Diffusion-tensor imaging for glioma grading at 3-T magnetic resonance imaging: Analysis of fractional anisotropy and mean diffusivity

PURPOSE: To retrospectively determine whether fractional anisotropy (FA) or mean diffusivity (MD) value at 3-T diffusion-tensor imaging is different between low- and high-grade gliomas and may be useful for glioma grading. METHODS: Review board approval was obtained, and informed consent was waived. Diffusion-tensor imaging was performed in 27 patients with surgically proved gliomas (19 high-grade and 8 low-grade gliomas). Fractional anisotropy and MD values were measured in 3 regions; peritumoral edema, and enhancing and nonenhancing tumor regions. We compared mean FA and MD values of nonenhancing tumor regions between low- and high-grade gliomas and compared the FA and MD values among the 3 mentioned regions in high-grade gliomas. The relationship between FA and MD values of tumors was also investigated. Statistical analysis was performed using the Student t test and Pearson correlation coefficients. RESULTS: In the nonenhancing regions of tumors, FA ratios were not significantly different between low- and high-grade gliomas (0.472 and 0.701, P = 0.075), but MD ratios were significantly lower in high-grade gliomas (1.899 and 1.23, P < 0.001). In high-grade gliomas, enhancing tumors showed a tendency toward a lower FA ratio than nonenhancing tumors (P = 0.034), but FA values or ratios of peritumoral edema were not significantly different from those of enhancing or nonenhancing tumor. No strong relationship was found between FA and MD values. CONCLUSIONS: Fractional anisotropy values of low- and high-grade gliomas were not significantly different. However, MD values of nonenhancing low-grade gliomas were significantly higher than those of nonenhancing high-grade gliomas, which will be useful for the grading of nonenhancing infiltrative gliomas.