Malignancy of brain tumors evaluated by proton magnetic resonance spectroscopy (1H-MRS) in vitro

Biopsies of 6 malignant gliomas (grade 3 or 4) and 11 low-grade meningiomas were extracted with perchloric acid or methanol/water, and the fully-relaxed 1H-MRS spectra of the extracts containing water-soluble metabolites and a concentration and chemical shift standard were recorded at 11.4 T. The resonance signals assigned to inositol (Ino), glycerophospho- and phosphocholine (GPC + PC), choline (Cho), creatine and phosphocreatine (Cr + PCr), glutamate (Glu), acetate (Ac), alanine (Ala) and lactate (Lac) were integrated, and analyzed by two methods. First, the concentrations of the aforementioned substances in the bioptates were estimated from their resonance signals in the extracts. Second, these signals were normalized to the Cr + PCr resonance signal. The Mann-Whitney U-test was used to verify statistical significance between the data sets obtained for gliomas and meningiomas. When the first method of analysis was used, the only difference was in the Ala concentration, which in meningiomas was on average 4 times higher than in gliomas (P < 0.01). However, when the second method of analysis was applied, gliomas expressed lower normalized resonance signals of Ala and Glu (P < 0.001, ranges not overlapping), Lac (P < 0.005), as well as Ino and GPC + PC (P < 0.05). In proton MR spectra of brain tumor tissue extracts containing water soluble metabolites, the resonance signals normalized to that of total creatine may provide a very good discrimination between malignant gliomas and low-grade meningiomas.