The Impact of Operating Surgeon Experience, Supervised Trainee vs. Trained Surgeon, in Vascular Surgery Procedures: A Systematic Review and Meta-Analysis.

OBJECTIVE: The operative caseload of a surgeon has a positive influence on post-operative outcomes. For surgical trainees to progress effectively, maximising operating room exposure is essential, vascular surgery being no exception. Our aim was to ascertain the impact of supervised trainee led vs. expert surgeon led procedures on post-operative outcomes, across three commonly performed vascular operations. METHODS: A literature search was undertaken using the MEDLINE, Web of Science, and Cochrane databases up to 1 January 2018. Studies reporting outcomes following major lower limb amputation, fistula formation, or carotid endarterectomy (CEA) that involved a direct comparison between supervised trainee and experts were included, with odds ratios (ORs) calculated. Primary outcomes varied depending on the specific procedure: amputations-rate of amputation revision within 30 days; fistula formation-primary patency; CEA-stroke rate at 30 days. Meta-analysis with the Mantel-Haenszel method was performed for each outcome. RESULTS: Sixteen studies were included in the final review. Overall, trainees accounted for a third of all procedures analysed (n = 2 421/7 017; 34.5%). Only one study was identified that described rates of amputation revision, precluding any further analysis. Four studies on fistula formation were included, showing no significant difference in outcomes between trainees and experts in primary patency (OR 1.68, 95% confidence interval [CI] 0.42-6.75). Nine studies were identified reporting post-CEA stroke rates, also demonstrating no difference between trainees and experts (OR 0.89, 95% CI 0.59-1.32). CONCLUSION: In select cases, with appropriate training and suitable experience, supervised trainees can perform surgical procedures without any detriment to patient care. To ensure high standards for patients of the future, supported training programmes are essential for today's surgical trainees.

Neovascularization in Vertebral Artery Atheroma-A Dynamic Contrast-Enhanced Magnetic Resonance Imaging-Based Comparative Study in Patients with Symptomatic and Asymptomatic Carotid Artery Disease.

BACKGROUND: Atherosclerosis is a systemic inflammatory disease intertwined with neovascularization. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) enables the assessment of plaque neovascularization. This study aimed to explore the systemic nature of atherosclerosis by assessing difference in severity of neovascularization as quantified by DCE-MRI of vertebral arteries (VAs) between patients with symptomatic and asymptomatic carotid artery disease. METHODS: Ten consecutive patients with asymptomatic VA stenosis and concomitant symptomatic carotid artery disease (group 1) and 10 consecutive patients with asymptomatic VA stenosis and concomitant asymptomatic carotid artery disease (group 2) underwent 3-dimensional DCE-MRI of their cervical segment of VAs. A previously validated pharmacokinetic modeling approach was used for DCE-MRI analysis. Ktrans was calculated in the adventitia and plaque as a measure of neovessel permeability. RESULTS: Both patient groups were comparable for demographics and comorbidities. Mean luminal stenosis was comparable for both groups (54.4% versus 52.27%, P = .32). Group 1 had higher adventitial Ktrans and plaque Ktrans (.08 ± .01 min-1, .07 ± .01 min-1) compared with Group 2 (.06 ± .01 min-1, .06 ± .01 min-1) (P = .004 and .03, respectively). Good correlation was present among the two image analysts (intraclass correlation coefficient = .78). CONCLUSIONS: Vertebral Artery atheroma of patients with symptomatic carotid artery disease had increased neovessel permeability compared with the patients with asymptomatic carotid artery disease. These findings are consistent with the hypothesis that atherosclerosis is a systemic inflammatory disease. The VA atherosclerosis is likely to have increased severity of neovascularization if another arterial territory is symptomatic in the same patient cohort.

Imaging pathobiology of carotid atherosclerosis with ultrasmall superparamagnetic particles of iron oxide: an update.

PURPOSE OF REVIEW: To provide brief overview of the developments regarding use of ultrasmall superparamagnetic particles of iron oxide in imaging pathobiology of carotid atherosclerosis. RECENT FINDINGS: MRI is a promising technique capable of providing morphological and functional information about atheromatous plaques. MRI using iron oxide particles, called ultrasmall superparamagnetic iron oxide (USPIO) particles, allows detection of macrophages in atherosclerotic tissue. Ferumoxytol has emerged as a new USPIO agent, which has an excellent safety profile. Based on the macrophage-selective properties of ferumoxytol, there is increasing number of recent reports suggesting its effectiveness to detect pathological inflammation. SUMMARY: USPIO particles allow magnetic resonance detection of macrophages in atherosclerotic tissue. Ferumoxytol has emerged as a new USPIO agent, with an excellent safety profile. This has the potential to be used for MRI of the pathobiology of atherosclerosis.

Mechanochemical Ablation for Treatment of Truncal Venous Insufficiency: A Review of the Current Literature.

Mechanochemical ablation (MOCA) is a nonthermal nontumescent technique used in the treatment of superficial venous disease. This review analyzed the available data on the efficacy and safety of MOCA. A systematic literature search was performed. Of 101 studies identified, 14 were suitable for inclusion. The studies were found to be heterogeneous in design, and the quality of evidence was found to be low or very low. MOCA was demonstrated to be effective in the short-term with minimal complications. Consensus guidelines and definitions of reporting outcome measures must be standardized to allow comparison with other techniques.

Neoaortic Xenoprosthetic Grafts for Treatment of Mycotic Aneurysms and Infected Aortic Grafts.

BACKGROUND: There is no international consensus regarding the optimum management of infected aortae (mycotic aneurysms, infected aortic grafts). Neoaortoiliac reconstruction has advantages over extra-anatomical bypass grafting; however, the use of autologous vein is associated with venous hypertension and compartment syndrome, alternatively cadaveric homografts are associated with high rates of perianastomotic hemorrhage, limb occlusion, and pseudoaneurysm. Arterial repair using xenoprosthetic patches is associated with lower infection rates compared to the use of prosthetic material. The aim of this case series and literature review is to report the use of xenoprosthetic bovine biomaterial for neoaortic repair of mycotic aneurysmal disease and infected aortic grafts. METHODS: Patients with evidence of infected aortic grafts or mycotic aneurysms who were suitable for open aortic surgery were included. Following removal of the graft/excision of the aneurysmal sac, a 10 × 16 cm XenoSure Biologic Surgical Patch (LeMaitre, Germany) was rolled into a tube, or bifurcated tube graft, and secured with prolene sutures. Proximal and distal anastomoses were conducted as per standard aortic anastomoses. Patients were continued on long-term antibiotics and surveyed with computerized tomography at 1, 3, 6, and 12 months. RESULTS: Six patients underwent bovine aortic repair between 2013 and 2015: an infected Dacron aortobi-iliac graft causing iliac pseudoaneurysm, an infected Dacron aortic graft from open repair later relined with endovascular stent graft, a mycotic iliac aneurysm, and 3 mycotic aortic aneurysms. All were treated with bovine reconstructed aortic grafts or patches. Patients had a median age of 69.5 years (range 67-75), with perioperative and 30-day mortality of 0%. Median follow-up was 13 months (range 2-23). Postoperative contrast-enhanced computed tomography revealed no evidence of infection at the operative site in all patients. Freedom from reinfection and reintervention was 100%. CONCLUSIONS: Xenoprosthetic (bovine) neoaortic grafts are an alternative method to treat infected aortae with excellent short-term freedom from infection and reintervention. Optimum duration of postoperative antibiotic therapy remains undetermined. Further cases and longer follow-up are required to determine the true efficacy of this technique.

Assessment of Carotid Plaque Inflammation in Diabetic and Nondiabetic Patients-An Exploratory Ultrasmall Superparamagnetic Iron Oxide-Enhanced Magnetic Resonance Imaging Study.

BACKGROUND: Ultrasmall superparamagnetic iron oxide (USPIO)-enhanced magnetic resonance (MR) imaging enables the identification of inflammation within the atheroma, predominantly by USPIO uptake by macrophages present in atherosclerotic tissue. Diabetic patients, however, may have dysfunctional macrophage activity, which may affect utilization of USPIO in identifying plaque inflammation in this patient cohort. METHODS: Fifteen diabetic and fifteen nondiabetic patients underwent USPIO-enhanced carotid MR imaging using 1.5T MR system. Pre- and post-USPIO carotid MR images were manually coregistered. The percentage decrease in the signal intensity after USPIO administration was calculated as a relative measure of the USPIO uptake. RESULTS: Diabetic and nondiabetic patients had comparable demographics and comorbidities. The mean global, maximum quadrant, and maximum slice changes showing change in relative signal intensity as a result of USPIO administration were comparable for the two patient cohorts (P > .05). CONCLUSIONS: USPIO can identify inflammatory burden with carotid atheroma in both diabetic and nondiabetic patients.

Magnetic Resonance Imaging-Based Assessment of Carotid Atheroma: a Comparative Study of Patients with and without Coronary Artery Disease.

BACKGROUND: Functional magnetic resonance (MR) imaging of atheroma using contrast media enables assessment of the systemic severity of atherosclerosis in different arterial beds. Whether black-blood imaging has similar ability remains widely unexplored. In this study, we evaluate whether black-blood imaging can differentiate carotid plaques of patients with and without coronary artery disease (CAD) in terms of morphological and biomechanical features of plaque vulnerability, thereby allowing assessment of the systemic severity nature of atherosclerosis in different arterial beds. METHODS: Forty-one patients with CAD and 59 patients without CAD underwent carotid black-blood MR imaging. Plaque components were segmented to identify large lipid core (LC), ruptured fibrous cap (FC), and plaque hemorrhage (PH). These segmented contours of plaque components were used to quantify maximum structural biomechanical stress. RESULTS: Patients with CAD and without CAD had comparable demographics and comorbidities. Both groups had comparable prevalence of morphological features of plaque vulnerability (FC rupture, 44% versus 41%, P = .90; PH, 58% versus 47%, P = .78; large LC, 32% versus 47%, P = .17), respectively. The maximum biomechanical stress was not significantly different for both groups (241versus 278 kPa, P = .14) respectively. CONCLUSIONS: Black-blood imaging does not appear to have the ability to differentiate between the morphological and biomechanical features of plaque vulnerability when comparing patients with and without symptomatic atherosclerotic disease in a distant arterial territory such as coronary artery.

Improved long-term survival after resection of colorectal liver metastases following staging with FDG positron emission tomography.

BACKGROUND AND OBJECTIVES: Actual long-term survival of patients with colorectal liver metastases staged by PET CT has not been reported. Objectives were to investigate whether PET CT staging results in actual improved long-term survival, to examine outcome in patients with 'equivocal' PET CT scans, and those excluded from hepatectomy by PET CT. METHODS: A retrospective analysis of patients undergoing hepatectomy for colorectal liver metastases between March 1998 and September 2008. RESULTS: Overall 5- and 10-year survival was 44.8% and 23.9%. PET CT staging resulted in management changes in 23% of patients. PET CT staged patients showed significantly better survival than those staged by CT alone at 3 years (79.8% vs. 54.1%) and at 5 years (54.1% vs. 37.3%) with median survivals of 6.4 years versus 3.9 years (log rank P = 0.018). Patients with equivocal PET CT scans showed worse median survival than those with favourable PET CT (log rank P = 0.002), but may include a subpopulation whose prognosis trends towards a more favourable outcome than those excluded from liver resection by PET CT, whose median survival remains limited to 21 months. CONCLUSIONS: Staging of patients with colorectal liver metastases by PET CT is associated with significantly improved actual long-term survival, and provides valuable prognostic information which guides surgical and oncological treatments.

Optimization of improved motion-sensitized driven-equilibrium (iMSDE) blood suppression for carotid artery wall imaging.

BACKGROUND: Improved motion-sensitized driven-equilibrium (iMSDE) preparations have been successfully used in carotid artery wall imaging to achieve blood suppression, but it causes notable signal loss, mostly due to inherent T2 decay, eddy current effects and B1 + inhomogeneity. In this study, we investigate the signal to noise ratio (SNR) and blood suppression performance of iMSDE using composite RF pulses and sinusoidal gradients. Optimized first moment (m1) values for iMSDE prepared T1- and T2- weighted (T1- and T2-w) imaging are presented. METHODS: Twelve healthy volunteers and six patients with carotid artery disease underwent iMSDE and double inversion recovery (DIR) prepared T1- and T2-w fast spin echo (FSE) MRI of the carotid arteries. Modified iMSDE module using composite RF pulses and sinusoidal gradients were evaluated with a range of m1. SNR of adjacent muscle, vessel wall and the lumen were reported. The optimized iMSDE module was also tested in a 3D variable flip angle FSE (CUBE) acquisition. RESULTS: The SNR of muscle was highest using sinusoidal gradients, and the relative improvement over the trapezoidal gradient increased with higher m1 (p<0.001). Optimal SNR was observed using an iMSDE preparation scheme containing two 180° composite pulses and standard 90° and -90° pulses (p=0.151). iMSDE produced better blood suppression relative to DIR preparations even with a small m1 of 487 mT*ms2/m (p<0.001). In T1-w iMSDE, there was a SNR decrease and an increased T2 weighting with increasing m1. In T2-w iMSDE, by matching the effective echo time (TE), the SNR was equivalent when m1 was <= 1518 mT*ms2/m, however, higher m1 values (2278 - 3108 mT*ms2/m) reduced the SNR. In the patient study, iMSDE improved blood suppression but reduced vessel wall CNR efficiency in both T1-w and T2-w imaging. iMSDE also effectively suppressed residual flow artifacts in the CUBE acquisition. CONCLUSIONS: iMSDE preparation achieved better blood suppression than DIR preparation with reduced vessel wall CNR efficiency in T1-w and T2-w images. The optimized m1s are 487 mT*ms2/m for T1-w imaging and 1518 mT*ms2/m for T2-w imaging. Composite 180° refocusing pulses and sinusoidal gradients improve SNR performance. iMSDE further improves the inherent blood suppression of CUBE.

Carotid artery stiffness in patients with symptomatic carotid artery disease with contralateral asymptomatic carotid artery disease and in patients with bilateral asymptomatic carotid artery disease: a cine phase-contrast carotid MR study.

BACKGROUND: Atherosclerosis is a systemic inflammatory disease that may affect multiple arterial beds simultaneously. Vascular distensibility is increasingly used in the clinical assessment of patients with atherosclerotic disease. In this study, we assess distensibility of symptomatic atherosclerotic carotid artery and of contralateral asymptomatic side. We also investigate the distensibility of bilaterally asymptomatic atherosclerotic carotid arteries using cine phase-contrast carotid magnetic resonance (MR) imaging. METHODS: Nineteen patients with bilateral carotid artery disease underwent cine phase-contrast carotid imaging on a 1.5 T MR system. Ten patients had ipsilateral symptomatic carotid artery disease and contralateral asymptomatic stenosis. Nine additional patients with bilateral asymptomatic carotid artery disease constituted historical control group. Cine phase-contrast MR imaging acquired at the common carotid artery, maximum luminal stenosis, and internal carotid artery was used to determine carotid distensibility bilaterally for carotid arteries in both patient groups. RESULTS: Symptomatic carotid arteries were found to be significantly less distensible (mean distensibility coefficient [DC] 35.4 ± 6.12 × 10(-3)/kPa) than the contralateral asymptomatic vessels (mean DC 54.4 ± 7.88 × 10(-3)/kPa, P = .03) at the level of the common carotid artery. A similar trend of high distensibility for asymptomatic side in the area of maximum stenosis and the internal carotid artery was seen, but it was not found to be statistically significant. Plaque burden was comparable between the 2 groups at all locations. DC was comparable for patients with bilateral asymptomatic carotid artery stenoses. Distensibility of bilaterally asymptomatic carotid arteries was greater than that of asymptomatic carotid artery contralateral to the symptomatic side. CONCLUSIONS: Symptomatic carotid artery is stiffer than the contralateral asymptomatic side, despite comparable plaque burden. Patients with bilateral asymptomatic carotid artery disease have comparable stiffness. Larger studies are warranted to further investigate the findings of this MR study.

Robustness and classification capabilities of MRI radiomic features in identifying carotid plaque vulnerability.

OBJECTIVES: To assess how radiomic features may be combined with plaque morphological and compositional features identified by multi-contrast MRI to improve upon conventional risk assessment models in determining culprit carotid artery lesions. METHODS: Fifty-five patients (mean age: 62.6; 35 males) with bilateral carotid stenosis who experienced transient ischaemic attack (TIA) or stroke were included from the CARE-II multi-centre carotid imaging trial (ClinicalTrials.gov Identifier: NCT02017756). They underwent MRI within 2 weeks of the event. Classification capability in distinguishing culprit lesions was assessed by machine learning. Repeatability and reproducibility of the results were investigated by assessing the robustness of the radiomic features. RESULTS: Radiomics combined with a relatively conventional plaque morphological and compositional metric-based model provided incremental value over a conventional model alone (area under curve [AUC], 0.819 ± 0.002 vs 0.689 ± 0.019, respectively, P = .014). The radiomic model alone also provided value over the conventional model (AUC, 0.805 ± 0.003 vs 0.689 ± 0.019, respectively, P = .031). T2-weighted imaging-based radiomic features had consistently higher robustness and classification capabilities compared with T1-weighted images. Higher-dimensional radiomic features outperformed first-order features. Grey Level Co-occurrence Matrix, Grey Level Dependence Matrix, and Grey Level Size Zone Matrix sub-types were particularly useful in identifying textures which could detect vulnerable lesions. CONCLUSIONS: The combination of MRI-based radiomic features and lesion morphological and compositional parameters provided added value to the reference-standard risk assessment for carotid atherosclerosis. This may improve future risk stratification for individuals at risk of major adverse ischaemic cerebrovascular events. ADVANCES IN KNOWLEDGE: The clinical relevance of this work is that it addresses the need for a more comprehensive method of risk assessment for patients at risk of ischaemic stroke, beyond conventional stenosis measurement. This paper shows that in the case of carotid stroke, high-dimensional radiomics features can improve classification capabilities compared with stenosis measurement alone.

Comparison of the endurant bifurcated endograft vs. aortouni-iliac stent-grafting in patients with abdominal aortic aneurysms: experience from the ENGAGE registry.

PURPOSE: To compare the 1-year outcomes after repair of abdominal aortic aneurysms (AAA) with the bifurcated vs. aortouni-iliac (AUI) configuration of the Endurant stent-graft. METHODS: The study population comprised 1172 patients (1053 men; mean age 73.1±8.1 years, range 43-93) with unruptured infrarenal AAAs treated as part of the Endurant Stent Graft Natural Selection Global Post-market Registry (ENGAGE; ClinicalTrials.gov identifier NCT00870051). The primary outcome measure was treatment success at 12 months, defined by the composite of successful endograft deployment and the absence of type I/III endoleak, migration, rupture, or conversion to open surgery. Secondary outcome measures included endoleak, graft patency, migration, secondary procedures, and all-cause mortality. RESULTS: Among 1172 patients in ENGAGE, 1089 (92.9%) were treated with a bifurcated device and 83 (7.1%) received an AUI with femorofemoral bypass. Both groups were comparable with regard to demographics and baseline comorbidities, with the exception of a higher rate of cardiopulmonary disease in the AUI group. Successful deployment was achieved in all patients in the both groups. Postoperative complications occurred more frequently in the AUI patients, and the AUI group had an increased length of hospital stay (p=0.01). Endoleaks were more frequent in the AUI group at the conclusion of the procedure, a difference that vanished by 30 days. At 1 year, there were no incidences of graft kinking or stent fracture in either group. The rate of secondary procedures (5.3% in AUI patients and 4.9% for bifurcated cases) and all-cause mortality (10.5% and 8.6%, respectively) were similar in the two groups at 30 days and 1 year. CONCLUSION: The results of endovascular aneurysm repair with an Endurant AUI device appear similar to that after a bifurcated endovascular repair, with the exception of an increased length of hospital stay in the AUI group. An AUI device should be considered as an option in patients with anatomy unsuitable for a bifurcated repair.

In vivo MRI-based simulation of fatigue process: a possible trigger for human carotid atherosclerotic plaque rupture.

BACKGROUND: Atherosclerotic plaque is subjected to a repetitive deformation due to arterial pulsatility during each cardiac cycle and damage may be accumulated over a time period causing fibrous cap (FC) fatigue, which may ultimately lead to rupture. In this study, we investigate the fatigue process in human carotid plaques using in vivo carotid magnetic resonance (MR) imaging. METHOD: Twenty seven patients with atherosclerotic carotid artery disease were included in this study. Multi-sequence, high-resolution MR imaging was performed to depict the plaque structure. Twenty patients were found with ruptured FC or ulceration and 7 without. Modified Paris law was used to govern crack propagation and the propagation direction was perpendicular to the maximum principal stress at the element node located at the vulnerable site. RESULTS: The predicted crack initiations from 20 patients with FC defect all matched with the locations of the in vivo observed FC defect. Crack length increased rapidly with numerical steps. The natural logarithm of fatigue life decreased linearly with the local FC thickness (R(2) = 0.67). Plaques (n=7) without FC defect had a longer fatigue life compared with those with FC defect (p = 0.03). CONCLUSION: Fatigue process seems to explain the development of cracks in FC, which ultimately lead to plaque rupture.

Sequential imaging of asymptomatic carotid atheroma using ultrasmall superparamagnetic iron oxide-enhanced magnetic resonance imaging: a feasibility study.

BACKGROUND: Inflammation within atheromatous plaques is a known risk factor for plaque vulnerability. This can be detected in vivo on high-resolution magnetic resonance imaging (MRI) using ultrasmall superparamagnetic iron oxide (USPIO) contrast medium. The purpose of this study was to assess the feasibility of performing sequential USPIO studies over a 1-year period. METHODS: Ten patients with moderate asymptomatic carotid stenosis underwent carotid MRI imaging both before and 36 hours after USPIO infusion at 0, 6, and 12 months. Images were manually segmented into quadrants, and the signal change per quadrant was calculated at these time points. A mixed repeated measures statistical model was used to determine signal change attributable to USPIO uptake over time. RESULTS: All patients remained asymptomatic during the study. The mixed model revealed no statistical difference in USPIO uptake between the 3 time points. Intraclass correlation coefficients revealed a good agreement of quadrant signal pre-USPIO infusion between 0 and 6 months (0.70) and 0 and 12 months (0.70). Good agreement of quadrant signal after USPIO infusion was shown between 0 and 6 months (0.68) and moderate agreement was shown between 0 and 12 months (0.33). CONCLUSIONS: USPIO-enhanced sequential MRI of atheromatous carotid plaques is clinically feasible. This may have important implications for future longitudinal studies involving pharmacologic intervention in large patient cohorts.

Clinical feasibility of diffuse speckle contrast analysis for real-time tissue perfusion monitoring.

BACKGROUND: Adequate tissue perfusion is an important prognostic and diagnostic factor during the management of lower limb peripheral arterial disease. Convenient and real-time tissue perfusion monitoring remains an elusive challenge. METHODS: Tissue perfusion on the dorsal and plantar surfaces of both feet of 20 participants was measured during and after cuff-induced ischemia using a novel 4-channel, laser-based perfusion monitoring device based on diffuse speckle contrast analysis technology (Pedra sensors). Participants were free of significant peripheral arterial disease. Transcutaneous partial pressure of oxygen (TcPO2) measurements were recorded concurrently for comparison. RESULTS: Pedra sensors detected perfusion changes significantly more quickly than TcPO2 sensors. One minute after induced ischemia, the mean percent changes from baseline values (before ischemia) were -22.7±32.0% and -3.1±8.8% (P<0.001) for Pedra and TcPO2 sensors, respectively. One minute into induced ischemia, Pedra sensors had reached 50.5% of the 5-minute ischemia reading whereas TcPO2 sensors had reached only 18.6% of the 5-minute reading (P=0.046). Pedra sensors reported hyperemia immediately after cuff release with a mean percent change from baseline of 143.8±122.3%/173.4±121.8% on the dorsal/plantar surfaces while TcPO2 measurements were still recording negative changes at that time (-26.7±19.4%/-18.6±24.4% dorsal/plantar). Pedra sensors exhibited markedly lower interobserver and intraobserver variability than TcPO2 sensors. CONCLUSIONS: A device based on diffuse speckle contrast analysis reported tissue perfusion in real time. Cuff-induced ischemia and hyperemia following cuff release were rapidly and consistently detected on both the dorsal and plantar surfaces of the foot. Diffuse speckle contrast analysis may have value for real-time perfusion monitoring during angiography procedures.

Estimation of the zero-pressure computational start shape of atherosclerotic plaques: Improving the backward displacement method with deformation gradient tensor.

Advances in medical imaging have enabled patient-specific biomechanical modelling of arterial lesions such as atherosclerosis and aneurysm. Geometry acquired from in-vivo imaging is already pressurized and a zero-pressure computational start shape needs to be identified. The backward displacement algorithm was proposed to solve this inverse problem, utilizing fixed-point iterations to gradually approach the start shape. However, classical fixed-point implementations were reported with suboptimal convergence properties under large deformations. In this paper, a dynamic learning rate guided by the deformation gradient tensor was introduced to control the geometry update. The effectiveness of this new algorithm was demonstrated for both idealized and patient-specific models. The proposed algorithm led to faster convergence by accelerating the initial steps and helped to avoid the non-convergence in large-deformation problems.

Association between aneurysm shoulder stress and abdominal aortic aneurysm expansion: a longitudinal follow-up study.

BACKGROUND: Aneurysm expansion rate is an important indicator of the potential risk of abdominal aortic aneurysm (AAA) rupture. Stress within the AAA wall is also thought to be a trigger for its rupture. However, the association between aneurysm wall stresses and expansion of AAA is unclear. METHODS AND RESULTS: Forty-four patients with AAAs were included in this longitudinal follow-up study. They were assessed by serial abdominal ultrasonography and computed tomography scans if a critical size was reached or a rapid expansion occurred. Patient-specific 3-dimensional AAA geometries were reconstructed from the follow-up computed tomography images. Structural analysis was performed to calculate the wall stresses of the AAA models at both baseline and final visit. A nonlinear large-strain finite element method was used to compute the wall-stress distribution. The relationship between wall stresses and expansion rate was investigated. Slowly and rapidly expanding aneurysms had comparable baseline maximum diameters (median, 4.35 cm [interquartile range, 4.12 to 5.0 cm] versus 4.6 cm [interquartile range, 4.2 to 5.0 cm]; P=0.32). Rapidly expanding AAAs had significantly higher shoulder stresses than slowly expanding AAAs (median, 300 kPa [interquartile range, 280 to 320 kPa] versus 225 kPa [interquartile range, 211 to 249 kPa]; P=0.0001). A good correlation between shoulder stress at baseline and expansion rate was found (r=0.71; P=0.0001). CONCLUSION: A higher shoulder stress was found to have an association with a rapidly expanding AAA. Therefore, it may be useful for estimating the expansion of AAAs and improve risk stratification of patients with AAAs.

Contrast-induced nephropathy: do statins offer protection?

PURPOSE OF REVIEW: Contrast-induced nephropathy (CIN) is a commonly occurring complication associated with the use of contrast media in radiological studies. Various clinical studies have been reported investigating the nephroprotective role of statins. In this article, we review relevant clinical studies reported in 2010. RECENT FINDINGS: An overview of these indicates that the evidence for the use of statins specifically for offering renal protection against CIN is conflicting and inconclusive. SUMMARY: Pending large, well designed, adequately powered randomized controlled trials, it can be concluded that at present there is no definite evidence for their use in preventing CIN apart from their antiatherosclerotic use. However, using the analogy of beneficial effect of statin preloading with percutaneous coronary intervention, it can be speculated that high-dose statin may be beneficial in affording nephroprotection against CIN.

Characterization of healing following atherosclerotic carotid plaque rupture in acutely symptomatic patients: an exploratory study using in vivo cardiovascular magnetic resonance.

BACKGROUND: Carotid plaque rupture, characterized by ruptured fibrous cap (FC), is associated with subsequent cerebrovascular events. However, ruptured FC may heal following stroke and convey decreased risk of future events. This study aims to characterize the healing process of ruptured FC by assessing the lumen conditions, quantified by the lumen curvature and roughness, using in vivo carotid cardiovascular magnetic resonance (CMR). METHODS: Patients suffering from transient ischemic attack underwent high resolution carotid MR imaging within 72 hours of the acute cerebrovascular ischemic event. CMR imaging was repeated at 3 and 12 months in 26 patients, in whom FC rupture/erosion was observed on baseline images and subsequent cerebrovascular events were recorded during the follow-up period. Lumen curvature and roughness were quantified from carotid CMR images and changes in these values were monitored on follow-up imaging. RESULTS: Healing of ruptured plaque was observed in patients (23 out of 26) without any ischemic symptom recurrence as shown by the lumen surface becoming smoother during the follow-up period, characterized by decreasing maximum lumen curvature (p < 0.05), increasing minimum lumen curvature (p < 0.05) and decreasing lumen roughness (p < 0.05) during the one year follow-up period. CONCLUSIONS: Carotid plaque healing can be assessed by quantification of the lumen curvature and roughness and the incidence of recurrent cerebrovascular events may be high in plaques that do not heal with time. The assessment of plaque healing may facilitate risk stratification of recent stroke patients on the basis of CMR results.

Utility of magnetic resonance imaging-based finite element analysis for the biomechanical stress analysis of hemorrhagic and non-hemorrhagic carotid plaques.

BACKGROUND: Biomechanical stress analysis has been used for plaque vulnerability assessment. The presence of plaque hemorrhage (PH) is a feature of plaque vulnerability and is associated with thromboembolic ischemic events. The purpose of the present study was to use finite element analysis (FEA) to compare the stress profiles of hemorrhagic and non-hemorrhagic profiles. METHODS AND RESULTS: Forty-five consecutive patients who had suffered a cerebrovascular ischemic event with an underlying carotid artery disease underwent high-resolution magnetic resonance imaging (MRI) of their symptomatic carotid artery in a 1.5-T MRI system. Axial images were manually segmented for various plaque components and used for FEA. Maximum critical stress (M-Cstress(SL)) for each slice was determined. Within a plaque, the maximum M-Cstress(SL) for each slice of a plaque was selected to represent the maximum critical stress of that plaque (M-Cstress(PL)) and used to compare hemorrhagic and non-hemorrhagic plaques. A total of 62% of plaques had hemorrhage. It was observed that plaques with hemorrhage had significantly higher stress (M-Cstress(PL)) than plaques without PH (median [interquartile range]: 315 kPa [247-434] vs. 200 kPa [171-282], P=0.003). CONCLUSIONS: Hemorrhagic plaques have higher biomechanical stresses than non-hemorrhagic plaques. MRI-based FEA seems to have the potential to assess plaque vulnerability.