MRI receiver frequency response as a contributor to Nyquist ghosting in echo planar imaging
MRI receiver frequency response as a contributor to Nyquist ghosting in echo planar imaging
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DOI：
10.1002/jmri.20365
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发表时间：
2005-08-01
影响因子：
4.4
通讯作者：
De Wilde, JP
中科院分区：
文献类型：
--
作者：
Delakis, I;Petala, K;De Wilde, JP
目的：研究MRI信号接收系统的频率响应特性对回波平面成像（EPI）中Nyquist重影形成的影响。用EPI在正交发射-接收头线圈的中心对充满水的圆柱形测试对象进行轴向成像。在第一组实验中，随着EPI采集之间盐的加入，水电导率逐渐增加。在第二组实验中，测试对象中水的电导率保持恒定，并在几个不同的带宽下获取EPI图像。结果：实验和仿真结果表明，在图像带宽所决定的有效频率范围内，信号接收系统的频率响应特性的变化对EPI Nyquist重影的影响是显著的。一个可以通过增加其陡峭度超过图像的带宽窗口时，线圈负载降低，或通过增加有效的频率范围时，图像带宽increased.Conclusions：本研究的结果可能有助于减少Nyquist重影EPI研究时，成像线圈负载不足，如在儿科和幻影研究的频率响应特性的变化。
Purpose: To study the frequency response characteristic of the MRI signal receiver system as a contributing factor to the formation of Nyquist ghosting in echo-planar imaging (EPI).Materials and Methods: Experimental work was undertaken on a 1.5 T system. A cylindrical test object filled with water was imaged axially with EPI in the center of the quadrature, transmit-receive head coil. In the first set of experiments, the water conductivity was increased progressively with the addition of salt between EPI acquisitions. In the second set of experiments, the conductivity of the water in the test object was kept constant and EPI images were acquired at several different bandwidths. A computer simulation was also implemented to demonstrate the impact of changes in the frequency response characteristic of the signal receiver system on EPI Nyquist ghosting.Results: Experimental and simulation results showed that Nyquist ghosting increased with the variation of the frequency response characteristic within the effective frequency range determined by the image bandwidth. One can increase the variation in the frequency response characteristic by increasing its steepness over the image's bandwidth window when coil loading is decreased, or by increasing the effective frequency range when image bandwidth is increased.Conclusions: The results of this research may help reduce Nyquist ghosting in EPI studies when the imaging coil is not sufficiently loaded, such as in pediatric and phantom studies.