Feasibility of shear wave sonoelastography to detect endoleak and evaluate thrombus organization after endovascular repair of abdominal aortic aneurysm.

PURPOSE: To investigate the feasibility of shear wave sonoelastography (SWS) for endoleak detection and thrombus characterization of abdominal aortic aneurysm (AAA) after endovascular repair (EVAR). MATERIALS AND METHODS: Participants who underwent EVAR were prospectively recruited between November 2014 and March 2016 and followed until March 2019. Elasticity maps of AAA were computed using SWS and compared to computed tomography angiography (CTA) and color Doppler ultrasound (CDUS). Two readers, blinded to the CTA and CDUS results, reviewed elasticity maps and B-mode images to detect endoleaks. Three or more CTAs per participant were analyzed: pre-EVAR, baseline post-EVAR, and follow-ups. The primary endpoint was endoleak detection. Secondary endpoints included correlation between total thrombus elasticity, proportion of fresh thrombus, and aneurysm growth between baseline and reference CTAs. A 3-year follow-up was made to detect missed endoleaks, EVAR complication, and mortality. Data analyses included Cohen's kappa; sensitivity, specificity, and positive predictive value (PPV); Pearson coefficient; and Student's t tests. RESULTS: Seven endoleaks in 28 participants were detected by the two SWS readers (k = 0.858). Sensitivity of endoleak detection with SWS was 100%; specificity and PPV averaged 67% and 50%, respectively. CDUS sensitivity was estimated at 43%. Aneurysm growth was significantly greater in the endoleak group compared to sealed AAAs. No correlation between growth and thrombus elasticity or proportion of fresh thrombus in AAAs was found. No new endoleaks were observed in participants with SWS negative studies. CONCLUSION: SWS has the potential to detect endoleaks in AAA after EVAR with comparable sensitivity to CTA and superior sensitivity to CDUS. KEY POINTS: • Dynamic elastography with shear wave sonoelastography (SWS) detected 100% of endoleaks in abdominal aortic aneurysm (AAA) follow-up that were identified by a combination of CT angiography (CTA) and color Doppler ultrasound (CDUS). • Based on elasticity maps, SWS differentiated endoleaks from thrombi within the aneurysm sac (p < 0.001). • After 3-year follow-up, no new endoleaks were observed in SWS negative examinations.

A Cohort Longitudinal Study Identifies Morphology and Hemodynamics Predictors of Abdominal Aortic Aneurysm Growth.

Abdominal aortic aneurysms (AAA) are localized, commonly occurring aortic dilations. Following rupture only immediate treatment can prevent morbidity and mortality. AAA maximal diameter and growth are the current metrics to evaluate the associated risk and plan intervention. Although these criteria alone lack patient specificity, predicting their evolution would improve clinical decision. If the disease is known to be associated with altered morphology and blood flow, intraluminal thrombus deposit and clinical symptoms, the growth mechanisms are yet to be fully understood. In this retrospective longitudinal study of 138 scans, morphological analysis and blood flow simulations for 32 patients with clinically diagnosed AAAs and several follow-up CT-scans, are performed and compared to 9 control subjects. Several metrics stratify patients between healthy, low and high risk groups. Local correlations between hemodynamic metrics and AAA growth are also explored but due to their high inter-patient variability, do not explain AAA heterogeneous growth. Finally, high-risk predictors trained with successively clinical, morphological, hemodynamic and all data, and their link to the AAA evolution are built from supervise learning. Predictive performance is high for morphological, hemodynamic and all data, in contrast to clinical data. The morphology-based predictor exhibits an interesting effort-predictability tradeoff to be validated for clinical translation.

Clinical Validation of a Semi-Automated Software for Maximal Diameter Measurements for Endovascular Repair Follow-up.

PURPOSE: To compare automated measurements of maximal diameter (Dmax) of abdominal aortic aneurysm (AAA) orthogonal to luminal or outer wall envelope centerline for endovascular repair (EVAR) follow-up. MATERIAL AND METHODS: Eighty-three consecutive patients with AAA treated by EVAR who had at least 1 computed tomography (CT) scan before and 2 CT scans after EVAR with at least 5 months' interval were included. Three-dimensional reconstruction of the AAA was achieved with dedicated segmentation software. Performances of automated calculation algorithms of Dmax perpendicular to lumen or outer wall envelope centerlines were then compared to manual measurement of Dmax on double-oblique multiplanar reconstruction (gold standard). Accuracy of automated Dmax measurements at baseline, follow-up, and progression over time was evaluated by calculation of mean error, Bland-Altman plot, and regression models. RESULTS: Disagreement in Dmax measurements between outer wall envelope algorithm and manual method was insignificant (mean error: baseline, -0.07 ± 1.66 mm, P = .7; first follow-up, 0.24 ± 1.69 mm, P = .2; last follow-up, -0.41 ± 2.74 mm, P = .17); whereas significant discrepancies were found between the luminal algorithm and the manual method (mean error: baseline, -1.24 ± 2.01 mm, P < .01; first follow-up, -1.49 ± 3.30 mm, P < .01; last follow-up, -1.78 ± 3.60 mm, P < .01). Dmax progression results were more accurate with AAA outer wall envelope algorithm compared to luminal method (P = .2). CONCLUSIONS: AAA outer wall envelope segmentation is recommended to enable automated calculation of Dmax perpendicular to its centerline during EVAR follow-up.

Shear wave elasticity imaging for residual endoleak and thrombus characterisation after endoleak embolisation following endovascular aneurysm repair: a canine animal study.

BACKGROUND: To evaluate residual endoleak and thrombus organisation with shear wave imaging (SWI) after endoleak embolisation through an animal study. METHODS: This prospective experimental study involved eight dogs with creation of 16 iliac aneurysms and type I endoleak after endovascular aneurysm repair (EVAR). Embolisation agents were injected into the sac to seal endoleak. SWI and colour flow Doppler ultrasound (DUS) were performed at implantation, one week, and one and three months after implantation; for three dogs, SWI and DUS were also performed six months after implantation. Digital subtraction angiography and contrast-enhanced computed tomography were performed at sacrifice. Macroscopic and histopathological analyses were processed to identify regions of interest (ROIs) for endoleak, fresh thrombus, organised thrombus and embolisation agent, where SWI elasticity moduli were compared. RESULTS: At sacrifice, nine aneurysms had residual endoleak, while seven were sealed. Ten had a fresh and 15 had an organised thrombus. SWI was able to detect all endoleaks, including two cases undetected with DUS. Elasticity moduli of 0.2 kPa ± 0.1 kPa (mean ± SD), 9.5 kPa ± 3.3 kPa, 48.1 kPa ± 21.3 kPa and 44.9 kPa ± 23.7 kPa were found in the ROIs positioned in endoleaks, fresh thrombi, organised thrombi and embolisation agent, respectively. Elasticity values of endoleak and fresh thrombus were lower than those of organised thrombi and embolisation agent (p < 0.001). Stiffness of fresh thrombus at one week (8.7 kPa ± 3.6 kPa) increased at three months (30.2 kPa ± 13.8 kPa), indicating thrombus maturation (p < 0.001). CONCLUSIONS: In a dog model of iliac EVAR, SWI was able to identify endoleak, thrombus maturation and embolising agents after endoleak embolisation.

Flow stagnation volume and abdominal aortic aneurysm growth: Insights from patient-specific computational flow dynamics of Lagrangian-coherent structures.

Abdominal aortic aneurysms (AAA) are localized, commonly-occurring dilations of the aorta. When equilibrium between blood pressure (loading) and wall mechanical resistance is lost, rupture ensues, and patient death follows, if not treated immediately. Experimental and numerical analyses of flow patterns in arteries show direct correlations between wall shear stress and wall mechano-adaptation with the development of zones prone to thrombus formation. For further insights into AAA flow topology/growth interaction, a workout of patient-specific computational flow dynamics (CFD) is proposed to compute finite-time Lyapunov exponents and extract Lagrangian-coherent structures (LCS). This computational model was first compared with 4-D phase-contrast magnetic resonance imaging (MRI) in 5 patients. To better understand the impact of flow topology and transport on AAA growth, hyperbolic, repelling LCS were computed in 1 patient during 8-year follow-up, including 9 volumetric morphologic AAA measures by computed tomography-angiography (CTA). LCS defined barriers to Lagrangian jet cores entering AAA. Domains enclosed between LCS and the aortic wall were considered to be stagnation zones. Their evolution was studied during AAA growth. Good correlation - 2-D cross-correlation coefficients of 0.65, 0.86 and 0.082 (min, max, SD) - was obtained between numerical simulations and 4-D MRI acquisitions in 6 specific cross-sections from 4 patients. In follow-up study, LCS divided AAA lumens into 3 dynamically-isolated zones: 2 stagnation volumes lying in dilated portions of the AAA, and circulating volume connecting the inlet to the outlet. The volume of each zone was tracked over time. Although circulating volume remained unchanged during 8-year follow-up, the AAA lumen and main stagnation zones grew significantly (8 cm3/year and 6 cm3/year, respectively). This study reveals that transient transport topology can be quantified in patient-specific AAA during disease progression by CTA, in parallel with lumen morphology. It is anticipated that analysis of the main AAA stagnation zones by patient-specific CFD on a yearly basis could help to predict AAA growth and rupture.

Liver segmentation: indications, techniques and future directions.

OBJECTIVES: Liver volumetry has emerged as an important tool in clinical practice. Liver volume is assessed primarily via organ segmentation of computed tomography (CT) and magnetic resonance imaging (MRI) images. The goal of this paper is to provide an accessible overview of liver segmentation targeted at radiologists and other healthcare professionals. METHODS: Using images from CT and MRI, this paper reviews the indications for liver segmentation, technical approaches used in segmentation software and the developing roles of liver segmentation in clinical practice. RESULTS: Liver segmentation for volumetric assessment is indicated prior to major hepatectomy, portal vein embolisation, associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) and transplant. Segmentation software can be categorised according to amount of user input involved: manual, semi-automated and fully automated. Manual segmentation is considered the "gold standard" in clinical practice and research, but is tedious and time-consuming. Increasingly automated segmentation approaches are more robust, but may suffer from certain segmentation pitfalls. Emerging applications of segmentation include surgical planning and integration with MRI-based biomarkers. CONCLUSIONS: Liver segmentation has multiple clinical applications and is expanding in scope. Clinicians can employ semi-automated or fully automated segmentation options to more efficiently integrate volumetry into clinical practice. TEACHING POINTS: • Liver volume is assessed via organ segmentation on CT and MRI examinations. • Liver segmentation is used for volume assessment prior to major hepatic procedures. • Segmentation approaches may be categorised according to the amount of user input involved. • Emerging applications include surgical planning and integration with MRI-based biomarkers.

In vivo coronary artery plaque assessment with computed tomography angiography: is there an impact of iterative reconstruction on plaque volume and attenuation metrics?

Background Coronary computed tomography angiography (CTA) allows the evaluation of coronary plaque volume and low attenuation (lipid-rich) component, for plaque vulnerability assessment. Purpose To determine the effect of iterative reconstruction (IR) on coronary plaque volume and composition. Material and Methods Consecutive patients without coronary artery disease were prospectively enrolled for 256-slice CT. Images were reconstructed with both filtered back projection (FBP) and a hybrid IR algorithm (iDose4, Philips) levels 1, 3, 5, and 7. Coronary plaques were assessed according to predefined Hounsfield unit (HU) attenuation intervals, for total plaque and HU-interval volumes. Results Fifty-three patients (mean age, 53.6 years) were included. Noise was significantly decreased and signal-to-noise ratio (SNR) / contrast-to-noise (CNR) were both significantly improved at all IR levels in comparison to FBP. Plaque characterization was performed in 41 patients for a total of 125 plaques. Total plaque volume ranged from 104.4 ± 120.7 to 107.4 ± 128.9 mm3 and low attenuation plaque component from 40.5 ± 54.7 to 43.5 ± 58.9 mm3, with no statistically significant differences between all IR levels and FBP ( P = 0.786 and P ≥ 0.078, respectively). Conclusion IR improved image quality. Total and low attenuation plaque volumes were similar using either IR or FBP.

Abdominal aortic aneurysm follow-up by shear wave elasticity imaging after endovascular repair in a canine model.

OBJECTIVES: To investigate if shear wave imaging (SWI) can detect endoleaks and characterize thrombus organization in abdominal aortic aneurysms (AAAs) after endovascular aneurysm repair. METHODS: Stent grafts (SGs) were implanted in 18 dogs after surgical creation of type I endoleaks (four AAAs), type II endoleaks (13 AAAs) and no endoleaks (one AAA). Color flow Doppler ultrasonography (DUS) and SWI were performed before SG implantation (baseline), on days 7, 30 and 90 after SG implantation, and on the day of the sacrifice (day 180). Angiography, CT scans and macroscopic tissue sections obtained on day 180 were evaluated for the presence, size and type of endoleaks, and thrombi were characterized as fresh or organized. Endoleak areas in aneurysm sacs were identified on SWI by two readers and compared with their appearance on DUS, CT scans and macroscopic examination. Elasticity moduli were calculated in different regions (endoleaks, and fresh and organized thrombi). RESULTS: All 17 endoleaks (100 %) were identified by reader 1, whereas 16 of 17 (94 %) were detected by reader 2. Elasticity moduli in endoleaks, and in areas of organized thrombi and fresh thrombi were 0.2 ± 0.4, 90.0 ± 48.2 and 13.6 ± 4.5 kPa, respectively (P < 0.001 between groups). SWI detected endoleaks while DUS (three endoleaks) and CT (one endoleak) did not. CONCLUSIONS: SWI has the potential to detect endoleaks and evaluate thrombus organization based on the measurement of elasticity. KEY POINTS: • SWI has the potential to detect endoleaks in post-EVAR follow-up. • SWI has the potential to characterize thrombus organization in post-EVAR follow-up. • SWI may be combined with DUS in post-EVAR surveillance of endoleak.

Experimental validation of more realistic computer models for stent-graft repair of abdominal aortic aneurysms, including pre-load assessment.

Although the endovascular repair of abdominal aortic aneurysms is a less invasive alternative than classic open surgery, complications such as endoleak and kinking still need to be addressed. Numerical simulation of endovascular repair is becoming a valuable tool in stent-graft (SG) optimization, patient selection and surgical planning. The experimental and numerical forces required to produce SG deformations were compared in a range of in vivo conditions in the present study. The deformation modes investigated were: bending as well as axial, transversal and radial compressions. In particular, an original method was developed to efficiently account for radial pre-load because of the pre-compression of stents to match the graft dimensions during manufacturing. This is important in order to compute the radial force exerted on the vessel after deployment more accurately. Variations of displacement between the experimental and numerical results ranged from 1.39% for simple leg bending to 5.93% for three-point body bending. Finally, radial pre-load was modeled by increasing Young's modulus of each stent. On average, it was found that Young's modulus had to be augmented by a factor of 2. Copyright © 2016 John Wiley & Sons, Ltd.

Automatic detection of selective arterial devices for advanced visualization during abdominal aortic aneurysm endovascular repair.

Here we address the automatic segmentation of endovascular devices used in the endovascular repair (EVAR) of abdominal aortic aneurysms (AAA) that deform vascular tissues. Using this approach, the vascular structure is automatically reshaped solving the issue of misregistration observed on 2D/3D image fusion for EVAR guidance. The endovascular devices we considered are the graduated pigtail catheter (PC) used for contrast injection and the stent-graft delivery device (DD). The segmentation of the DD was enhanced using an asymmetric Frangi filter. The segmented geometries were then analysed using their specific features to remove artefacts. The radiopaque markers of the PC were enhanced using a fusion of Hessian and newly introduced gradient norm shift filters. Extensive experiments were performed using a database of images taken during 28 AAA-EVAR interventions. This dataset was divided into two parts: the first half was used to optimize parameters and the second to compile performances using optimal values obtained. The radiopaque markers of the PC were detected with a sensitivity of 88.3% and a positive predictive value (PPV) of 96%. The PC can therefore be positioned with a majority of its markers localized while the artefacts were all located inside the vessel lumen. The major parts of the DD, the dilatator tip and the pusher surfaces, were detected accurately with a sensitivity of 85.9% and a PPV of 88.7%. The less visible part of the DD, the stent enclosed within the sheath, was segmented with a sensitivity of 63.4% because the radiopacity of this region is low and uneven. The centreline of the DD in this stent region was alternatively traced within a 0.74 mm mean error. The automatic segmentation of endovascular devices during EVAR is feasible and accurate; it could be useful to perform elastic registration of the vascular lumen during endovascular repair.

Value of C-Arm Computed Tomography to Evaluate Stent Deployment During Femoro-Popliteal Revascularization.

PURPOSE: To compare the accuracy of C-arm computed tomography (CT) and digital subtraction angiography (DSA) in detecting incomplete stent expansion (ISE) after superficial femoral artery (SFA) stenting using intravascular ultrasound (IVUS) as a gold standard. MATERIALS: Fifty patients with symptomatic SFA occlusive disease requiring angioplasty were prospectively included. Once technical success (<30 % residual stenosis) was obtained on post-procedural DSA, C-arm CT and IVUS were acquired. DSA and C-arm CT examinations were reviewed by 2 investigators and correlated with IVUS. C-arm CT image quality was rated on a four-point scale. Doppler ultrasound was performed at 1-year follow-up. RESULTS: The ankle-brachial index was 0.69 ± 0.10 and 0.99 ± 0.40, respectively, pre- and post-procedure. C-arm CT imaging quality was rated as good or excellent in 80%. In-stent minimal luminal diameter (MLD) was evaluated at 4.71 ± 0.7 mm on DSA, 3.39 ± 0.6 mm on IVUS, and 3.12 ± 0.9 mm on C-arm CT. Compared to IVUS, DSA demonstrated an overestimation of MLD (p = 0.0001), an underestimation of ISE (DSA = 18.8% ± 7.6; IVUS = 29.8% ± 9) (p < 0.0001), and a poor inter-technique intra-class correlation coefficient (ICC = 0.24). No difference was observed between IVUS and C-arm CT in ISE as calculated by diameter (29.8 ± 9 vs. 28.2 ± 12.5%, p = 0.5) and area (30.2 ± 8.4 vs. 33.3 ± 9.5%, p = 0.2). Inter-technique ICC between C-arm CT and IVUS was 0.72 [95%CI 0.49; 0.85] for MLA measurements. The inter-observer ICC for MLD and MLA measurements on C-arm CT were, respectively, estimated at 0.75 [95% CI 0.40, 0.89] and 0.77 [95% CI 0.43, 0.90)]. CONCLUSIONS: C-arm CT presents a better correlation with IVUS than DSA to determine lumen diameter and ISE immediately after percutaneous revascularization.

Source of errors and accuracy of a two-dimensional/three-dimensional fusion road map for endovascular aneurysm repair of abdominal aortic aneurysm.

PURPOSE: To evaluate the accuracy and source of errors using a two-dimensional (2D)/three-dimensional (3D) fusion road map for endovascular aneurysm repair (EVAR) of abdominal aortic aneurysm. MATERIALS AND METHODS: A rigid 2D/3D road map was tested in 16 patients undergoing EVAR. After 3D/3D manual registration of preoperative multidetector computed tomography (CT) and cone beam CT, abdominal aortic aneurysm outlines were overlaid on live fluoroscopy/digital subtraction angiography (DSA). Patient motion was evaluated using bone landmarks. The misregistration of renal and internal iliac arteries were estimated by 3 readers along head-feet and right-left coordinates (z-axis and x-axis, respectively) before and after bone and DSA corrections centered on the lowest renal artery. Iliac deformation was evaluated by comparing centerlines before and during intervention. A score of clinical added value was estimated as high (z-axis < 3 mm), good (3 mm ≤ z-axis ≤ 5 mm), and low (z-axis > 5 mm). Interobserver reproducibility was calculated by the intraclass correlation coefficient. RESULTS: The lowest renal artery misregistration was estimated at x-axis = 10.6 mm ± 11.1 and z-axis = 7.4 mm ± 5.3 before correction and at x-axis = 3.5 mm ± 2.5 and z-axis = 4.6 mm ± 3.7 after bone correction (P = .08), and at 0 after DSA correction (P < .001). After DSA correction, residual misregistration on the contralateral renal artery was estimated at x-axis = 2.4 mm ± 2.0 and z-axis = 2.2 mm ± 2.0. Score of clinical added value was low (n = 11), good (n= 0), and high (n= 5) before correction and low (n = 5), good (n = 4), and high (n = 7) after bone correction. Interobserver intraclass correlation coefficient for misregistration measurements was estimated at 0.99. Patient motion before stent graft delivery was estimated at x-axis = 8 mm ± 5.8 and z-axis = 3.0 mm ± 2.7. The internal iliac artery misregistration measurements were estimated at x-axis = 6.1 mm ± 3.5 and z-axis = 5.6 mm ± 4.0, and iliac centerline deformation was estimated at 38.3 mm ± 15.6. CONCLUSIONS: Rigid registration is feasible and fairly accurate. Only a partial reduction of vascular misregistration was observed after bone correction; minimal DSA acquisition is still required.

Evidence of Cyclic Changes in the Metabolism of Abdominal Aortic Aneurysms During Growth Phases: ¹8F-FDG PET Sequential Observational Study.

UNLABELLED: The rates of growth of medically treated abdominal aortic aneurysms (AAA) are difficult to determine, and relationships with parietal inflammation and with metabolic parameters from (18)F-FDG PET remain unclear. This (18)F-FDG PET sequential observational study was aimed at analyzing the metabolic changes accompanying the growth phases of medically treated AAA. METHODS: Thirty-nine patients (37 men; age [mean ± SD], 71 ± 12 y) exhibiting small and medically treated AAA (maximal diameter, 46 ± 3 mm) underwent (18)F-FDG PET and CT angiography at baseline and 9 mo later. Clinical and imaging parameter correlates of the 9-mo increase in maximal diameter were investigated; these included (18)F-FDG maximal standardized uptake values (SUVmax) averaged for slices encompassing the AAA volume. RESULTS: Of the 39 patients, 9 (23%) had a significant (≥2.5 mm) increase in maximal diameter at 9 mo, whereas the remaining 30 did not. The patients with an increase in maximal diameter at 9 mo exhibited lower SUVmax within the AAA at baseline than patients who did not have such an increase (1.80 ± 0.45 vs. 2.21 ± 0.52; P = 0.04); they also displayed a trend toward greater changes in SUVmax at 9 mo (difference between 9 mo and baseline: +0.40 ± 0.85 vs. -0.06 ± 0.57; P = 0.07). Similar levels were ultimately reached in both groups at 9 mo (2.20 ± 0.83 and 2.15 ± 0.66). SUVmax was a significant, yet modest, baseline predictor of the absolute change in maximal diameter during follow-up (P = 0.049). CONCLUSION: The enhancement in the maximal diameter of small AAA was preceded by a stage with a low level of (18)F-FDG uptake, but this low level of uptake was no longer documented after the growth phases, suggesting a pattern of cyclic metabolic changes.

Automated peroperative assessment of stents apposition from OCT pullbacks.

This study's aim was to control the stents apposition by automatically analyzing endovascular optical coherence tomography (OCT) sequences. Lumen is detected using threshold, morphological and gradient operators to run a Dijkstra algorithm. Wrong detection tagged by the user and caused by bifurcation, struts'presence, thrombotic lesions or dissections can be corrected using a morphing algorithm. Struts are also segmented by computing symmetrical and morphological operators. Euclidian distance between detected struts and wall artery initializes a stent's complete distance map and missing data are interpolated with thin-plate spline functions. Rejection of detected outliers, regularization of parameters by generalized cross-validation and using the one-side cyclic property of the map also optimize accuracy. Several indices computed from the map provide quantitative values of malapposition. Algorithm was run on four in-vivo OCT sequences including different incomplete stent apposition's cases. Comparison with manual expert measurements validates the segmentation׳s accuracy and shows an almost perfect concordance of automated results.

Impact of contrast injection and stent-graft implantation on reproducibility of volume measurements in semiautomated segmentation of abdominal aortic aneurysm on computed tomography.

PURPOSE: To assess the impact of contrast injection and stent-graft implantation on feasibility, accuracy, and reproducibility of abdominal aortic aneurysm (AAA) volume and maximal diameter (D-max) measurements using segmentation software. MATERIALS AND METHODS: CT images of 80 subjects presenting AAA were divided into four equal groups: with or without contrast enhancement, and with or without stent-graft implantation. Semiautomated software was used to segment the aortic wall, once by an expert and twice by three readers. Volume and D-max reproducibility was estimated by intraclass correlation coefficients (ICC), and accuracy was estimated between the expert and the readers by mean relative errors. RESULTS: All segmentations were technically successful. The mean AAA volume was 167.0 ± 82.8 mL and the mean D-max 55.0 ± 10.6 mm. Inter- and intraobserver ICCs for volume and D-max measurements were greater than 0.99. Mean relative errors between readers varied between -1.8 ± 4.6 and 0.0 ± 3.6 mL. Mean relative errors in volume and D-max measurements between readers showed no significant difference between the four groups (P ≥ 0.2). CONCLUSION: The feasibility, accuracy, and reproducibility of AAA volume and D-max measurements using segmentation software were not affected by the absence of contrast injection or the presence of stent-graft. KEY POINTS: • AAA volumetry by semiautomated segmentation is accurate on CT following endovascular repair. • AAA volumetry by semiautomated segmentation is accurate on unenhanced CT. • Standardization of the segmentation technique maximizes the reproducibility of volume measurements.

Rupture signs on computed tomography, treatment, and outcome of abdominal aortic aneurysms.

OBJECTIVES: Abdominal aortic aneurysm (AAA) rupture has a high mortality rate. Although the diagnosis of a ruptured AAA is usually straightforward, detection of impending rupture signs can be more challenging. Early diagnosis of impending AAA rupture can be lifesaving. Furthermore, differentiating between impending and complete rupture has important repercussions on patient management and prognosis. The purpose of this article is to classify and illustrate the entire spectrum of AAA rupture signs and to review current treatment options for ruptured AAAs. METHODS: Using medical illustrations supplemented with computed tomography (CT), this essay showcases the various signs of impending rupture and ruptured AAAs. Endovascular aneurysm repair (EVAR) and open surgical repair are also discussed as treatment options for ruptured AAAs. RESULTS: CT imaging findings of ruptured AAAs can be categorised according to location: intramural, luminal, and extraluminal. Intramural signs generally indicate impending AAA rupture, whereas luminal and extraluminal signs imply complete rupture. EVAR has emerged as an alternative and possibly less morbid method to treat ruptured AAAs. CONCLUSIONS: AAA rupture occurs at the end of a continuum of growth and wall weakening. This review describes the CT imaging findings that may help identify impending rupture prior to complete rupture. TEACHING POINTS: • AAA rupture occurs at the end of a continuum of growth and wall weakening. • Intramural imaging findings indicate impending AAA rupture. • Luminal and extraluminal imaging findings imply complete AAA rupture. • Some imaging findings are not specific to AAA ruptures and can be seen in other pathologies. • EVAR has emerged as an alternative and possibly less morbid method of treating ruptured AAAs.

Morphologic evaluation of ruptured and symptomatic abdominal aortic aneurysm by three-dimensional modeling.

OBJECTIVE: To identify geometric indices of abdominal aortic aneurysms (AAAs) on computed tomography that are associated with higher risk of rupture. METHODS: This retrospective case-control, institutional review board-approved study involved 63 cases with ruptured or symptomatic AAA and 94 controls with asymptomatic AAA. Three-dimensional models were generated from computed tomography segmentation and used for the calculation of 27 geometric indices. On the basis of the results of univariate analysis and multivariable sequential logistic regression analyses with a forward stepwise model selection based on likelihood ratios, a traditional model based on gender and maximal diameter (Dmax) was compared with a model that also incorporated geometric indices while adjusting for gender and Dmax. Receiver operating characteristic (ROC) curves were calculated for these two models to evaluate their classification accuracy. RESULTS: Univariate analysis revealed that gender (P = .024), Dmax (P = .001), and 14 other geometric indices were associated with AAA rupture at P < .05. In the multivariable analysis, adjusting for gender and Dmax, the AAA with a higher bulge location (P = .020) and lower mean averaged area (P = .005) were associated with AAA rupture. With these two geometric indices, the area under the ROC curve showed an improvement from 0.67 (95% confidence interval, 0.58-0.77) to 0.75 (95% confidence interval, 0.67-0.83; P < .001). Our predictive model showed comparable sensitivity (64% vs 60%) and specificity (79% vs 77%) with current treatment criteria based on gender and diameter at the point optimizing the Youden index (sensitivity + specificity - 1) on the ROC curve. CONCLUSIONS: Two geometric indices derived from AAA three-dimensional modeling were independently associated with AAA rupture. The addition of these indices in a predictive model based on current treatment criteria modestly improved the accuracy to detect aneurysm rupture.

Clinical validation of semi-automated software for volumetric and dynamic contrast enhancement analysis of soft tissue venous malformations on magnetic resonance imaging examination.

OBJECTIVES: To evaluate venous malformation (VM) volume and contrast-enhancement analysis on magnetic resonance imaging (MRI) compared with diameter evaluation. METHODS: Baseline MRI was undertaken in 44 patients, 20 of whom were followed by MRI after sclerotherapy. All patients underwent short-tau inversion recovery (STIR) acquisitions and dynamic contrast assessment. VM diameters in three orthogonal directions were measured to obtain the largest and mean diameters. Volumetric reconstruction of VM was generated from two orthogonal STIR sequences and fused with acquisitions after contrast medium injection. Reproducibility (interclass correlation coefficients [ICCs]) of diameter and volume measurements was estimated. VM size variations in diameter and volume after sclerotherapy and contrast enhancement before sclerotherapy were compared in patients with clinical success or failure. RESULTS: Inter-observer ICCs were similar for diameter and volume measurements at baseline and follow-up (range 0.87-0.99). Higher percentages of size reduction after sclerotherapy were observed with volume (32.6 ± 30.7%) than with diameter measurements (14.4 ± 21.4%; P = 0.037). Contrast enhancement values were estimated at 65.3 ± 27.5% and 84 ± 13% in patients with clinical failure and success respectively (P = 0.056). CONCLUSIONS: Venous malformation volume was as reproducible as diameter measurement and more sensitive in detecting therapeutic responses. Patients with better clinical outcome tend to have stronger malformation enhancement. KEY POINTS: • Magnetic resonance imaging readily demonstrates diameters and volumes of venous malformations • MRI diameter calculations are reproducible in estimating the size of venous malformations • But volumetric models of malformations are more sensitive in detecting therapeutic response • Dynamic enhancement is also better assessed with automated volumetric software • Volumetric analysis of malformations offers promise to guide therapy and assess response.

Early detection of liver steatosis by magnetic resonance imaging in rats infused with glucose and intralipid solutions and correlation to insulin levels.

OBJECTIVE: Magnetic resonance (MR) techniques allow noninvasive fat quantification. We aimed to investigate the accuracy of MR imaging (MRI), MR spectroscopy (MRS) and histological techniques to detect early-onset liver steatosis in three rat phenotypes assigned to an experimental glucolipotoxic model or a control group. MATERIALS AND METHODS: This study was approved by the institutional committee for the protection of animals. Thirty-two rats (13 young Wistar, 6 old Wistar and 13 diabetic Goto-Kakizaki rats) fed a standard diet were assigned to a 72h intravenous infusion of glucose and Intralipid fat emulsion or a saline infusion. Plasma insulin levels were measured. Steatosis was quantified in ex vivo livers with gradient-recalled multi-echo MRI, MRS and histology as fat fractions (FF). RESULTS: A significant correlation was found between multi-echo MRI-FF and MRS-FF (r=0.81, p<0.01) and a weaker correlation was found between histology and MRS-FF (r=0.60, p<0.01). MRS and MRI accurately distinguished young Wistar and Goto-Kakizaki rats receiving the glucose+Intralipid infusion from those receiving the saline control whereas histology did not. Significant correlations were found between MRI or MRS and insulin plasma level (r=0.63, p<0.01; r=0.57, p<0.01), and between MRI or MRS and C-peptide concentration (r=0.54, p<0.01; r=0.44, p<0.02). CONCLUSIONS: Multi-echo MRI and MRS may be more sensitive to measure early-onset liver steatosis than histology in an experimental glucolipotoxic rat model.

A literature review of the numerical analysis of abdominal aortic aneurysms treated with endovascular stent grafts.

The purpose of this paper is to present the basic principles and relevant advances in the computational modeling of abdominal aortic aneurysms and endovascular aneurysm repair, providing the community with up-to-date state of the art in terms of numerical analysis and biomechanics. Frameworks describing the mechanical behavior of the aortic wall already exist. However, intraluminal thrombus nonhomogeneous structure and porosity still need to be well characterized. Also, although the morphology and mechanical properties of calcifications have been investigated, their effects on wall stresses remain controversial. Computational fluid dynamics usually assumes a rigid artery wall, whereas fluid-structure interaction accounts for artery compliance but is still challenging since arteries and blood have similar densities. We discuss alternatives to fluid-structure interaction based on dynamic medical images that address patient-specific hemodynamics and geometries. We describe initial stresses, elastic boundary conditions, and statistical strength for rupture risk assessment. Special emphasis is accorded to workflow development, from the conversion of medical images into finite element models, to the simulation of catheter-aorta interactions and stent-graft deployment. Our purpose is also to elaborate the key ingredients leading to virtual stenting and endovascular repair planning that could improve the procedure and stent-grafts.