Multisection 1H magnetic resonance spectroscopic imaging assessment of glioma response to chemotherapy
This study evaluated the role of proton magnetic resonance spectroscopic imaging (1H MRSI) in assessing the response of low-grade brain tumors to a chemotherapy-only treatment regimen. Specifically, it was of interest to assess if 1H MRSI could detect early tumor response to therapy prior to magnetic resonance imaging (MRI) changes, and to establish which spectral markers were sensitive to regional changes within and around a heterogeneous tumor mass. A total of 14 patients with lower-grade gliomas were evaluated by multislice 1H MRSI, MRI and clinical examination. Changes associated with chemotherapy were assessed by longitudinal comparisons of regional levels of choline (Cho), N-acetyl-L-aspartate (NAA), and lactate (Lac) relative to total creatine. These changes were, in turn, compared to changes on pre- and post-contrast MR images and to each patient's clinical status. In enhancing tumor regions, there was a significant association between an increase in Lac/Cr during treatment and decreased progression-free survival time. At baseline, a low NAA/Cr in normal-appearing brain tissue adjacent to non-enhancing tumor was associated with decreased progression-free survival time, as was an increase in Cho/Cr during chemotherapy. An increase in Cho/Cr and Lac/Cr in normal-appearing brain regions next to non-enhancing tumor in one patient was noted 2 months before MRI showed progressive disease. These results suggest that 1H MRSI can be a powerful adjunct to MRI in the assessment of tumor response to chemotherapy, and that Cho/Cr and Lac/Cr appear to be the most reliable markers of tumor progression and may predict response prior to MRI changes.