Collins Christopher M, Liu Wanzhan, Swift Bryan J, Smith Michael B
Center for NMR Research, Penn State College of Medicine, Hershey, PA 17033, USA.
Magn Reson Med. 2005 Dec;54(6):1327-32. doi: 10.1002/mrm.20729.
Image inhomogeneity related to high radiofrequencies is one of the major challenges for high field imaging. This inhomogeneity can be thought of as having 2 radiofrequency-field related contributors: the transmit field distribution and the reception field distribution. Adjusting magnitude and phase of currents in elements of a transmit array can significantly improve flip angle homogeneity at high field. Effective application of some well-known parallel imaging and other receive array post-processing methods removes receptivity patterns from the intensity distribution in the final image, though noise then becomes a function of position in the final image. Here simulations are used to show that, assuming high signal-to-noise ratio, very homogeneous images in the human head can be acquired with the combination of transmit arrays and some receive array reconstruction methods at frequencies as high as 600 MHz.
与高射频相关的图像不均匀性是高场成像的主要挑战之一。这种不均匀性可被认为有两个与射频场相关的因素：发射场分布和接收场分布。调整发射阵列元件中电流的幅度和相位可显著提高高场下的翻转角均匀性。一些著名的并行成像和其他接收阵列后处理方法的有效应用可从最终图像的强度分布中去除接收模式，不过噪声随后会成为最终图像中位置的函数。在此，通过模拟表明，假设高信噪比，在高达600兆赫兹的频率下，结合发射阵列和一些接收阵列重建方法，可以获取人头部非常均匀的图像。
