Single-voxel proton brain spectroscopy exam (PROBE/SV) in patients with primary brain tumors

The Single-Voxel Proton Brain Exam (PROBE/SV) is an automated MR spectroscopic technique. The purpose of this study was to investigate the use of PROBE/SV as a diagnostic tool in patients with primary brain tumors and to compare our findings with the known information obtained from conventional nonautomated MR spectroscopic techniques.

We used PROBE/SV to image 10 normal adults and 46 patients with primary brain tumors: 29 glioblastoma multiformes (GBMs), five anaplastic astrocytomas, and 12 low-grade astrocytomas. All studied were performed on a 1.5-T Signa unit. Average voxel sizes were 6-8 cm3. A corresponding point-resolved spectroscopy spectrum was obtained from normal-appearing brain parenchyma in each patient for comparison with the spectra from known areas of pathology.

In patients with low-grade gliomas (grades 1 and 2), we observed decreased N-acetylaspartate (12 of 12) and slightly increased choline (11 of 12) when we compared these metabolites with those in the spectra of patients' normal brains. This comparison in patients with GBM yielded markedly decreased N-acetylaspartate (29 of 29) and prominently increased choline (27 of 29). In the short TE spectra, we frequently saw lipid signal in high-grade tumors, especially in GBMs (12 of 20). We identified lactate peaks in high-grade tumors (anaplastic astrocytoma and GBM, 29 of 34) and also in low-grade tumors (four of 12). The creatine signal in all gliomas was slightly less than that of healthy brain tissue. The lowest N-acetylaspartate, choline, and creatinine levels in conjunction with the highest lactate levels were usually found in necrotic portions of high-grade tumors.

PROBE/SV is a simplified MR spectroscopy technique that reduces setup time and provides automatic on-line data processing and display. The voxel location can be selected to focus on the area of interest and to minimize voxel contamination from unwanted tissue. The results from our experimentation with PROBE/SV in patients with brain tumors generally concur with published reports of tumor spectra obtained by conventional MR spectroscopic techniques. The ease and accuracy of this new technique make it a useful clinical tool in differentiating human brain tumor grades.