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9 times the SNR at 3?T, which is largely in agreement with the ~?4.1 factor gain observed. In addition to SNR, the SNR efficiency was calculated for 3?T and 7?T over a range of gradient strengths. SNR efficiency was computed as the product of the field strength dependent SNR optimized DW-SSFP signal (using aforementioned field dependent T1, T2, and ADC) and the square root of the fraction of the TR period dedicated to signal acquisition. The model assumes that the 3?T and 7?T systems are identical except for field strength. Fig.?2 demonstrates that the effect of increased polarization due to higher field strength outweighs the field strength dependent changes in T1 and T2, indicating that the 7?T system should out-perform a similar 3?T system. Because diffusion contrast is direction LMTK2 Metabolism inhibitor dependent, it is not trivial to compute the CNR from diffusion data. We instead use the computed angular uncertainty of the primary and secondary fiber estimates (from the aforementioned modified version of BEDPOST) as a proxy for CNR, where high CNR would in general result in low uncertainty. Normalized histograms were generated of the voxel-wise angular uncertainty in pooled 3?T and 7?T data acquired with the same beff value. These provide a method of direct comparison of diffusion contrast between results at 3?T and 7?T. These estimates are shown in Figs.?3a,b and d,e for primary and secondary fibers, respectively. All primary fiber distributions were found to be statistically significantly different from one another by a non-parametric, two-sample Kolmogorov�CSmirnov (K�CS) test (p?Selleck Romidepsin accurate estimates of both primary and secondary fiber diffusion directions, and that the range of estimates is smaller (i.e. more precise) at 7?T than at 3?T, given the same diffusion weighting. Additionally, we see a hump in the secondary fiber histogram at 3?T at very high angular uncertainty (~?0.4) that is not present at 7?T, indicating a large proportion of voxels with very high angular uncertainty. These results suggest that the diffusion CNR at 7?T is higher than that at 3?T. Our 7?T scanner has a higher achievable maximum gradient strength than our 3?T system (70 and 38?mT/m, respectively), making it useful to determine potential gains of larger beff. Figs.?3b,c and e,f demonstrate an analogous comparison of histograms as those described above (Inter-field strength comparison (3?T vs. 7?T, beff?��?5150?s/mm??2)), but for intra-field strength variations in beff..