Improved coronary calcium detection and quantification with low-dose full field-of-view photon-counting CT: a phantom study.

OBJECTIVE: The aim of the current study was to systematically assess coronary artery calcium (CAC) detection and quantification for spectral photon-counting CT (SPCCT) in comparison to conventional CT and, in addition, to evaluate the possibility of radiation dose reduction. METHODS: Routine clinical CAC CT protocols were used for data acquisition and reconstruction of two CAC containing cylindrical inserts which were positioned within an anthropomorphic thorax phantom. In addition, data was acquired at 50% lower radiation dose by reducing tube current, and slice thickness was decreased. Calcifications were considered detectable when three adjacent voxels exceeded the CAC scoring threshold of 130 Hounsfield units (HU). Quantification of CAC (as volume and mass score) was assessed by comparison with known physical quantities. RESULTS: In comparison with CT, SPCCT detected 33% and 7% more calcifications for the small and large phantoms, respectively. At reduced radiation dose and reduced slice thickness, small phantom CAC detection increased by 108% and 150% for CT and SPCCT, respectively. For the large phantom size, noise levels interfered with CAC detection. Although comparable between CT and SPCCT, routine protocols CAC quantification showed large deviations (up to 134%) from physical CAC volume. At reduced radiation dose and slice thickness, physical volume overestimations decreased to 96% and 72% for CT and SPCCT, respectively. In comparison with volume scores, mass score deviations from physical quantities were smaller. CONCLUSION: CAC detection on SPCCT is superior to CT, and was even preserved at a reduced radiation dose. Furthermore, SPCCT allows for improved physical volume estimation. KEY POINTS: • In comparison with conventional CT, increased coronary artery calcium detection (up to 156%) for spectral photon-counting CT was found, even at 50% radiation dose reduction. • Spectral photon-counting CT can more accurately measure physical volumes than conventional CT, especially at reduced slice thickness and for high-density coronary artery calcium. • For both conventional and spectral photon-counting CT, reduced slice thickness reconstructions result in more accurate physical mass approximation.

Coronary calcium scoring potential of large field-of-view spectral photon-counting CT: a phantom study.

OBJECTIVE: The aim of the current study was, first, to assess the coronary artery calcium (CAC) scoring potential of spectral photon-counting CT (SPCCT) in comparison with computed tomography (CT) for routine clinical protocols. Second, improved CAC detection and quantification at reduced slice thickness were assessed. METHODS: Raw data was acquired and reconstructed with several combinations of reduced slice thickness and increasing strengths of iterative reconstruction (IR) for both CT systems with routine clinical CAC protocols for CT. Two CAC-containing cylindrical inserts, consisting of CAC of different densities and sizes, were placed in an anthropomorphic phantom. A specific CAC was detectable when 3 or more connected voxels exceeded the CAC scoring threshold of 130 Hounsfield units (HU). For all reconstructions, total CAC detectability was compared between both CT systems. Significant differences in CAC quantification (Agatston and volume scores) were assessed with Mann-Whitney U tests. Furthermore, volume scores were compared with the known CAC physical. RESULTS: CAC scores for routine clinical protocols were comparable between SPCCT and CT. SPCCT showed 34% and 4% higher detectability of CAC for the small and large phantom, respectively. At reduced slice thickness, CAC detection increased by 142% and 169% for CT and SPCCT, respectively. In comparison with CT, volume scores from SPCCT were more comparable with the physical volume of the CAC. CONCLUSION: CAC scores using routine clinical protocols are comparable between conventional CT and SPCCT. The increased spatial resolution of SPCCT allows for increased detectability and more accurate CAC volume estimation. KEY POINTS: • Coronary artery calcium scores using routine clinical protocols are comparable between conventional CT and spectral photon-counting CT. • In comparison with conventional CT, increased coronary artery calcium detectability was shown for spectral photon-counting CT due to increased spatial resolution. • Volumes scores were more accurately determined with spectral photon-counting CT.

Three artificial intelligence data challenges based on CT and MRI.

PURPOSE: The second edition of the artificial intelligence (AI) data challenge was organized by the French Society of Radiology with the aim to: (i), work on relevant public health issues; (ii), build large, multicentre, high quality databases; and (iii), include three-dimensional (3D) information and prognostic questions. MATERIALS AND METHODS: Relevant clinical questions were proposed by French subspecialty colleges of radiology. Their feasibility was assessed by experts in the field of AI. A dedicated platform was set up for inclusion centers to safely upload their anonymized examinations in compliance with general data protection regulation. The quality of the database was checked by experts weekly with annotations performed by radiologists. Multidisciplinary teams competed between September 11th and October 13th 2019. RESULTS: Three questions were selected using different imaging and evaluation modalities, including: pulmonary nodule detection and classification from 3D computed tomography (CT), prediction of expanded disability status scale in multiple sclerosis using 3D magnetic resonance imaging (MRI) and segmentation of muscular surface for sarcopenia estimation from two-dimensional CT. A total of 4347 examinations were gathered of which only 6% were excluded. Three independent databases from 24 individual centers were created. A total of 143 participants were split into 20 multidisciplinary teams. CONCLUSION: Three data challenges with over 1200 general data protection regulation compliant CT or MRI examinations each were organized. Future challenges should be made with more complex situations combining histopathological or genetic information to resemble real life situations faced by radiologists in routine practice.

Head-to-head comparison of lung perfusion with dual-energy CT and SPECT-CT.

PURPOSE: To compare the quantitative and qualitative lung perfusion data acquired with dual energy CT (DECT) to that acquired with a large field-of-view cadmium-zinc-telluride camera single-photon emission CT coupled to a CT system (SPECT-CT). MATERIALS AND METHODS: A total of 53 patients who underwent both dual-layer DECT angiography and perfusion SPECT-CT for pulmonary hypertension or pre-operative lobar resection surgery were retrospectively included. There were 30 men and 23 women with a mean age of 65.4±17.5 (SD)years (range: 18-88years). Relative lobar perfusion was calculated by dividing the amount (of radiotracer or iodinated contrast agent) per lobe by the total amount in both lungs. Linear regression, Bland-Altman analysis, and Pearson's correlation coefficient were also calculated. Kappa test was used to test agreements in morphology and severity of perfusion defects assessed on SPECT-CT and on DECT iodine maps with a one-month interval. Wilcoxon rank sum test was used to compare the sharpness of perfusion defects and radiation dose among modalities. RESULTS: Strong correlations for relative lobar perfusion using linear regression analysis and Pearson's correlation coefficient (r=0.93) were found. Bland-Altman analysis revealed a -0.10 bias, with limits of agreement between [-6.01; 5.81]. With respect to SPECT- CT as standard of reference, the sensitivity, specificity, PPV, NPV, accuracy for lobar perfusion defects were 89.4% (95% CI: 82.6-93.4%), 96.5% (95% CI: 92.1-98.5%), 95.6% (95% CI: 90.9-97.8%), 91.4% (95% CI: 85.6-94.9%) and 93.0% (95% CI: 87.6-96.1%) respectively. High level of agreement was found for morphology and severity of perfusion defects between modalities (Kappa=0.84 and 0.86 respectively) and on DECT images among readers (Kappa=0.94 and 0.89 respectively). A significantly sharper delineation of perfusion defects was found on DECT images (P<0.0001) using a significantly lower equivalent dose of 4.1±2.3 (SD) mSv (range: 1.9-11.85mSv) compared to an equivalent dose of 5.3±1.1 (SD) mSv (range: 2.8-7.3mSv) for SPECT-CT, corresponding to a 21.2% dose reduction (P=0.0004). CONCLUSION: DECT imaging shows strong quantitative correlations and qualitative agreements with SPECT-CT for the evaluation of lung perfusion.

CT dose optimization for the detection of pulmonary arteriovenous malformation (PAVM): A phantom study.

PURPOSE: To determine the lowest suitable dose level for the detection of pulmonary arteriovenous malformation (PAVM) using a task-based image quality assessment. MATERIAL AND METHODS: A phantom was scanned using the standard chest protocol (STD) and 4 other ultra-low dose protocols (ULD) using various kVp. Raw data were reconstructed using level 5 of the hybrid iterative reconstruction algorithm (iDose4) for the STD protocol, and level 6 of iDose4 and levels 1 to 3 of model-based iterative reconstruction (IMR) for the ULD protocols. Both quantitative criteria and qualitative analysis were used to compare protocols. Noise-power-spectrum and Task-based transfer function were computed using imQuest software. The detectability-index (d') was computed for the detection of PAVM. A subjective analysis was performed by 2 chest radiologists to validate the image-quality obtained on the anthropomorphic phantom for all protocols. RESULTS: Similar d' values were found for ULD-140 using iDose4 6 compared to STD protocol. Greater d' values were found for all ULD protocols using IMR compared to STD. Subjective image quality was rated as acceptable to excellent for ULD-140 and ULD-120 for all reconstruction types, for ULD-100 and ULD-80 using IMR2, and for ULD-100 using IMR1. Image smoothing was poor for IMR3 for ULD-100 and ULD-80. Finally, the ULD-80 protocol reconstructed with IMR2 was chosen for the detection of PAVM. With this protocol, the dose (CTDIvol of 0.3mGy) was reduced by 91% compared with the STD protocol. CONCLUSION: A dose level as low as 0.3mGy reconstructed with IMR2 provides an image quality suitable for the detection of PAVM.

Pubic osteomyelitis: Epidemiology and factors associated with treatment failure.

OBJECTIVE: To describe the epidemiology of pubic osteomyelitis (PO) and to look for factors associated with treatment failure. METHOD: Retrospective study describing PO according to outcome: success or failure of initial management. Factors associated with failure determined by univariate Cox analysis. Kaplan-Meier curve compared between groups by log-rank test. RESULTS: Twenty-five patients were included over a 13-year period; 24% of PO had blood-borne infection. Failure (44%) was always observed in chronic postoperative presentations (76%). Fistula (32%) was only observed in postoperative presentations and was significantly associated with failure (HR 5.1; P=0.011). Other risk factors were pelvic malignant tumor history, abscess, infection due to extended-spectrum beta-lactamase-producing Enterobacteriaceae, and polymicrobial infection. CONCLUSION: PO is most often a chronic postoperative polymicrobial infection in patients with comorbidities at high risk of relapse. Studies in larger cohorts could assess the efficacy of more aggressive surgical strategies in patients at high risk of failure.

Kidney cortex segmentation in 2D CT with U-Nets ensemble aggregation.

PURPOSE: This work presents our contribution to one of the data challenges organized by the French Radiology Society during the Journées Francophones de Radiologie. This challenge consisted in segmenting the kidney cortex from coronal computed tomography (CT) images, cropped around the cortex. MATERIALS AND METHODS: We chose to train an ensemble of fully-convolutional networks and to aggregate their prediction at test time to perform the segmentation. An image database was made available in 3 batches. A first training batch of 250 images with segmentation masks was provided by the challenge organizers one month before the conference. An additional training batch of 247 pairs was shared when the conference began. Participants were ranked using a Dice score. RESULTS: The segmentation results of our algorithm match the renal cortex with a good precision. Our strategy yielded a Dice score of 0.867, ranking us first in the data challenge. CONCLUSION: The proposed solution provides robust and accurate automatic segmentations of the renal cortex in CT images although the precision of the provided reference segmentations seemed to set a low upper bound on the numerical performance. However, this process should be applied in 3D to quantify the renal cortex volume, which would require a marked labelling effort to train the networks.

Automatic knee meniscus tear detection and orientation classification with Mask-RCNN.

PURPOSE: This work presents our contribution to a data challenge organized by the French Radiology Society during the Journées Francophones de Radiologie in October 2018. This challenge consisted in classifying MR images of the knee with respect to the presence of tears in the knee menisci, on meniscal tear location, and meniscal tear orientation. MATERIALS AND METHODS: We trained a mask region-based convolutional neural network (R-CNN) to explicitly localize normal and torn menisci, made it more robust with ensemble aggregation, and cascaded it into a shallow ConvNet to classify the orientation of the tear. RESULTS: Our approach predicted accurately tears in the database provided for the challenge. This strategy yielded a weighted AUC score of 0.906 for all three tasks, ranking first in this challenge. CONCLUSION: The extension of the database or the use of 3D data could contribute to further improve the performances especially for non-typical cases of extensively damaged menisci or multiple tears.

Convolutional neural network evaluation of over-scanning in lung computed tomography.

INTRODUCTION: The purpose of this study was to develop a convolutional neural network (CNN) to determine the extent of over-scanning in the Z-direction associated with lung computed tomography (CT) examinations. MATERIALS AND METHODS: The CT examinations of 250 patients were used to train the machine learning software and 100 were used to validate the results. Each lung CT examination was divided into cervical, lung, and abdominal areas by the CNN and 2 independent radiologists, and the length of each area was measured. Every part above or below the lung marks was labeled as over-scanning. The accuracy of the CNN was calculated after the training phase and agreement between CNN and radiologists was assessed using kappa statistics during the validation phase. After validation the software was used to estimate the length of each of the three areas and the total over-scanning in further 1000 patients. RESULTS: An accuracy of 0.99 was found for the testing dataset and a very good agreement (kappa=0.98) between the CNN and the radiologists' evaluation was found for the validation dataset. Over-scanning was 22.8% with the CNN and 22.2% with the radiologists. The degree of over-scanning was 22.6% in 1000 lung CT examinations. CONCLUSION: Our study shows a substantial over estimation of the length of the area to be scanned during lung CT and thus an unnecessary patient's over-exposure to ionizing radiation. This over-scanning can be assessed easily, reliably and quickly using CNN.

Reduction of patient radiation dose with a new organ based dose modulation technique for thoraco-abdominopelvic computed tomography (CT) (Liver dose right index).

PURPOSE: To evaluate the radiation dose reduction, image quality and diagnostic confidence with thoraco-abdominopelvic computed tomography (TACT) using a new organ based dose modulation system (liver dose right index [Liver DRI]), compared to TACT using a standard automatic exposure control adjusting mA according to attenuation. METHODS: A total of 37 patients who had two TACT examinations on 2 different CT scanners, one using standard automatic exposure control (combination of a DoseRight automatic current selection and Z modulation) and one using Liver DRI were included. There were 19 men and 18 women with a mean age of 67.6±11.7 (SD) years (range: 36-85 years) For each patient, volume CT dose index (CTDIvol), size-specific dose estimates (SSDE) and signal-to-noise ratio (SNR) were evaluated at each anatomic level (lung, breast, liver and pelvis area) for each protocol. Two radiologists assessed independently image quality, artifacts and diagnostic confidence. RESULTS: The radiation dose decreased significantly using Liver DRI compared to standard automatic exposure control on the total scan length, lung, breast and pelvis area, with a significant CTDIvol reduction of 27% (P=0.0001), 23% (P=0.0002), 24% (P=0.0002) and 31% (P=0.0001), respectively; and a significant SSDE reduction of 23% (P=0.0001), 28% (P=0.0001), 23% (P=0.0002) and 29% (P=0.0001), respectively. No significant SNR reductions were observed in all measured tissues at the level of the aortic arch, celiac trunk and iliac bifurcation, except in the muscle (P=0.0013) and fat tissue (P=0.0052) at the level of the ureteral meatus. No significant differences were noted between both protocols in overall image quality, artifacts and diagnostic confidence with an excellent inter observer agreement between radiologists (Kappa values of 0.83, 0.85 and 0.88, respectively). CONCLUSION: Liver DRI organ based dose modulation technique allows significant dose reduction compared to standard automatic exposure control while preserving diagnostic image quality in all thoraco-abdominopelvic areas.

[Pelvic nodules in a young woman: All is not endometriosis!] / Nodules pelviens chez une femme jeune : tout n'est pas de l'endométriose !

Splenosis is a pathology resulting from a rupture of the spleen due to a trauma or a surgery. We report the case of a patient presenting with a splenosis, initially diagnosed as endometriosis-related pelvic nodules, the most frequent cause of pelvic nodules in women. We will describe the imaging strategy that led to the final diagnosis of splenosis.

Computational modeling of flow-altering surgeries in basilar aneurysms.

In cases where surgeons consider different interventional options for flow alterations in the setting of pathological basilar artery hemodynamics, a virtual model demonstrating the flow fields resulting from each of these options can assist in making clinical decisions. In this study, image-based computational fluid dynamics (CFD) models were used to simulate the flow in four basilar artery aneurysms in order to evaluate postoperative hemodynamics that would result from flow-altering interventions. Patient-specific geometries were constructed using MR angiography and velocimetry data. CFD simulations carried out for the preoperative flow conditions were compared to in vivo phase-contrast MRI measurements (4D Flow MRI) acquired prior to the interventions. The models were then modified according to the procedures considered for each patient. Numerical simulations of the flow and virtual contrast transport were carried out in each case in order to assess postoperative flow fields and estimate the likelihood of intra-aneurysmal thrombus deposition following the procedures. Postoperative imaging data, when available, were used to validate computational predictions. In two cases, where the aneurysms involved vital pontine perforator arteries branching from the basilar artery, idealized geometries of these vessels were incorporated into the CFD models. The effect of interventions on the flow through the perforators was evaluated by simulating the transport of contrast in these vessels. The computational results were in close agreement with the MR imaging data. In some cases, CFD simulations could help determine which of the surgical options was likely to reduce the flow into the aneurysm while preserving the flow through the basilar trunk. The study demonstrated that image-based computational modeling can provide guidance to clinicians by indicating possible outcome complications and indicating expected success potential for ameliorating pathological aneurysmal flow, prior to a procedure.

Use of an automatic recording system for CT doses: evaluation of the impact of iterative reconstruction on radiation exposure in clinical practice.

OBJECTIVE: Despite the obligatory recording of doses administered to patients during CT scans, this data is not easily accessible. The objective of this study was to implement and validate a computerised automated dose-recording system for CT scans, for a single radiology department. MATERIAL AND METHODS: Every patient undergoing a CT scan in our department over a one-year period was included in the study. The CT scanner was upgraded after eight months (installation of iterative reconstruction and choice of an additional voltage of 100 kV). The system recorded, from DICOM image headers, the patient data and technical acquisition parameters. The statistical analysis compared the dose length products (DLP) before and after the upgrade, and compared them with the diagnostic reference levels (DRL). RESULTS: Four thousand seven hundred and ninety-five CT scans were included (2141 before the upgrade and 2654 after). For all of the acquisition protocols tested, there was a reduction in DLP after the upgrade. The mean reduction was 30%, with a range of 17% to 44% depending on the protocol. After the upgrade, all of the mean DLPs were under the DRL thresholds (P<0.0001). CONCLUSION: The proposed tool enabled systematic recording of the doses of radiation used in CT scans. It confirmed the significant reduction in the dose resulting from the implementation of iterative reconstruction, and enabled an exhaustive and rapid control of the respect of DRLs.

Grading of small hepatocellular carcinomas (≤2 cm): correlation between histology, T2 and diffusion-weighted imaging.

OBJECTIVE: To evaluate the capacity of diffusion-weighted imaging (DWI) to determine the histological grade of small-sized hepatocellular carcinomas (HCCs) in liver cirrhosis in comparison with T2 weighted imaging. METHODS: 51 cirrhotic patients with 63 histologically proven HCCs ≤2 cm underwent abdominal MRI, including DWI (b-values 50, 400 and 800 s mm(-2)) and T2 weighted sequences. HCCs were classified into well-differentiated HCCs (n = 37) and moderately differentiated HCCs (n = 26). Relative contrast ratios (RCRs) between the lesions and the surrounding liver were performed and compared between the two groups for T2 weighted images, each b-value and apparent diffusion coefficients (ADCs). A receiver operating characteristic (ROC) analysis was performed to compare RCRs in T2 and diffusion-weighted images. RESULTS: We found significant differences in RCRs between well-differentiated vs moderately differentiated HCCs for b = 50, 400 and 800 s mm(-2) and T2 weighted images (1.35 ± 0.36 vs 1.86 ± 0.62; 1.35 ± 0.38 vs 1.82 ± 0.60; 1.27 ± 0.30 vs 1.74 ± 0.53; 1.14 ± 0.18 vs 1.43 ± 0.28, respectively; p < 0.001), whereas no significant differences were observed in ADC and ADC RCR (1.05 ± 0.19 vs 0.99 ± 0.15 and 1.1 ± 0.22 vs 1.09 ± 0.23; p = 0.16 and p = 0.82, respectively). No significant difference was found in the areas under the ROC curve for RCRs of T2 weighted images and every DWI b-value (p = 0.18). CONCLUSION: The RCR measurement performed in DWI 50, 400 and 800 b-values and T2 demonstrated a significant difference between well-differentiated and moderately differentiated small-sized HCCs. Furthermore, no difference was shown by using either ADC or ADC RCR. ADVANCES IN KNOWLEDGE: DWI with RCR measurement may be a valuable tool for non-invasively predicting the histological grade of small HCCs.

Photon counting spectral CT component analysis of coronary artery atherosclerotic plaque samples.

OBJECTIVE: To evaluate the capabilities of photon counting spectral CT to differentiate components of coronary atherosclerotic plaque based on differences in spectral attenuation and iodine-based contrast agent concentration. METHODS: 10 calcified and 13 lipid-rich non-calcified histologically demonstrated atheromatous plaques from post-mortem human coronary arteries were scanned with a photon counting spectral CT scanner. Individual photons were counted and classified in one of six energy bins from 25 to 70 keV. Based on a maximum likelihood approach, maps of photoelectric absorption (PA), Compton scattering (CS) and iodine concentration (IC) were reconstructed. Intensity measurements were performed on each map in the vessel wall, the surrounding perivascular fat and the lipid-rich and the calcified plaques. PA and CS values are expressed relative to pure water values. A comparison between these different elements was performed using Kruskal-Wallis tests with pairwise post hoc Mann-Whitney U-tests and Sidak p-value adjustments. RESULTS: RESULTS for vessel wall, surrounding perivascular fat and lipid-rich and calcified plaques were, respectively, 1.19 ± 0.09, 0.73 ± 0.05, 1.08 ± 0.14 and 17.79 ± 6.70 for PA; 0.96 ± 0.02, 0.83 ± 0.02, 0.91 ± 0.03 and 2.53 ± 0.63 for CS; and 83.3 ± 10.1, 37.6 ± 8.1, 55.2 ± 14.0 and 4.9 ± 20.0 mmol l(-1) for IC, with a significant difference between all tissues for PA, CS and IC (p < 0.012). CONCLUSION: This study demonstrates the capability of energy-sensitive photon counting spectral CT to differentiate between calcifications and iodine-infused regions of human coronary artery atherosclerotic plaque samples by analysing differences in spectral attenuation and iodine-based contrast agent concentration. ADVANCES IN KNOWLEDGE: Photon counting spectral CT is a promising technique to identify plaque components by analysing differences in iodine-based contrast agent concentration, photoelectric attenuation and Compton scattering.

Multilevel assessment of atherosclerotic extent using a 40-section multidetector scanner after transient ischemic attack or ischemic stroke.

BACKGROUND AND PURPOSE: The first part of this study assessed the potential of MDCT with a CTA examination of the aorta and the coronary, cervical, and intracranial vessels in the etiologic work-up of TIA or ischemic stroke compared with established imaging methods. The objective of the second part of this study was to assess the atherosclerotic extent by use of MDCT in these patients. MATERIALS AND METHODS: From August 2007 to August 2011, a total of 96 patients with ischemic stroke or TIA without an evident cardioembolic source were enrolled. All patients underwent MDCT. Atherosclerotic extent was classified in 0, 1, 2, 3, and 4 atherosclerotic levels according to the number of arterial territories (aortic arch, coronary, cervical, intracranial) affected by atherosclerosis defined as ≥ 50% cervical, intracranial, or coronary stenosis or ≥ 4-mm aortic arch plaque. RESULTS: There were 91 patients who had an interpretable MDCT. Mean age was 67.4 years (± 11 years), and 75 patients (83.3%) were men. The prevalence of 0, 1, 2, 3, and 4 atherosclerotic levels was 48.3%, 35.2%, 12.1%, 4.4%, and 0%, respectively. Aortic arch atheroma was found in 47.6% of patients with 1 atherosclerotic level. The combination of aortic arch atheroma and cervical stenosis was found in 63.6% of patients with ≥ 2 atherosclerotic levels. Patients with ≥ 2 atherosclerotic levels were older than patients with < 2 atherosclerotic levels (P = .04) in univariate analysis. CONCLUSIONS: MDCT might be useful to assess the extent of atherosclerosis. It could help to screen for high-risk patients who could benefit from a more aggressive preventive strategy.

Image registration and analysis for quantitative myocardial perfusion: application to dynamic circular cardiac CT.

Large area detector computed tomography systems with fast rotating gantries enable volumetric dynamic cardiac perfusion studies. Prospectively, ECG-triggered acquisitions limit the data acquisition to a predefined cardiac phase and thereby reduce x-ray dose and limit motion artefacts. Even in the case of highly accurate prospective triggering and stable heart rate, spatial misalignment of the cardiac volumes acquired and reconstructed per cardiac cycle may occur due to small motion pattern variations from cycle to cycle. These misalignments reduce the accuracy of the quantitative analysis of myocardial perfusion parameters on a per voxel basis. An image-based solution to this problem is elastic 3D image registration of dynamic volume sequences with variable contrast, as it is introduced in this contribution. After circular cone-beam CT reconstruction of cardiac volumes covering large areas of the myocardial tissue, the complete series is aligned with respect to a chosen reference volume. The results of the registration process and the perfusion analysis with and without registration are evaluated quantitatively in this paper. The spatial alignment leads to improved quantification of myocardial perfusion for three different pig data sets.

Dose and image quality comparison between prospectively gated axial and retrospectively gated helical coronary CT angiography.

OBJECTIVE: Our aim was to compare image quality, coronary segment assessability and radiation dose in prospectively gated axial (PGA) coronary CT angiography (CTA) and conventional retrospectively gated helical (RGH) coronary CTA. METHODS: Institutional review committee approval and informed consent were obtained. RGH CTA was performed in 41 consecutive patients (33 males, 8 females; mean age 52.6 years), then the PGA CTA technique was evaluated in 41 additional patients (24 males, 17 females; mean age 57.3 years) all with a pre-scan heart rate of ≤70 beats per minute (bpm). Two radiologists, blinded to clinical information, independently scored subjective image quality on a five-point ordinal scale. RESULTS: The mean effective dose in the PGA group was 4.7±0.9 mSv, representing a 69% dose reduction compared with the RGH CTA group (15.1±1.9 mSv, p<0.001). The mean segmental image quality score was significantly higher in the PGA group (3.4 vs 3.2) than in the RGH CTA group (p<0.005). The percentage of assessable segments was 98.1% in the PGA group and 97.3% in the RGH group (p = 0.610). CONCLUSION: PGA CTA offers a significant reduction in radiation dose compared with RGH CTA, with comparable image quality for patients with heart rates below 70 bpm.

Flow residence time and regions of intraluminal thrombus deposition in intracranial aneurysms.

Thrombus formation in intracranial aneurysms, while sometimes stabilizing lesion growth, can present additional risk of thrombo-embolism. The role of hemodynamics in the progression of aneurysmal disease can be elucidated by patient-specific computational modeling. In our previous work, patient-specific computational fluid dynamics (CFD) models were constructed from MRI data for three patients who had fusiform basilar aneurysms that were thrombus-free and then proceeded to develop intraluminal thrombus. In this study, we investigated the effect of increased flow residence time (RT) by modeling passive scalar advection in the same aneurysmal geometries. Non-Newtonian pulsatile flow simulations were carried out in base-line geometries and a new postprocessing technique, referred to as "virtual ink" and based on the passive scalar distribution maps, was used to visualize the flow and estimate the flow RT. The virtual ink technique clearly depicted regions of flow separation. The flow RT at different locations adjacent to aneurysmal walls was calculated as the time the virtual ink scalar remained above a threshold value. The RT values obtained in different areas were then correlated with the location of intra-aneurysmal thrombus observed at a follow-up MR study. For each patient, the wall shear stress (WSS) distribution was also obtained from CFD simulations and correlated with thrombus location. The correlation analysis determined a significant relationship between regions where CFD predicted either an increased RT or low WSS and the regions where thrombus deposition was observed to occur in vivo. A model including both low WSS and increased RT predicted thrombus-prone regions significantly better than the models with RT or WSS alone.