Construction of 3-D arterial volume meshes from magnetic resonance angiography

Abstract

Finite element methods are well-suited for solving problems in arterial fluid dynamics; primarily due to their ability to handle flows in complex geometries. However, in order to use these computational methods to develop realistic models of pulsatile flow in intracranial arteries and associated aneurysms, it is necessary to construct a 3-D mesh, or grid, that accurately duplicates the arterial geometry of interest In this paper, we present an efficient method to accurately develop realistic 3-D computational meshes of human intracranial arteries and aneurysms from serial magnetic resonance angiography images. However, these techniques may be applied to any other form of imaging data including computed tomographic angiography. First, raw grayscale images are segmented, converted to their binary form and arterial contours are extracted at each image slice. Next, the arterial contours are stacked and cubic splines are computed along the axial direction. This creates an affect similar to smooth integration in the axial direction and provides a set of points that define the 3-D arterial surface geometry. Then, surface patches are constructed and merged. A surface mesh is then computed with the ability to locally vary the mesh density as desired. Finally, nodal points on the surface mesh are used to compute the finite element volume mesh. The 3-D volume mesh accurately describes the arterial geometry and is used to develop patient-specific computational fluid dynamic models of flow phenomena in intracranial arteries and aneurysms. These flow models are then suitable for investigating the hemodynamics of intracranial aneurysm formation and test the end-effects of various medical and surgical treatments. [Neurol Res 1996; 18: 354-360]     

Hemodynamic relationship between intracranial aneurysm and carotid stenosis: review of clinical cases and numerical analyses

Abstract

Objective: Coexistence of both an intracranial aneurysm and a stenosis at the same internal carotid artery is infrequent, but it may complicate therapeutic management of either disease. It is unclear if a stenosis plays any role in development of intracranial aneurysms. We study patients with intracranial aneurysms at our hospital and investigate if there is a relationship between a carotid stenosis and an intracranial aneurysm.

Methods: Two hundred and nine patients who were treated for their intracranial aneurysms in a 2-year period were reviewed. Fifty-four patients were found to have at least one intracranial aneurysm and one intracranial or extracranial carotid stenosis. Ten of them had bilateral stenoses; 17 aneurysms were on the ipsilateral side of the stenosis, and eight on the contralateral side. Nineteen aneurysms were elsewhere. Two cases were selected for detailed computational fluid dynamics (CFD) analyses: one with an intracranial and the other with an extracranial stenosis.

Results: Aneurysms on the contralateral side of a carotid stenosis are significantly larger than those aneurysms on the ipsilateral side or with bilateral stenoses (13.6 versus 6.6 mm; P < 0.01). CFD studies show that wall shear stress at the aneurysm is more likely affected by an adjacent intracranial stenosis than by an extracranial stenosis.

Conclusions: Intracranial carotid aneurysms contralateral to a carotid stenosis are significantly larger than aneurysms with a carotid stenosis elsewhere. Rupture can occur on aneurysms with an extracranial carotid stenosis on the contralateral side or with an intracranial carotid stenosis on the ipsilateral side.     

下肢动脉狭窄三维模型建立及流体力学计算

背景：随着计算机技术的发展，血管虚拟现实已成为可能。 目的：基于CT断层图像建立下肢动脉局部狭窄的三维立体模型并进行有限元数字网格划分，用于下肢动脉局部狭窄血管的血液动力学分析。 方法：采集患者下肢动脉CTA中一段局部狭窄血管的DICOM数据，在MIMICS14.0中建立三维模型，再导入到有限元软件ANSYS11.0中进行有限元模型的建立，并模拟真实血流条件下的流体力学分析。 结果与结论：在MIMICS14.0软件中得到了局部狭窄血管的三维模型。在ANSYS workbench中得到了血管的有限元模型，模型节点总数7 335，单元总数为43 415。有限元计算得到了一系列的可视化的计算流体数据。表明该方法可以得到下肢动脉局部狭窄段流体力学分析所需的三维立体模型和有限元模型，得到流体力学分析所需相关数据。     

Comparative bioinformatics analysis between proteomes of rabbit aneurysm model and human intracranial aneurysm with label-free quantitative proteomics

AimsThis study aimed to find critical proteins involved in the development of intracranial aneurysm by comparing proteomes of rabbit aneurysm model and human aneurysms.MethodsFive human intracranial aneurysm samples and 5 superficial temporal artery samples, and 4 rabbit aneurysm samples and 4 control samples were collected for protein mass spectrometry. Four human intracranial aneurysm samples and 4 superficial temporal artery samples, and 6 rabbit aneurysm samples and 6 control samples were used for immunochemistry.ResultsProteomic analysis revealed 180 significantly differentially expressed proteins in human intracranial aneurysms and 716 significantly differentially expressed proteins in rabbit aneurysms. Among them, 57 proteins were differentially expressed in both species, in which 24 were increased and 33 were decreased in aneurysms compared to the control groups. Proteins were involved in focal adhesion and extracellular matrix‐receptor interaction pathways. We found that COL4A2, MYLK, VCL, and TAGLN may be related to aneurysm development.ConclusionProteomics analysis provided fundamental insights into the pathogenesis of aneurysm. Proteins related to focal adhesion and extracellular matrix‐receptor interaction pathways play an important role in the occurrence and development of intracranial aneurysm.     

The Effect of Intracarotid Perfusion of Cerebrospinal Fluid from Patients with Subarachnoid Hemorrhage on Cerebrovascular Reactivity in Rats

Abstract

Cerebrovascular resistance was measured in 10 rats with increasing dosages of 5-Hydroxytryptamine (5-HT). The internal carotid artery was perfused at constant flow with cerebrospinal fluid (CSF) from patients with ruptured intracranial aneurysms, and dose-response curves to 10 μ 1 boluses of 5-HT were compared with similar dose-response curves obtained during perfusion with Krebs' solution and with nonnal CSF (CSF-N). CSF from patients with subarachnoid hemorrhage (CSF-SAH) produced increased sensitivity to 5-HT.     

Assessing the Hemodynamics in Residual Cavities of Intracranial Aneurysm after Coil Embolization with Combined Computational Flow Dynamics and Silent Magnetic Resonance Angiography

Background and PurposeMetal artifacts limit computational fluid dynamics analysis after coil embolization. Silent magnetic resonance angiography reduces metal artifacts and improves visualization of the residual cavity of coil-embolized aneurysms. This study investigated the flow dynamics of the residual cavity after coil embolization using silent magnetic resonance angiography and computational fluid dynamics to elucidate the hemodynamic characteristics of recanalization.MethodsTwenty internal carotid-posterior communicating aneurysm cases treated with coil embolization and without stent assistance were followed up (mean±standard deviation, 13.0±6.1 months) and assessed using silent magnetic resonance angiography. The hemodynamic characteristics of the residual cavities in both types of aneurysms were compared between neck remnants, which persisted for >12 months (NR group), and those treated with coil compaction-induced body filling (BF group). Computational fluid dynamics analysis of each aneurysm was performed using morphological data obtained from silent magnetic resonance angiography. Pressure, pressure difference, normalized wall shear stress, and flow velocity were measured.ResultsThe residual cavity was well-visualized using silent magnetic resonance angiography and compared with those imaged using conventional time-of-flight magnetic resonance angiography, and eight internal carotid-posterior communicating aneurysms with neck remnants and body filling were investigated. The maximum pressure area was localized to the aneurysm wall in the NR group (n=4) and to sides of the coil surface in the BF group (n=4). No significant differences were observed for each hemodynamic parameter.ConclusionsCombination of silent magnetic resonance angiography and computational fluid dynamics helps to understand the hemodynamic characteristics of residual cavity in coil- embolized aneurysms. The flow-impingement zone at the coil surface (maximum pressure area) may influence the risk for future coil compaction.     

Cerebrospinal compensation of pulsating cerebral blood volume in hydrocephalus

Abstract

Objective: The aim of the study was to develop a computational method for the assessment of brain pressure compensation of cerebrospinal arterial blood inflow. The method was verified using clinical recordings performed during infusion studies in a group of patients diagnosed with hydrocephalus.

Materials and methods: We studied 27 patients suspected of having normal pressure hydrocephalus. The infusion test was used to measure the resistance to cerebrospinal fluid outflow, and the elastance coefficient was performed together with recording of the blood flow velocity in the middle cerebral artery. From the blood flow velocity waveform, the pulsatile pattern of increasing cerebral blood volume during one heart cycle was evaluated as a time integral of the arterial blood flow velocity minus the mean arterial blood flow. Cerebrospinal 'compliance index' (C _i) was calculated as the amplitude of change in blood volume divided by the amplitude of intracranial pressure pulse waveform.

Results: Compliance index C _i decreased during the infusion test, proportionally inverse to the rise in intracranial pressure controlled by the external infusion of saline (R=?0·76; p<0·005). A relative change in compliance (from baseline to the plateau phase of the study) was positively associated with greater brain elasticity (R=0·61; p<0·005) and poorer compensatory reserve at the phase of infusion (R=0·51; p=0·009)

Conclusion: C _i decreases during the infusion study and seems to well replicate the relative changes in cerebrospinal compensatory reserve in hydrocephalus.     

基于计算流体力学技术的个体化颅内动脉瘤三维刚性血流动力学模型

目的 建立基于计算流体力学技术（CFD）的个体化颅内动脉瘤血流动力学刚性模型.方法 用MIMICS软件读取病人颅内动脉瘤影像DICOM数据,进行三维实体重建.应用ANSYS-CFX软件进行三维刚性模型的数值仿真,分析与动脉瘤生长及破裂相关的血流动力学参数.结果 建立了个体化颅内动脉瘤血流动力学刚性模型,可以直观模拟动脉瘤血流动力学变化过程,形象地给出动脉瘤表面应力场的变化情况.在血流冲击瘤颈处,壁剪切力最大.结论 本研究建立的个体化颅内动脉瘤血流动力学模型快速、精确.动脉瘤的发生、发展和破裂与剪切力等血流动力学因素有关.动力学模型数值仿真结果可能为临床诊治提供理论分析基础.     

A mathematical model of the intracranial system including autoregulation

Abstract

Cerebral autoregulation plays an important role in the dynamic processes of intracranial physiology. This work develops a four-compartment, lumped-parameter model for the interactions of intracranial pressures, volumes, and flows as a test bed for examining the consistent inclusion of explicit autoregulation in mathematical models of the intracranial system. It is hypothesized that au.toregulation of the blood supply from the arterioles to the capillary bed can be modeled by allowing the flow resistance at the interface of the artery and capillary compartments in the model to be a function of pressure rather than a constant. The functional dependence on pressure of this resistance parameter is not specified in advance, but emerges naturally from the assumed relationship between pressure differences and flows. Results show that a constant flow from the artery to the capillary compartment can be maintained by a flow resistance which is directly proportional to the pressure difference between these two compartments. Oscillatory flow is re-established in the model at the capillary-cerebrospinal fluid and capillary-venous interfaces. [Neural Res 1997; 19: 441-450]     

颅内动脉瘤壁面压力分布的数值模拟研究

目的探讨颅内动脉瘤壁面压力的强度和分布,分析壁面压力对动脉瘤发生及生长的影响。方法结合数字减影血管造影（DSA）,采用计算流体力学（CFD）软件,对20例动脉瘤行血流动力学数值模拟分析,包括分叉管顶瘤8例,侧壁瘤12例。分别记录瘤顶、瘤颈和临近载瘤动脉区域的平均压力值,并分析动脉瘤流场情况。结果20例动脉瘤瘤顶处壁面压力平均为（620．64±446．09）Pa,瘤颈处为（618．89±431．09）Pa,载瘤动脉处为（633．81±448．59）Pa,3个区域压力差异无统计学意义。分叉管顶瘤（411．23±126．28）Pa（766．59±515．46）Pa与侧壁瘤相比,平均壁面压力差异有统计学意义（P〈0．05）。结论动脉瘤内壁面压力与载瘤血管内无明显不同,推测局部压力的改变对动脉瘤发生、生长无影响,由于流场模式的差异导致侧壁瘤与分叉管顶瘤的平均壁面压力显著不同。     

单纯支架治疗梭形动脉瘤的计算机仿真及血流动力研究

目的血流导向是治疗颅内梭形或宽颈动脉瘤的重要概念。本研究拟通过计算机仿真技术,探讨单纯多支架治疗梭形动脉瘤的血流导向作用。方法选用病例特异性的椎动脉梭形动脉瘤CFD模型。使用快速虚拟支架植入法植入1～3枚Enterprise支架。使用ICEMCFD软件进行网格化处理,ANSYS软件进行血流动力学分析,比较不同数量支架植入后的各项血流动力学参数的变化。结果虚拟支架植入后支架位置良好、贴壁满意。虚拟植入1～3枚支架后,梭形动脉瘤壁的平均瘤壁面切应力（WSS）分别下降了10％、20．4％和28．3％;经过瘤体最大截面的血流量分别下降了9．6％、21％和32．6％;相对滞留时间延长至支架植入前的1．45倍、2．07倍和2．79倍;动脉瘤壁平均压力变化不大。结论单纯支架治疗颅内梭形动脉瘤具有血流导向作用,随着支架数量增加,上述作用明显增强。快速虚拟支架植入法仿真度高、操作时间短,是适用于临床的虚拟支架植入技术。‘     

Implantation of Two Flow Diverter Devices in a Child With a Giant,Fusiform Vertebral Artery Aneurysm: Case Report

BackgroundIntracranial aneurysms in children and adolescents are uncommon; they account for 0.5% to 4.6% of the total intracranial aneurysms cases.MethodsA 15-year-old boy presented with a 6-month history of occipital headache that worsened over time. A magnetic resonance imaging scan revealed a giant, fusiform aneurysm of the V4 segment of the right vertebral artery with mass effect but no signs of hemorrhage. This lesion was confirmed by the catheter digital subtraction angiography. The posterior inferior cerebellar artery arose from the distal part of the aneurysm. Two flow-diverter devices were implanted in the V4 segment of the right vertebral artery. Follow-up angiograms performed 1 and 2 years after the procedure revealed a total aneurysm occlusion.ConclusionFlow-diverter device implantation may be a viable alternative to parent artery occlusion in a symptomatic, giant, fusiform vertebral artery aneurysm in a child.     

Intracranial aneurysms in sickle cell disease: Aneurysms characteristics and modalities of endovascular approach to treat these patients

IntroductionThe neurological complications of Sickle Cell Disease (SCD) include cerebral infarction and haemorrhage with rarely subarachnoid haemorrhage due to cerebral aneurysms.Materials and methodsIn our interventional department, working with SCD referral department, we reported our experience concerning management of adult's patients with cerebral aneurysms. We identified 26 adults with 48 intracranial aneurysms documented by imaging.Results18 patients, with 26 cerebral aneurysms were treated by endovascular approach for their aneurysms. No patient was treated by surgical way in our institution. 50% of patients had multiple aneurysms. Locations of aneurysms treated were typical with 70% of cerebral anterior artery and 30% of posterior artery. Three patients suffered from subarachnoid haemorrhage. Two procedure-related complications occurred during the treatment: one thrombo-embolic event with good recovery after medical treatment and one aneurismal perforation leading to the death of patient. Hypercoagulability is a major specific risk in SCD and use of permanent device as stent of flow diverter should be discussed to prevent complications.ConclusionEndovascular management of these aneurysms seems to be a good alternative to treat these patients, with stability of occlusion at follow-up.     

Endovascular treatment of blood blister-like aneurysms of internal carotid artery: Stent-assisted coiling and pipeline flow diversion

ObjectiveTo report the stent-assisted coil embolization and flow diversion treatments of blood-blister-like aneurysms based on the theory of acute dissection of the internal carotid artery.Patients and methodsFrom July 2016 through July 2020, 27 patients presenting with subarachnoid hemorrhage (SAH) due to rupture of internal carotid artery blood blister-like aneurysms were subjected to endovascular treatment with stent-assisted coiling or Pipeline flow diversion. Clinical outcomes were evaluated using modified Rankin Scale score (mRS).ResultsA proximal stenosis caused by angiopathology adjacent to aneurysms were found on internal carotid artery angiograms in all 27 cases. The angiopathology combining with the aneurysms implement that acute dissection of the supraclinoid segment of the internal carotid artery indicated the pathogenesis of blood blister-like aneurysm formation. All aneurysms were treated successfully with alleviation of the adjacent angiopathology after stenting on angiograms. During 1–12 months, mean 3.5 months, complete aneurysm obliteration without adjacent stenosis were found in 25(92.6%) patients. Two (7.4%) cases of recanalization were retreated with complete obliteration at 1 week and 3 months after initial treatment. Clinical mRS 0 and 1 outcomes were observed in 23(85.2%) patients, mRS 2 in 3(11.1%) patients and mRS 6 in 1(3.7%) not related to aneurysm treatment during follow-up.ConclusionsAcute focal dissection of supraclinoid segment of internal carotid artery underlies the development of blood blister-like aneurysm. Stent-assisted coiling and flow diversion treatments constitute appropriate treatment based on the arterial dissection pathology.     

顶端动脉瘤的血流动力学数值模拟压力分析

目的探讨顶端动脉瘤的血流动力学特点,分析动脉瘤的生长、破裂的可能机制。方法采用计算瘤体力学(CFD)软件结合顶端动脉瘤的医学影像,对动脉瘤内血液流动行数值模拟。结果流场压力呈周期性变化,压力剧烈变化的时间窗为0～0.62T (T为周期),与速度剧烈变化时间窗一致;动脉瘤内各处压力周期变化与流场的周期变化一致;每一个具体的时刻,流场压力分布不均衡。结论压力是动脉瘤破裂的危险因子之一,压力急剧变化的时间窗是0～0.62T,与流场速度急剧变化窗一致,是动脉瘤破裂的的危险窗。每一个时刻动脉瘤流场内压力分布不均衡。CFD数值模拟是一种反映动脉瘤血流动力学较好的方法,能为动脉瘤的病理生理机制和临床治疗提供较好的帮助。     

Dense,deep learning-based intracranial aneurysm detection on TOF MRI using two-stage regularized U-Net

Background and purposeThe prevalence of unruptured intracranial aneurysms in the general population is high and aneurysms are usually asymptomatic. Their diagnosis is often fortuitous on MRI and might be difficult and time consuming for the radiologist. The purpose of this study was to develop a deep learning neural network tool for automated segmentation of intracranial arteries and automated detection of intracranial aneurysms from 3D time-of-flight magnetic resonance angiography (TOF-MRA).Materials and methods3D TOF-MRA with aneurysms were retrospectively extracted. All were confirmed with angiography. The data were divided into two sets: a training set of 24 examinations and a test set of 25 examinations. Manual annotations of intracranial blood vessels and aneurysms were performed by neuroradiologists. A double convolutional neuronal network based on the U-Net architecture with regularization was used to increase performance despite a small amount of training data. The performance was evaluated for the test set. Subgroup analyses according to size and location of aneurysms were performed.ResultsThe average processing time was 15 min. Overall, the sensitivity and the positive predictive value of the proposed algorithm were 78% (21 of 27; 95% CI: 62–94) and 62% (21 of 34; 95%CI: 46–78) respectively, with 0.5 FP/case. Despite gradual improvement in sensitivity regarding aneurysm size, there was no significant difference of sensitivity detection between subgroups of size and location.ConclusionsThis developed tool based on a double CNN with regularization trained with small dataset, enables accurate intracranial arteries segmentation as well as effective aneurysm detection on 3D TOF MRA.     

镜像破裂与未破裂后交通动脉瘤血流动力学的数值模拟分析

目的 探讨镜像破裂与未破裂动脉瘤的血流动力学特征差异.方法 1例镜像破裂与未破裂后交通动脉瘤的三维血管造影资料,采用数学建模的方法,利用流体力学软件分析两者的血流动力学参数及流场特征.结果 双侧动脉瘤的血流方式一致,但破裂动脉瘤射入流更宽且冲击域分布不一致;最大流速高于未破裂动脉瘤;破裂动脉瘤壁面切应力(wall shear stress,WSS)分布不均,低WSS区域较大.结论 血流动力学在镜像的破裂与未破裂动脉瘤中存在差异,高流速与低壁面切应力可能与动脉瘤破裂出血相关.     

Flow Diversion for Acutely Ruptured Intracranial Aneurysms Treatment: A Retrospective Study and Literature Review

ObjectiveFlow diversion is becoming an increasingly established practice for the treatment of acutely ruptured intracranial aneurysms. In this study the authors present a literature review and meta-analysis, adding a retrospective review of institutional registry on emergency treatment of aRIA with flow diverter stent.Materials and methodsA systematic search of PubMed, SCOPUS, Ovid MEDLINE, and Ovid EMBASE was performed on April 20^th, 2021, extrapolating 35 articles. R language ‘meta’ and ‘metafor’ packages were used for data pooling. The DerSimonian-Laird model was used to calculate the pooled effect. The I² value and Q statistic evaluated study heterogeneity. Additionally, the authors retrospectively reviewed their institutional database for the treatment and outcomes of all patients with acutely ruptured intracranial aneurysms treated with flow diverter stent placement from May 2010 to November 2020 was performed.ResultsFrom the systematic literature review and meta-analysis, the pooled proportion of complete aneurysm occlusion was 78%, with a pooled rate of 79%, 71%, 80%, and 50% for dissecting, saccular, fusiform, and mycotic aneurysms, respectively. The pooled proportion of aneurysm rebleeding and intrastent stenosis was 12% and 15% respectively, for a total of 27% rate. The analysis of authors retrospective register showed an overall mortality rate of 16.7% (3/18), with a low but not negligible postprocedural rebleeding and intrastent thrombosis rates (5.6% and 11.1% respectively).ConclusionAlthough increasingly utilized in the management of selected patients with acutely ruptured intracranial aneurysms, flow diversion for acutely ruptured intracranial aneurysms treatment presents rebleeding and intrastent stenosis rates not negligible.     

A1 asynchrony,a potential risk factor for the rupture of anterior communicating artery aneurysms: A computational fluid dynamics study

Introduction and objectivesThe anterior communicating complex is one the most common locations for aneurysm development. It receives blood from both carotid circulations and the effect of synchrony on the arrival of blood flow has not been previously studied. The objective of this study was to compare the asynchrony conditions of the A1 pulse and its effects on the haemodynamic conditions of anterior communicating artery (ACoA) aneurysms.Materials and methodsFrom 2008 to 2017, 54 anterior communicating artery aneurysms treated at our centre were included in the study. Computational fluid dynamics (CFD) techniques were employed and simulations consisted of complete conditions of synchrony and introducing a delay of 0.2 s in the non-dominant A1 artery. Time-averaged wall shear stress (TAWSS), low shear area (LSA), A1 diameter and ACoA angles were measured.ResultsThe difference in the LSA in conditions of synchrony and asynchrony resulted in a broad range of positive and negative values. The symmetry index (p = 0.04) and A1/A2 angle on the dominant artery (p = 0.04) were associated with changes in LSA.ConclusionsIn asynchrony, LSA increased in the absence of A1 asymmetry and low A1/A2 angles, potentially increasing the risk of aneurysm rupture in this location.