Computational Fluid Dynamics Analysis of Lateral Striate Arteries in Acute Ischemic Stroke Using 7T High-resolution Magnetic Resonance Angiography

Role of the vessel morphology on the lenticulostriate arteries hemodynamics during atrial fibrillation: A CFD-based multivariate regression analysis

BACKGROUND AND OBJECTIVE

Atrial fibrillation (AF) is the most common cardiac arrhythmia, inducing accelerated and irregular beating. Beside well-known disabling symptoms - such as palpitations, reduced exercise tolerance, and chest discomfort - there is growing evidence that an alteration of deep cerebral hemodynamics due to AF increases the risk of vascular dementia and cognitive impairment, even in the absence of clinical strokes. The alteration of deep cerebral circulation in AF represents one of the least investigated among the possible mechanisms. Lenticulostriate arteries (LSAs) are small perforating arteries mainly departing from the middle cerebral artery (MCA) and susceptible to small vessel disease, which is one of the mechanisms of subcortical vascular dementia development. The purpose of this study is to investigate the impact of different LSAs morphologies on the cerebral hemodynamics during AF.

METHODS

By combining a computational fluid dynamics (CFD) analysis of LSAs with 7T high-resolution magnetic resonance imaging (MRI), we performed different CFD-based multivariate regression analyses to detect which geometrical and morphological vessel features mostly affect AF hemodynamics in terms of wall shear stress. We exploited 17 cerebral 7T-MRI derived LSA vascular geometries extracted from 10 subjects and internal carotid artery data from validated 0D cardiovascular-cerebral modeling as inflow conditions.

RESULTS

Our results revealed that few geometrical variables - namely the size of the MCA and the bifurcation angles between MCA and LSA - are able to satisfactorily predict the AF impact. In particular, the present study indicates that LSA morphologies exhibiting markedly obtuse LSA-MCA inlet angles and small MCA size downstream of the LSA-MCA bifurcation may be more prone to vascular damage induced by AF.

CONCLUSIONS

The present MRI-based computational study has been able for the first time to: (i) investigate the net impact of LSAs vascular morphologies on cerebral hemodynamics during AF events; (ii) detect which combination of morphological features worsens the hemodynamic response in the presence of AF. Awaiting necessary clinical confirmation, our analysis suggests that the local hemodynamics of LSAs is affected by their geometrical features and some LSA morphologies undergo greater hemodynamic alterations in the presence of AF.

Flow Diversion Effect in a Saphenous Vein Graft Aneurysm Using a Double-Layer Micromesh Stent: A Case Report

BACKGROUND AND IMPORTANCE

A double-layer micromesh stent is designed for the treatment of carotid artery stenosis that has been reported to potentially provide a flow diversion effect. However, the actual flow diversion effect of stents remains unclear. Here, we present a case of a growing saphenous vein graft (SVG) aneurysm treated with the placement of the double-layer micromesh stent using its flow diversion effect.

CLINICAL PRESENTATION

A 66-year-old woman, who underwent high-flow bypass using a SVG for a blister-like internal carotid artery aneurysm 13 years earlier at our institute, was referred to our hospital with a pulsatile cervical mass. Magnetic resonance angiography showed a 9-mm aneurysm on the left SVG, although the aneurysm was a small pouch 4 years earlier. Digital subtracted angiography demonstrated a 9.4 × 8.3-mm aneurysm from the SVG at the auricular level. Because the diameter of the graft was larger than that of the available flow diverter stents in Japan, we decided to place the double-layer micromesh stent (CASPER RX, 7 × 25 mm MicroVention) using its flow diversion effect. Computational fluid dynamics analysis before and after stent deployment showed a significant reduction in the average flow velocity and wall shear stress in the aneurysm, indicating actual flow diversion. An angiogram 2 months postoperatively showed complete obliteration of the aneurysm.

CONCLUSION

Obliteration of the saphenous vein aneurysm was achieved because of the flow diversion effect of the double-layer micromesh stent. The stents might be a feasible alternative for treating cervical carotid aneurysms.

Cerebral hemodynamics during atrial fibrillation: Computational fluid dynamics analysis of lenticulostriate arteries using 7 T high-resolution magnetic resonance imaging

Atrial fibrillation (AF) is the most common cardiac arrhythmia, inducing irregular and faster heart beating. Aside from disabling symptoms-such as palpitations, chest discomfort, and reduced exercise capacity-there is growing evidence that AF increases the risk of dementia and cognitive decline, even in the absence of clinical strokes. Among the possible mechanisms, the alteration of deep cerebral hemodynamics during AF is one of the most fascinating and least investigated hypotheses. Lenticulostriate arteries (LSAs)-small perforating arteries perpendicularly departing from the anterior and middle cerebral arteries and supplying blood flow to basal ganglia-are especially involved in silent strokes and cerebral small vessel diseases, which are considered among the main vascular drivers of dementia. We propose for the first time a computational fluid dynamics analysis to investigate the AF effects on the LSAs hemodynamics by using 7 T high-resolution magnetic resonance imaging (MRI). We explored different heart rates (HRs)-from 50 to 130 bpm-in sinus rhythm and AF, exploiting MRI data from a healthy young male and internal carotid artery data from validated 0D cardiovascular-cerebral modeling as inflow condition. Our results reveal that AF induces a marked reduction of wall shear stress and flow velocity fields. This study suggests that AF at higher HR leads to a more hazardous hemodynamic scenario by increasing the atheromatosis and thrombogenesis risks in the LSAs region.

Geometric features of middle cerebral artery are associated with spontaneous basal ganglia intracerebral haemorrhage

BACKGROUND AND PURPOSE

Haemodynamics around the middle cerebral artery (MCA) and lenticulostriate arteries is believed to play important roles in the vascular rupture and local haemodynamics is subject to vascular geometry. Nonetheless, the relationship between the geometric features of MCA and spontaneous basal ganglia intracerebral haemorrhage (ICH) has not been investigated. To examine the relationship between the MCA geometric features and spontaneous basal ganglia ICH.

METHODS

This study was of retrospective and observational nature. The study recruited 158 consecutive hospitalised patients with consecutive CT-confirmed unilateral spontaneous basal ganglia ICH. Clinical data were extracted from electronic medical records, and imaging data were evaluated by two trained radiologists. The MCA-related geometric features were examined and their relationship with spontaneous basal ganglia ICH was analysed. Haemodynamic analyses under different MCA structural features were conducted.

RESULTS

Compared with the contralateral MCA, the ipsilateral MCA had greater M1 diameter ratio (proximal/distal) and a smaller M1/M2 angle and MCA bifurcation angle (p＜0.01). Imaging study showed differences in the MCA shape in both sides on coronal plane (p＜0.05). These MCA features were significantly correlated with the spontaneous ICH in basal ganglia. The greater M1 diameter ratio (proximal/distal), the inferior-oriented M1, the smaller M1/M2 angle and the superior-oriented M1 conditions increased the pressure, from high to low. The greater M1 diameter ratio (proximal/distal) and the inferior-oriented M1 increased the shear stress at the distal end of M1 segment.

CONCLUSIONS

The geometric features of MCA were significantly related to the spontaneous ICH in basal ganglia. The risk of haemorrhage, from high to low, included the greater M1 diameter ratio (proximal/distal), the inferior-oriented M1 (distal end), the smaller M1/M2 angle and the superior-oriented M1. Mechanistically, these vascular structural features contribute to increased vascular wall pressure and shear stress, which eventually lead to haemorrhage.

Virtual test occlusion for assessing ischemic tolerance using computational fluid dynamics

BACKGROUND

Ischemic tolerance has been evaluated by the balloon test occlusion (BTO) for cerebral aneurysms and tumors that might require parent artery occlusion during surgery. However, because of its invasiveness, a non-invasive evaluation method is needed. In this study, we assessed the possibility of virtual test occlusion using computational fluid dynamics (CFD) as a non-invasive alternative to BTO for evaluating ischemic tolerance.

METHODS

Twenty-one patients who underwent BTO were included in the study. Virtual test occlusion was performed using CFD analysis, and the flow rate (FR) and wall shear stress (WSS) of the middle cerebral artery on the occlusion side were calculated. The correlations between these parameters and examination data including the parameters of computed tomography perfusion during BTO were assessed and the cutoff value of CFD parameters for detecting the good collateral group was calculated.

RESULTS

The FR was strongly correlated with mean transit time (MTT) during BTO and moderately correlated with collateral flow grade based on angiographic appearance. The WSS was moderately correlated with collateral flow grade, mean stump pressure (MSP), and MTT. Furthermore, the FR and WSS were strongly correlated with the total FR and the diameters of the inlet vessels. The cutoff value of FR for detecting the good collateral group was 126.2 mL/min, while that of the WSS was 4.54 Pa.

CONCLUSION

The parameters obtained through CFD analysis were correlated with collateral flow grade and MSP in addition to MTT. CFD analysis may be useful to evaluate ischemic tolerance as a non-invasive alternative to BTO.

Impact of Endothelial Shear Stress on the Bilateral Progression of Unilateral Moyamoya Disease

Background and Purpose—

In unilateral moyamoya disease, altered endothelial shear stress on the intact-side terminal internal carotid artery might trigger the progression to bilateral disease. We analyzed the endothelial shear stress parameters of the normally appearing terminal internal carotid artery in unilateral moyamoya disease and its association with the progression to bilateral disease.

Methods—

This retrospective cohort study included patients diagnosed with unilateral moyamoya disease by cerebral angiography and followed-up with regular magnetic resonance imaging/magnetic resonance angiography evaluations for >1 year. Endothelial shear stress parameters acquired were mean and maximum signal intensity gradients (SIG) and SIG SD at the vessel boundary in time-of-flight sequences in initial brain magnetic resonance imaging/magnetic resonance angiography. Contralateral disease progression defined as the detection of newly developed vessel steno-occlusion with an magnetic resonance angiography steno-occlusive stage of ≥2, in the previously intact side of the brain on follow-up magnetic resonance imaging/magnetic resonance angiography evaluation.

Results—

Among 146 patients (66 males [45.2%] and 80 females [54.8%]; 76 pediatric [52.1%]), contralateral disease progression was detected in 43 patients (29.5%) after a mean follow-up of 4.3±2.4 years. Multivariate analysis showed that SIG SD was significantly associated with this progression (odds ratio, 13.001 [95% CI, 1.764−95.794], P =0.012). In receiver operating characteristic curve analysis, SIG SD predicted the contralateral progression with area under the curve values of 0.803 (95% CI, 0.726−0.880, P <0.001). The regression model was reproduced in the external cohort of 31 patients.

Conclusions—

Increased spatial variability of the endothelial shear stress around the normally appearing terminal internal carotid artery, as measured by SIG SD in time-of-flight sequences, may predict the contralateral progression of unilateral moyamoya disease.