[Evaluation of Improvement of Tissue Contrast and Reduction of Imaging Time by Shortening TR in Brain T2 FLAIR Using MTC Pulse].

T2 fluid-attenuated inversion recovery (FLAIR) using inversion recovery pulse to suppress cerebrospinal fluid signal needs adequate T1 recovery time after data acquisition, otherwise, the T2-weighted contrast in brain tissue will get lower. Over 10000 ms of repetition time (TR) is recommended for the 1.5 T MR scanner, so it is difficult to shorten the imaging time. We verified whether T2 FLAIR combined with the magnetization transfer contrast (MTC) pulse shows better gray-to-white matter (GM/WM) and lesion-to-normal tissue contrasts even when the TR is shortened compared to the conventional T2 FLAIR. Optimal parameters of the MTC pulse were determined with a self-produced phantom, which modeled on cerebral cortical gray and white matters. GM/WM contrasts of the phantom were measured in T2 FLAIR with the MTC pulse while decreasing TR gradually from 10000 ms to 6500 ms. Although GM/WM contrast of the phantom in T2 FLAIR with the MTC pulse gradually decreased as the TR got shortened, the T2 FLAIR with the MTC pulse of 6500 ms of TR still showed 27% higher contrast than the conventional T2 FLAIR (TR 10000 ms). GM/WM contrast in T2 FLAIR with the MTC pulse was improved also in healthy volunteers, but improvement in thalamo-medullary contrast was less than that of cerebral cortico-medullary and putamino-medullary contrasts. It seems to be because thalamus, which is a deep gray matter, shows a higher MTC effect than other gray matters. Thus, it is necessary to note that the tissue contrast might differ between T2 FLAIR with the MTC pulse and the conventional T2 FLAIR. Because general lesions with an elongated T2 value show lower MTC effect compared to the normal brain tissue, a clinical case with thalamic lesion showed that the lesion-to-normal tissue contrast improved in T2 FLAIR with the MTC pulse of 6500 ms of TR. Although it is necessary to note the difference in contrast between some tissues, T2 FLAIR with the MTC pulse improves GM/WM and lesion-to-normal tissue contrasts even when the TR is shortened compared to the conventional T2 FLAIR, and it enables to shorten the imaging time.

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.

Effect of a notch at the distal end of a microcatheter on vein deformation in segmental adrenal venous sampling: a preliminary study using computational fluid dynamics.

This study aimed to evaluate the effect of a notch at the distal end of a microcatheter on vein deformation in segmental adrenal venous sampling. A three-dimensional fluid-structure interaction simulation was performed using commercial finite element software. A computational model of a vein with a catheter inserted into it was constructed. The outer and inner diameters of the vein were 0.9 mm and 0.6 mm, respectively, whereas those of the catheter were 0.6 mm and 0.5 mm, respectively. The velocity of the blood flow at the outlet was 85 mm/s. The pressure at the inlet was 0 Pa. The mesh consisted of approximately 660,000 elements. The effect of the number (0-4) and shape (no notch, 1/4 circular, 1/3 circular, semicircular, 2/3 circlecircular, and 3/4 circular) of the notches at the distal end of the microcatheter on the vein deformation when a suction pressure was applied was evaluated. The venous wall displacement was the smallest with the one-notch catheter, followed by the four-notch catheter, and was the smallest with the catheter having 1/4-circular notches, followed by the one with 1/3-circular notches. In conclusion, microcatheters having one notch and 1/4-circular notches reduce vein deformation and lead to successful segmental adrenal venous sampling. Graphical abstract Comparing catheters having different notch shapes.