Bryant R G, Marill K, Blackmore C, Francis C
Department of Biophysics, University of Rochester, School of Medicine and Dentistry, New York 14642.
Magn Reson Med. 1990 Jan;13(1):133-44. doi: 10.1002/mrm.1910130112.
Nuclear magnetic relaxation rates are measured for whole blood, blood plasma, whole blood clots, and plasma clots in vitro. Relaxation rates are linear in the hematocrit and transverse relaxation rates are significantly greater than longitudinal relaxation rates. Longitudinal relaxation rates measured from 0.01 to 42 MHz for proton Larmor frequencies are found to decline monotonically with increasing magnetic field strength; however, the dispersion curves do not follow a simple Lorentzian behavior, which is anticipated in a suspension of particles in a solution of proteins having a distribution of molecular weights. The transverse relaxation rate is a function of the acquisition parameters, in particular, the choice of TE in either Hahn echo experiments or in echo-train experiments. The origin of this dependence of T2 on TE or the interpulse spacing in an echo train is identified with the exchange of water from inside the red blood cell to the outside and is only an important relaxation mechanism in the case where the blood cell membrane is intact and the cell contains deoxygenated hemoglobin. The dependence of the apparent transverse relaxation rate on the interpulse spacing in a Meiboom-Gill-Carr-Purcell pulse sequence provides the estimate that the mean residence time of water inside the blood cell is about 10 ms. These data provide a sound basis for understanding the dependence of magnetic images on magnetic field strength and the choices of the image acquisition parameters, TE and TR.
在体外测量了全血、血浆、全血凝块和血浆凝块的核磁共振弛豫率。弛豫率与血细胞比容呈线性关系，横向弛豫率显著大于纵向弛豫率。对于质子拉莫尔频率，在0.01至42MHz范围内测量的纵向弛豫率随磁场强度增加而单调下降；然而，色散曲线并不遵循简单的洛伦兹行为，而这种行为在具有分子量分布的蛋白质溶液中的颗粒悬浮液中是可以预期的。横向弛豫率是采集参数的函数，特别是在哈恩回波实验或回波串实验中TE的选择。T2对TE或回波串中脉冲间隔的这种依赖性的起源与水从红细胞内部交换到外部有关，并且仅在血细胞细胞膜完整且细胞含有脱氧血红蛋白的情况下才是重要的弛豫机制。在梅博姆-吉尔-卡尔-珀塞尔脉冲序列中，表观横向弛豫率对脉冲间隔的依赖性提供了估计，即血细胞内水的平均停留时间约为10毫秒。这些数据为理解磁共振图像对磁场强度的依赖性以及图像采集参数TE和TR的选择提供了坚实的基础。
