Kim Hyeonjin, Thompson Richard B, Hanstock Christopher C, Allen Peter S
Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta T6G 2G3, Canada.
Magn Reson Med. 2005 Apr;53(4):760-9. doi: 10.1002/mrm.20434.
Using as an example the myo-inositol (mI) band at approximately 3.6 ppm in the proton spectrum from brain, an evaluation is presented that highlights the difficulties of quantifying metabolites with strongly coupled spins with either STEAM or PRESS and demonstrates some advantages of prospective sequence analysis when measuring their concentrations. The analysis emphasizes the variation in coupled-spin signal yield and lineshape, compared with that of uncoupled singlets such as N-acetylaspartate, a variation that differs from one metabolite spin system to another. This difference in variation between a target metabolite (e.g., mI) and its contaminating background metabolites (e.g., glutamate and taurine, etc.) is shown to provide in certain circumstances a substantial reduction in background contamination (both metabolite and macromolecule) while maintaining sufficient signal-to-noise ratio for precise quantification. For example, sequence times are demonstrated, both for STEAM and for PRESS, that, relative to the short echo-time sequences typical in the literature, enhance the signal to metabolite background of the 3.6-ppm band of mI by factors of 1.7 and 1.3, respectively, essentially eliminate the macromolecular baseline, and yet in vivo retain an S/N approximately 10 in both cases.
以脑质子谱中约3.6 ppm处的肌醇（mI）峰为例，本文进行了一项评估，该评估突出了使用STEAM或PRESS对具有强耦合自旋的代谢物进行定量分析的困难，并展示了在测量其浓度时进行前瞻性序列分析的一些优势。该分析强调了与未耦合单峰（如N - 乙酰天门冬氨酸）相比，耦合自旋信号产率和线形的变化，这种变化在不同的代谢物自旋系统之间有所不同。结果表明，目标代谢物（如mI）与其污染背景代谢物（如谷氨酸和牛磺酸等）之间这种变化的差异，在某些情况下可大幅减少背景污染（包括代谢物和大分子），同时保持足够的信噪比以进行精确量化。例如，对于STEAM和PRESS，都展示了相对于文献中典型的短回波时间序列的序列时间，它们分别将mI的3.6 ppm峰的信号与代谢物背景的比值提高了1.7倍和1.3倍，基本消除了大分子基线，并且在两种情况下体内信噪比均保持在约10。
