Mapping fluid-suppressed diffusivity in brain tumors

BACKGROUND AND PURPOSE: The apparent diffusion coefficient (ADC) provides valuable information about tumor microstructure. However, partial volume effects with free water, from cerebrospinal fluid or edema, may bias the ADC and obscure areas of reduced diffusion. This work evaluated a new method for mapping diffusivity in tissue without free water contamination in brain tumors. MATERIALS AND METHODS: We used high b-value spherical b-tensor encoding to map fluid suppressed mean diffusivity in tissue. The method was evaluated using simulations and analysis of 3 T MRI data in 60 patients: 55 adult-type diffuse gliomas and 5 brain metastases. RESULTS: Mapping the mean diffusivity in tissue visualized areas with reduced diffusivity better than the ADC, both in simulations designed to illustrate the mechanism and in the brain tumor patients. Regions with a mean diffusivity in tissue substantially lower than the ADC were more frequently observed in isocitrate dehydrogenase wildtype tumors, i.e. glioblastomas, than in isocitrate dehydrogenase mutant tumors. The mean diffusivity in tissue was significantly associated with isocitrate dehydrogenase status. CONCLUSIONS: Mapping the mean diffusivity in tissue helps reveal areas with low diffusivity in diffuse gliomas, which may be obscured by free water on conventional ADC maps.