Preoperative grading of gliomas by using metabolite quantification with high-spatial-resolution proton MR spectroscopic imaging

Purpose: To evaluate proton magnetic resonance (MR) spectro scopic imaging with high spatial resolution for preoperative grading of suspected World Health Organization grades II and III gliomas. Materials and Methods: Institutional ethics committee approval and informed con: sent were obtained for control subjects but were not required for the retrospective component involving patients. Twenty-six patients (10 women, 16 men; mean age, 37.5 years) suspected of having gliomas and 26 age- and sex-matched control subjects underwent proton MR spectroscopy. Absolute metabolite concentrations for choline-containing compounds (Cho), creatine (Cr), and N-acetylaspartate (NAA)-N-acetylaspartylglutamate (total NAA [tNAA]) were calculated by using a user-independent spectral fit program. Metabolic maps of Cho/tNAA ratios were calculated, segmented, and used for MR spectroszpcopy- guided stereotactic brain biopsy. Two-sided paired Student t tests were used to test for statistical significance. Results: Significantly lower Cho levels (P = .002) and higher tNAA levels (P = .010) were found in grade H tumors (n = 9) compared with grade III tumors (n = 17). The average Cho/tNAA ratio over the voxels in the tumor center showed a distinct difference (P < .001) between grade 11 and III gliomas at a threshold of 0.8 (with ratios < 0.8 for grade 11). The maximum Cr concentration in the tumor showed a clear-cut threshold between grade III oligodendrogliomas and oligoastrocytomas (Cr level, < 7 mol/L) and grade III astrocytomas (Cr level, > 7 mmol/L; P = .020). Comparison between the histopathologic findings from the MR spectroscopy-guided biopsy samples (76 biopsies from 26 patients) and molar metabolite values in corresponding voxels located at the biopsy sampling points showed a negative linear correlation for tNAA (r -0.905) and a positive exponential correlation for Cho (r = 0.769) and Cho/tNAA (r = 0.885). Conclusion: Proton MR spectroscopic imaging with high spatial resolution allows preoperative grading of gliomas. (c) RSNA 2006.