DEVELOPMENT OF FUNCTIONAL OXYGENE METABOLIC IMAGING

为了建立一种磁共振成像（MRI）技术来绘制激活灶增加的氧代谢图，本研究进行了如下研究。毛细血管MR造影研究激活灶毛细血管内红细胞比容明显增高。为了研究MR信号与红细胞数量和毛细血管氧合变化之间的关系，我们使用快速袖带充气机在多个袖带压力下压迫大腿，并通过MRI和NIBS测量下肢充血。大腿的闭塞使小腿缺氧，从而增加顺磁脱氧血红蛋白。随着压缩压力的增加，MR信号强度先降低后恢复。这种现象可以通过血管内外的磁化率差异来理解。血管内磁化率先随缺氧血红蛋白的增加而升高，血管外磁化率随缺氧血红蛋白的增加而升高。磁共振造影反映红细胞数量和氧合的澄清毛细血管中红细胞周围的磁场畸变反映了神经元激活引起的组织氧合变化。为了阐明MR对比度与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畸变，发现血液T2^*和T2在血氧浓度为90%时均达到最大。这种现象是基于红细胞和血浆的磁化率在血液氧合时相等。当加入顺磁磁共振造影剂增加血浆磁化率时，最大血氧T2^*和T2降低。我们阐明了红细胞周围磁场畸变对磁共振信号的影响。氧代谢成像的发展为了成像氧代谢，应关注通过毛细血管供氧的组织区域的MR对比。红细胞在毛细血管中的磁化率反映了组织氧浓度。红细胞周围的磁场畸变沿毛细血管移动，当加入顺磁性磁共振造影剂增加等离子体的磁化率时，磁场畸变发生变化。特别是当红细胞和血浆的磁化率相等时，红细胞和血浆之间将没有磁性差异，红细胞周围的移动磁畸变消失，使组织中的T2最大化。对毛细血管红细胞周围磁场畸变敏感的磁共振脉冲序列正在研制中。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