Ham C L, Engels J M, van de Wiel G T, Machielsen A
Philips Medical Systems, DA Best, The Netherlands.
J Magn Reson Imaging. 1997 Sep-Oct;7(5):933-7. doi: 10.1002/jmri.1880070524.
The application of high gradient amplitudes and switching rates for MRI and spectroscopy, resulting in short rise times for the gradient field and high changes of the magnetic flux density in the patient, is known to possibly evoke peripheral nerve stimulation (PNS) in patients. These effects have been studied on 20 volunteers under different experimental circumstances. The results of these measurements are partially in line with earlier findings reported in the literature. New information is found for the dependence of the PNS threshold level as a function of the rise time of the gradient waveform. The PNS threshold level, expressed in terms of dB/dt, is found to be proportional with t-0.5, where t is the switch time for the gradients. Indications are found that magnitude of B, the modulus of the gradient vector field, is more closely related to the PNS threshold level than Bx, the imaging component of the gradient field. From the experiments, it is furthermore concluded that only for the imaging protocols characterized by the application of long bipolar repetitive gradient pulse trains, such as echoplanar imaging, PNS is expected at the reported threshold levels. For the protocols based on spin echo, turbo spin echo, inversion recovery, fast field echo, etc., characterized by shorter gradient pulse trains, the threshold levels are expected to be much higher.
在MRI和光谱学中应用高梯度幅度和切换速率，会导致梯度场的上升时间短且患者体内磁通密度变化大，已知这可能会在患者中引发周围神经刺激（PNS）。已在20名志愿者身上于不同实验条件下对这些效应进行了研究。这些测量结果部分与文献中先前报道的结果一致。发现了关于PNS阈值水平与梯度波形上升时间的函数关系的新信息。以dB/dt表示的PNS阈值水平与t-0.5成正比，其中t是梯度的切换时间。有迹象表明，梯度矢量场的模量B的大小比梯度场的成像分量Bx与PNS阈值水平的关系更密切。此外，从实验得出的结论是，只有对于应用长双极重复梯度脉冲序列的成像方案，如回波平面成像，才会在报告的阈值水平出现PNS。对于基于自旋回波、快速自旋回波、反转恢复、快速场回波等以较短梯度脉冲序列为特征的方案，预计阈值水平会高得多。
