gms | German Medical Science

In this study we investigated the potential use of 1H-MRSI to correlate absolute metabolite concentrations with histopathologic findings to establish a presurgical non-invasive grading for brain tumors.

20 patients with gliomas (WHO Grade II-III) were examined in a 1.5 MR Tesla scanner with a standard head coil using a standard CSI sequence with PRESS volume preselection and CHESS water suppression. Absolute metabolite concentrations for Cho, tCr and tNAA were calculated using LCModel and corrected for relaxation time effects. The 1H-MRSI data were verified by stereotactic biopsies with co-registered metabolic maps.

In all spectra, we obtained SNR> 3 and FWHM < ppm for 0.25 cm³ voxels. Metabolite ratios with standard deviations SD>20%, as given by the LCModel, were excluded from the statistical analysis. Tumor spectra showed significantly higher absolute concentrations of Cho and lower concentrations for tCr and tNAA (t-test for paired samples), respectively. Most important we found a marked difference for the Cho/tNAA value averaged over the tumor center voxels which were less than 0.8 for all patients with a WHO Grade II tumor, whereas for all patients with a WHO Grade III tumor, this value was greater than 0.8.

Absolute quantification of 1H MRSI data helps to evaluate and compare the metabolic changes and the tumor infiltration across different patients. By ratio forming of Cho over tNAA averaged over the voxels in the tumor center, a non-invasive grading between WHO Grade II and Grade III seems to be feasible, which can be essential for therapeutic planning.