3.1. Metabolite Concentrations in Human Brain Tumors

Quantitation measurements of metabolite concentrations are becoming increasingly common in proton spectroscopy studies of human brain pathology (39,40). Presented here is one example of a pilot study of quantitative MRSI in patients with low- and highgrade, primary, untreated brain tumors.

All patients were studied at 1.5T using a multi-slice MRSI technique with TR/TE = 2300/280 msec and a nominal 0.8 cm3 voxel size. Metabolite concentrations were estimated using the phantom replacement technique as described previously (6). The patient population consisted of two cases of oligodendroglioma (grade II and grade III), one astrocytoma grade II, and four cases of glioblastoma multiforme (GBM). Metabolic images were reconstructed and abnormal spectra from the lesion voxels with the highest visible Cho signal were selected for analysis. A mirror-image region of interest in the contralateral hemisphere was also analyzed as an internal control. Two groups were defined, low-grade tumors (oligodendrogliomas and grade II astrocyotoma) and highgrade tumors (GBM). Examples of spectroscopic images and selected spectra are shown in Figures 3 and 4 for low- and high-grade tumors respectively. Figure 5 summarizes the results for Cho, Cr and NAA. It can be seen that NAA is lower in both high and low grade brain tumors compared to the contralateral hemisphere. However, the Cho metabolite is only significantly elevated for the high-grade tumors. No consistent changes were observed in the Cr resonance.

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