Proton Magnetic Resonance Spectroscopy Of Normal Human Brain And Glioma: The In-vivo And In-vitro Quantitive Studies

ObjectiveIn vivo proton magnetic resonance spectroscopy (MRS) provides a nonin-vasive method of examining a wide variety of cerebral metabolites in both healthy subjects and patients with various brain diseases. It is expected to aid in diagnosis by characterizing gliomas and in evaluating the effects of antitumor therapy by measuring tumor - containing metabolites, but it has not been extensively used for differential diagnosis because of the low resolution of in vivo proton MR spectra and its difficulty to quantify absolute concentrations. In vitro study is advantageous , because the spectra that are obtained in vitro using a very high magnetic field have much better resolution than those obtained in vivo, and it makes feasible the identification of peaks and the measurement of the absolute concentration of each metabolite. The purpose of this study were to quantitatively analyze the metabolite concentrations in normal adult brains and gliomas by in vivo proton MRS using the fully relaxed water signal as an internal standard and the complex mixture of compounds in extracts of normal adult brains and gliomas by in vitro proton MRS and to provide a better interpretation of the spectra obtained by in vivo proton MRS.MethodsIn vivo quantitative study: Between January 2004 and December 2005, 28healthy volunteers and 66 patients with gliomas were examined by in vivo proton MRS. Single - voxel spectra were acquired using the point - resolved spectro-scopic pulse sequence with a 1. 5 T scanner ( TR/TE/Ave = 3000ms/30ms/ 64).In vitro quantitative study: Between January 2004 and December 2005, 5 normal adult brains and 39 gliomas were examined by in vitro proton MRS. All specimens were extracted with perchloric acid. The precipitated perchlorate salts were removed by centrifugation and the supernatants lyophilized. Proton MR spectra of extracts were obtained on a nuclear MR spectrometer of 300MHz.ResultsIn vivo quantitative study: The calculated concentrations of N - acetyl - as-paratate ( NAA) , creatine ( Cre ) , choline ( Cho ) , and water ( H2 0 ) in the normal hemispheric white matter were (23.59 ±2. 62)mmol/L, (13.06 ±1. 80)mmol/L, (4.28 ± 0. 80)mmol/L, and (47280. 96 ± 5414. 85)mmol/L, respectively. The metabolite concentrations were not necessarily uniform in different parts of the brain. The concentrations of NAA and Cre decreased in all gliomas (P <0.001). The ratios of NAA/Cho and NAA/H20 showed a significant difference between the normal brains and gliomas, and also between the high and low grades ( P < 0.001).In vitro quantitative study: The calculated concentrations of NAA, Cre and Cho in the normal hemispheric gray matter were (3026.6 ± 102.4) , (3049.2 ±168.3) and (1139. 8 ± 104. 9) jxmol/lOOg wet weight, respectively. The concentrations of NAA and Cre decreased in all gliomas ( P <0.001). The concentrations of NAA and Cre showed a significant difference between the low -grade and high - grade gliomas ( P < 0.001).ConclusionsQuantitative analysis of in vivo proton MR spectra using the fully relaxed water signal as an internal standard is useful. The concentrations of NAA andCre examined by in vivo and in vitro proton MRS conduce to discriminate between the normal brains and gliomas, and also between the low - grade and high - grade gliomas.