Comparison of diffusion tensor imaging measurements at 3.0 T versus 1.5 T with and without parallel imaging.

The diffusion properties of biological tissues are independent of magnetic field strength. Field strength, however, does affect the signal-to-noise ratio (SNR) and artifacts of diffusion-weighted (DW) images, which ultimately will influence the quantitative and spatial accuracy of diffusion tensor imaging (DTI). In this article, the effects of field strength on DTI are reviewed. The effects of parallel imaging also are discussed. A small study comparing DTI measurements both as a function of field strength (1.5 T and 3.0 T) and parallel imaging was performed. Overall, the SNR of the DW images roughly doubled going from 1.5 T to 3.0 T, and there was a relatively small decrease in SNR (15% to 30%) when parallel imaging was used. The increased SNR at 3.0 T resulted in smaller variances in the estimated mean diffusivities and fractional anisotropies. As expected, the amount of echo-planar image distortion roughly doubled going from 1.5 T to 3.0 T, but was reduced by 50% when using parallel imaging. In summary, DTI studies at 3.0 T using parallel imaging will provide significantly improved DTI measurements relative to studies at 1.5 T.