Pike G B, Glover G H, Hu B S, Enzmann D R
Department of Radiology, Lucas MRS Center, Stanford University, CA 94305.
J Magn Reson Imaging. 1993 May-Jun;3(3):531-9. doi: 10.1002/jmri.1880030316.
Cross relaxation between macromolecular protons and water protons is known to be important in biologic tissue. In magnetic resonance (MR) imaging sequences, selective saturation of the characteristically short T2 macromolecular proton pool can produce contrast called magnetization transfer contrast, based on the cross-relaxation process. Selective saturation can be achieved with continuous wave irradiation several kilohertz off resonance or short, intense 0 degree pulses on resonance. The authors analyze 0 degree binomial pulses for T2 selective saturation, present design guidelines, and demonstrate the use of these pulses in spin-echo imaging sequences in healthy volunteers and patients. Using the phenomenologic Bloch equations modified for two-site exchange, the authors derive the analytic expressions for water proton relaxation under periodic pulsed saturation of the macromolecular protons. This relaxation is shown to be monoexponential, with a rate constant dependent on the saturation pulse repetition rate and the individual and cross-relaxation rates.
已知大分子质子与水质子之间的交叉弛豫在生物组织中很重要。在磁共振（MR）成像序列中，基于交叉弛豫过程，对特征性短T2大分子质子池进行选择性饱和可产生称为磁化传递对比的对比度。选择性饱和可以通过偏离共振几千赫兹的连续波照射或共振时的短而强的0度脉冲来实现。作者分析了用于T2选择性饱和的0度二项式脉冲，给出了设计指南，并展示了这些脉冲在健康志愿者和患者自旋回波成像序列中的应用。作者使用针对两点交换修改的现象学布洛赫方程，推导了大分子质子周期性脉冲饱和下水质子弛豫的解析表达式。这种弛豫表现为单指数形式，其速率常数取决于饱和脉冲重复率以及个体弛豫率和交叉弛豫率。
