Computational Fluid Dynamics for the Prediction of Endograft Thrombosis in the Superficial Femoral Artery.

PURPOSE: Contemporary diagnostic modalities, including contrast-enhanced computed tomography (CTA) and duplex ultrasound, have been insufficiently able to predict endograft thrombosis. This study introduces an implementation of image-based computational fluid dynamics (CFD), by exemplification with 4 patients treated with an endograft for occlusive disease of the superficial femoral artery (SFA). The potential of personalized CFD for predicting endograft thrombosis is investigated. MATERIALS AND METHODS: Four patients treated with endografts for an occluded SFA were retrospectively included. CFD simulations, based on CTA and duplex ultrasound, were compared for patients with and without endograft thrombosis to investigate potential flow-related causes of endograft thrombosis. Time-averaged wall shear stress (TAWSS) was computed, which highlights areas of prolonged residence times of coagulation factors in the graft. RESULTS: CFD simulations demonstrated normal TAWSS (>0.4 Pa) in the SFA for cases 1 and 2, but low levels of TAWSS (<0.4 Pa) in cases 3 and 4, respectively. Primary patency was achieved in cases 1 and 2 for over 2 year follow-up. Cases 3 and 4 were complicated by recurrent endograft thrombosis. CONCLUSION: The presence of a low TAWSS was associated with recurrent endograft thrombosis in subjects with otherwise normal anatomic and ultrasound assessment and a good distal run-off.

Coronary angiography-derived contrast fractional flow reserve.

BACKGROUND: Based on coronary angiography and mean aortic pressure, a specially designed computational flow dynamics (CFD) method is proposed to determine contrast fractional flow reserve (cFFR) without using invasive pressure wire. This substudy assessed diagnostic performance of coronary angiography-derived cFFR in catheterization laboratory, based on a previous multicenter trial for online assessment of coronary angiography-derived FFR (caFFR). METHODS: Patients with diagnosis of stable angina pectoris or unstable angina pectoris were enrolled in six centers. Wire-based FFR was measured in coronary arteries with 30-90% diameter stenosis. Offline angiography-derived cFFR was computed in blinded fashion against the wire-based FFR and caFFR at an independent core laboratory. RESULTS: A total of 330 patients were enrolled to fulfill inclusion/exclusion criteria from June 26 to December 18, 2018. Offline angiography-derived cFFR and wire-based FFR results were compared in 328 interrogated vessels. The statistical analysis showed the highest diagnostic accuracy of 89.0 and 86.6% for angiography-derived cFFR with a cutoff value of 0.94 and 0.93 against the wire-based FFR with a cutoff value of 0.80 and 0.75, respectively. The corresponding sensitivity and specificity were 92.2 and 87.3% for the cutoff value of 0.94 and 80.0 and 88.4% for the cutoff value of 0.93, which are similar to those against the caFFR. The receiver-operating curve has area under the curve of 0.951 and 0.972 for the wire-based FFR with the cutoff value of 0.80 and 0.75, respectively. CONCLUSIONS: Coronary angiography-derived cFFR showed higher accuracy, sensitivity, and specificity against wired-based FFR and caFFR. Hence, angiography-derived cFFR could enhance the hemodynamic assessment of coronary lesions.

Dynamics of nitrogen transformation and bacterial community with different aeration depths in malodorous river.

In this research, the dynamics of nitrogen transformation and bacterial community in malodorous river were investigated with different aeration depths. Computational flow dynamics (CFD) and Reynolds number (Re) were specially used to characterize the hydrodynamics condition under different aeration depths. The results indicated that aeration depth had vital impact on nitrogen transformation and bacterial community structure. It was found that a range of aeration depth (0.20-0.45 m above sediment-water interface) facilitated the removal of NH4+-N and TN with Re ranging between 6211 and 8930. Proteobacteria took over Firmicutes to become the predominant phylum (36-78%) under aeration, and the main subdivisions of γ-, ß- and δ-Proteobacteria also varied greatly with different aeration depths. Interestingly, there was a marked shift of the inferentially identified dominant functional role within Proteobacteria from organic-matter degradation to nitrogen metabolism and then to sulfur metabolism as well as the coupling of nitrogen and sulfur with the increase of disturbance. The redundancy analysis (RDA) further confirmed the importance of aeration disturbance in shaping bacterial community. These findings help to gain improved understanding of endogenous N-behavior and aquatic microbial ecology, and underline the need for integrating the hydrodynamics factors with microbial community.

Virtual Resting Pd/Pa From Coronary Angiography and Blood Flow Modelling: Diagnostic Performance Against Fractional Flow Reserve.

BACKGROUND: Fractional flow reserve (FFR) has been established as a useful diagnostic tool. The distal coronary pressure to aortic pressure (Pd/Pa) ratio at rest is a simpler physiologic index but also requires the use of the pressure wire, whereas recently proposed virtual functional indices derived from coronary imaging require complex blood flow modelling and/or are time-consuming. Our aim was to test the diagnostic performance of virtual resting Pd/Pa using routine angiographic images and a simple flow model. METHODS: Three-dimensional quantitative coronary angiography (3D-QCA) was performed in 139 vessels (120 patients) with intermediate lesions assessed by FFR. The resting Pd/Pa for each lesion was assessed by computational fluid dynamics. RESULTS: The discriminatory power of virtual resting Pd/Pa against FFR (reference: ≤0.80) was high (area under the receiver operator characteristic curve [AUC]: 90.5% [95% CI: 85.4-95.6%]). Diagnostic accuracy, sensitivity and specificity for the optimal virtual resting Pd/Pa cut-off (≤0.94) were 84.9%, 90.4% and 81.6%, respectively. Virtual resting Pd/Pa demonstrated superior performance (p<0.001) versus 3D-QCA %area stenosis (AUC: 77.5% [95% CI: 69.8-85.3%]). There was a good correlation between virtual resting Pd/Pa and FFR (r=0.69, p<0.001). CONCLUSIONS: Virtual resting Pd/Pa using routine angiographic data and a simple flow model provides fast functional assessment of coronary lesions without requiring the pressure-wire and hyperaemia induction. The high diagnostic performance of virtual resting Pd/Pa for predicting FFR shows promise for using this simple/fast virtual index in clinical practice.

Longer coronary anastomosis provides lower energy loss in coronary artery bypass grafting.

Distal anastomosis technique affects graft patency and long-term outcomes in coronary artery bypass grafting, however, there is no standard for the appropriate length of distal anastomosis. The purpose of this study is to evaluate whether longer distal anastomosis provides higher quality of distal anastomosis and better hemodynamic patterns. Off pump CABG training simulator, YOUCAN (EBM Corporation, Japan), was used for distal anastomosis model. Two lengths of distal anastomosis model (10 versus 4 mm) were prepared by end-to-side anastomosis technique. After CT scan constructed three-dimensional inner shape of distal anastomosis, computational flow dynamics (CFD) was used to analyze hemodynamic patterns. The working flow was defined as Newtonian fluid with density of 1050 kg/m3 and viscosity of 4 mPa s. The boundary condition was set to 100 mmHg at inlet, 50 ml/min at outlet, and 100 % stenosis of proximal coronary artery. Three-dimensional CT imaging showed quality of distal anastomosis in 10 mm model was more uniform without vessel wall inversion or kinking compared to 4 mm model. Anastomotic flow area was significantly larger in 10 mm model than that in 4 mm model (28.67 ± 4.91 versus 8.89 ± 3.18 mm2, p < 0.0001). Anastomotic angle was significantly smaller in 10 mm model compared to 4 mm model (10.2 ± 5.65° versus 20.6 ± 3.31°, p < 0.0001). CFD analysis demonstrated 10 mm model had streamlined flow with smooth graft curvature, whereas 4 mm model had abrupt blood flow direction changes with flow separation at the toe. 10 mm model had significantly lower energy loss than 4 mm model (34.78 ± 6.90 versus 77.10 ± 21.47 µW, p < 0.0001). Longer distal anastomosis provided higher quality of distal anastomosis, larger anastomotic flow area, smaller anastomotic angle, and smoother graft curvatures. These factors yielded lower energy loss at distal anastomosis.

Prey fish escape by sensing the bow wave of a predator.

Prey fish possess a remarkable ability to sense and evade an attack from a larger fish. Despite the importance of these events to the biology of fishes, it remains unclear how sensory cues stimulate an effective evasive maneuver. Here, we show that larval zebrafish (Danio rerio) evade predators using an escape response that is stimulated by the water flow generated by an approaching predator. Measurements of the high-speed responses of larvae in the dark to a robotic predator suggest that larvae respond to the subtle flows in front of the predator using the lateral line system. This flow, known as the bow wave, was visualized and modeled with computational fluid dynamics. According to the predictions of the model, larvae direct their escape away from the side of their body exposed to more rapid flow. This suggests that prey fish use a flow reflex that enables predator evasion by generating a directed maneuver at high speed. These findings demonstrate a sensory-motor mechanism that underlies a behavior that is crucial to the ecology and evolution of fishes.

Patient-specific computational flow simulation reveals significant differences in paravisceral aortic hemodynamics between fenestrated and branched endovascular aneurysm repair.

Background: Endovascular aneurysm repair with four-vessel fenestrated endovascular aneurysm repair (fEVAR) or branched endovascular aneurysm repair (bEVAR) currently represent the forefront of minimally invasive complex aortic aneurysm repair. This study sought to use patient-specific computational flow simulation (CFS) to assess differences in postoperative hemodynamic effects associated with fEVAR vs bEVAR. Methods: Patients from two institutions who underwent four-vessel fEVAR with the Cook Zenith Fenestrated platform and bEVAR with the Jotec E-xtra Design platform were retrospectively selected. Patients in both cohorts were treated for paravisceral and extent II, II, and V thoracoabdominal aortic aneurysms. Three-dimensional finite element volume meshes were created from preoperative and postoperative computed tomography scans. Boundary conditions were adjusted for body surface area, heart rate, and blood pressure. Pulsatile flow simulations were performed with equivalent boundary conditions between preoperative and postoperative states. Postoperative changes in hemodynamic parameters were compared between the fEVAR and bEVAR groups. Results: Patient-specific CFS was performed on 20 patients (10 bEVAR, 10 fEVAR) with a total of 80 target vessels (40 renal, 20 celiac, 20 superior mesenteric artery stents). bEVAR was associated with a decrease in renal artery peak flow rate (-5.2% vs +2.0%; P < .0001) and peak pressure (-3.4 vs +0.1%; P < .0001) compared with fEVAR. Almost all renal arteries treated with bEVAR had a reduction in renal artery perfusion (n = 19 [95%]), compared with 35% (n = 7) treated with fEVAR. There were no significant differences in celiac or superior mesenteric artery perfusion metrics (P = .10-.27) between groups. Time-averaged wall shear stress in the paravisceral aorta and branches also varied significantly depending on endograft configuration, with bEVAR associated with large postoperative increases in renal artery (+47.5 vs +13.5%; P = .002) and aortic time-averaged wall shear stress (+200.1% vs -31.3%; P = .001) compared with fEVAR. Streamline analysis revealed areas of hemodynamic abnormalities associated with branched renal grafts which adopt a U-shaped geometry, which may explain the observed differences in postoperative changes in renal perfusion between bEVAR and fEVAR. Conclusions: bEVAR may be associated with subtle decreases in renal perfusion and a large increase in aortic wall shear stress compared with fEVAR. CFS is a novel tool for quantifying and visualizing the unique patient-specific hemodynamic effect of different complex EVAR strategies. Clinical Relevance: This study used patient-specific CFS to compare postoperative hemodynamic effects of four-vessel fenestrated endovascular aneurysm repair (fEVAR) and branched endovascular aneurysm repair (bEVAR) in patients with complex aortic aneurysms. The findings indicate that bEVAR may result in subtle reductions in renal artery perfusion and a significant increase in aortic wall shear stress compared with fEVAR. These differences are clinically relevant, providing insights for clinicians choosing between these approaches. Understanding the patient-specific hemodynamic effects of complex EVAR strategies, as revealed by CFS, can aid in future personalized treatment decisions, and potentially reduce postoperative complications in aortic aneurysm repair.

Accuracy and Reproducibility of Coronary Angiography-Derived Fractional Flow Reserve in the Assessment of Coronary Lesion Severity.

Purpose: Coronary angiography-derived fractional flow reserve (caFFR) is a novel computational flow dynamics (CFD)-derived assessment of coronary vessel flow with good diagnostic performance. Herein, we performed a retrospective study to evaluate the reproducibility of caFFR findings between observers and investigate the diagnostic performance of caFFR for coronary stenosis defined as FFR ≤0.80, especially in the grey zone (0.75≤caFFR ≤0.80). Patients and Methods: A total of 150 patients (167 coronary vessels) underwent caFFR (with FlashAngio used for calculation of flow variables) and subsequent invasive fractional flow reserve (FFR) measurements. Outcomes, including reproducibility, were compared for vessels in and outside the grey zone. Results: The correlation of caFFR findings was good between the two laboratories (r = 0.723, p<0.001). The AUC of ROC were both high for caFFR-CoreLab1 and caFFR-CoreLab2 (0.975 and 0.883). The diagnostic accuracy, sensitivity, specificity, and negative and positive predictive values were not significantly different between the two laboratories (p>0.05). caFFR had a strong correlation with measures to FFR (r=0.911, p<0.001). There was no systematic difference between caFFR and FFR on Bland-Altman analysis in and outside the grey zone. There was no difference in diagnostic accuracy between the grey and non-grey zones in the prediction of FFR ≤0.80 (p=0.09). Conclusion: The inter-observer reproducibility for caFFR was high, and the diagnostic accuracy of caFFR was good compared to that of FFR.

Microarchitectural mimicking of stroma-induced vasculature compression in pancreatic tumors using a 3D engineered model.

Fibrotic tumors, such as pancreatic ductal adenocarcinoma (PDAC), are characterized for high desmoplastic reaction, which results in high intra-tumoral solid stress leading to the compression of blood vessels. These microarchitectural alterations cause loss of blood flow and poor intra-tumoral delivery of therapeutics. Currently, there is a lack of relevant in vitro models capable of replicating these mechanical characteristics and to test anti-desmoplastic compounds. Here, a multi-layered vascularized 3D PDAC model consisting of primary human pancreatic stellate cells (PSCs) embedded in collagen/fibrinogen (Col/Fib), mimicking tumor tissue within adjunct healthy tissue, is presented to study the fibrosis-induced compression of vasculature in PDAC. It is demonstrated how the mechanical and biological stimulation induce PSC activation, extracellular matrix production and eventually vessel compression. The clinical relevance is confirmed by correlating with patient transcriptomic data. Furthermore, the effects of gradual vessel compression on the fluid dynamics occurring within the channel is evaluated in silico. Finally, it is demonstrated how cancer-associated fibroblast (CAF)-modulatory therapeutics can inhibit the cell-mediated compression of blood vessels in PDAC in vitro, in silico and in vivo. It is envisioned that this 3D model is used to improve the understanding of mechanical characteristics in tumors and for evaluating novel anti-desmoplastic therapeutics.

Unruptured cerebral aneurysm risk stratification: Background, current research, and future directions in aneurysm assessment.

Background: The optimal management of unruptured cerebral aneurysms is widely debated in the medical field. Rapid technology advances, evolving understanding of underlying pathophysiology, and shifting practice patterns have made the cerebrovascular field particularly dynamic in recent years. Despite progress, there remains a dearth of large randomized studies to help guide the management of these controversial patients. Methods: We review the existing literature on the natural history of unruptured cerebral aneurysms and highlight ongoing research aimed at improving our ability to stratify risk in these patients. Results: Landmark natural history studies demonstrated the significance of size, location, and other risk factors for aneurysm rupture, but prior studies have significant limitations. We have begun to understand the underlying pathophysiology behind aneurysm formation and rupture and are now applying new tools such as flow dynamics simulations and machine learning to individualize rupture risk stratification. Conclusion: Prior studies have identified several key risk factors for aneurysmal rupture, but have limitations. New technology and research methods have enabled us to better understanding individual rupture risk for patients with unruptured cerebral aneurysms.

Patient-specific fluid-structure simulations of anomalous aortic origin of right coronary arteries.

Objectives: Anomalous aortic origin of the right coronary artery (AAORCA) may cause ischemia and sudden death. However, the specific anatomic indications for surgery are unclear, so dobutamine-stress instantaneous wave-free ratio (iFR) is increasingly used. Meanwhile, advances in fluid-structure interaction (FSI) modeling can simulate the pulsatile hemodynamics and tissue deformation. We sought to evaluate the feasibility of simulating the resting and dobutamine-stress iFR in AAORCA using patient-specific FSI models and to visualize the mechanism of ischemia within the intramural geometry and associated lumen narrowing. Methods: We developed 6 patient-specific FSI models of AAORCA using SimVascular software. Three-dimensional geometries were segmented from coronary computed tomography angiography. Vascular outlets were coupled to lumped-parameter networks that included dynamic compression of the coronary microvasculature and were tuned to each patient's vitals and cardiac output. Results: All cases were interarterial, and 5 of 6 had an intramural course. Measured iFRs ranged from 0.95 to 0.98 at rest and 0.80 to 0.95 under dobutamine stress. After we tuned the distal coronary resistances to achieve a stress flow rate triple that at rest, the simulations adequately matched the measured iFRs (r = 0.85, root-mean-square error = 0.04). The intramural lumen remained narrowed with simulated stress and resulted in lower iFRs without needing external compression from the pulmonary root. Conclusions: Patient-specific FSI modeling of AAORCA is a promising, noninvasive method to assess the iFR reduction caused by intramural geometries and inform surgical intervention. However, the models' sensitivity to distal coronary resistance suggests that quantitative stress-perfusion imaging may augment virtual and invasive iFR studies.

Estimation of endothelial shear stress in atherosclerotic lesions detected by intravascular ultrasound using computational fluid dynamics from coronary CT scans with a pulsatile blood flow and an individualized blood viscosity.

INTRODUCTION: Endothelial shear stress (ESS) is a local hemodynamic factor that is dependent on vessel geometry and influences the process of atherogenesis. As in vivo measurements of ESS are not possible, it must be calculated using computational fluid dynamics (CFD). In this feasibility study we explore CFD-models generated from coronary CT-angiography (CCTA) using an individualised blood viscosity and a pulsatile flow profile derived from in vivo measurements. MATERIALS AND METHODS: We retrospectively recruited 25 consecutive patients who received a CCTA followed by a coronary angiography including intravascular ultrasound (IVUS) and generated 3D models of the coronary arteries from the CT-datasets. We then performed CFD-simulations on these models. Hemodynamically non-relevant stenosis were identified in IVUS. They were isolated in the CFD-model and separated longitudinally into a half with atherosclerotic lesion (AL) and one without (NAL). ESS was measured and compared for both halves. RESULTS: After excluding vessels with no IVUS data or relevant stenosis we isolated 31 hemodynamically non-relevant excentric AL from a total of 14 vessels. AL segments showed consistently significantly lower ESS when compared to their corresponding NAL segments when regarding minimum (0.9 Pa, CI [0.6, 1.2] vs. 1.3 Pa, CI [0.9, 1.8]; p = 0.004), mean (5.0 Pa, CI [3.4, 6.0] vs. 6.7 Pa, CI [5.5, 8.4]; p = 0.008) and maximum ESS values (12.4 Pa, CI [8.6, 14.6] vs. 19.6 Pa, CI [12.4, 21.0]; p = 0.005). Qualitatively ESS was lower on the inside of bifurcations and curvatures. CONCLUSION: CFD simulations of coronary arteries from CCTA with an individualised flow profile and blood viscosity are feasible and could provide further prognostic information and a better risk stratification in coronary artery disease. Further prospective studies are needed to investigate this claim.

Surgical Management of Complex Middle Cerebral Artery Aneurysms: An Institutional Review.

BACKGROUND: Complex middle cerebral artery (MCA) aneurysms are defined as large (≥10 mm) or giant (≥25 mm) aneurysms with M2 branches arising from the aneurysm rather than M1 segments and usually require some form of reconstruction of the bifurcation. Their management is difficult and surgery is preferred over endovascular modalities because of their peculiar angioarchitecture and association with critical branch points or perforators. OBJECTIVES: The study was aimed at analyzing surgically managed complex MCA aneurysms and discussing characteristics not favorable for endovascular management, surgical nuances and clipping strategies, patient outcomes, and newer diagnostic modalities which help improve management. METHODS: Nine cases of surgically operated complex MCA aneurysms were identified from January 2017 to July 2019. The aneurysm characteristics, surgical nuances, clipping strategies, patient outcomes and points not favoring endovascular management were tabulated and analyzed. RESULTS: The mean maximum aneurysm diameter was 13.4 mm and the mean fundus/neck ratio was 1.6. The average microscope time was 124 min, and the most common method was clip reconstruction. The average number of clips used was 2.7 and the mean follow-up was 13 months. All patients have good postoperative outcome (Modified Rankin Score 0-2). The complete occlusion rate was 88.9% with one intraoperative voluntary residual sac which was coated. Computational fluid dynamic study results done preoperatively correlated with intraoperative findings. CONCLUSIONS: MCA aneurysms pose a significant challenge for endovascular treatment because of various factors such as luminal thrombi, complex angio-architecture, precarious branch/perforator locations, broad necks, and fusiform characteristics. Surgical management in experienced hands can tackle all these problems with an armamentarium of clipping techniques and bypass procedures.

Endothelial cell distributions and migration under conditions of flow shear stress around a stent wire.

BACKGROUND: Blood vessels are constantly exposed to flow-induced stresses, and endothelial cells (ECs) respond to these stresses in various ways. OBJECTIVE: In order to facilitate endothelialization after endovascular implantation, cell behaviors around a metallic wire using a flow circulation system are observed. METHODS: A parallel flow chamber was designed to reproduce constant shear stresses (SSs) on cell surfaces and to examine the effects of a straight bare metal wire on cell monolayers. Cells were then exposed to flow for 24 h under SS conditions of 1, 2, and 3 Pa. Subsequently, cell distributions were observed on the plate of the flow chamber and on the surface of the bare metal wire. Flow fields inside the flow chamber were analyzed using computational fluid dynamics under each SS condition. RESULTS: After 24 h, ECs on the bottom plate were concentrated toward the area of flow reattachment. The matching of higher cell density and CFD result suggests that flow-induced stimuli have an influence on EC distributions. CONCLUSION: Typical cell concentration occurs on dish plate along the vortexes, which produces large changes in SSs on cell layer.

Highlights of the fourteenth annual scientific meeting of the Society of Cardiovascular Computed Tomography.

The 14th Annual Scientific Meeting of the SCCT, held from July 11 to July 14 in Baltimore, MA, was attended by 830 attendees from 31 countries, with a program that included 45 sessions, and 26 exhibitors. This article summarizes several of the key themes and topics that were presented at this meeting, and provides an overview of the technical advances that are likely to impact future clinical practice in cardiovascular computed tomography.

Highlights of the 15th annual scientific meeting of the Society of Cardiovascular Computed Tomography.

The 15th Society of Cardiovascular Computed Tomography (SCCT) annual scientific meeting (ASM) welcomed 770 digital attendees from 44 countries, over 2 days, with a program that included 30 sessions across three simultaneously streaming channels, 10 exhibitors and a diverse range of scientific abstracts. In addition, #SCCT2020 generated >5900 tweets from nearly 700 engaged social media participants resulting in an estimated 38 million digital impressions and becoming #1 trending medical meeting in social media in the world during the meeting time period. This article summarizes the many themes and topics of presentation and discussion in this meeting, and the many technical advances that are likely to impact future clinical practice in cardiovascular computed tomography.

Highlights of the thirteenth annual scientific meeting of the Society of Cardiovascular Computed Tomography.

The 13th Annual Scientific Meeting of the SCCT, held from July 13 to July 15 in Dallas, TX, was attended by 690 attendees from 39 countries, 55 sessions with 140 speakers, and 18 exhibitors with the abstracts of all scientific posters published in the Journal of the Cardiovascular Computed Tomography. This article summarizes the many themes and topics of presentation and discussion in this meeting, and the many technical advances that are likely to impact future clinical practice in cardiac computed tomography and feature in future meetings.

Comparison of computational fluid dynamics findings with intraoperative microscopy findings in unruptured intracranial aneurysms- An initial analysis.

CONTEXT: The increase in the detection of unruptured cerebral aneurysms has led to management dilemma. Prediction of risk based on the size of the aneurysm is not always accurate. There is no objective way of predicting rupture of aneurysm so far. Computational fluid dynamics (CFDs) was proposed as a tool to identify the rupture risk. AIMS: To know the correlation of CFD findings with intraoperative microscopic findings and to know the relevance of CFD in the prediction of rupture risk and in the management of unruptured intracranial aneurysms. SETTINGS AND DESIGN: A prospective study involving nine cases over a period of 6 months as an initial analysis. SUBJECTS AND METHODS: Both males and females were included in the study. Preoperative analysis was performed using computed tomography angiogram, magnetic resonance imaging in all cases and digital substraction angiogram in some cases. Intraoperatively microscopic examination of the aneurysm wall was carried out and images recorded. The correlation was done between microscopic and CFD images. RESULTS: Seven cases were found intraoperatively to have a higher risk of rupture based on the thinning of the wall. Two cases had an atherosclerotic wall. All cases had low wall shear stress (WSS).Only two cases with atherosclerotic wall had a correlation with low WSS. CONCLUSIONS: While the pressure measured with CFD technique is a good predictor of rupture risk, the WSS component is controversial. Multicentric trials involving a larger subset of population are needed before drawing any definite conclusions. On-going development in the CFD analysis may help to predict the rupture chances accurately in future.

Cerebrospinal fluid flow in adults.

This chapter uses magnetic resonance imaging phase-contrast cerebrospinal fluid (CSF) flow measurements to predict which clinical normal-pressure hydrocephalus (NPH) patients will respond to shunting as well as which patients with Chiari I are likely to develop symptoms of syringomyelia. Symptomatic NPH patients with CSF flow (measured as the aqueductal CSF stroke volume) which is shown to be hyperdynamic (defined as twice normal) are quite likely to respond to ventriculoperitoneal shunting. The hyperdynamic CSF flow results from normal systolic brain expansion compressing the enlarged ventricles. When atrophy occurs, there is less brain expansion, decreased aqueductal CSF flow, and less likelihood of responding to shunting. It appears that NPH is a "two-hit" disease, starting as benign external hydrocephalus in infancy, followed by deep white-matter ischemia in late adulthood, which causes increased resistance to CSF outflow through the extracellular space of the brain. Using computational flow dynamics (CFD), CSF flow can be modeled at the foramen magnum and in the upper cervical spine. As in the case of NPH, hyperdynamic CSF flow appears to cause the signs and symptoms in Chiari I and can provide an additional indication for surgical decompression. CFD can also predict CSF pressures over the cardiac cycle. It has been hypothesized that elevated pressure pulses may be a significant etiologic factor in some cases of syringomyelia.