Background and Purpose-Cerebrovascular events are related to atherosclerotic disease in the carotid arteries and are frequently caused by rupture of a vulnerable plaque. These ruptures are often observed at the upstream region of the plaque, where the wall shear stress (WSS) is considered to be highest. High WSS is known for its influence on many processes affecting tissue regression. Until now, there have been no serial studies showing the relationship between plaque rupture and WSS. Summary of Case-We investigated a serial MRI data set of a 67-year-old woman with a plaque in the carotid artery at baseline and an ulcer at 10-month follow up. The lumen, plaque components (lipid/necrotic core, intraplaque hemorrhage), and ulcer were segmented and the lumen contours at baseline were used for WSS calculation. Correlation of the change in plaque composition with the WSS at baseline showed that the ulcer was generated exclusively at the high WSS location. Conclusions-In this serial MRI study, we found plaque ulceration at the high WSS location of a protruding plaque in the carotid artery. Our data suggest that high WSS influences plaque vulnerability and therefore may become a potential parameter for predicting future events. Key Words: carotid artery Ⅲ MRI Ⅲ shear stress Ⅲ ulceration C erebrovascular events are related to atherosclerotic disease in the carotid arteries and are frequently caused by rupture of a vulnerable plaque. These plaques are characterized by the presence of a large lipid pool covered by a thin fibrous cap with infiltration of macrophages and a scarcity of smooth muscle cells. Plaque rupture has been more frequently observed at the proximal, upstream side of the minimal lumen diameter, 1 which is supposedly exposed to higher wall shear stress (WSS). There is ample evidence that the endothelium responds to high WSS such that it induces antiproliferative action, 2 which may lead to cap thinning. For that reason, we hypothesized that high WSS at the upstream side of the plaque has a biological effect on the fibrous cap and therefore enhances plaque vulnerability. 3 We present a case study in which we demonstrate the relation between high WSS and plaque rupture. Materials and Methods PatientSerial carotid MRI examinations were performed on a 67-year-old individual who was found to have moderate carotid stenosis by duplex ultrasonography. The institutional review committee approved the study and the patient gave informed consent. The patient's baseline MRI showed a plaque in the right carotid artery and the 10-month follow-up MRI showed plaque rupture with an ulcer. 4 MRIThe high-resolution, multisequence MRI protocol at baseline and follow up included 4 sequences: 3-dimensional time of flight, T1, T2, and proton density weightings. The in-plane resolution was 0.3ϫ0.3 mm with a slice thickness of 2 mm. The image segmentation was based on the signal intensities relative to the adjacent sternocleidomastoid muscle. A validated scheme 5 of hyper-, iso-, and hypointense signal intensities from the time of...

Patient specific geometrical data on human coronary arteries can be reliably obtained multislice computer tomography (MSCT) imaging. MSCT cannot provide hemodynamic variables, and the outflow through the side branches must be estimated. The impact of two different models to determine flow through the side branches on the wall shear stress (WSS) distribution in patient specific geometries is evaluated. Murray's law predicts that the flow ratio through the side branches scales with the ratio of the diameter of the side branches to the third power. The empirical model is based on flow measurements performed by Doriot et al. (2000) in angiographically normal coronary arteries. The fit based on these measurements showed that the flow ratio through the side branches can best be described with a power of 2.27. The experimental data imply that Murray's law underestimates the flow through the side branches. We applied the two models to study the WSS distribution in 6 coronary artery trees. Under steady flow conditions, the average WSS between the side branches differed significantly for the two models: the average WSS was 8% higher for Murray's law and the relative difference ranged from -5% to +27%. These differences scale with the difference in flow rate. Near the bifurcations, the differences in WSS were more pronounced: the size of the low WSS regions was significantly larger when applying the empirical model (13%), ranging from -12% to +68%. Predicting outflow based on Murray's law underestimates the flow through the side branches. Especially near side branches, the regions where atherosclerotic plaques preferentially develop, the differences are significant and application of Murray's law underestimates the size of the low WSS region.

Introduction: Articular cartilage needs sulfated-glycosaminoglycans (sGAGs) to withstand high pressures while mechanically loaded. Chondrocyte sGAG synthesis is regulated by exposure to compressive forces. Moderate physical exercise is known to improve cartilage sGAG content and might protect against osteoarthritis (OA). This study investigated whether rat knee joints with sGAG depleted articular cartilage through papain injections might benefit from moderate exercise, or whether this increases the susceptibility for cartilage degeneration.