Center for Functional and Metabolic Mapping, Robarts Research Institute, London, Ontario, Canada.
Magn Reson Med. 2009 Nov;62(5):1282-91. doi: 10.1002/mrm.22134.
Image contrast associated with paramagnetic chemical exchange saturation transfer agents can be generated by off-resonance irradiation of agent-bound water or amide protons or on-resonance irradiation of bulk water. Previously, a four-pool model was developed to describe an in vivo system. The model incorporated the magnetization transfer effect from macromolecules when using off-resonance irradiation. In the current study, this four-pool model is modified to describe the in vivo system when using on-resonance irradiation. The influences of pulse power, pulse duration, the chemical shift of bound water, the proton exchange rate between bulk water and bound water, and agent concentration on the on-resonance paramagnetic agent chemical exchange effects were simulated using a WALTZ-16 pulse train in the absence and presence of the macromolecule pool. The results demonstrated that while contrast increases with pulse duration in aqueous solution, there is an optimal pulse duration that maximizes on-resonance paramagnetic agent chemical exchange effects contrast in vivo. This predication was verified by experimental spectroscopic and imaging results from aqueous solution, bovine serum albumin phantoms, and a tissue phantom containing thulium-DOTAM (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetamide)-glycine-lysine. This model can be used to optimize sequence parameters to maximize in vivo on-resonance paramagnetic agent chemical exchange effects contrast.
顺磁化学交换饱和转移试剂的图像对比可以通过对结合水或酰胺质子的离共振辐照或对体相水的共振辐照产生。以前，开发了一个四池模型来描述体内系统。该模型在使用离共振辐照时纳入了来自大分子的磁化转移效应。在当前的研究中，修改了这个四池模型以描述使用共振辐照时的体内系统。使用 WALTZ-16 脉冲序列模拟了脉冲功率、脉冲持续时间、结合水的化学位移、体相水和结合水之间的质子交换率以及试剂浓度对顺磁试剂化学交换效应的影响，在不存在和存在大分子池的情况下。结果表明，虽然在水溶液中对比度随脉冲持续时间增加，但在体内存在最佳的脉冲持续时间，可以最大化顺磁试剂化学交换效应对比度。该预测通过来自水溶液、牛血清白蛋白模型和包含铥-DOTAM（1,4,7,10-四氮杂环十二烷-1,4,7,10-四乙酸-甘氨酸-赖氨酸）的组织模型的实验光谱和成像结果得到验证。该模型可用于优化序列参数以最大化体内顺磁试剂化学交换效应对比度。
