High-b-value diffusion-weighted MR imaging of adult brain: Image contrast and apparent diffusion coefficient map features

BACKGROUND AND PURPOSE: Recent improvements in MR gradient technology allow significant increases in diffusion weighting without prohibitive signal-to -noise degradation. The purpose of our investigation was to establish norma tive references for the signal intensity characteristics and apparent diffu sion coefficient values of the adult brain at high b values. METHODS: Fifty adults underwent diffusion-weighted single-shot spin-echo ec ho-planar MR imaging, Isotropic diffusion-weighted images were obtained wit h b values of 0, 1000, 2000, 2500, 3000, and 3500 s/mm(2). Qualitative asse ssments were made in multiple regions of interest in gray and white matter. Three apparent diffusion coefficient maps mere generated for each of six p atients with a 2-point technique at a b value of 0 and at b values of 1000, 2000, and 3000 s/mm(2). RESULTS: Increasing b values result in a progressive decrease in the gray t o white matter signal intensity ratio. Isointensity between gray and white matter results at b values between 1000 and 2000 s/mm(2). At b values great er than 2000, the gray-white pattern reverses relative to the usual b value of 1000. Apparent diffusion coefficient values were shown to decrease with increasing b values. CONCLUSION: Attention to the reversal of gray-white contrast and the depend ence of apparent diffusion coefficient on the b value are important in avoi ding erroneous assignment of pathologic abnormalities to normal regions. Th is study provides the normative data for future diffusion investigations pe rformed at high b values.