Gruetter R, Weisdorf S A, Rajanayagan V, Terpstra M, Merkle H, Truwit C L, Garwood M, Nyberg S L, Uğurbil K
Department of Radiology, University of Minnesota, Minneapolis, Minnesota, 55112, USA.
J Magn Reson. 1998 Nov;135(1):260-4. doi: 10.1006/jmre.1998.1542.
The measurement of cerebral metabolites using highly homologous localization techniques and similar shimming methods was performed in the human brain at 1.5 and 4 T as well as in the dog and rat brain at 9.4 T. In rat brain, improved resolution was achieved by shimming all first- and second-order shim coils using a fully adiabatic FASTMAP sequence. The spectra showed a clear improvement in spectral resolution for all metabolite resonances with increased field strength. Changes in cerebral glutamine content were clearly observed at 4 T compared to 1.5 T in patients with hepatic encephalopathy. At 9.4 T, glutamine H4 at 2.46 ppm was fully resolved from glutamate H4 at 2.37 ppm, as was the potential resonance from gamma-amino-butyric acid at 2.30 ppm and N-acetyl-aspartyl-glutamate at 2.05 ppm. Singlet linewidths were found to be as low as 6 Hz (0.015 ppm) at 9.4 T, indicating a substantial decrease in ppm linewidth with field strength. Furthermore, the methylene peak of creatine was partially resolved from phosphocreatine, indicating a close to 1:1 relationship in gray matter. We conclude that increasing the magnetic field strength increases spectral resolution also for 1H NMR, which can lead to more than linear sensitivity gains.
使用高度同源定位技术和类似的匀场方法，在1.5T和4T的人脑以及9.4T的犬脑和大鼠脑中进行了脑代谢物的测量。在大鼠脑中，通过使用完全绝热的FASTMAP序列对所有一阶和二阶匀场线圈进行匀场，实现了分辨率的提高。随着场强增加，所有代谢物共振的光谱分辨率都有明显提高。在肝性脑病患者中，与1.5T相比，在4T时清楚地观察到脑谷氨酰胺含量的变化。在9.4T时，2.46ppm处的谷氨酰胺H4与2.37ppm处的谷氨酸H4完全分辨开，2.30ppm处的γ-氨基丁酸和2.05ppm处的N-乙酰天冬氨酰谷氨酸的潜在共振也被分辨开。在9.4T时发现单线宽低至6Hz（0.015ppm），表明ppm线宽随场强大幅降低。此外，肌酸的亚甲基峰与磷酸肌酸部分分辨开，表明在灰质中二者比例接近1:1。我们得出结论，增加磁场强度也会提高1H NMR的光谱分辨率，这可能导致灵敏度增益超过线性增长。
