DEVELOPMENT OF FUNCTIONAL OXYGENE METABOLIC IMAGING

为建立活化灶中氧代谢增高的磁共振成像(MRI)成像技术，本研究进行了如下研究：1.毛细血管磁共振对比研究激活灶毛细血管内红细胞压积明显升高。为了探讨MR信号与RBC数量和毛细血管氧合变化的关系，用快速袖带充气器按不同的袖带压力压迫小腿，并用MRI和NIBS进行测量。大腿的闭塞使小腿缺氧，从而增加顺磁性脱氧血红蛋白。MR信号强度随压缩压力的增加先降低后恢复。这一现象可以通过血管内外磁化率的差异来理解。血管内磁化率随脱氧血红蛋白的增加而增加，血管外磁化率随De…的增加而增加更多的肌红蛋白氧合。2.MR对比分析反映了红细胞的数量和氧合。毛细血管中红细胞周围的磁场变形反映了组织的氧合作用，这种变化是由于神经元的激活所致。为了阐明MR对比度和红细胞饱和度之间的关系，我们详细研究了红细胞周围的磁场失真，发现血液T2^*和T2在血氧含量为90%时都达到最大值。这种现象是基于红细胞和血浆的磁化率在血液氧合时是相等的。当加入顺磁性MR造影剂提高血浆磁化率时，最大血T_2^*和T_2的血氧分压降低。3.氧代谢成像的发展为了成像氧代谢，需要关注通过毛细血管供氧的组织区域的MR对比。毛细血管中红细胞的磁化率反映了组织中的氧浓度。当加入顺磁性磁共振造影剂后，红细胞周围的磁场变形沿毛细血管移动，并随等离子体磁化率的增加而变化。特别是，当红细胞和血浆的磁化率相等时，红细胞和血浆之间就不会有磁性差异，红细胞周围的移动磁变形就会消失，从而使组织中的T2最大化。对毛细血管中红细胞周围磁场变形敏感的MR脉冲序列正在开发中。较少

To develop a magnetic resonance imaging (MRI) techtque for mapping of oxygen metabolism which increases in activation foci, this study was conducted as follows.1.Investigation of MR contrast in capillariesHematocrit increases obviously in capillaries of activation foci. To investigate the relation between MR signal and changes in RBC quantity and oxygenation in capillaries, a lower leg was congested by compressing a thigh at several cuff pressures with a rapid cuff inflator and was measured by MRI and NIBS. The occlusion of a thigh made a lower leg hypoxic so ass to increase paramagnetic deoxygenated hemoglobin. MR signal intensity first decreased, then resumed with an increase of compression pressure. This phenomenon is understood by the magnetic susceptibility difference between inside and outside blood vessels. The magnetic susceptibility inside blood vessels increased first with an increase of deoxygenated hemoglobin, then that outside blood vessels increased with an increase of de … More oxygenation of myoglobin.2.Clarification of MR contrast to reflect quantity and oxygenation of RBCsThe magnetic field distortion around RBCs in capillaries reflects tissue oxygenation which changes due to neuronal activation. To clarify the relation between MR contrast and RBC saturation, we investigated the magnetic field distortion around RBCs in detail and found that both blood T2^* and T2 is maximized at the blood oxygenation of 90%. This phenomenon is based on that the magnetic susceptibilities of RBC and plasma equalize at that blood oxygenation. When the magnetic susceptibility of plasma is increased by adding paramagnetic MR contrast agent, the blood oxygenation of maximum blood T2^* and T2 decreased. We clarified how the magnetic field distortion around RBC influences on MR signal.3.Development of oxygen metabolic imagingTo image oxygen metabolism, MR contrast of tissue area in which oxygen is supplied through capillaries should be concerned. The magnetic susceptibility of RBC in capillaries reflects tissue oxygen concentration. The magnetic field distortion around RBCs is moving along capillaries and changes when the magnetic susceptibility of the plasma is increased by adding paramagnetic MR contrast agent. In particular, where the magnetic susceptibilities of RBC and plasma equalize, there would be no magnetic difference between RBC and plasma and the moving magnetic distortion around RBC disappears, giving rise to maximize T2 in tissue. The MR pulse sequence which is sensitive to the magnetic field distortion around RBC in capillaries is under development. Less