Santyr G E
Department of Medical Physics, University of Wisconsin, Madison 53705.
Magn Reson Imaging. 1993;11(4):521-32. doi: 10.1016/0730-725x(93)90471-o.
A theoretical model is presented which describes the effects of magnetization transfer in multislice MR imaging of a tissue-mimicking phantom composed of cross-linked agar gel. The model is successful in explaining differences between single and multislice image signal intensities observed for the agar gel but not seen in a simple aqueous solution. Magnetization transfer leads to a reduction in the image signal intensity of a slice of interest due to off-resonance RF irradiation arising from 90 degrees and 180 degrees pulses intended for neighboring slices. The contribution of magnetization transfer to multislice MR imaging depends on the amount of off-resonance RF irradiation during the imaging sequence repetition interval. For the tissue-mimicking agar gel, conventional spin-echo multislice imaging gave rise to a negligible image signal intensity reduction (< or = 2%); however, fast spin-echo (FSE) imaging, which employs up to 16 times as many RF pulses per slice, exhibited as much as a 13% reduction in image signal intensity (13 slices). The reduction in multislice image signal intensity due to magnetization transfer is sample specific and is shown to be more dramatic for in vivo human leg muscle (10% for conventional spin echo, 40% for FSE) where magnetization transfer rates are greater than in the cross-linked agar gel.
本文提出了一个理论模型，该模型描述了磁化传递在由交联琼脂凝胶构成的组织模拟体模的多层磁共振成像中的作用。该模型成功地解释了琼脂凝胶单层面与多层面图像信号强度之间的差异，而在简单水溶液中并未观察到这种差异。由于用于相邻层面的90°和180°脉冲会产生失谐射频照射，磁化传递导致感兴趣层面的图像信号强度降低。磁化传递对多层磁共振成像的影响取决于成像序列重复间隔期间失谐射频照射的量。对于组织模拟琼脂凝胶，传统自旋回波多层成像导致的图像信号强度降低可忽略不计（≤2%）；然而，快速自旋回波（FSE）成像，每层使用的射频脉冲数量多达16倍，图像信号强度降低高达13%（13个层面）。由于磁化传递导致的多层图像信号强度降低具有样本特异性，并且对于体内人腿部肌肉而言更为显著（传统自旋回波为10%，FSE为40%），其中磁化传递率高于交联琼脂凝胶。
