重复时间对MR氢质子波谱定量脑组织代谢物浓度的影响

目的 探讨在体单体素氢质子MR波谱(1H-MRS)重复时间(TR)对定位测量脑组织代谢物绝对和相对浓度的影响.方法 正常志愿者30名采用1.5 T超导型MR成像系统行点分辨自旋回波(PRESS)序列单体素1H-MRS扫描,取左侧大脑半球顶枕部白质,体素8 cm3,TR分别为1500和5000 ms.采用线性拟合模型(LCModel)处理原始数据,测量肌酸和磷酸肌酸(tCr)、谷氨酸(Glu)、肌醇(mI)、N-乙酰天冬氨酸(NAA)、甘油磷酸胆碱(GPC)和谷氨酸和谷氨酰胺(Glx)等的绝对浓度和相对浓度,并采用配对t检验对不同TR下各代谢物的浓度进行比较.结果 大脑左顶枕部白质代谢物tCr、Clu、mI、NAA、GPC和Glx在TR为1500 ms时绝对浓度分别为(3.0±0.2)、(4.4±0.7)、(3.0±0.3)、(5.0±0.4)、(1.1±0.1)和(5.9±0.6)mmol/L;TR为5000 ms时分别为(4.2±0.4)、(5.3±0.5)、(3.7±0.5)、(6.7±0.7)、(1.4±0.1)和(6.6±0.6)mmol/L.TR为1500 ms时,Gh、mI、NAA、GPC和Glx的相对浓度分别为1.47±0.27、1.00±0.11、1.69±0.17、0.36±0.05和1.95±0.22;TR为5000 ms时分别为1.25±0.12、0.89±0.09、1.60±0.16、0.33±0.04和1.58±0.17.不同TR时,各代谢物绝对浓度和相对浓度差异均有统计学意义(P值均＜0.05).结论1H-MRS可有效地进行脐组织代谢物绝对浓度和相对浓度的测量,PRESS序列中不同的TR所获得的代谢物绝对和相对浓度均有较大差异,较短的TR可低估代谢物的绝对浓度.

The impact of different repetition time in quantifying normal brain metabolites concentrations by proton MR spectroscopy

Objective To investigate the variabihty of absolute and relative biochemical concenstrations at different repetition time(TR) in quantifying normal brain by single voxel proton MR spectroscopy.Methods Thirty normal volunteers signed informed consent were recruited for the study.Short echo time(TE=35 ms)single voxel spectroscopy of the left parieto-occipital white matter were performed on a 1.5 T MR scanner by using point-resolved selective spectroscopy(PRESS)sequence.Two spectra were obtained using the same voxel placement and acquisition parameters but at different TRs:first at TR=1500 ms then at TR=5000 ms.Raw data of spectra were processed on a commercial software Liinear combination model(LCModel)normalized to spectral date obtained from a reference phantom of known metabolite quantities.Measured metabohtes included total creatine(tCr,creatine and phosphocreatine),glutamate(Glu),myo-inositol(mI),N-acytalaspartate(NAA),glycerophosphorylcholine(GPC),glutamate and glutamine(Glx).The t test was performed by using SPSS 11.5 for windows.Results Both the absolute and relative concentrations of normal white matter were significanth different between spectra obtafined at TR=1500 ms and that at TR=5000 ms(P＜0.05).The absolute concentrations(mmol/L)at TR=1500 ms were tCr,3.0±0.2;Glu,4.4±0.7;ml,3.0±0.3;NAA,5.0±0.4;GPC,1.1±0.1:Glx,5.9±0.6;compared to concentration at TR=5000 ms,tCr,4.2±0.4;Gitu,5.3±0.5;mI.3.7±0.5;NAA,6.7±0.7;GPC,1.4±0.1;Glx,6.6±0.6;respectively.The concentrations relatively to tCr at TR=1500 ms,were Glu,1.47±0.27;mI,1.00±0.11;NAA,1.69±0.17;GPC,0.36±0.05;Glx,1.95±0.22;and relative concentrations at TR=5000 ms were Glu,1.25±0.12;mI,0.89±0.09;NAA,1.60±0.16;GPC,0.33±0.04;Glx,1.58±0.17;respectively.Conclusion Proton MR spectroscopy can accurately quantify absolute and relative concentrations of brain metabolites.Metabolites concentrations may be significant underestimated when using shorter repetition time in short TE spectroscopic study.