Hajnal J V, Baudouin C J, Oatridge A, Young I R, Bydder G M
Picker International, Wembley, Middlesex, England.
J Comput Assist Tomogr. 1992 Jan-Feb;16(1):7-18. doi: 10.1097/00004728-199201000-00003.
The transfer of magnetization between a free and a bound pool of spins is described in terms of the respective longitudinal relaxation times and the life times of spins in each pool. The effect of an off resonance radiofrequency (RF) pulse in producing saturation in the bound pool and a consequent decrease in both the available longitudinal magnetization and the T1 of spins in the free pool is described. The effects of increasing duration of the saturating RF pulse on image pixel signal intensity were used to determine values for the decrease in both T1 and the available magnetization in gray and white matter of the brain as well as in muscle, fat, and CSF. At 0.15 T the available magnetization of muscle was reduced by approximately 60% and its T1 was decreased from 350 to 150 ms. The available magnetization of white and gray matter was reduced by 40% and their values of T1 were reduced by 80-110 ms. The reduction in available magnetization was used to increase contrast on proton density weighted or T2-weighted SE pulse sequences. These changes were also used to design inversion recovery (IR) pulse sequences with particular contrast properties. A short inversion time (TI) magnetization transfer (MT) IR (MT-STIR) pulse sequence was used to reduce the signal from normal muscle to zero to produce an angiographic effect in the leg. Increased tissue contrast was observed with a T2-weighted (MT-SE) sequence in a patient with bilateral cerebral infarction and with an MT-IR pulse sequence in a patient who had an intracranial hematoma. Three patients with cerebral tumors showed high lesion contrast with MT-STIR sequences. Components within two tumors were changed to different degrees by MT and in one case change in the brain attributable to recent radiotherapy treatment was only identified with an MT-STIR sequence. Magnetization transfer can be used to manipulate both the available longitudinal magnetization and the T1 of normal and abnormal tissues. The changes in tissue contrast produced by this can be very substantial and are likely to be of importance in clinical imaging.
自由自旋池与束缚自旋池之间的磁化传递是根据各自的纵向弛豫时间以及每个池内自旋的寿命来描述的。描述了失谐射频（RF）脉冲在束缚池中产生饱和以及随之导致自由池中可用纵向磁化强度和自旋T1降低的效应。利用增加饱和RF脉冲持续时间对图像像素信号强度的影响来确定大脑灰质和白质以及肌肉、脂肪和脑脊液中T1和可用磁化强度降低的值。在0.15 T时，肌肉的可用磁化强度降低了约60%，其T1从350 ms降至150 ms。白质和灰质的可用磁化强度降低了40%，其T1值降低了80 - 110 ms。可用磁化强度的降低用于增加质子密度加权或T2加权SE脉冲序列的对比度。这些变化还用于设计具有特定对比度特性的反转恢复（IR）脉冲序列。使用短反转时间（TI）磁化传递（MT）IR（MT - STIR）脉冲序列将正常肌肉的信号降至零，以在腿部产生血管造影效果。在一名双侧脑梗死患者中，使用T2加权（MT - SE）序列观察到组织对比度增加；在一名患有颅内血肿的患者中，使用MT - IR脉冲序列观察到组织对比度增加。三名脑肿瘤患者在MT - STIR序列中显示出高病变对比度。两个肿瘤内的成分因MT而发生不同程度的变化，在一个病例中，仅通过MT - STIR序列才识别出因近期放疗治疗导致的脑部变化。磁化传递可用于操控正常和异常组织的可用纵向磁化强度和T1。由此产生的组织对比度变化可能非常显著，并且在临床成像中可能具有重要意义。
