Gabr Refaat E, Schär Michael, Edelstein Arthur D, Kraitchman Dara L, Bottomley Paul A, Edelstein William A
Division of MR Research, Department of Radiology, Johns Hopkins School of Medicine, 600 N Wolfe St., Park 328, Baltimore, MD, USA.
J Magn Reson. 2009 Jun;198(2):137-45. doi: 10.1016/j.jmr.2009.01.037. Epub 2009 Feb 4.
As the number of MRI phased array coil elements grows, interactions among cables connecting them to the system receiver become increasingly problematic. Fiber optic or wireless links would reduce electromagnetic interference, but their dynamic range (DR) is generally less than that of coaxial cables. Raw MRI signals, however, have a large DR because of the high signal amplitude near the center of k-space. Here, we study DR in MRI in order to determine the compatibility of MRI multicoil imaging with non-coaxial cable signal transmission. Since raw signal data are routinely discarded, we have developed an improved method for estimating the DR of MRI signals from conventional magnitude images. Our results indicate that the DR of typical surface coil signals at 3T for human subjects is less than 88 dB, even for three-dimensional acquisition protocols. Cardiac and spine coil arrays had a maximum DR of less than 75 dB and head coil arrays less than 88 dB. The DR derived from magnitude images is in good agreement with that measured from raw data. The results suggest that current analog fiber optic links, with a spurious-free DR of 60-70 dB at 500 kHz bandwidth, are not by themselves adequate for transmitting MRI data from volume or array coils with DR approximately 90 dB. However, combining analog links with signal compression might make non-coaxial cable signal transmission viable.
随着磁共振成像（MRI）相控阵线圈元件数量的增加，将这些元件连接到系统接收器的电缆之间的相互作用变得越来越棘手。光纤或无线链路可减少电磁干扰，但其动态范围（DR）通常小于同轴电缆。然而，由于k空间中心附近信号幅度较高，原始MRI信号具有较大的动态范围。在此，我们研究MRI中的动态范围，以确定MRI多线圈成像与非同轴电缆信号传输的兼容性。由于原始信号数据通常会被丢弃，我们开发了一种改进方法，用于从传统幅度图像估计MRI信号的动态范围。我们的结果表明，即使对于三维采集协议，3T下人体受试者典型表面线圈信号的动态范围也小于88dB。心脏和脊柱线圈阵列的最大动态范围小于75dB，头部线圈阵列小于88dB。从幅度图像得出的动态范围与从原始数据测量得出的结果高度一致。结果表明，目前模拟光纤链路在500kHz带宽下无杂散动态范围为60 - 70dB，仅靠自身不足以传输动态范围约为90dB的体线圈或阵列线圈的MRI数据。然而，将模拟链路与信号压缩相结合可能会使非同轴电缆信号传输成为可行方案。
