Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands.
Magn Reson Med. 2011 Nov;66(5):1234-40. doi: 10.1002/mrm.23152. Epub 2011 Aug 29.
This communication describes radiofrequency pulses capable of performing spatially periodic excitation, inversion, and refocusing. The generation of such pulses either by multiplication of existing radiofrequency pulses by a Dirac comb function or by means of Fourier series expansion is described. Practical schemes for the implementation of such pulses are given, and strategies for optimizing the pulse profile at fixed pulse duration are outlined. The pulses are implemented using a spin-echo sequence. The power deposition is independent of the number of slices acquired, and hence the power deposition per slice is considerably reduced compared to multislice imaging. Excellent image quality is obtained both in phantoms and in images of the human head. These pulses should find widespread application for multiplexed imaging, in particular at high static magnetic field strengths and for pulse sequences that have a high radiofrequency power deposition and could lead to dramatic increases in scanning efficiency.
本文介绍了能够进行空间周期性激发、反转和聚焦的射频脉冲。描述了通过狄拉克梳状函数对现有射频脉冲进行乘法运算或通过傅里叶级数展开来产生这种脉冲的方法。给出了实现这种脉冲的实用方案，并概述了在固定脉冲持续时间内优化脉冲轮廓的策略。这些脉冲是通过自旋回波序列实现的。功率沉积与采集的切片数无关，因此与多切片成像相比，每个切片的功率沉积大大降低。在人体头部的图像和体模中都获得了极好的图像质量。这些脉冲应该会在多路成像中得到广泛应用，特别是在高静磁场强度下，以及在那些射频功率沉积较高且可能导致扫描效率显著提高的脉冲序列中。
