Weisskoff R M
MGH-NMR Center, Charlestown, MA 02129, USA.
Magn Reson Med. 1996 Oct;36(4):643-5. doi: 10.1002/mrm.1910360422.
Functional MR imaging (fMRI) of activation in the brain is one of the more demanding applications required of an NMR imaging instrument. Since the signal changes in activation imaging are quite small, any instrumental variations can easily compromise the fMRI contrast. The authors describe a simple method for measuring these scanner instabilities, which is implementable on all scanners, to determine whether instability is degrading the fMRI contrast-to-noise. In this method, a long time series of images is acquired with identical imaging parameters to the chosen fMRI scans, the fluctuations are measured as a function of region-of-interest (ROI) size, and compared with the single image SNR. By plotting these fluctuations versus ROI size, and comparing them with the theoretically approachable value, the impact of these fluctuations can be assessed. We also present a simplified version of the test, which can be implemented with minimal calculations.
大脑激活功能磁共振成像（fMRI）是对核磁共振成像仪器要求较高的应用之一。由于激活成像中的信号变化非常小，任何仪器变化都很容易损害fMRI对比度。作者描述了一种测量这些扫描仪不稳定性的简单方法，该方法可在所有扫描仪上实施，以确定不稳定性是否正在降低fMRI的对比度噪声比。在该方法中，使用与所选fMRI扫描相同的成像参数采集长时间的图像序列，测量波动作为感兴趣区域（ROI）大小的函数，并与单幅图像的信噪比进行比较。通过绘制这些波动与ROI大小的关系图，并将它们与理论上可达到的值进行比较，可以评估这些波动的影响。我们还提出了该测试的简化版本，它可以通过最少的计算来实施。
