Ogawa S, Lee T M
AT&T Bell Laboratories, Murray Hill, New Jersey 07974.
Magn Reson Med. 1990 Oct;16(1):9-18. doi: 10.1002/mrm.1910160103.
Unusually high image contrast in vivo magnetic resonance imaging of the brain becomes observable at high magnetic fields when the blood oxygenation level is lowered. The cause of the contrast has been attributed to a magnetic susceptibility effect induced by paramagnetic deoxyhemoglobin in red cells. When the cylinder axis of a blood vessel is not parallel to the main magnetic field, the susceptibility difference produces varying local fields around the blood vessel. In gradient-echo images, not in spin-echo images, these local fields cause intravoxel dephasing of the water signal of the surrounding tissue. This description of the contrast enhancement has been confirmed by a series of in vitro blood sample experiments and image simulations. A predicted contrast change has been demonstrated in brain images of a mouse placed at two different orientations in the magnet. From the simulated images, the dependence of the contrast on the field strength has been estimated.
当血液氧合水平降低时，在高磁场下可观察到大脑活体磁共振成像中出现异常高的图像对比度。这种对比度的成因被归因于红细胞中顺磁性脱氧血红蛋白引起的磁化率效应。当血管的圆柱轴不平行于主磁场时，磁化率差异会在血管周围产生变化的局部磁场。在梯度回波图像而非自旋回波图像中，这些局部磁场会导致周围组织水信号的体素内失相。一系列体外血液样本实验和图像模拟已证实了这种对比度增强的描述。在置于磁体中两个不同方向的小鼠大脑图像中已证明了预测的对比度变化。从模拟图像中，已估计出对比度对场强的依赖性。
