Rosen B R, Belliveau J W, Vevea J M, Brady T J
Department of Radiology, Massachusetts General Hospital, Boston 02114.
Magn Reson Med. 1990 May;14(2):249-65. doi: 10.1002/mrm.1910140211.
Knowledge of regional hemodynamics has widespread application for both physiological research and clinical assessment. Here we review the use of MR contrast agents to measure tissue perfusion. Two primary mechanisms of image contrast are discussed: relaxivity and susceptibility effects. Relaxivity effects result from dipolar enhancement of T1 and T2 rates. Because tissue T1 rates are intrinsically smaller, the dominant effect is shortening of T1 relaxation times. The second mechanism of image contrast is the variation in tissue magnetic field produced by heterogeneous distribution of high magnetic susceptibility agents. Quantitation of tissue perfusion requires a detailed understanding of the relation between contrast agent concentration and associated MR signal changes. Studies to date show a linear relationship between contrast agent concentration and rate change in most organs. The exact nature of this relationship in the dynamic setting of rapid contrast agent passage through the microcirculatory bed is less well established. If this relationship is known, tracer kinetic modeling can be used to calculate regional blood flow and blood volume. Data are presented which indicate that this approach is feasible, and suggest the potential of contrast-enhanced NMR for high resolution in vivo mapping of both physiology and anatomy.
了解局部血流动力学在生理学研究和临床评估中都有广泛应用。在此，我们综述了利用磁共振造影剂测量组织灌注的方法。讨论了两种主要的图像对比机制：弛豫率和磁化率效应。弛豫率效应源于T1和T2速率的偶极增强。由于组织T1速率本质上较小，主要效应是T1弛豫时间缩短。图像对比的第二种机制是由高磁化率剂的不均匀分布产生的组织磁场变化。组织灌注的定量需要详细了解造影剂浓度与相关磁共振信号变化之间的关系。迄今为止的研究表明，在大多数器官中造影剂浓度与速率变化之间存在线性关系。在造影剂快速通过微循环床的动态情况下，这种关系的确切性质尚不太明确。如果知道这种关系，示踪动力学建模可用于计算局部血流量和血容量。所提供的数据表明这种方法是可行的，并显示了对比增强核磁共振在体内高分辨率绘制生理学和解剖学图谱方面的潜力。
