Том 47, № 4 (2016)

Nuclear magnetic resonance (NMR) T₂ distributions can be employed to understand the geometry of pores, but they are not sensitive enough to determine pore connectivity. In this paper, the pore space in reservoirs is regarded as a series of different sizes of the combination of spherical pores and cylinder pores based on the pore network model and Sphere–Cylinder model. In terms of the optimized T₂ inversion method, T₂ spectral distribution is decomposed into two groups, sphere pore distribution and cylinder pore distribution. It is assumed that cylinder pore controls the connectivity and permeability of the reservoir and the sphere pore is the main place of fluid storage. The more cylinder pores that exist, the better the connectivity and permeability are. The data of eight core plugs are analyzed using this method, and the results are in accordance with those of core analysis, which proves the practicability of our research and provides a basis for the direct evaluation of reservoir pore structure using NMR T₂ distribution.

An abnormal vascular structure such as a stenosis induces a turbulent flow that causes signal voids in MRA images. This study aimed to propose a new method to prevent signal voids in stenotic blood vessels in conventional 3D time-of-flight (TOF) MRA images. 2D local excitation radio frequency (2DRF) pulse sequence was used in 7T MRI, and the feasibility of using this technique for imaging abnormal and turbulent flow was evaluated. The images obtained using the sequence were compared with conventional TOF MRA image of patients with MCA stenosis. Compared to conventional TOF MRA images, the images obtained using 7T MRI with a 2DRF pulse sequence showed high signal intensity in vascular segments that were expected to be abnormal, such as the origins of perforating vessels such as lenticulostriate arteries which are branches of the proximal part of the middle cerebral artery. 2DRF pulse also obviously compensated for the signal void within the stenotic vessels in the patient. The conventional MRA technique is sensitive to a turbulent flow, which causes a loss of signal and overestimation of the stenosis. The method proposed in this study could provide clear images of vascular segments that are difficult to evaluate owing to a severe stenosis.

The aim of this study was to investigate hemodynamic differences in different brain regions of normal macaque brains using dynamic susceptibility contrast (DSC) perfusion magnetic resonance (MR) imaging. Twelve male subjects were selected for DSC perfusion MR imaging (age 4–8 years). The relative cerebral blood volume (rCBV) and relative cerebral blood flow (rCBF) images were obtained by post-processing software. The values of rCBV and rCBF were recorded from the frontal cortex, parietal cortex, occipital cortex, head of caudate nucleus, posterior limb of internal capsule, thalamus, midbrain, pons, cerebellar, semioval area and splenium of the corpus callosum. The figures of rCBV and rCBF can clearly demonstrate the hemodynamic differences in various cerebral parts. It has been noted that rCBV and rCBF values have no significant difference between the right and left hemisphere (P > 0.05). The values of rCBF from cerebral cortex were significantly higher than that of white matter (P < 0.05). The values of rCBF were different (P < 0.05) at frontal cortex, parietal cortex and occipital cortex. However, the highest value has been observed in occipital cortex compared with the others (P < 0.05). We observed higher correlation coefficient between the rCBF and rCBV (r = 0.92, P < 0.05). Results from this study show that the hemodynamic characteristics of healthy adult rhesus are similar to those of normal human studies. Moreover, the blood flow of cortex is found significantly higher than white matter and there was different flow perfusion among different parts, as the occipital cortex showed the highest value and frontal cortex the lowest value.

An optimized flow distribution is quintessential for hemodialyzers in order to maximize the mass transfer efficiency through the diffusion process. It is important to observe the flow pattern and the concentration profile within the hemodialyzer when evaluating its function. Thus experimental knowledge which can evaluate the above two parameters plays a significant part in the optimization of these modules. The objective of the present study was to propose an experimental method for evaluating the flow distribution pattern in the blood compartment of a hollow-fiber hemodialyzer using a contrast-enhanced spin echo T₁-weighted magnetic resonance imaging (MRI) technique by tracing the concentration profiles and theoretical interpretation. Considering a parabolic flow profile inside the hollow fibers, the relative signal intensities along the axial direction of the five types of hemodialyzers were measured after injecting the Gd-DTPA contrast solution into the blood inlet. Although uniformly decreasing concentration profiles towards the outlet ports were observed during the analysis, the calculated mean and standard deviation (SD) of all average relative signal intensities indicated that there were variations in concentration distribution between the transverse sections of the same hemodialyzer. However, most of these variabilities were found to be within one SD of this mean value. These results suggested that the contrast-enhanced MRI technique can provide a significant tool for characterizing flow distribution in hemodialyzers, both qualitatively and quantitatively.