Yasutaka Tobe

Experimental insights into flow impingement in cerebral aneurysm by stereoscopic particle image velocimetry: transition from a laminar regime.

This study experimentally investigated the instability of flow impingement in a cerebral aneurysm, which was speculated to promote the degradation of aneurysmal wall. A patient-specific, full-scale and elastic-wall replica of cerebral artery was fabricated from transparent silicone rubber. The geometry of the aneurysm corresponded to that found at 9 days before rupture. The flow in a replica was analysed by quantitative flow visualization (stereoscopic particle image velocimetry) in a three-dimensional, high-resolution and time-resolved manner. The mid-systolic and late-diastolic flows with a Reynolds number of 450 and 230 were compared. The temporal and spatial variations of near-wall velocity at flow impingement delineated its inherent instability at a low Reynolds number. Wall shear stress (WSS) at that site exhibited a combination of temporal fluctuation and spatial divergence. The frequency range of fluctuation was found to exceed significantly that of the heart rate. The high-frequency-fluctuating WSS appeared only during mid-systole and disappeared during late diastole. These results suggested that the flow impingement induced a transition from a laminar regime. This study demonstrated that the hydrodynamic instability of shear layer could not be neglected even at a low Reynolds number. No assumption was found to justify treating the aneurysmal haemodynamics as a fully viscous laminar flow.

Relationship between Pathology and Hemodynamics of Human Unruptured Cerebral Aneurysms

This research compared the intraoperative appearance, computational fluid dynamic (CFD) analysis, and scanning electron microscope (SEM) observation of endothelial cells (EC) of seven human cerebral aneurysms in an effort to find the relationship between hemodynamic patterns and wall-thinning of aneurysms.

Combined analysis of pathology and hemodynamics of human unruptured cerebral aneurysm with thin-walled region

Cerebral aneurysms are known as the top reason of subarachnoid hemorrhage (SAH). They are studied in the medical and the engineering field to reveal their pathogenesis, progression, and rupture mechanisms1,2. The pathological studies revealed the site of predilection, rupture rate, the risk factors1, inflammation within the aneurysm, and conditions of endothelial cells (EC) in the aneurysms3. The current pathological analyses of the cerebral aneurysms are all phenomenological and it does not consider the cause-and-effect mechanisms between the mechanical stimulation and the physiological effect although hemodynamics is thought to play an important role in the mechanisms of aneurysms. One reason that the aneurysms’ mechanisms remain unsolved is because the pathology and hemodynamics are studied independently. Purpose of this study is to reveal the relationship of endothelial cell, thickness, and hemodynamics of the cerebral aneurysms by comparing the scanning electron microscope (SEM) analyses, μCT, and the computational fluid dynamics (CFD) analyses of the cerebral aneurysms.© 2013 ASME

Investigation on a Relationship Between Hemodynamics and Wall-Thinning in an Unruptured Human Cerebral Aneurysm

Recent studies of cerebral aneurysms are held using the blood flow simulation with patient-specific luminal geometries. In the study of development of cerebral aneurysms, wall shear stress (WSS) is focused as one of the key factors1–2. But the answer to the relationship between the extension of aneurysm and the theory of low WSS and high WSS still remains a question. One reason this question remains unsolved is because the current research about the cerebral aneurysms are held only using the vascular geometry developed from the medical images. From the intra-operative observation of cerebral aneurysms, the appearance of the cerebral aneurysm is not unified. Certain parts of the cerebral aneurysm have thin-walled structures where the blood flow of the aneurysm can be observed through the aneurysm wall. These differences in the wall structures cannot be predicted from the medical images. The purpose of this study is to see the relationship between hemodynamic patterns and thin-walled structure in human cerebral aneurysms.Copyright