Felblinger J, Kreis R, Boesch C
Department of MR Spectroscopy and Methodology, University of Berne, Switzerland.
NMR Biomed. 1998 May;11(3):107-14. doi: 10.1002/(sici)1099-1492(199805)11:3<107::aid-nbm525>3.0.co;2-i.
Signal loss and absolute quantitation errors in 1H-MRS (localized proton MR spectroscopy) because of physiologic brain motion are analyzed quantitatively. Cardiac and respiratory related motion lead to substantial phase dispersion when using a standard, short echo-time STEAM sequence. The loss in signal area varies from 6-7% with TM (middle interval time in a STEAM sequence) = 13.7 ms, to 25-39% with TM = 100 ms. The variation in signal area because of motion-related phase dispersion is up to 16% for TM = 100 ms. The signal phase as a function of the position in the cardiac cycle is shown to be reproducible. Maximal differences in the signal phase are over 180 degrees for long TMs. ECG-gating reduces the phase dispersion considerably but introduces problems with variable repetition times. Using a phase calibration curve recorded with the water suppression turned off, it is possible to retrogate subsequent untriggered acquisitions with the water suppression activated, if the time points in the cardiac cycle are recorded for each acquisition. The gain in signal intensity is between 3 and 21%. For absolute quantification via brain water, this phase analysis has the important consequence that reference scans must be phased individually before co-adding, otherwise metabolite concentrations may be severely overestimated.
定量分析了由于生理性脑运动导致的1H-MRS（局部质子磁共振波谱）中的信号损失和绝对定量误差。使用标准的短回波时间STEAM序列时，心脏和呼吸相关运动导致大量相位离散。信号面积损失随STEAM序列中间间隔时间（TM）从13.7毫秒时的6 - 7%变化到TM = 100毫秒时的25 - 39%。对于TM = 100毫秒，与运动相关的相位离散导致的信号面积变化高达16%。信号相位作为心动周期中位置的函数被证明是可重复的。对于长TM，信号相位的最大差异超过180度。心电图门控显著减少了相位离散，但引入了重复时间可变的问题。如果为每次采集记录心动周期中的时间点，使用在水抑制关闭时记录的相位校准曲线，可以对随后水抑制激活的未触发采集进行回溯。信号强度增益在3%到21%之间。对于通过脑水进行的绝对定量，这种相位分析有一个重要结果，即参考扫描在叠加之前必须单独进行相位调整，否则代谢物浓度可能会被严重高估。
