not only in the detector row direction but also in the view and in the z-direction. This true three-dimensional filtering improves the quantum statistics of a measured projection value proportional to the third power of the filter size. Resolution tradeoffs are shared among these three dimensions and thus are considerably smaller as compared to one-dimensional smoothing approaches. Patient data of spiral and sequential single- and multi-slice CT scans as well as simulated spiral cone-beam data were processed to evaluate these new approaches. Image quality was assessed by evaluation of difference images, by measuring the image noise and the noise reduction, and by calculating the image resolution using point spread functions. The use of generalized adaptive filters helps to reduce image noise or, alternatively, patient dose. Image noise structures, typically along the direction of the highest attenuation, are effectively reduced. Noise reduction values of typically 30%-60% can be achieved in noncylindrical body regions like the shoulder. The loss in image resolution remains below 5% for all cases. In addition, the new method has a great potential to reduce metal artifacts, e.g., in the hip region.

Using medical models built with Rapid Prototyping (RP) technologies represents a new approach for surgical planning and simulation. These techniques allow one to reproduce anatomical objects as 3D physical models, which give the surgeon a realistic impression of complex structures before a surgical intervention. The shift from the visual to the visual-tactile representation of anatomical objects introduces a new kind of interaction called ‘touch to comprehend’. As can be seen, from the presented case studies of maxillo-cranio-facial surgery, the RP models are very well suited for use in the diagnosis and the precise preoperative simulation of skeleton modifying interventions.

We developed a highly automated three-dimensionally based method for the segmentation of bone in volumetric computed tomography (CT) datasets. The multistep approach starts with three-dimensional (3-D) region-growing using local adaptive thresholds followed by procedures to correct for remaining boundary discontinuities and a subsequent anatomically oriented boundary adjustment using local values of cortical bone density. We describe the details of our approach and show applications in the proximal femur, the knee, and the skull. The accuracy of the determination of geometrical parameters was analyzed using CT scans of the semi-anthropomorphic European spine phantom. Depending on the settings of the segmentation parameters cortical thickness could be determined with an accuracy corresponding to the side length of 1 to 2.5 voxels. The impact of noise on the segmentation was investigated by artificially adding noise to the CT data. An increase in noise by factors of two and five changed cortical thickness corresponding to the side length of one voxel. Intraoperator and interoperator precision was analyzed by repeated analysis of nine pelvic CT scans. Precision errors were smaller than 1% for trabecular and total volumes and smaller than 2% for cortical thickness. Intraoperator and interoperator precision errors were not significantly different. Our segmentation approach shows: 1) high accuracy and precision and is 2) robust to noise, 3) insensitive to user-defined thresholds, 4) highly automated and fast, and 5) easy to initialize.

We evaluated the influence of heart rate on image quality and diagnostic accuracy of dual-source computed tomography (DSCT) coronary angiography.Multidetector computed tomography (MDCT) coronary angiography has demonstrated an inverse relationship between heart rate and image quality. Dual-source CT provides a higher temporal resolution.One hundred patients were studied by DSCT (DEFINITION, Siemens Medical Solutions, Forchheim, Germany). A contrast-enhanced volume dataset was acquired (two tubes, 120 kV, 400 mAs/rot, collimation 64 x 0.6 mm). Datasets were evaluated concerning the presence of significant coronary stenoses and validated against invasive coronary angiography.In 44 patients with a heart rate > or =65 beats/min, 566 of 616 coronary segments were evaluable (92%), whereas in 56 patients with a heart rate <65 beats/min, 777 of 778 coronary segments were evaluable (100%, p < 0.001). On a per-patient basis, 93% of patients (> or =65 beats/min) and 100% of patients (<65 beats/min) were considered evaluable. By classifying unevaluable segments as positive for stenosis, per-patient sensitivity was 95% (19 of 20) for heart rates > or =65 beats/min and 100% (22 of 22) for heart rates <65 beats/min. Specificity was 87% (21 of 24) versus 76% (26 of 34), and overall diagnostic accuracy was 91% (40 of 44) versus 86% (48 of 56). None of these differences were statistically significant. Similarly, no difference in diagnostic accuracy was found in per-vessel and -segment analyses.In 100 patients studied without beta-blocker pre-medication, DSCT demonstrated slightly lower per-segment evaluability for high heart rates but no decrease in diagnostic accuracy for the detection of coronary artery stenoses.

The lack of standardization in bone mineral measurements of the lumbar spine and other skeletal sites is generally recognized as an important and unresolved issue. We report and discuss efforts at standardization and cross-calibration of DXA and QCT equipment. We have designed and tested a geometrically defined, semi-anthropomorphic phantom, the European Spine Phantom (ESP). It contains a spine insert consisting of three vertebrae of increasing bone mineral densities and thicknesses of cortical structures; the respective parameters are given in tabular form for the final phantom design. Results for cross-calibration with the ESP compare well with patient results. Measurements on the first 30 phantoms confirmed that the ESP can be manufactured with a variation of about 1%. We conclude that the ESP is suitable for daily quality assurance, cross-calibration of instruments and universal standardization. The ESP was used to establish standardized BMD (sBMD) units for DXA equipment going into effect in late 1995. Its acceptance by manufacturers as a calibration standard for DXA and QCT measurements appears imminent.

Background: Growing evidence indicates that physical exercise can prevent at least some of the negative effects on health associated with early menopause.Here we determine the effects of intense exercise on physical fitness, bone mineral density (BMD), back pain, and blood lipids in early postmenopausal women. Methods:The study population comprised 50 fully compliant women, with no medication or illness affecting bone metabolism, who exercised over 26 months (exercise group [EG]), and 33 women who served as a nontraining control group (CG).Two group training sessions per week and 2 home training sessions per week were performed in the EG.Both groups were individually supplemented with calcium and cholecalciferol.Physical fitness was determined by maximum strength and cardiovascular performance.Bone mineral density was measured at the lumbar spine (dual-energy x-ray absorptiometry [DXA] and quantitative computed tomography [QCT]), the proximal femur (DXA), and the forearm (DXA).In serum samples taken from a subset of the study participants, we determined bone formation (serum osteocalcin) and resorption (serum cross-links) mark-ers as well as blood lipid levels.Vasomotor symptoms related to menopause and pain were also assessed.Results: After 26 months, significant exercise effects determined as percentage changes compared with baseline were observed for physical fitness (isometric strength: trunk extensors [EG +36.5% vs CG +1.7%], trunk flexors [EG +39.3% vs CG -0.4%], and maximum oxygen consumption [EG +12.4% vs CG -2.3%]); BMD (lumbar spine [DXA L1-L4, EG +0.7% vs CG -2.3%], QCT L1-L3 trabecular region of interest [EG +0.4% vs CG -6.6%], QCT L1-L3 cortical region of interest [EG +3.1% vs CG -1.7%], and total hip [DXA, EG -0.3% vs CG -1.7%]); serum levels (total cholesterol [EG -5.0% vs CG +4.1%] and triglycerides [EG -14.2% vs CG +23.2%]); and pain indexes at the spine. Conclusion:General purpose exercise programs with special emphasis on bone density can significantly improve strength and endurance and reduce bone loss, back pain, and lipid levels in osteopenic women in their critical early postmenopausal years.

CT scanning in spiral geometry is achieved by continuously transporting the patient through the gantry in synchrony with continuous data acquisition over a multitude of 360-deg scans. Data for reconstruction of images in planar geometry are estimated from the spiral data by interpolation. The influence of spiral scanning on image quality is investigated. Most of the standard physical performance parameters, e.g., spatial resolution, image uniformity, and contrast, are not affected; results differ for pixel noise and slice sensitivity profiles. For linear interpolation, pixel noise is expected to be reduced by a factor of 0.82; reduction factors of 0.81 to 0.83 were measured. Slice sensitivity profiles are changed as a function of table feed d, measured in millimeters per 360-deg scan; they are smoothed as the original profile is convolved with the object motion function. The motion function is derived for linear interpolation that constitutes a triangle with a base line width of 2d and a maximal height equal to 1/d. Calculations of both the full width at half-maximum and the shape of the profiles were in good agreement with experimental results. The effect of the widened profiles, in particular of their extended tail ends, on image quality is demonstrated in phantom measurements.

Subsecond spiral computed tomography (CT) offers great potential for improving heart imaging. The new multi-row detector technology adds significantly to this potential. We therefore developed and validated dedicated cardiac reconstruction algorithms for imaging the heart with subsecond multi-slice spiral CT utilizing electrocardiogram (ECG) information. The single-slice cardiac z-interpolation algorithms 180 degrees CI and 180 degrees CD [Med. Phys. 25, 2417-2431 (1998)] were generalized to allow imaging of the heart for M-slice scanners. Two classes of algorithms were investigated: 180 degrees MCD (multi-slice cardio delta), a partial scan reconstruction of 180 degrees + delta data with a < phi (fan angle) resulting in effective scan times of 250 ms (central ray) when a 0.5 s rotation mode is available, and 180 degrees MCI (multi-slice cardio interpolation), a piecewise weighted interpolation between successive spiral data segments belonging to the same heart phase, potentially providing a relative temporal resolution of 12.5% of the heart cycle when a four-slice scanner is used and the table increment is chosen to be greater than or equal to the collimated slice thickness. Data segments are selected by correlation with the simultaneously recorded ECG signal. Theoretical studies, computer simulations, as well as patient measurements were carried out for a multi-slice scanner providing M = 4 slices to evaluate these new approaches and determine the optimal scan protocol. Both algorithms, 180 degrees MCD and 180 degrees MCI, provide significant improvements in image quality, including extremely arythmic cases. Artifacts in the reconstructed images as well as in 3D displays such as multiplanar reformations were largely reduced as compared to the standard z-interpolation algorithm 180 degrees MLI (multi-slice linear interpolation). Image quality appears adequate for precise calcium scoring and CT angiography of the coronary arteries with conventional subsecond multislice spiral CT. It turned out that for heart rates fH > or = 70 min(-1) the partial scan approach 180 degrees MCD yields unsatisfactory results as compared to 180 degrees MCI. Our theoretical considerations show that a freely selectable scanner rotation time chosen as a function of the patient's heart rate, would further improve the relative temporal resolution and thus further reduce motion artifacts. In our case an additional 0.6 s mode besides the available 0.5 s mode would be very helpful. Moreover, if technically feasible, lower rotation times such as 0.3 s or even less would result in improved image quality. The use of multi-slice techniques for cardiac CT together with the new z-interpolation methods improves the quality of heart imaging significantly. The high temporal resolution of 180 degrees MCI is adequate for spatial and temporal tracking of anatomic structures of the heart (4D reconstruction).

In this study we analysed the accuracy of computed tomography (CT) measurements in assessing cortical bone. We determined the dependency of thickness and density measurements on the true width and density of the cortex and on the spatial resolution in the CT images using two optimized segmentation methods. As a secondary goal, we assessed the ability of CT to reflect small changes in cortical thickness.

Subsecond computed tomography (CT) scanning offers potential for improved heart imaging. We therefore developed and validated dedicated reconstruction algorithms for imaging the heart with subsecond spiral CT utilizing electrocardiogram (ECG) information. We modified spiral CT z ‐interpolation algorithms on a subsecond spiral CT scanner. Two new classes of algorithms were investigated: (a) 180°CI (cardio interpolation), a piecewise linear interpolation between adjacent spiral data segments belonging to the same heart phase where segments are selected by correlation with the simultaneously recorded ECG signal and (b) 180°CD (cardio delta), a partial scan reconstruction of with angle, resulting in reduced effective scan times of less than 0.5 s. Computer simulations as well as processing of clinical data collected with 0.75 s scan time were carried out to evaluate these new approaches. Both 180°CI and 180°CD provided significant improvements in image quality. Motion artifacts in the reconstructed images were largely reduced as compared to standard spiral reconstructions; in particular, coronary calcifications were delineated more sharply and multiplanar reformations showed improved contiguity. However, new artifacts in the image plane are introduced, mostly due to the combination of different data segments. ECG‐oriented image reconstructions improve the quality of heart imaging with spiral CT significantly. Image quality and the display of coronary calcification appear adequate to assess coronary calcium measurements with conventional subsecond spiral CT.

In the assessment of vertebral bone mineral density (BMD) with quantitative computed tomography, accuracy is limited by systematic errors caused by beam-hardening effects and unknown marrow and fat concentrations in trabecular bone. Reproducibility depends on precise repositioning of the patient, selection of the region of interest (ROI), and apparatus stability. In an integrated approach, these error sources were taken into account. Dual-energy methods are incorporated and tested to avoid systematic errors. Contour-detection algorithms for automated ROI determination that work reliably and offer improved reproducibility and efficiency are presented. A new design of reference phantom with solid tissue-equivalent materials provides calibration in BMD units and checks apparatus stability. Dual-energy methods are necessary to achieve accuracy of 5% or better. Automated ROI definition and reference phantom methods are mandatory for reproducibility of 2% or better.

Although x‐ray computed tomography (CT) has been in clinical use for over 3 decades, spectral optimization has not been a topic of great concern; high voltages around 120 kV have been in use since the beginning of CT. It is the purpose of this study to analyze, in a rigorous manner, the energies at which the patient dose necessary to provide a given contrast‐to‐noise ratio (CNR) for various diagnostic tasks can be minimized. The authors used cylindrical water phantoms and quasianthropomorphic phantoms of the thorax and the abdomen with inserts of 13 mm diameter mimicking soft tissue, bone, and iodine for simulations and measurements. To provide clearly defined contrasts, these inserts were made of solid water with a 1% difference in density (DD) to represent an energy‐independent soft‐tissue contrast of 10 Hounsfield units (HU), calcium hydroxyapatite (Ca) representing bone, and iodine (I) representing the typical contrast medium. To evaluate CT of the thorax, an adult thorax phantom plus extension rings up to a size of to mimic different patient cross sections were used. For CT of the abdomen, we used a phantom of and an extension ring of . The CT scanner that the authors used was a SOMATOM Definition (Siemens Healthcare, Forchheim, Germany) at 80, 100, 120, and 140 kV. Further voltage settings of 60, 75, 90, and 105 kV were available in an experimental mode. The authors determined contrast for the density difference, calcium, and iodine, and noise and 3D dose distributions for the available voltages by measurements. Additional voltage values and monoenergetic sources were evaluated by simulations. The dose‐weighted contrast‐to‐noise ratio (CNRD) was used as the parameter for optimization. Simulations and measurements were in good agreement with respect to absolute values and trends regarding the dependence on energy for the parameters investigated. For soft‐tissue imaging, the standard settings of 120–140 kV were found as adequate choices with optimal values increasing for larger cross sections, e.g., for large abdomens voltages higher than 140 kV may be indicated. For bone and iodine imaging the optimum values were generally found at significantly lower voltages of typically below 80 kV. This offers a potential for dose reduction of up to 50%, but demands significantly higher power values in most cases. The authors concluded that voltage settings in CT should be varied more often than is common in practice today and should be chosen not only according to patient size but also according to the substance imaged in order to minimize dose while not compromising image quality. A reduction from 120 to 80 kV, for example, would yield a reduction in patient dose by more than half for coronary CT angiography. The use of lower voltages has to be recommended for contrast medium studies in cardiac and pediatric CT.

A new approach to reproducible measurement of lung attenuation and structure by means of respiratory-gated computed tomography (CT) was developed. The patient breathes through a microcomputer-controlled pocket spirometer during the complete CT examination, starting with a measurement of the vital capacity. At a user-selected respiratory level, the CT scan is triggered and air flow is inhibited mechanically. To exclude operator-related reproducibility errors, evaluation is based on semiautomated algorithms that isolate lung parenchyma by fast contour tracing. In a study on one volunteer, measurement of lung attenuation changed by a factor of about 2.6 (-895 to -730 HU) as a function of inspirational status. Reproducibility on the order of 5% or better can be achieved only with tight spirometric control of respiration.

X-ray coronary angiography, the reference standard for investigation of coronary artery bypass grafts, is an invasive and costly procedure that is not risk free. The development of rapid and reliable noninvasive imaging procedures would therefore be desirable. Evaluation of coronary bypass patients with computed tomography (CT) was first reported in 1980.1 In the following years, a number of studies described the application of conventional CT and electron beam tomography for investigation of bypass grafts.2–10 However, due to cardiac and respiration artifacts, conventional CT was restricted to assessment of bypass graft patency and the detection of stenoses in patent bypass grafts was not considered possible. Electron beam tomography is not widely available. Recently, contrast-enhanced multislice spiral CT (MSCT) with retrospective electrocardiographic gating has been shown to permit visualization of the coronary artery lumen.11,12 We therefore performed a prospective comparison of MSCT to invasive coronary angiography in a group of 65 patients after coronary artery bypass surgery to evaluate the method's accuracy to detect bypass graft occlusion and stenosis.

Dual-energy material density images obtained by prereconstruction-basis material decomposition techniques offer specific tissue information, but they exhibit relatively high pixel noise. It is shown that noise in the material density images is negatively correlated and that this can be exploited for noise reduction in the two-basis material density images. The algorithm minimizes noise-related differences between pixels and their local mean values, with the constraint that monoenergetic CT values, which can be calculated from the density images, remain unchanged. Applied to the material density images, a noise reduction by factors of 2 to 5 is achieved. While quantitative results for regions of interest remain unchanged, edge effects can occur in the processed images. To suppress these, locally adaptive algorithms are presented and discussed. Results are documented by both phantom measurements and clinical examples.

In a controlled patient study we investigated the potential of attenuation-based on-line modulation of the tube current to reduce milliampere values (mAs) in CT examinations of children without loss of image quality. mAs can be reduced for non-circular patient cross sections without an increase in noise if tube current is reduced at those angular positions where the patient diameter and, consequently, attenuation are small. We investigated a technical approach with an attenuation-based on-line control for the tube current realised as a work-in-progress implementation. The CT projection data are analysed in real time to determine optimal mAs values for each projection angle. We evaluated mAs reduction for 100 spiral CT examinations with attenuation-based on-line modulation of the tube current in a group of children. Two radiologists evaluated image quality by visual interpretation in consensus. We compared the mAs values read from the CT scanner with preset mAs of a standard protocol. Four different scan regions were examined in spiral technique (neck, thorax, abdomen, thorax and abdomen). We found the mAs product to be reduced typically by 10-60% depending on patient geometry and anatomical regions. The mean reduction was 22.3% (neck 20%, thorax 23%, abdomen 23%, thorax and abdomen 22%). In general, no deterioration of image quality was observed. There was no correlation between the age and the mean mAs reduction in the different anatomical regions. By classifying the children respectively to their weight, there is a positive trend between increasing weight and mAs reduction. We conclude that mAs in spiral CT examinations of children can be reduced substantially by attenuation-based on-line modulation of the tube current without deterioration of image quality. Attenuation-based on-line modulation of tube current is efficient and practical for reducing dose exposure to children.

This paper reviews current technical approaches to the optimisation of CT practice, i.e. approaches to reduce patient dose to the necessary minimum. The most important step towards this goal appears to be the technology of tube current modulation (TCM), which came into practice in the early 2000s and has become the standard approach recently. Anatomy- or attenuation-based TCM allows for a dose reduction between 10 and 60% as compared to scans with constant tube current. Automatic exposure control (AEC) approaches are the next step; based on TCM technology, AEC adapts the tube current both with the rotation angle alpha (alpha-modulation) and along the z-axis (z-modulation) to achieve a pre-selected image quality level at minimal dose. To pre-select the image quality level, i.e. primarily the pixel noise level, tools for simulation are important to investigate the necessary noise levels pro- and retrospectively for given cases and diagnostic tasks. Respective "dose tutor" approaches have become available recently and are presented. The most recent technical innovation which may lead to substantial dose reduction is the investigation of optimal spectra taking the type of contrast and 3D dose distributions into account. A high potential has been shown especially for pediatric CT and for thoracic CT where dose reduction of a factor of 2 and more is possible when using reduced tube voltages.

It is accepted that spiral CT scanning may offer significant advantages in a number of clinical applications. There is still some concern with respect to image quality, however, since slice sensitivity profiles are slightly broadened due to the table motion. We carried out theoretical analysis, phantom measurements, and computer simulations to evaluate and to compare contrast and spatial resolution for conventional and for spiral scanning. Special emphasis was put on the task of detecting spherical lesions.For standard test objects that measure only resolution in the scan plane, no significant difference between conventional and spiral scanning was observed. We therefore designed a phantom setup that allowed us to place spheres of arbitrary diameter and contrast in arbitrary positions to test three-dimensional (3D) resolution.For conventional CT, both lesion contrast and the degree of spatial separation of lesions observed depend on the relation of the start position of the scan series to the random location of a sphere or lesion. Spiral CT offers space-invariant resolution due to its continuous scanning. Small lesion contrast may be improved by up to a factor of 1.8 when compared with conventional CT since slices can be centered retrospectively. Measurements and simulations were in excellent agreement.We conclude that spiral CT can offer improved 3D contrast and spatial resolution. To exploit these advantages, images should be reconstructed in spiral CT at increments of less than half the distance traveled during one 360 degrees tube rotation. With four to five images per such interval, usually equal to the slice width, results very close to the theoretical optimum are achieved. Many of the presented considerations and results apply to other slice imaging modalities like MRI in analogous fashion.

Accuracy, reproducibility, and objectivity are important in quantitative assessment of lung density and structure by CT, and the measurement has to be carried out under tightly controlled conditions. We therefore employ respiratory gating at defined levels of inspiration for CT scanning. In the evaluation process, we found operator-induced errors of 2–6 HU standard deviation for the relatively simple task of global lung density estimates; in regional evaluations, they frequently exceeded 10 HU. We therefore developed semiautomated evaluation algorithms that isolate lung parenchyma by fast contour tracking and define subregions by shrinking, radial segmenting, and anteroposterior subdividing of the left and the right lung. Global and regional mean density values and histogram parameters were extracted. Based on our clinical studies, we estimate that an overall precision of better than 5% can be achieved in quantitative CT of the lung with cooperative patients.

We have developed a new hierarchical 3D technique to segment the vertebral bodies in order to measure bone mineral density (BMD) with high trueness and precision in volumetric CT datasets. The hierarchical approach starts with a coarse separation of the individual vertebrae, applies a variety of techniques to segment the vertebral bodies with increasing detail and ends with the definition of an anatomic coordinate system for each vertebral body, relative to which up to 41 trabecular and cortical volumes of interest are positioned. In a pre-segmentation step constraints consisting of Boolean combinations of simple geometric shapes are determined that enclose each individual vertebral body. Bound by these constraints viscous deformable models are used to segment the main shape of the vertebral bodies. Volume growing and morphological operations then capture the fine details of the bone-soft tissue interface. In the volumes of interest bone mineral density and content are determined. In addition, in the segmented vertebral bodies geometric parameters such as volume or the length of the main axes of inertia can be measured. Intra- and inter-operator precision errors of the segmentation procedure were analyzed using existing clinical patient datasets. Results for segmented volume, BMD, and coordinate system position were below 2.0%, 0.6%, and 0.7%, respectively. Trueness was analyzed using phantom scans. The bias of the segmented volume was below 4%; for BMD it was below 1.5%. The long-term goal of this work is improved fracture prediction and patient monitoring in the field of osteoporosis. A true 3D segmentation also enables an accurate measurement of geometrical parameters that may augment the clinical value of a pure BMD analysis.

To evaluate the potential effectiveness of adaptive collimation in reducing computed tomographic (CT) radiation dose owing to z-overscanning by using dose measurements and Monte Carlo (MC) dose simulations.Institutional review board approval was not necessary. Dose profiles were measured with thermoluminescent dosimeters in CT dose index phantoms and in an Alderson-Rando phantom without and with adaptive section collimation for spiral cardiac and chest CT protocols and were compared with the MC simulated dose profiles. Additional dose measurements were performed with an ionization chamber for scan ranges of 5-50 cm and pitch factors of 0.5-1.5.The measured and simulated dose profiles agreed to within 3%. By using adaptive section collimation, a substantial dose reduction of up to 10% was achieved for cardiac and chest CT when measurements were performed free in air and of 7% on average when measurements were performed in phantoms. For scan ranges smaller than 12 cm, ionization chamber measurements and simulations indicated a dose reduction of up to 38%.Adaptive section collimation allows substantial reduction of unnecessary exposure owing to z-overscanning in spiral CT. It can be combined in synergy with other means of dose reduction, such as spectral optimization and automatic exposure control.

Physical exercise affects many risk factors and diseases and therefore can play a vital role in general disease prevention and treatment of elderly individuals and may reduce costs. We sought to determine whether a single exercise program affects fracture risk (bone mineral density [BMD] and falls), coronary heart disease (CHD) risk factors, and health care costs in community-dwelling elderly women.We conducted a randomized, single-blinded, controlled trial from May 1, 2005, through July 31, 2008, recruiting women 65 years or older who were living independently in the area of Erlangen-Nuremberg, Germany. In all, 246 women were randomly assigned to an 18-month exercise program (exercise group) or a wellness program (control group). The exercise group (n = 123) performed a multipurpose exercise program with special emphasis on exercise intensity; the controls (n = 123) focused on well-being with a low-intensity, low-frequency program. The main outcome measures were BMD, the number of falls, the Framingham-based 10-year CHD risk, and direct health care costs.For the 227 women who completed the 18-month study, significant exercise effects were observed for BMD of the lumbar spine (mean [95% confidence interval (CI)] percentage of change in BMD [baseline to follow-up] for the exercise group: 1.77% [1.26% to 2.28%] vs controls: 0.33% [-0.24% to 0.91%]; P < .001), femoral neck (exercise group: 1.01% [0.37% to 1.65%] vs controls: -1.05% [-1.70% to -0.40%]; P < .001), and fall rate per person during 18 months (exercise group: 1.00 [0.76 to 1.24] vs controls: 1.66 [1.33 to 1.99]; P = .002). The 10-year CHD risk was significantly affected in both subgroups (absolute change for the exercise group: -1.96% [95% CI, -2.69% to -1.23%] vs controls: -1.15% [-1.69% to -0.62%]; P = .22), with no significant difference between the groups. The direct health care costs per participant during the 18-month intervention showed nonsignificant differences between the groups (exercise group: 2255 euros[95% CI, 1791 euros-2718 euros] vs controls: 2780 euros [2187 euros-3372 euros]; P = .20).Compared with a general wellness program, our 18-month exercise program significantly improved BMD and fall risk, but not predicted CHD risk, in elderly women. This benefit occurred at no increase in direct costs.clinicaltrials.gov Identifier: NCT00267839.

The authors adapted the transport system of a computed tomographic (CT) scanner with continuous rotation capability to examine complete lung subvolumes during a single breath hold. Twenty-four adult patients underwent scanning with up to 12 continuous 1-second rotations, and data acquisition was synchronized with longitudinal patient motion at one section thickness per second. Interpolated planar raw data were obtained retrospectively from any level within the volume, and these afforded high-quality images that were comparable to standard images. Solitary pulmonary nodules were not omitted, their centers could always be depicted, and secondary reformations as well as three-dimensional reconstructions were obtained easily. The authors conclude that spiral volumetric CT, by completely surveying a subvolume of the lung, is an attractive new application of CT.

To determine the dose-length product (DLP)-effective dose (ED) (DLP/ED) conversion coefficient (k) tables for the lower extremities that can be used for calculating ED.Dose calculations were performed on standard phantoms using a validated Monte Carlo calculation tool. Calculations were performed to obtain ED values for tube voltages from 80 kV to 140 kV in steps of 20 kV for the following examinations: hip (femur), knee, ankle, and computed tomographic (CT) angiography of the lower extremities. Values of the DLP were calculated by multiplying measured CT dose index values by the scan length; k values resulted as the quotients of the ED and DLP values. DLP/ED coefficients averaged over the range of voltage values and their standard deviations were determined for the given lower-extremity CT examinations for all age groups and for both sexes.Coefficients depend strongly on the phantom age and size, but little on the kilovolt value. In the case of the newborn, for example, k values were 0.0612, 0.0046, 0.0014, and 0.047 for hip, knee, ankle, and CT angiography, respectively, while in the case of the adult, these respective values were 0.0110, 0.0004, 0.0002, and 0.0062. A substantial difference up to 20% between coefficients in male and female phantoms was observed for CT angiographic examination.DLP/ED conversion coefficients are provided for lower extremities and allow estimation of ED for commonly used clinical musculoskeletal CT and CT angiographic protocols.

BACKGROUND AND PURPOSE:The viability of both brain parenchyma and vascular anatomy is important in estimating the risk and potential benefit of revascularization in patients with acute cerebral ischemia.We tested the hypothesis that when used in conjunction with IV contrast, FD-CT imaging would provide both anatomic and physiologic information that would correlate well with that obtained by using standard multisection CT techniques. MATERIALS AND METHODS:Imaging of brain parenchyma (FD-CT), cerebral vasculature (FD-CTA), and cerebral blood volume (FD-CBV) was performed in 10 patients.All patients also underwent conventional multisection CT, CTA, CTP (including CBV, CTP-CBV), and conventional catheter angiography.Correlation of the corresponding images was performed by 2 experienced neuroradiologists. RESULTS:There was good correlation of the CBV color maps and absolute values between FD-CBV and CTP-CBV (correlation coefficient, 0.72; P Ͻ .001).The Bland-Altman test showed a mean difference of CBV values between FD-CT and CTP-CBV of 0.04 Ϯ 0.55 mL/100 mL.All vascular lesions identified with standard CTA were also visualized with FD-CTA.Visualization of brain parenchyma by using FD-CT was poor compared with that obtained by using standard CT.CONCLUSIONS: Both imaging of the cerebral vasculature and measurements of CBV by using FD-CT are feasible.The resulting vascular images and CBV measurements compared well with ones made by using standard CT techniques.The ability to measure CBV and also visualize cerebral vasculature in the angiography suite may offer significant advantages in the management of patients.FD-CT is not yet equivalent to CT for imaging of brain parenchyma.ABBREVIATIONS: CBF ϭ cerebral blood flow; CBV ϭ cerebral blood volume; CTA ϭ CT angiography (IV contrast); CTP ϭ perfusion multisection CT; CTP-CBV ϭ perfusion multisection CT cerebral blood volume (IV contrast); DSA ϭ digital subtraction angiography; DWI ϭ diffusion-weighted imaging; FD ϭ flat detector; FD-CBV ϭ flat detector cerebral blood volume (IV contrast); FD-CT ϭ flat detector CT; FD-CTA ϭ flat detector CT angiography (IV contrast); HU ϭ Hounsfield unit; ICA ϭ internal carotid artery; IV ϭ intravenous; MCA ϭ middle cerebral artery; MIP ϭ maximum intensity projection; MPR ϭ multiplanar reconstruction; MSCT ϭ multisection CT; MTT ϭ mean transit time; PWI ϭ perfusion-weighted imaging; TIA ϭ transient ischemic attack; TTP ϭ time-to-peak; VA ϭ vertebral artery

To quantify differences in regional myocardial perfusion in coronary artery stenosis by the use of dual source computed tomography (DSCT) in an animal model.In 5 pigs, an 80% stenosis of the left anterior descending artery was successfully induced by partial balloon occlusion (ischemia group). Five animals served as control group. All animals underwent contrast enhanced whole heart DSCT (Definition Flash, Siemens, Germany) perfusion imaging using a prototype electrocardiogram -triggered dynamic scan mode. Imaging was performed at rest as well as under stress conditions during continuous infusion of adenosine (240 mg/kg/min). For contrast enhancement 60 mL Iopromide 300 (Ultravist 300, Bayer-Schering Pharma, Berlin, Germany) were injected at a rate of 6 mL/s. Myocardial blood flow (MBF), first pass distribution volume, and intravascular blood volume were volumetrically quantified.In the control group MBF increased significantly from 98.2 mL/100 mL/min to 134.0 mL/100 mL/min if adenosine was administered (P = 0.0153). There were no significant differences in the perfusion parameters comparing the control and ischemia group at rest. In the ischemia group MBF under stress was 74.0 +/- 21.9 mL/100 mL/min in the poststenotic myocardium and 117.4 +/- 18.6 mL/100 mL/min in the remaining normal myocardium (P = 0.0024).DSCT permits quantitative whole heart perfusion imaging. As this technique is able to show the hemodynamic effect of high grade coronary artery stenosis, it exceeds the present key limitation of cardiac computed tomography, which currently only allows a morphologic assessment of coronary artery stenosis.

Objectives Integrated whole-body positron emission tomography (PET)/magnetic resonance (MR) scanners have recently been introduced and potentially offer new possibilities in hybrid imaging of oncologic patients. Integration of PET in a whole-body MR system requires new PET detector technology and new approaches to attenuation correction of PET data based on MR imaging. The aim of this study was to evaluate the clinical performance and image quality parameters of integrated whole-body PET/MR hybrid imaging in intraindividual comparison with PET/CT in oncologic patients. Materials and Methods Eighty patients underwent a single-injection, dual-imaging protocol including whole-body PET/computed tomography (CT) and subsequent whole-body PET/MR hybrid imaging. Positron emission tomography/computed tomography was performed after adequate resting time (73 ± 13 minutes post injectionem of 227 ± 52.7 MBq Fluor-18-Fluordesoxyglucose, 3 minutes of acquisition time for each of 7 bed positions), followed by PET/MR (172 ± 33 minutes post injectionem, 10 minutes acquisition time for each of 4 bed positions). Positron emission tomographic data for both modalities were reconstructed iteratively. Two observers evaluated the following parameters: qualitative correlation of tracer-avid lesions in PET/CT versus PET/MR and PET image quality of PET/CT versus PET/MR. Magnetic resonance image quality of standard sequences (T1-weighted, T2-weighted), performance of the Dixon sequence for MR-based attenuation correction in comparison with corresponding T1-weighted images, artifacts in PET/MR data, and spatial coregistration of PET and MR data were evaluated by another observer. Results In 70 of the 80 patients, both image data sets were complete. In these patients, 192 tracer-avid lesions were identified on PET/CT; 195, on PET/MR. A total of 187 lesions were identified concordantly by both modalities, and this corresponds to an agreement rate of 97.4%. The overall PET image quality was rated good to excellent for PET from PET/CT (12/28, excellent, 42.9%; 16/28, good, 57.1%; 0/28, poor, 0.0%) and slightly superior compared with PET from PET/MR, which was rated good (3/28, excellent, 10.7%; 20/28, good, 71.4%; 5/28, poor, 17.9%) in a subset of 28 patients. The overall image quality of the MR image data sets in all 70 of the 80 patients was rated excellent (260/280, excellent, 92.8%; 15/280, good, 5.4%; 5/280, poor, 1.8%). The Dixon sequence and conversion to μ-maps for MR-based attenuation correction provided robust tissue segmentation in all 280 bed positions of the acquired PET/MR data. No artifacts such as elevated noise and radiofrequency disturbances related to hardware cross talk between the PET and MR components in the hybrid system could be detected in the MR images. Nomajor spatial mismatches between PET and MR data were detected. Conclusions Integrated PET/MR hybrid imaging is feasible in a clinical setting with similar detection rates as those of PET/CT. Attenuation correction can be performed sufficiently with Dixon sequences, although bone is disregarded. The administration of specific radiotracers and dedicated imaging sequences will foster this hybrid imaging modality in various indications.

We examined whether the effect of multipurpose exercise can be enhanced by whole-body vibration (WBV). One hundred and fifty-one post-menopausal women (68.5 ± 3.1 years) were randomly assigned to three groups: (1) a training group (TG); (2) training including vibration (VTG); and (3) a wellness control group (CG). TG and VTG performed the same training program twice weekly (60 min), consisting of aerobic and strength exercises, with the only difference that leg strength exercises (15 min) were performed with (VTG) or without (TG) vibration. CG performed a low-intensity "wellness" program. At baseline and after 18 months, body composition was determined using dual-X-ray-absorptiometry. Maximum isometric strength was determined for the legs and the trunk region. Leg power was measured by countermovement jumps using a force-measuring plate. In the TG lean body mass, total body fat, and abdominal fat were favorably affected, but no additive effects were generated by the vibration stimulus. However, concerning muscle strength and power, there was a tendency in favor of the VTG. Only vibration training resulted in a significant increase of leg and trunk flexion strength compared with CG. In summary, WBV embedded in a multipurpose exercise program showed minor additive effects on body composition and neuromuscular performance.

To achieve higher volume coverage at improved z-resolution in computed tomography (CT), systems with a large number of detector rows are demanded. However, handling an increased number of detector rows, as compared to today's four-slice scanners, requires to accounting for the cone geometry of the beams. Many so-called cone-beam reconstruction algorithms have been proposed during the last decade. None met all the requirements of the medical spiral cone-beam CT in regard to the need for high image quality, low patient dose and low reconstruction times. We therefore propose an approximate cone-beam algorithm which uses virtual reconstruction planes tilted to optimally fit 180 degrees spiral segments, i.e., the advanced single-slice rebinning (ASSR) algorithm. Our algorithm is a modification of the single-slice rebinning algorithm proposed by Noo et al. [Phys. Med. Biol. 44, 561-570 (1999)] since we use tilted reconstruction slices instead of transaxial slices to approximate the spiral path. Theoretical considerations as well as the reconstruction of simulated phantom data in comparison to the gold standard 180 degrees LI (single-slice spiral CT) were carried out. Image artifacts, z-resolution as well as noise levels were evaluated for all simulated scanners. Even for a high number of detector rows the artifact level in the reconstructed images remains comparable to that of 180 degrees LI. Multiplanar reformations of the Defrise phantom show none of the typical cone-beam artifacts usually appearing when going to larger cone angles. Image noise as well as the shape of the respective slice sensitivity profiles are equivalent to the single-slice spiral reconstruction, z-resolution is slightly decreased. The ASSR has the potential to become a practical tool for medical spiral cone-beam CT. Its computational complexity lies in the order of standard single-slice CT and it allows to use available 2D backprojection hardware.

Physical exercise has a favorable impact on bones, but optimum training strategies are still under discussion. In this study, we compared the effect of slow and fast resistance exercises on various osteodensitometric parameters. Fifty-three postmenopausal women were randomly assigned to a strength training (ST) or a power training group (PT). Both groups carried out a progressive resistance training, a gymnastics session, and a home training over a period of 12 mo. During the resistance training, the ST group used slow and the PT group fast movements; otherwise there were no training differences. All subjects were supplemented with Ca and vitamin D. At baseline and after 12 mo, bone mineral density (BMD) was measured at the lumbar spine, proximal femur, and distal forearm by dual-energy X-ray absorptiometry. We also measured anthropometric data and maximum static strength. Frequency and grade of pain were assessed by questionnaire. After 12 mo, significant between-group differences were observed for BMD at the lumbar spine (P < 0.05) and the total hip (P < 0.05). Whereas the PT group maintained BMD at the spine (+0.7 +/- 2.1%, not significant) and the total hip (0.0 +/- 1.7%, not significant), the ST group lost significantly at both sites (spine: -0.9 +/- 1.9%; P < 0.05; total hip: -1.2 +/- 1.5%; P < 0.01). No significant between-group differences were observed for anthropometric data, maximum strength, BMD of the forearm, or frequency and grade of pain. These findings suggest that power training is more effective than strength training in reducing bone loss in postmenopausal women.

We present a new high-precision method for the geometric calibration in cone-beam computed tomography. It is based on a Fourier analysis of the projection-orbit data, recorded with a flat-panel area detector, of individual point-like objects. For circular scan trajectories the complete set of misalignment parameters which determine the deviation of the detector alignment from the ideal scan geometry are obtained from explicit analytic expressions. To derive these expressions we show how to disentangle the problems of calculating misalignment parameters and point coordinates. The calculation of the coordinates of the point objects inside the scanned volume, in units of the distance from the focal spot to the center of rotation, is then possible analytically likewise. We simulate point-projection data on a misaligned detector with various amounts of randomness added to mimic measurement uncertainties. This data is then employed in our calibration to validate the method by comparing the resulting misalignment parameters and point coordinates to the known true ones. We also present our implementation and results for the geometric calibration of micro-CT systems. The effectiveness of the corresponding misalignment correction in reducing image artifacts is exemplified by reconstructed micro-CT images.

A prototype dual‐energy computed tomographic (CT) scanner (Siemens Somatom DR3) with rapid kVp switching and prereconstruction processing has been used to measure vertebral bone mineral density. With this approach misregistration and beam hardening inaccuracies can be reduced considerably. Basis material images of aluminum‐ and Lucite‐equivalent density enable measurements of bone mineral density that are nearly independent of the amount of marrow fat. To simulate variable marrow fat, alcohol–water mixtures were used as media in calibration standards. A section of dried trabecular bone was also scanned immersed in varying alcohol–water mixtures. In both simulations it was shown that the dual‐energy measurement is nearly independent of marrow composition whereas the single‐energy measurement would be strongly influenced by marrow fat. Dual‐energy CT was compared to dual‐photon absorptiometry ( 1 5 3 Gd) for the measurement of bone mineral mass of ten excised human vertebrae. There was a high degree of correlation between the two measurements ( r =0.97). Dual‐energy and single‐energy CT measurements on 17 patients with suspected metabolic bone disease strongly support the conclusion that the influence of fat can lead to significant errors in single‐energy determinations of the mineral density of trabecular bone.

We propose an empirical cupping correction (ECC) algorithm to correct for CT cupping artifacts that are induced by nonlinearities in the projection data. The method is raw data based, empirical, and requires neither knowledge of the x‐ray spectrum nor of the attenuation coefficients. It aims at linearizing the attenuation data using a precorrection function of polynomial form. The coefficients of the polynomial are determined once using a calibration scan of a homogeneous phantom. Computing the coefficients is done in image domain by fitting a series of basis images to a template image. The template image is obtained directly from the uncorrected phantom image and no assumptions on the phantom size or of its positioning are made. Raw data are precorrected by passing them through the once‐determined polynomial. As an example we demonstrate how ECC can be used to perform water precorrection for an in vivo micro‐CT scanner (TomoScope 30 s, VAMP GmbH, Erlangen, Germany). For this particular case, practical considerations regarding the definition of the template image are given. ECC strives to remove the cupping artifacts and to obtain well‐calibrated CT values. Although ECC is a first‐order correction and cannot compete with iterative higher‐order beam hardening or scatter correction algorithms, our in vivo mouse images show a significant reduction of bone‐induced artifacts as well. A combination of ECC with analytical techniques yielding a hybrid cupping correction method is possible and allows for channel‐dependent correction functions.

X-ray computerised tomography (CT) scanning with continuous patient transport has been established under the name Spiral CT since several years as the standard clinical examination procedure. This technique has been improved continuously with respect to scan speed, temporal response and z-axis resolution by the use of latest technical developments: Rotation times up to 0.5 s and multi-row detector array systems. Today detector systems with M + 4 simultaneously measured slices are available. We report about recent progress of spiral CT reconstruction algorithms that are based on multi-slice data. It is demonstrated that the new technology not only provides significant reduction in overall scan times and thereby of the CT scanner?s X-ray tube load; beyond that, the new technology allows CT imaging of the beating heart with high level image quality in standard clinical routine.

A side effect of increased volume coverage by using multi-row and flat-panel detectors in computed tomography (CT) is the concurrently growing contribution of scattered radiation to the measured signal. In order to investigate the effect of scatter on x-ray projections used for CT imaging, our study aimed at the development of a simulation tool for fast calculation of primary and scatter intensities. We developed a deterministic method to assess the contribution of single-scatter events to the measured signal. The investigation of multiple scatter by Monte Carlo simulations showed that it results in a smooth signal as compared to single scatter. A hybrid method is proposed in order to optimize the performance of the scatter simulation: a fast and exact analytical calculation of the single-scatter intensity combined with a coarse Monte Carlo (MC) estimate of multiple scatter to reduce overall computational expenses, while assuring an acceptable signal quality. The results of the hybrid simulation of total scatter were in excellent agreement with the corresponding MC only simulations, thereby allowing us to reduce computational time by orders of magnitude. Estimates of two-dimensional scatter distributions for flat-panel CT imaging took about 30–40 s (per projection). The hybrid method provides a realistic simulation of x-ray scatter and offers a basis for scatter correction approaches.

In flat-detector CT, imperfect or defect detector elements may cause concentric ring artifacts due to their continuous over- or underestimation of attenuation values, which often disturb image quality. Especially due to the demand for high-spatial resolution images and the necessary pixel read-out without arbitrary pixel-binning, ring artifacts become more pronounced and the reduction of these artifacts becomes a necessity. We here present a comparison of two dedicated ring artifact correction methods for flat-detector CT, on the basis of different median and mean filterings of the reconstructed image but each working in different geometric planes. While the first method works in Cartesian coordinates, the second method performs a transformation to polar coordinates. Both post-processing methods efficiently reduce ring artifacts in the reconstructed images and improve image quality. The transformation to polar coordinates turned out to be a necessary step for efficient ring artifact correction, since correction in Cartesian coordinates suffers from newly introduced artifacts as well as insufficient correction of artifacts close to the center of rotation.

Metallic implants generate streak-like artifacts in flat-detector computed tomography (FD-CT) reconstructed volumetric images. This study presents a novel method for reducing these disturbing artifacts by inserting discarded information into the original rawdata using a three-step correction procedure and working directly with each detector element. Computation times are minimized by completely implementing the correction process on graphics processing units (GPUs). First, the original volume is corrected using a three-dimensional interpolation scheme in the rawdata domain, followed by a second reconstruction. This metal artifact-reduced volume is then segmented into three materials, i.e. air, soft-tissue and bone, using a threshold-based algorithm. Subsequently, a forward projection of the obtained tissue-class model substitutes the missing or corrupted attenuation values directly for each flat detector element that contains attenuation values corresponding to metal parts, followed by a final reconstruction. Experiments using tissue-equivalent phantoms showed a significant reduction of metal artifacts (deviations of CT values after correction compared to measurements without metallic inserts reduced typically to below 20 HU, differences in image noise to below 5 HU) caused by the implants and no significant resolution losses even in areas close to the inserts. To cover a variety of different cases, cadaver measurements and clinical images in the knee, head and spine region were used to investigate the effectiveness and applicability of our method. A comparison to a three-dimensional interpolation correction showed that the new approach outperformed interpolation schemes. Correction times are minimized, and initial and corrected images are made available at almost the same time (12.7 s for the initial reconstruction, 46.2 s for the final corrected image compared to 114.1 s and 355.1 s on central processing units (CPUs)).

Current guidelines and literature on screening for coronary artery calcium for cardiac risk assessment are reviewed for both general and special populations. It is shown that for both general and special populations a zero score excludes most clinically relevant coronary artery disease. The importance of standardization of coronary artery calcium measurements by multi-detector CT is discussed.

Current guidelines and literature on screening for coronary artery calcium for cardiac risk assessment are reviewed for both general and special populations. It is shown that for both general and special populations a zero score excludes most clinically relevant coronary artery disease. The importance of standardization of coronary artery calcium measurements by multidetector CT is discussed.

BACKGROUND AND PURPOSE: Metallic implants induce massive artifacts in CT images which deteriorate image quality and often superimpose structures of interest.The purpose of this study was to apply and evaluate a dedicated MAR method for neuroradiologic intracranial clips and detachable platinum coiling events.We here report the first clinical results for MAR in FDCT. MATERIALS AND METHODS:FDCT volume scans of several patients treated with endovascular coiling or intracranial clipping were corrected by using a dedicated FDCT MAR correction algorithm combined with an edge-preserving attenuation-normalization method in the projection space.Corrected and uncorrected images were compared by 2 experienced radiologists and evaluated for several imagequality features.RESULTS: After application of our algorithm, implant delineation and visibility were highly improved.CT values compared with values in metal artifactϪunaffected areas showed good agreement (average correction of 1300 HU).Image noise was reduced overall by 27%.Intracranial hemorrhage in the direct surroundings of the implanted coil or clip material was displayed without worrisome metal artifacts, and our algorithm even allowed diagnosis in areas where extensive information losses were seen.The high spatial resolution provided by FDCT imaging was well preserved.CONCLUSIONS: Our MAR method provided metal artifactϪreduced images in every studied case.It reduced image noise and corrected CT values to levels comparable with images measured without metallic implants.An overall improvement of brain tissue modeling and implant visibility was achieved.MAR in neuroradiologic FDCT imaging is a promising step forward for better image quality and diagnosis in the presence of metallic implants.

Whole-body vibration (WBV) is a new nonpharmacological approach to counteract osteoporosis. However, the specific vibration protocol to most effectively reduce osteoporotic risk has not been reported. In the ELVIS II (Erlangen Longitudinal Vibration Study II) trial, we determined the effect of different WBV devices on bone mineral density (BMD) and neuromuscular performance.A total of 108 postmenopausal women (65.8 ± 3.5 yr) were randomly allocated to 1) rotational vibration training (RVT), i.e., 12.5 Hz, 12 mm, three sessions per week, for 15 min, including dynamic squat exercises; 2) vertical vibration training (VVT), i.e., 35 Hz, 1.7 mm, as above; and 3) a wellness control group (CG), i.e., two blocks of 10 low-intensity gymnastics sessions. BMD was measured at the hip and lumbar spine at baseline and after 12 months of training using dual-energy x-ray absorptiomety. Maximum isometric leg extension strength and leg power were determined using force plates.A BMD gain at the lumbar spine was observed in both vibration VT groups (RVT = +0.7% ± 2.2%, VVT = +0.5% ± 2.0%), which was significant compared with the CG value (-0.4% ± 2.0%) for RVT (P = 0.04) and borderline nonsignificant for VVT (P = 0.08). In the neck region, no significant treatment effect occurred. Neck BMD values tended to increase in both VT groups (RVT = +0.3% ± 2.7%, VVT = +1.1% ± 3.4%) and remained stable in CG (-0.0% ± 2.1%).Both VT groups gained maximum leg strength (RVT = +27% ± 22%, VVT = +24% ± 34%) compared with CG (+6% ± 20%, P = 0.000), whereas power measurements did not reach the level of significance (P = 0.1).WBV training is effective for reducing the risk for osteoporosis by increasing lumbar BMD and leg strength.

In women, age and the menopausal transition contribute to an increase of body fat and a reduction of lean body mass associated with functional decline, affecting independent living.Sarcopenia and adiposity in the elderly has been associated with increased mortality and functional decline affecting independent living.This study was conducted to determine the effect of a multipurpose exercise program on the body composition and functional ability of elderly women living in a community.An 18-month single-blinded RCT comparing participants in an exercise program with an active control group was conducted from May 2005 through December 2007. Analyses were conducted from January 2008 to July 2008.Two hundred forty-six women (aged 69.1+/-4.0 years) living independently in the area of Erlangen-Nürnberg (Germany) participated in the study.Subjects (n=123) performed a multipurpose exercise program with special emphasis on exercise intensity but with low-level requirements for training facilities and materials. The 123 women in the control group focused primarily on well-being.Body composition was assessed by dual-energy x-ray absorptiometry. Further, strength was evaluated using isometric techniques for the back and legs. Aerobic fitness was determined from a progressive-intensity treadmill test.After 18 months, significant effects in favor of the exercise program for body composition were increases in appendicular skeletal muscle mass and lean body mass along with reductions in abdominal fat and total body fat. Significant performance effects also favored the exercise program and included enhanced isometric maximum trunk-extensor and leg press strength, leg press power, timed up-and-go test, and aerobic fitness.A high-intensity multipurpose exercise program produced significant improvements in body composition and functional ability in a cohort of elderly women living in a community.

Purpose: Monte Carlo (MC) simulation is an established technique for dose calculation in diagnostic radiology. The major drawback is its high computational demand, which limits the possibility of usage in real‐time applications. The aim of this study was to develop fast on‐site computed tomography (CT) specific MC dose calculations by using a graphics processing unit (GPU) cluster. Methods: GPUs are powerful systems which are especially suited to problems that can be expressed as data‐parallel computations. In MC simulations, each photon track is independent of the others; each launched photon can be mapped to one thread on the GPU, thousands of threads are executed in parallel in order to achieve high performance. For further acceleration, the authors considered multiple GPUs. The total computation was divided into different parts which can be calculated in parallel on multiple devices. The GPU cluster is an MC calculation server which is connected to the CT scanner and computes 3D dose distributions on‐site immediately after image reconstruction. To estimate the performance gain, the authors benchmarked dose calculation times on a 2.6 GHz Intel Xeon 5430 Quad core workstation equipped with two NVIDIA GeForce GTX 285 cards. The on‐site calculation concept was demonstrated for clinical and preclinical datasets on CT scanners (multislice CT, flat‐detector CT, and micro‐CT) with varying geometry, spectra, and filtration. To validate the GPU‐based MC algorithm, the authors measured dose values on a 64‐slice CT system using calibrated ionization chambers and thermoluminesence dosimeters (TLDs) which were placed inside standard cylindrical polymethyl methacrylate (PMMA) phantoms. Results: The dose values and profiles obtained by GPU‐based MC simulations were in the expected good agreement with computed tomography dose index (CTDI) measurements and reference TLD profiles with differences being less than 5%. For 10 9 photon histories simulated in a 256 × 256 × 12 voxel thorax dataset with voxel size of 1.36 × 1.36 × 3.00 mm 3 , calculation times of about 70 and 24 min were necessary with single‐core and multiple‐core central processing unit (CPU) solutions, respectively. Using GPUs, the same MC calculations were performed in 1.27 min (single card) and 0.65 min (two cards) without a loss in quality. Simulations were thus speeded up by factors up to 55 and 36 compared to single‐core and multiple‐core CPU, respectively. The performance scaled nearly linearly with the number of GPUs. Tests confirmed that the proposed GPU‐based MC tool can be easily adapted to different types of CT scanners and used as service providers for fast on‐site dose calculations. Conclusions: The Monte Carlo software package provides fast on‐site calculation of 3D dose distributions in the CT suite which makes it a practical tool for any type of CT‐specific application.

Objectives The purpose of this work is to present the data obtained from the first clinical in vivo application of a new dedicated spiral breast computed tomography (B-CT) equipped with a photon-counting detector. Materials and Methods The institutional review board approved this retrospective study. Twelve women referred for breast cancer screening were included and underwent bilateral spiral B-CT acquired in prone position. Additional sonography was performed in case of dense breast tissue or any B-CT findings. In 3 women, previous mammography was available for comparison. Soft tissue (ST) and high-resolution (HR) images were reconstructed. Two independent radiologists performed separately the readout for subjective image quality and for imaging findings detection. Objective image quality evaluation was performed in consensus and included spatial resolution, contrast resolution, signal-to-noise ratio (SNR), and contrast-to-noise ratio. All women were asked to report about positioning comfort and overall comfort during data acquisition. Results The major pectoral muscle was included in 15 breast CT scans (62.5%); glandular component was partially missing in 2 (8.3%) of the 24 scanned breasts. A thin “ring artifact” was present in all scans but had no influence on image interpretations; no other artifacts were present. Subjective image quality assessment showed excellent agreement between the 2 readers (κ = 1). Three masses were depicted in B-CT and were confirmed as simple cysts in sonography. Additional 5 simple cysts and 2 solid benign lesions were identified only in sonography. A total of 12 calcifications were depicted with a median size of 1.1 mm (interquartile range, 0.7–1.7 mm) on HR and 1.4 mm (interquartile range, 1.1–1.8 mm) on ST images. Median SNR gl , SNR fat , and contrast-to-noise ratio were significantly higher in ST than in HR reconstructions (each, P &lt; 0.001). A mild discomfort due to positioning of the rib cage on the table was reported by 2 women (16.7%); otherwise, no discomfort was reported. Conclusions The new dedicated B-CT equipped with a photon-counting detector provides high-quality images with potential for screening of breast cancer along with minor patient discomfort.

To determine the effect of an intense exercise training on physical fitness, coronary heart disease (CHD), bone mineral density (BMD), and parameters related to quality of life in early postmenopausal women with osteopenia.Fifty-nine fully compliant women (55.1 +/- 3.4 yr) without any medication or illness affecting bone metabolism took part in intensive exercise training (>2 sessions per week); 41 women served as nontraining control. Both groups received calcium and vitamin D (cholecalciferol) up to a maximum of 1500 mg x d(-1) calcium and 500 IU x d(-1) vitamin D. Bone density of the lumbar spine and hip (DXA Hologic QDR 4500), maximum isometric and dynamic strength (Schnell M3, Schnell-Trainer), VO2max (ZAN 600), and quality of life parameters including vasomotor symptoms related to menopause were measured at baseline and after 14 months.After 14 months, there were significant differences between exercise and control groups concerning changes of bone density (LS exercise: +1.3%, P < 0.001 vs control: -1.2%, P < 0.001), maximum isometric strength (exercise: +11 to +32% (P < 0.001) vs control: -1.1 to +3.9%), VO2max (exercise: +11% (P < 0.001) vs control: -4% (P < 0.05)), and quality of life parameters (e.g., lower back pain). Dynamic strength (1RM tests) at four exercises, which was assessed in the exercise group only, increased significantly by 15-43% (all P < 0.001).The intense exercise training program presented here was effective in improving strength, endurance, quality of life parameters, and even BMD in women in their critical early postmenopausal years.

To compare the image quality of electron beam tomography (EBT) and multislice spiral CT (MSCT) for coronary artery visualization.Two groups of 30 patients without coronary stenoses were studied by MSCT (4 x 1 mm collimation) or EBT (3 mm slice thickness). Contrast-to-noise ratio (CNR), overall length of the visualized arteries and vessel length free of motion artifacts were measured.Length of visualized arteries was equal in MSCT and EBT. In EBT, longer segments were depicted free of motion artifacts (MSCT: 73%, EBT: 92% of visualized length, P< 0.001) and CNR was significantly higher than in MSCT (15.4 vs. 9.0; P< 0.001). In both modalities, vessel diameters correlated closely to quantitative coronary angiography.EBT and MSCT permit reliable coronary artery visualization and measurement of vessel diameters. For the used scan protocol, MSCT images had a lower CNR and were more frequently affected by motion.

Up to now it has not been possible to reliably cross-calibrate dual-energy X-ray absorptiometry (DXA) densitometry equipment made by different manufacturers so that a measurement made on an individual subject can be expressed in the units used with a different type of machine. Manufacturers have adopted various procedures for edge detection and calibration, producing various normal ranges which are specific to each individual manufacturer's brand of machine. In this study we have used the recently described European Spine Phantom (ESP, prototype version), which contains three semi-anthropomorphic "vertebrae" of different densities made of stimulated cortical and trabecular bone, to calibrate a range of DXA densitometers and quantitative computed tomography (QCT) equipment used in the measurement of trabecular bone density of the lumbar vertebrae. Three brands of QCT equipment and three brands of DXA equipment were assessed. Repeat measurements were made to assess machine stability. With the large majority of machines which proved stable, mean values were obtained for the measured low, medium and high density vertebrae respectively. In the case of the QCT equipment these means were for the trabecular bone density, and in the case of the DXA equipment for vertebral body bone density in the posteroanterior projection. All DXA machines overestimated the projected area of the vertebral bodies by incorporating variable amounts of transverse process. In general, the QCT equipment gave measured values which were close to the specified values for trabecular density, but there were substantial differences from the specified values in the results provided by the three DXA brands. For the QCT and Norland DXA machines (posteroanterior view), the relationships between specified densities and observed densities were found to be linear, whereas for the other DXA equipment (posteroanterior view), slightly curvilinear, exponential fits were found to be necessary to fit the plots of observed versus specified densities. From these plots, individual calibration equations were derived for each machine studied. For optimal cross-calibration, it was found to be necessary to use an individual calibration equation for each machine. This study has shown that it is possible to cross-calibrate DXA as well as QCT equipment for the measurement of axial bone density. This will be of considerable benefit for large-scale epidemiological studies as well as for multi-site clinical studies depending on bone densitometry.

Medical PhysicsVolume 19, Issue 3 p. 583-586 A phantom for standarization and quality control in spinal bone mineral measurements by QCT and DXA: Design considerations and specifications Willi A. Kalender, Willi A. Kalender Siemens Medical Systems, Henkestr. 127, D-8520 Erlangen, GermanySearch for more papers by this author Willi A. Kalender, Willi A. Kalender Siemens Medical Systems, Henkestr. 127, D-8520 Erlangen, GermanySearch for more papers by this author First published: May 1992 https://doi.org/10.1118/1.596899Citations: 84AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume19, Issue3May 1992Pages 583-586 RelatedInformation

Twenty-seven patients with diffuse fibrosing alveolitis (DFA), 27 patients with granulomatous lung disease (GLD), 3 patients with homozygous α1-proteinase inhibitor deficiency (α1-PID), and 6 healthy volunteers (C) were studied using thin section high resolution CT (HRCT) at 50% of actual vital capacity (VC), determined and controlled spirometrically during each exposure. A fast contour tracing algorithm was used to isolate the lung parenchyma followed by a quantitative histogram analysis of the frequencies of CT values. Mean CT values enabled us to discriminate significantly between the groups of C and α1-PID. Significant differences were found between the groups of GLD and DFA versus C by applying suitably selected intervals of CT values. Moreover, if the patients were assigned to four different groups according to their lung function results (normal, restrictive, obstructive, restrictive and obstructive), again significant differences existed with respect to defined intervals of CT values. Mean CT values showed a significant negative correlation with lung function tests representative of lung parenchymal disease, i.e., VC, diffusing capacity, and exercise Pao2. Moreover, CT values ranging from - 899 to - 800 HU correlated positively, whereas CT value frequencies above −699 HU correlated inversely with these same lung function parameters. These results indicated that certain intervals of CT values do reflect functionally different abnormalities of lung parenchyma. It is concluded that an analysis of frequencies of CT values determined by spirometrically standardized HRCT provides objective quantitative data that reflect changes of pulmonary structure corresponding to lung function impairments. Thus, spirometrically standardized HRCT may be helpful for evaluating and staging patients with diffuse pulmonary diseases.

Common Terminology for Single and Multislice Helical CTPaul M. Silverman1, Willi A. Kalender2 and John D. Hazle1Audio Available | Share

The new spiral multislice computed tomography (CT) scanners and the significant increase in rotation speed offer great potential for cardiac imaging with X-ray CT. We have therefore developed the dedicated cardiac reconstruction algorithms 180 degrees multislice cardio interpolation (MCI) and 180 degrees multislice cardio delta (MCD) and here offer further details and validation. The algorithm 180 degreesMCI is an electrocardiogram (ECG)-correlated filtering (or weighting) algorithm in both the cardiac phase and in the z-position. Effective scan times (absolute temporal resolution) of as low as t(eff) = 56 ms are possible, assuming M 4 simultaneously measured slices at a rotation time of t(rot) = 0.5 s and S < or = d < or = 3S for the table feed d per rotation, where S denotes the collimated slice thickness. The relative temporal resolution w (fraction of the heart cycle depicted in the image), which is the more important parameter in cardiac imaging, will then be as low as w = 12.5% of the heart cycle. The second approach, 180 degreesMCD, is an ECG-correlated partial scan reconstruction of 180 degrees + delta data with delta << phi (fan-angle). Its absolute temporal resolution lies in the order of 250 ms (for the central ray, i.e., for the center of rotation), and the relative temporal resolution w increases with increasing heart rate, e.g., from typically w = 25% at fH = 60 min(-1) to w = 50% at fH = 120 min(-1), assuming again t(rot) = 0.5 s. For validation purposes, we have done simulations of a virtual cardiac motion phantom, measurements of a dedicated cardiac calibration and motion phantom, and we have reconstructed patient data with simultaneously acquired ECG. Both algorithms significantly improve the image quality compared with the standard reconstruction algorithms 180 degrees multislice linear interpolation (MLI) and 180 degrees multislice filtered interpolation (MFI). However, 180 degreesMCI is clearly superior to 180 degreesMCD for all heart rates. This is best illustrated by multiplanar reformations (MPR) or other three-dimensional (3-D) displays of the volume. 180 degreesMCI, due to its higher temporal resolution, is best for spatial and temporal four-dimensional (4-D) tracking of the anatomy. A tunable scanner rotation time to avoid resonance behavior of the heart rate and the scanner's rotation and shorter rotation times would be of further benefit.

Subsecond single-slice, multi-slice or cone-beam spiral computed tomography (SSCT, MSCT, CBCT) offer great potential for improving heart imaging. Together with the newly developed phase-correlated cardiac reconstruction algorithms 180 degrees MCD and 180 degrees MCI [Med. Phys. 27, 1881-1902 (2000)] or related algorithms provided by the CT manufacturers, high image quality can be achieved. These algorithms require information about the cardiac motion, i.e., typically the simultaneously recorded electrocardiogram (ECG), to synchronize the reconstruction with the cardiac motion. Neither data acquired without ECG information (standard patients) nor acquisitions with corrupted ECG information can be handled adequately. We developed a method to extract the appropriate information about cardiac motion directly from the measured raw data (projection data). The so-called kymogram function is a measure of the cardiac motion as a function of time t or as a function of the projection angle alpha. In contrast to the ECG which is a global measure of the heart's electric excitation, the kymogram is a local measure of the heart motion at the z-position z(a) at projection angle a. The patient's local heart rate as well as the necessary synchronization information to be used with phase-correlated algorithms can be extracted from the kymogram by using a series of signal processing steps. The kymogram information is shown to be adequate to substitute the ECG information. Computer simulations with simulated ECG and patient measurements with simultaneously acquired ECG were carried out for a multislice scanner providing M = 4 slices to evaluate these new approaches. Both the ECG function and the kymogram function were used for reconstruction. Both were highly correlated regarding the periodicity information used for reconstruction. In 21 out of 25 consecutive cases the kymogram approach was equivalent to the ECG-correlated reconstruction; only minor differences in image quality between both methods were observed. For one patient the synchronization information detected by the ECG monitor turned out to be wrong; here, the kymogram constituted the only approach that provided useful reconstructions. Patient studies with 12 and 16 slices indicate the usefulness of our approach for cone-beam CT scans. Kymogram-correlated reconstructions also appear to have the potential to improve imaging of pericardial lung areas in general.

Segmentation is an important part of image processing, which often has a large impact on quantitative image analysis results. Fully automated operator independent segmentation procedures that successfully work in a population with a larger biological variation are extremely difficult to design and usually some kind of operator intervention is required, at least in pathological cases. We developed a variety of 3D editing tools that can be used to correct or improve results of initial automatic segmentation procedures. Specifically we will discuss and show examples for three types of editing tools that we termed: hole-filling (tool 1), point-bridging (tool 2), and surface-dragging (tool 3). Each tool comes in a number of flavors, all of which are implemented in a truly 3D manner. We describe the principles, evaluate efficiency and flexibility, and discuss advantages and disadvantages of each tool. We further demonstrate the superiority of the 3D approach over the time-consuming slice-by-slice editing of 3D datasets, which is still widely used in medical image processing today. We conclude that performance criteria for automatic segmentation algorithms may be eased significantly by including 3D editing tools early in the design process.

In conventional computed tomography (CT), ramps, typically thin sheets of aluminum inclined at 45°, are established tools for measurements of slice sensitivity profiles (SSP). In spiral CT, however, they yield inconsistent results for different positions along the longitudinal axis. It is explained herein how ramp profiles result as a superposition of true SSPs and artifacts, the artifacts being caused by the slice interpolation process due to the difficult interpolation condition in this particular geometry. In direct consequence, ramp tests yield spatially variant results. As an alternative tool for measuring the slice sensitivity profile, the use of a thin high‐contrast sheet held between two disks which approximate the ideal test of a delta impulse in the longitudinal direction is suggested. Resulting SSPs are shown for both methods; the delta method, in agreement with theoretical predictions, provided smooth symmetrical SSPs independent of table position in agreement with theoretical predictions. It is concluded that ramps are inadequate test objects to determine SSPs in spiral CT.

Currently, CT scanning is often performed using flat detectors which are mounted on C-arm units or dedicated gantries as in radiation therapy or micro CT. For perspective cone-beam backprojection of the Feldkamp type (FDK) the geometry of an approximately circular scan trajectory has to be available for reconstruction. If the system or the scan geometry is afflicted with geometrical instabilities, referred to as misalignment, a non-perfect approximate circular scan is the case. Reconstructing a misaligned scan without knowledge of the true trajectory results in severe artefacts in the CT images. Unlike current methods which use a pre-scan calibration of the geometry for defined scan protocols and calibration phantoms, we propose a real-time iterative restoration of reconstruction geometry by means of entropy minimization. Entropy minimization is performed combining a simplex algorithm for multi-parameter optimization and iterative graphics card (GPU)-based FDK-reconstructions. Images reconstructed with the misaligned geometry were used as an input for the entropy minimization algorithm. A simplex algorithm changes the geometrical parameters of the source and detector with respect to the reduction of entropy. In order to reduce the size of the high-dimensional space required for minimization, the trajectory was described by only eight fix points. A virtual trajectory is generated for each iteration using a least-mean-squares algorithm to calculate an approximately circular path including these points. Entropy was minimal for the ideal dataset, whereas strong misalignment resulted in a higher entropy value. For the datasets used in this study, the simplex algorithm required 64–200 iterations to achieve an entropy value equivalent to the ideal dataset, depending on the grade of misalignment using random initialization conditions. The use of the GPU reduced the time per iteration as compared to a quad core CPU-based backprojection by a factor of 10 resulting in a total of 15–20 ms per iteration, and thus providing an online geometry restoration after a total computation time of approximately 1–3 s, depending on the number of iterations. The proposed method provides accurate geometry restoration for approximately circular scans and eliminates the need for an elaborate off-line calibration for each scan. If a priori information about the trajectory is used to initialize the simplex algorithm, it is expected that the entropy minimization will converge significantly faster.

We report on a new calibration phantom for quantitative computed tomography which has been improved with respect to reference materials and geometrical setup. Instead of liquid calibration solutions, we use polyethylene‐based water‐ and bone‐equivalent plastics. The size of the phantom is considerably reduced by using only two samples. This design guarantees long‐term stability and it offers advantages with respect to radiation geometry.

Objectives: To investigate the effect of two different schemes of loading in resistance training on bone mineral density (BMD) and pain in pretrained postmenopausal women. Methods: 53 pretrained women (mean (SD) age 58.2 (3.7) years) who carried out a mixed resistance and gymnastics programme were randomly assigned to a strength training (ST) or power training (PT) group. The difference between the two groups was the movement velocity during the resistance training (ST, 4 s (concentric)/4 s (eccentric); PT, explosive/4 s). Otherwise both groups carried out periodised progressive resistance training (10–12 exercises, 2–4 sets, 4–12 repetitions at 70–92.5% of the one-repetition maximum (2/week) for 2 years. Mechanical loading was determined with a force measuring plate during the leg press exercise. At baseline and after 2 years, BMD was measured at different sites with dual x -ray absorptiometry. Pain was assessed by questionnaire. Results: Loading magnitude, loading/unloading rate, loading amplitude and loading frequency differed significantly (p<0.001) between the two groups. After 2 years, significant between-group differences were detected for BMD (PT, −0.3%; ST, −2.4%; p<0.05) and bone area (PT, 0.4%; ST, −0.9%; p<0.05) at the lumbar spine. At the hip, there was a non-significant trend in favour of the PT group. Also the incidence of pain indicators at the lumbar spine was more favourable in the PT group. Conclusion: The results show that PT may be superior for maintaining BMD in postmenopausal women. Furthermore, PT was safe as it did not lead to increased injury or pain.

BACKGROUND AND PURPOSE:The purpose of this work was to evaluate angiographic CT (ACT) in the combined application of a self-expanding neurovascular stent and detachable platinum coils in the management of broad-based and fusiform intracranial aneurysms. MATERIALS AND METHODS:Eleven patients harboring wide-necked intracranial aneurysms were treated with a flexible self-expanding neurovascular stent and subsequent aneurysm embolization with platinum microcoils.ACT was performed after the interventional procedure to analyze stent position and the relationship of coils to the stent.Postprocessing included multiplanar reconstructions (MPRs) and maximum intensity projections (MIPs).ACT volume datasets were postprocessed for soft tissue visualization.RESULTS: Accurate stent placement with subsequent coil occlusion of the aneurysms was feasible in all of the patients.Similar to nonsubtracted digital subtraction angiography (DSA) images, radiopaque platinum stent markers showed excellent visibility in ACT as well.The stent struts themselves, hardly visible in nonsubtracted DSA, were visible in MPRs and MIPs of ACT in all of the patients.In aneurysms larger than 10 mm in diameter, accurate stent assessment at the level of the coils was limited due to beam hardening artifacts.Postprocedural ACT in all of the patients did not reveal any evidence of procedure-related intracranial hemorrhage.CONCLUSION: ACT provides cross-sectional, 3D visualization of endovascular stents otherwise hardly visible with plain fluoroscopy.ACT enables us to accurately determine stent position, which may be helpful in complex stent-assisted aneurysm coiling procedures.However, in aneurysms larger than 10 mm in diameter, beam hardening artifacts caused by the endoaneurysmal coil package impair visibility of the stent.Further data are necessary to evaluate the usefulness of ACT in stent-assisted aneurysm coiling.

Chest pain is one of the most frequent symptoms in the emergency department. A variety of different diseases, some of them acutely life threatening, can be the underlying cause. Electrocardiogram (ECG)-gated computed tomography angiography of the thorax has been proposed as a cost and time effective imaging technique for these patients. We describe a new high-pitch scan mode, which has been developed specifically for low-dose ECG-triggered computed tomography angiography using dual source computed tomography (CT).Twenty-four patients were examined with this technique on a second generation dual source CT system. The scan mode uses a pitch of 3.2 to acquire a spiral CT data set of the complete thorax in less than 1 second with a temporal resolution of 75 ms (scan parameters: 128 x 0.6 mm collimation, 0.28 seconds gantry rotation time, 370 mAs at 100 kV [15 patients] and 320 mAs at 120 kV [9 patients], reconstructed slice thickness 0.6 mm, increment 0.4 mm). Data acquisition was prospectively triggered at 50% to 60% of the RR interval to cover the range over the heart in diastole. A triple phase contrast injection protocol (total volume: 80 mL) was used to optimize enhancement of the pulmonary and systemic arterial vessels. Image quality was evaluated using a 4-point scale (1 = absence of motion artifacts; 2 = slight motion artifacts, fully evaluable; 3 = motion artifacts, but evaluable; 4 = unevaluable) on a per-segment basis.The patients had an average heart rate of 68 +/- 15 bpm (range: 43-111 bpm) during data acquisition. Motion artifact free visualization of the aorta and pulmonary vessels was possible in each case, of 344 coronary artery segments, 242 (70%) had an image quality score of 1, 60 segments (17%) a score of 2, 28 segments (8%) a score of 3, and 14 segments (4%) were rated as "unevaluable." In 17 patients (10 patients with a heart rate < or =60 bpm) all segments were evaluable. The average dose length product was 113 +/- 11 mGy x cm per scan (mean effective dose 1.6 +/- 0.2 mSv) at 100 kV and 229 +/- 31 mGy x cm per scan (mean effective dose 3.2 +/- 0.4 mSv) at 120 kV.Our initial results indicate that this high-pitch scan mode allows motion artifact free and accurate visualization of the thoracic vessels, and diagnostic image quality of the coronary arteries in patients with low and stable heart rates at a very low radiation exposure.

X-ray scatter data have been calculated by Monte Carlo methods for diagnostic radiology applications. The scatter intensities relative to the primary intensities are given for different detectors for various values of object thickness, field size, object-to-detector distance, and primary energy. The results are compared with those from previous investigations. The calculations made it possible to resolve contradictions in published measurements regarding the dependence of scatter intensities on primary X-ray energy and detector response.

Tube current modulation (TCM) is one of the recent developments in multislice CT that has proven to reduce the patient radiation dose without affecting the image quality. Presently established methods and published coefficients for estimating organ doses from the dose measured free in air on the axis of rotation or in the CT dose index (CTDI) dosimetry phantoms do not take into account this relatively new development in CT scanner design and technology. Based on these organ dose coefficients effective dose estimates can be made. The estimates are not strictly valid for CT scanning protocols utilizing TCM. In this study, the authors investigated the need to take TCM into account when estimating organ and effective dose values.A whole-body adult anthropomorphic phantom (Alderson Rando) was scanned with a multislice CT scanner (Somatom Definition, Siemens, Forchheim, Germany) utilizing TCM (CareDose4D). Tube voltage was 120 kV, beam collimation 19.2 mm, and pitch 1. A voxelized patient model was used to define the tissues and organs in the phantom. Tube current values as a function of tube angle were obtained from the raw data for each individual tube rotation of the scan. These values were used together with the Monte Carlo dosimetry tool IMPACTMC (VAMP GmbH, Erlangen, Germany) to calculate organ dose values both with and without account of TCM. Angular and longitudinal modulations were investigated separately. Finally, corresponding effective dose conversion coefficients were determined for both cases according to the updated 2007 recommendations of the ICRP.TCM amplitude was greatest in the shoulder and pelvic regions. Consequently, dose distributions and organ dose values for particular cross sections changed considerably when taking angular modulation into account. The effective dose conversion coefficients were up to 11% lower for a single rotation in the shoulder region and 17% lower in the pelvis when taking angular TCM into account. In the head, neck, thorax, and upper abdominal regions, conversion coefficients changed similarly by only 5% or less. Conversion coefficients for estimating effective doses for scans of complete regions, e.g., chest or abdomen, were approximately 8% lower when taking angular and longitudinal TCMs into account.The authors conclude that for accurate organ and effective dose estimates in individual cross sections in the shoulder or pelvic regions, the angular tube current modulation should be taken into account. In general, using the average of the modulated tube current causes an overestimation of the effective dose.