In vivo characterization of downfield peaks at 9.4 T: T2relaxation times, quantification, pH estimation, and assignments
In vivo characterization of downfield peaks at 9.4 T: T2relaxation times, quantification, pH estimation, and assignments
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DOI：
10.1002/mrm.28442
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发表时间：
2020-08-11
影响因子：
3.3
通讯作者：
Henning, Anke
中科院分区：
文献类型：
--
作者：
Borbath, Tamas;Murali-Manohar, Saipavitra;Henning, Anke
目的在确定光谱分配时，弛豫时间是一项宝贵的资产。在这项研究中，在9.4T时，人脑中场下峰的表观T(2)弛豫时间(T2app)被报道，并被用来指导一些场下代谢物峰的光谱指认。方法采用代谢物循环半激光序列，在9.4T采集下场代谢物频谱回声时间序列。使用LC Model V6.3-1L进行代谢物光谱拟合，同时拟合pH扫描以估计高肌苷(HCS)咪唑环的pH。通过将得到的峰的相对幅度拟合为TE序列中的单指数衰减来计算T2 app.此外，使用松弛时间和内部水作为参考来计算估计的组织分子浓度。结果下场代谢产物的T2app值为16~32ms，高肌苷的T2app值为50ms。对汇率(T2 Corr)进行T2校正后，松弛时间在20到33毫秒之间。受试者之间基于HCS咪唑的估计PH值范围为7.07至7.12。此外，分析下场峰的线宽和它们的T2峰贡献导致了可能的峰分配。结论指定的代谢物峰比未指定的代谢物峰的T2吸附时间更长。用质子磁共振波谱和8.30+/-0.15ppm的同时定量的酰胺质子在体内估计组织的pH是可能的。基于浓度、线宽和交换率的测量，讨论了三磷酸腺苷(ATP)、N-乙酰天冬氨酸谷氨酸(NAAG)和尿素的暂定峰归属。
Purpose Relaxation times are a valuable asset when determining spectral assignments. In this study, apparent T(2)relaxation times (T2app) of downfield peaks are reported in the human brain at 9.4 T and are used to guide spectral assignments of some downfield metabolite peaks. Methods Echo time series of downfield metabolite spectra were acquired at 9.4 T using a metabolite-cycled semi-LASER sequence. Metabolite spectral fitting was performed using LCModel V6.3-1L while fitting a pH sweep to estimate the pH of the homocarnosine (hCs) imidazole ring.T2appwere calculated by fitting the resulting relative amplitudes of the peaks to a mono-exponential decay across the TE series. Furthermore, estimated tissue concentrations of molecules were calculated using the relaxation times and internal water as a reference. Results T2appof downfield metabolites are reported within a range from 16 to 32 ms except for homocarnosine withT2appof 50 ms. CorrectingT2appfor exchange rates (T2corr) resulted in relaxation times between 20 and 33 ms. The estimated pH values based on hCs imidazole range from 7.07 to 7.12 between subjects. Furthermore, analyzing the linewidths of the downfield peaks and theirT2appcontribution led to possible peak assignments. Conclusion T2apprelaxation times were longer for the assigned metabolite peaks compared to the unassigned peaks. Tissue pH estimation in vivo with proton MRS and simultaneous quantification of amide protons at 8.30 +/- 0.15 ppm is likely possible. Based on concentration, linewidth, and exchange rates measurements, tentative peak assignments are discussed for adenosine triphosphate (ATP), N-acetylaspartylglutamate (NAAG), and urea.