The Influence of Patient Positioning in Breast CT on Breast Tissue Coverage and Patient Comfort.

PURPOSE: The presented study aimed at optimizing a patient table design for breast CT (BCT) systems with respect to breast tissue coverage and patient comfort. Additionally, the benefits and acceptance of an immobilization device for BCT using underpressure were evaluated. MATERIALS AND METHODS: Three different study parts were carried out. In a positioning study women were investigated on an MRI tabletop with exchangeable inserts (flat and cone-shaped with different opening diameters) to evaluate their influence on breast coverage and patient comfort in various positioning alternatives. Breast length and volume were calculated to compare positioning modalities including various opening diameters and forms. In the second study part, an underpressure system was tested for its functionality and comfort on a stereotactic biopsy table mimicking a future CT scanner table. In the last study part, this system was tested regarding breast tissue coverage. RESULTS: Best results for breast tissue coverage were shown for cone-shaped table inserts with an opening of 180 mm. Flat inserts did not provide complete coverage of breast tissue. The underpressure system showed robust function and tended to pull more breast tissue into the field of view. Patient comfort was rated good for all table inserts, with highest ratings for cone-shaped inserts. CONCLUSION: Cone-shaped tabletops appeared to be adequate for BCT systems and to allow imaging of almost the complete breast. An underpressure system proved promising for the fixation of the breast during imaging and increased coverage. Patient comfort appears to be adequate. KEY POINTS: Tissue coverage in breast CT is highly dependent on patient table design. An underpressure fixation system shows potential to increase breast coverage. The proposed breast CT patient table design combines good coverage and patient comfort.

The influence of patient positioning in breast CT on breast tissue coverage and patient comfort.

PURPOSE: The presented study aimed at optimizing a patient table design for breast CT (BCT) systems with respect to breast tissue coverage and patient comfort. Additionally, the benefits and acceptance of an immobilization device for BCT using underpressure were evaluated. MATERIALS AND METHODS: Three different study parts were carried out. In a positioning study women were investigated on an MRI tabletop with exchangeable inserts (flat and cone-shaped with different opening diameters) to evaluate their influence on breast coverage and patient comfort in various positioning alternatives. Breast length and volume were calculated to compare positioning modalities including various opening diameters and forms. In the second study part, an underpressure system was tested for its functionality and comfort on a stereotactic biopsy table mimicking a future CT scanner table. In the last study part, this system was tested regarding breast tissue coverage. RESULTS: Best results for breast tissue coverage were shown for cone-shaped table inserts with an opening of 180 mm. Flat inserts did not provide complete coverage of breast tissue. The underpressure system showed robust function and tended to pull more breast tissue into the field of view. Patient comfort was rated good for all table inserts, with highest ratings for cone-shaped inserts. CONCLUSION: Cone-shaped tabletops appeared to be adequate for BCT systems and to allow imaging of almost the complete breast. An underpressure system proved promising for the fixation of the breast during imaging and increased coverage. Patient comfort appears to be adequate.

Comparison of methods for acceptance and constancy testing in dental cone-beam computed tomography.

PURPOSE: The aim of this work was to implement, validate, and compare two procedures for routine image quality (IQ) assurance in dental cone-beam computed tomography (CBCT): 1. the German standard DIN 6868 - 161 introduced in 2013 and 2. the established standard IEC 61,223 - 3-5 for clinical CT x-ray equipment referenced as "DIN" and "IEC" below. MATERIALS AND METHODS: The approximated in-plane modulation transfer function (MTF), the contrast-to-noise indicator (CNI), and the uniformity indicator (UI*) were determined in accordance with DIN. Image noise, the uniformity index (UI), the contrast-to-noise ratio (CNR), and the 3 D MTF were measured according to IEC 61,223 - 3-5 using a previously proposed quality assurance (QA) framework. For this, a modular phantom was used. All experiments were performed on a clinical dental CBCT unit. The severity of image artefacts was measured at different z-positions. A dedicated computer program was implemented to allow for automated QA procedure. RESULTS: The position and orientation of the phantoms were detected automatically in all of the measurements providing a reproducible placement of the evaluation regions and volumes. 50 % and 10 % in-plane MTF values of the approximated and the exact MTF calculation procedure were in agreement to within 5 %. With increasing axial distance from the isocentre, UI* and CNI dropped by 30 % and 19 %, respectively. Conventional IQ parameters showed higher sensitivity to image artefacts; i. e., UI and CNR were reduced by about 197 % and 37 %. CONCLUSION: The implemented automated QA routines are compatible with both the DIN and the IEC approach and offer reliable and quantitative tracking of imaging performance in dental CBCT for clinical practice. However, there is no equivalence between the DIN and the IEC metrics. In addition, direct measurements of physical IQ parameters such as image contrast and noise, uniformity, and axial resolution are not supported by the new concept according to DIN. KEY POINTS: The new DIN 6868 - 161 is not equivalent to the established IEC 61 223 - 3-5. Noise, uniformity, and contrast are well-suited to assess image artefacts. The implemented automated quality assurance program fits clinical routine.

A low-radiation exposure protocol for 3D QCT of the spine.

SUMMARY: Cadaver and phantom measurements and simulations confirmed that radiation exposure in 3D QCT of the spine can be reduced if 80 kV instead of 120 kV protocols are used; 120 mAs and slice thicknesses of 1-1.3 mm should be usable but obese patient will require higher milliampere-second settings. PURPOSE: To develop a low-radiation exposure CT acquisition protocol for 3D QCT of the thoracolumbar spine. METHODS: Twenty-six cadavers were scanned with a standard protocol of 120 kV, 100 mAs and with a low-dose protocol using 90 kV, 150 mAs. The scan range included the vertebrae T6 to L4. Each vertebra was segmented and the integral volume and BMD of the total vertebral body were determined. Effective dose values were estimated. The impact of milliampere-second reduction on image quality was simulated by adding noise. RESULTS: One hundred ninety-six vertebrae were analyzed. Integral volume as well as integral BMD correlated significantly (p < 0.001) between standard and low-dose protocols (volume, r (2) = 0.991, residual root mean square (RMS) error, 0.77 cm(3); BMD, r (2) = 0.985, RMS error, 4.21 mg/cm(3)). The slope significantly differed from 1 for integral BMD but not for volume hinting at residual field inhomogeneity differences between the two voltage settings that could be corrected by cross-calibration. Compared to the standard protocol, effective dose was reduced by over 50 % in the low-dose protocol. Adding noise in the 90 kV images to simulate a reduction from 150 to 100 mAs did not affect the results for integral volume or BMD. CONCLUSIONS: For 3D QCT of the spine, depending on scanner type, 80 or 90 kV instead of 120 kV protocols may be considered as an important option to reduce radiation exposure; 120 mAs and slice thicknesses of 1-1.5 mm are usable if segmentation is robust to noise. In obese patients, higher milliampere-second settings will be required.

A Digital Model to Simulate Effects of Bone Architecture Variations on Texture at Spatial Resolutions of CT, HR-pQCT, and µCT Scanners.

The quantification of changes in the trabecular bone structure induced by musculoskeletal diseases like osteoarthritis, osteoporosis, rheumatoid arthritis, and others by means of a texture analysis is a valuable tool which is expected to improve the diagnosis and monitoring of a disease. The reaction of texture parameters on different alterations in the architecture of the fine trabecular network and inherent imaging factors such as spatial resolution or image noise has to be understood in detail to ensure an accurate and reliable determination of the current bone state. Therefore, a digital model for the quantitative analysis of cancellous bone structures was developed. Five parameters were used for texture analysis: entropy, global and local inhomogeneity, local anisotropy, and variogram slope. Various generic structural changes of cancellous bone were simulated for different spatial resolutions. Additionally, the dependence of the texture parameters on tissue mineralization and noise was investigated. The present work explains changes in texture parameter outcomes based on structural changes originating from structure modifications and reveals that a texture analysis could provide useful information for a trabecular bone analysis even at resolutions below the dimensions of single trabeculae.

Bone marrow lesions identified by MRI in knee osteoarthritis are associated with locally increased bone mineral density measured by QCT.

OBJECTIVE: Bone marrow lesions (BMLs) in the knee are associated with pain and compartment-specific joint space narrowing. However, the correlation of BMLs with bone mineral density (BMD) has rarely been investigated. The aim of the present study was to examine whether BMD in BMLs is altered compared to the surrounding bone. DESIGN: Thirty-four BMLs detected in osteoarthritis (OA) knees (KL grade 2 and 3) of 26 patients were investigated. A 3D-segmentation was used to determine BML volumes of interest (VOI) and their surrounding bone in MR images. These VOIs were registered to corresponding single-energy QCT images and a BMD analysis was performed. The same VOIs were transferred to control datasets (19 OA patients without BMLs) by an elastic registration, where the BMD analysis was repeated. To account for the dependence of bone marrow composition on BMD measures derived using single-energy QCT, simulations were performed to evaluate how changing fat-water compositions likely occurring with BML development may influence BMD measures and observed BMD differences between patients with and without BMLs. The association between loading in the knee and the occurrence of BMLs was investigated by medial to lateral (M:L) BMD ratios. RESULTS: BMD was significantly increased at BML locations, even with a fat-to-water conversion rate of 39%. The M:L BMD ratio was significantly increased in bones with medial BMLs. CONCLUSIONS: BMD was examined exactly at BML locations and surrounding bone using highly accurate segmentation and registration methods. BMD was significantly increased at BML locations (P < 0.05).

Effect of block-periodized exercise training on bone and coronary heart disease risk factors in early post-menopausal women: a randomized controlled study.

The purpose of this 12 month randomized exercise intervention was to determine the effect of a block-periodized multipurpose exercise program on bone mineral density (BMD) and parameters of the metabolic syndrome (MetS) in early post-menopausal women. Eighty-five subjects (52.3 ± 2.4 years) living in the area of Erlangen (Germany) were randomly assigned into an exercise (EG, n=43) or a wellness-control group (CG: n=42). The EG performed a periodized multipurpose exercise program with 4-6-week blocks of high-intensity bone-specific exercise intermitted by 10-12 weeks of exercise dedicated to increase endurance and reduce cardiac and metabolic risk factors. The CG performed a low-volume/low-intensity "wellness" program to increase well-being. After 12 months, significant exercise effects were observed for the lumbar spine (LS) BMD as assessed by quantitative computed tomography [total BMD (EG: -0.3 ± 2.1% vs CG: -2.1 ± 2.2%, P=0.015); trabecular BMD (EG: -0.7 ± 3.4% vs CG: -4.7 ± 4.9%, P=0.001) and dual-energy x-ray absorptiometry (DXA) (EG: -0.1 ± 2.2% vs CG: -2.0 ± 2.0%, P=0.002)]. However, no significant effects were observed for total hip BMD as assessed by DXA (P=0.152). Although all MetS parameters were favorably affected among the EG, only the effect for waist circumference was significant. In summary, short periods of bone-specific intervention embedded in longer periods of exercises dedicated to improve cardiovascular and metabolic risk factors positively affected BMD at the LS.

[Current strategies for dosage reduction in computed tomography]. / Aktuelle Strategien zur Dosisreduktion in der Computertomographie.

The potential risks of radiation exposure associated with computed tomography (CT) imaging are reason for ongoing concern for both medical staff and patients. Radiation dose reduction is, according to the as low as reasonably achievable principle, an important issue in clinical routine, research and development. The complex interaction of preparation, examination and post-processing provides a high potential for optimization on the one hand but on the other a high risk for errors. The radiologist is responsible for the quality of the CT examination which requires specialized and up-to-date knowledge. Most of the techniques for radiation dose reduction are independent of the system and manufacturer. The basic principle should be radiation dose optimization without loss of diagnostic image quality rather than just reduction.

An integrated segmentation and analysis approach for QCT of the knee to determine subchondral bone mineral density and texture.

We have developed a new integrated approach for quantitative computed tomography of the knee in order to quantify bone mineral density (BMD) and subchondral bone structure. The present framework consists of image acquisition and reconstruction, 3-D segmentation, determination of anatomic coordinate systems, and reproducible positioning of analysis volumes of interest (VOI). Novel segmentation algorithms were developed to identify growth plates of the tibia and femur and the joint space with high reproducibility. Five different VOIs with varying distance to the articular surface are defined in the epiphysis. Each VOI is further subdivided into a medial and a lateral part. In each VOI, BMD is determined. In addition, a texture analysis is performed on a high-resolution computed tomography (CT) reconstruction of the same CT scan in order to quantify subchondral bone structure. Local and global homogeneity, as well as local and global anisotropy were measured in all VOIs. Overall short-term precision of the technique was evaluated using double measurements of 20 osteoarthritic cadaveric human knees. Precision errors for volume were about 2-3% in the femur and 3-5% in the tibia. Precision errors for BMD were about 1-2% lower. Homogeneity parameters showed precision errors up to about 2% and anisotropy parameters up to about 4%.

Effect of whole-body vibration on neuromuscular performance and body composition for females 65 years and older: a randomized-controlled trial.

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.

Exercise and fractures in postmenopausal women: 12-year results of the Erlangen Fitness and Osteoporosis Prevention Study (EFOPS).

UNLABELLED: This trial is the first exercise study that focuses on fracture incidence as a primary study endpoint. Although we marginally failed to determine significant effects on "overall" fracture risk (p = .074) or rate ratio (p = .095), our findings further increased the evidence that exercise relevantly prevents fractures in the elderly. INTRODUCTION: The purpose of this study is to determine the effect of strictly supervised long-term exercise training on "overall" fracture incidence and bone mineral density (BMD) in postmenopausal osteopenic women. METHODS: Eighty-five early postmenopausal (1-8 years), osteopenic women living in the area of Erlangen-Nuremberg, Germany without any medication or diseases affecting bone metabolism were assessed after 12 years of supervised exercise (EG) or unvarying lifestyle (control, CG). Exercisers were encouraged to perform two group sessions/week and two home training sessions/week. Calcium and vitamin D supplementation was provided for both groups. "Overall" fractures were determined by questionnaires and structured interviews. The BMD was assessed at lumbar spine and proximal femur by dual-energy X-ray absorptiometry. RESULTS: "Overall" fracture risk ratio in the EG was 0.32 (95% confidence interval (CI), 0.08 to 1.05; p = .074), and the rate ratio for "overall" fractures was 0.38 (95% CI, 0.11 to 1.15; p = .095). BMD changes at lumbar spine (EG, -0.8%; 95% CI, 0.8% to -2.7% vs. CG, -4.0%; 95% CI, -2.4% to -5.7%; p = .011) and femoral neck (EG, -3.7%; 95% CI, -2.4% to -5.0% vs. CG, -6.7%; 95% CI, -5.3% to -8.2%; p = .003) significantly differed between both groups. CONCLUSION: Although we marginally failed to determine significant effects on overall fracture risk or rate ratio, our study increased the body of evidence for the fracture prevention efficiency of exercise programs, with special regard on bone strength (as assessed by bone mineral density measurement). Future studies should focus on subjects more prone to fractures to generate enough statistical power to clearly determine this issue.

Volume-of-interest imaging of the inner ear in a human temporal bone specimen using a robot- driven C-arm flat panel detector CT system.

VOI imaging can provide higher image quality at a reduced dose for a subregion. In this study with a robot-driven C-arm FDCT system, the goals were proof of feasibility for inner ear imaging, higher flexibility during data acquisition, and easier processing during reconstruction. First a low-dose OV scan was acquired allowing an orientation and enabling the selection of the VOI. The C-arm was then moved by the robotic system without a need for patient movement and the VOI was scanned with adapted parameters. Uncompromised artifact-free image quality was achieved by the 2-scan approach and the dose was reduced by 80%-90% in comparison with conventional MSCT and FPCT scans.

TU-D-217A-01: CTDI and Patient Dose: A European Perspective.

Dose in CT has been a dominant topic in Medical Physics for at least a decade. This was for good reason since increasing use of CT necessarily led to an increase of cumulative dose to the population and inappropriate use of CT in some cases led to an unnecessarily high exposure of patients with subsequent coverage in the U.S. media. Fortunately, this situation also triggered a number of positive technical developments and fruitful initiatives worldwide. Currently, even "sub-mSv CT" is a realistic topic. However, we also engage in extensive discussions of the topic "CTDI and patient dose". They do not always seem to be pragmatic and sometimes are unnecessarily complicated. One reason may be that the topics computed tomography dose index (CTDI) and patient dose are seen necessarily combined. This lecture aims at discussing and hopefully helping to resolve some of the issues. Key points and suggestions are the following: • CTDI is a proven and reasonably good concept for scanner dosimetry and quality control (QC) on standard 64-row scanners. There is no major debate on CTDI efficiency and similar issues in Europe. • The new IEC scanner dosimetry concept to be used for wider detectors is acceptable; there is no need for new and heavy phantoms. • There still is a need of phantoms and concepts for QC of automated exposure control systems in CT. • CTDI should not and need not be changed and expanded to assess patient dose. • Patient dose estimates (both organ and effective dose) are based on air kerma measurements (without a CTDI phantom) and MC calculations using mathematical phantoms and/or voxel models. The DLP-to-E conversion which is accepted in Europe for more than a decade was based on this approach. • Patient dose estimates, both organ and effective dose, should be scanner- and patient-specific. Fast MC programs and dose software allow for this. Manufacturer cooperation is a necessity, and there are first positive examples. • The concept of diagnostic reference levels (DRL) which was started in Europe in the 1990s and is in wide use today has to be revisited. It need not be based on CTDI further on but, for example, on a revised scanner- and patient-specific DLP-to-E conversion. • An international consensus on the topics CTDI and patient dose appears desirable. All these points do not mean a revolution but rather aim at staying with established equipment. The two major objectives are to • avoid unnecessary QC burden of medical physicists who are threatened with extended CTDI measurements • provide more reliable and understandable information regarding patient dose in real time. Organ dose and effective dose are preferable to DLP. LEARNING OBJECTIVES: 1. Understand that CTDI is a technical concept for scanner acceptance and constancy testing 2. Learn about concepts for patient- and scanner-specific patient dose estimates 3. Learn about the concept of diagnostic reference levels and its strengths and weaknesses Research sponsored by Siemens Healthcare and by CT Imaging GmbH, both in Erlangen, Germany.

[Effects of two different types of whole body vibration on neuromuscular performance and body composition in postmenopausal women]. / Effekte unterschiedlicher Ganzkörpervibrationssysteme auf die neuromuskuläre Leistungsfähigkeit und die Körperzusammensetzung postmenopausaler Frauen.

PURPOSE: The effects of different types of whole body vibration (WBV) training on neuromuscular performance and body composition were determined in postmenopausal women. METHODS: In the Erlangen Longitudinal Vibration Study II (ELVIS-II-Study) 108 postmenopausal women between 60 and 75 years of age (average 65.8 ± 3.5 years) were randomly assigned to one of three groups: two WBV training-groups (n = 36 each), each performing an identical program thrice a week for 15 min on two different types of vibration plates for one year: 1. vertical vibrating, 35 Hz, 1.7 mm (VG); 2. rotational vibrating 12.5 Hz, 12 mm (RG). A control group (n = 36) conducted a low intensity gymnastic and relaxation program. Muscular strength and power were assessed, body composition was determined by Dual-energy X-ray absorptiometry (DXA), and pain intensity was assessed by a questionnaire. RESULTS: Maximum leg strength (VG: 24.4 %; RG: 26.6 %; KG: 6.2 %; p < 0.001) and maximum trunk flexion strength (VG: 12.2 %; RG: 11.5 %; KG: -5.5 %; p = 0.01) significantly increased in both vibration groups. No changes were found for body composition parameters (lean body mass, appendicular muscle mass, fat mass). Pain intensity in the big joints (p < 0.05) decreased in both vibration groups, in the lumbar spine region this was not significant. There was no difference between vibration types. No vibration-related side effects were observed. CONCLUSION: The study results suggest that WBV might be an alternative to classic training contents to increase maximum strength and reduce pain.

Effects of whole body vibration on bone mineral density and falls: results of the randomized controlled ELVIS study with postmenopausal women.

UNLABELLED: We determined whether the effect of exercise on bone mineral density (BMD) and falls can be enhanced by whole body vibration (WBV). In summary, the multi-purpose exercise training was effective to increase lumbar BMD but added WBV did not enhance this effect. However, falls were lowest in the exercise program combined with WBV. INTRODUCTION: WBV is a new approach to reduce the risk of osteoporotic fractures. In the "Erlangen Longitudinal Vibration Study" (ELVIS), we investigated whether WBV enhances the effect of multifunctional exercise on BMD and falls. METHODS: One hundred fifty-one postmenopausal women (68.5 ± 3.1 years) were randomly assigned to a: (1) conventional training group (TG); (2) conventional training group including vibration (TGV); and (3) wellness control group (CG). TG conducted an exercise program consisting of 20 min dancing aerobics, 5 min balance training, 20 min functional gymnastics, and 15 min dynamic leg-strength training on vibration plates (without vibration) twice a week. TGV performed an identical exercise regimen with vibration (25-35 Hz) during the leg-strengthening sequence. CG performed a low-intensity wellness program. BMD was measured at the hip and lumbar spine at baseline and follow-up using the DXA method. Falls were recorded daily via the calendar method. RESULTS: After 18 months, an increase in BMD at the lumbar spine was observed in both training groups (TGV: +1.5% vs. TG: +2.1%). The difference between the TG and the CG (1.7%) was significant. At the hip no changes were determined in either group. The fall frequency was significantly lower in TGV (0.7 falls/person) compared with CG (1.5), whereas the difference between TG (0.96) and CG was not significant. CONCLUSIONS: A multifunctional training program had a positive impact on lumbar BMD. The application of vibration did not enhance these effects. However, only the training including WBV affected the number of falls significantly.

[Digital volume tomography (DVT) and multislice spiral CT (MSCT): an objective examination of dose and image quality]. / Digitale Volumentomografie (DVT) und Mehrschicht-Spiral-CT (MSCT): eine objektive Untersuchung von Dosis und Bildqualität.

PURPOSE: In the last five years digital volume tomographs (DVT) have found their way into the diagnostic imaging of the facial skull. In this study both the image quality and dose of DVT and multislice spiral CT (MSCT) in this field of application were investigated using established physical methods for CT. MATERIALS AND METHODS: Measurements on DVT scanners of various manufacturers and on a modern MSCT scanner were performed. The investigation was based on equivalent dose levels for both modalities (CT dose index, CTDI). For this purpose, the dose was measured with an ionization chamber in a cylindrical PMMA phantom. For the evaluation of image quality, the spatial resolution, contrast and noise were investigated with phantoms established for CT. RESULTS: MSCT exhibited spatial resolution values of 1.0 to 1.6 lp/mm, while DVT provided resolution between 0.6 and 1.0 lp/mm only. Thus, MSCT offered similar or better resolution at an equivalent dose. For soft tissue resolution, DVT showed significant image artifacts. MSCT yielded higher homogeneity and no significant artifacts, and the contrast steps of the phantom were more verifiable. The different DVT devices, from image intensifiers to modern flat-detector (FD) devices, showed significant differences in favor of the FD devices. CONCLUSION: For medium and high contrast applications (teeth/bones), DVT scanners can be an alternative to MSCT at comparable radiation exposure. However, MSCT offers advantages in terms of constantly good and controlled image quality with significantly more flexible scan parameters at a constant or lower dose and should therefore be given preference.

Development, implementation and evaluation of a dedicated metal artefact reduction method for interventional flat-detector CT.

The purpose of this study was to develop, implement and evaluate a dedicated metal artefact reduction (MAR) method for flat-detector CT (FDCT). The algorithm uses the multidimensional raw data space to calculate surrogate attenuation values for the original metal traces in the raw data domain. The metal traces are detected automatically by a three-dimensional, threshold-based segmentation algorithm in an initial reconstructed image volume, based on twofold histogram information for calculating appropriate metal thresholds. These thresholds are combined with constrained morphological operations in the projection domain. A subsequent reconstruction of the modified raw data yields an artefact-reduced image volume that is further processed by a combining procedure that reinserts the missing metal information. For image quality assessment, measurements on semi-anthropomorphic phantoms containing metallic inserts were evaluated in terms of CT value accuracy, image noise and spatial resolution before and after correction. Measurements of the same phantoms without prostheses were used as ground truth for comparison. Cadaver measurements were performed on complex and realistic cases and to determine the influences of our correction method on the tissue surrounding the prostheses. The results showed a significant reduction of metal-induced streak artefacts (CT value differences were reduced to below 22 HU and image noise reduction of up to 200%). The cadaver measurements showed excellent results for imaging areas close to the implant and exceptional artefact suppression in these areas. Furthermore, measurements in the knee and spine regions confirmed the superiority of our method to standard one-dimensional, linear interpolation.

The influence of the heel effect in cone-beam computed tomography: artifacts in standard and novel geometries and their correction.

For decades, the heel effect has been known to cause an angular dependence of the emitted spectrum of an x-ray tube. In radiography, artifacts were observed and attributed to the heel effect. However, no problems due to the heel effect were discerned in multi-slice computed tomography (MSCT) so far. With flat-detector CT (FDCT), involving larger cone angles and different system geometries, the heel effect might cause new artifacts. These artifacts were analyzed in this paper for system geometries different from the ones widely used nowadays. Simulations and measurements were performed. Simulations included symmetric as well as asymmetric detector layouts and different x-ray tube orientations with respect to the detector plane. The measurements were performed on a micro-CT system in an asymmetric detector layout. Furthermore, an analytical correction scheme is proposed to overcome heel effect artifacts. It was shown that the type of artifact greatly depends on the orientation of the x-ray tube and also on the type of detector alignment (i.e. symmetric or different types of asymmetric alignment). Certain combinations exhibited almost no significant artifact while others greatly influenced the quality of the reconstructed images. The proposed correction scheme showed good results that were further improved when also applying a scatter correction. When designing CT systems, care should be taken when placing the tube and the detector. Orientation of the x-ray tube like in most MSCT systems seems advisable in asymmetric detector layouts. However, a different type of tube orientation can be overcome with suitable correction schemes.

Flat detector CT in the evaluation of brain parenchyma, intracranial vasculature, and cerebral blood volume: a pilot study in patients with acute symptoms of cerebral ischemia.

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 < .001). The Bland-Altman test showed a mean difference of CBV values between FD-CT and CTP-CBV of 0.04 ± 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.

In vivo imaging of MSCT and micro-CT: a comparison.

PURPOSE: To evaluate the potential of MSCT and a novel AmicroCT system to assess the volume of malignant brain tumors in rats compared to histology. MATERIALS AND METHODS: Fourteen rats underwent stereotactic implantation of GFP-marked F 98-glioma cells. On day 10 after implantation, animals received double-dose contrast-enhanced AmicroCT and MSCT imaging using Iomeprol. MSCT- and AmicroCT-derived tumor volumes were calculated and compared to histology (fluorescence staining) as the gold standard. RESULTS: There was good correlation between the AmicroCT-derived tumor volume (69 A+ or - 23 mm(3)) and histology (81 A + or - 14 mm(3); p > 0.14). MSCT, however, showed significantly smaller tumor volumes (55 A + or - 25 mm(3)) compared to histology (p < 0.01) but was able to detect the tumors in all animals. CONCLUSION: AmicroCT allows in vivo imaging of the contrast-enhancing parts of experimental gliomas with high correlation to histology. Although MSCT is less suitable for assessing exact tumor volume, this method reliably detects tumors in rats. Due to the high spatial resolution, AmicroCT-systems could play an important role for fusion imaging, e. g. to assess experimental brain gliomas with multimodal AmicroCT/PET- or AmicroCT/MRI-fusion images.