Figure 6.

Comparison of DTI parametric maps with different b-value, number of b-values (N_b) and number of b₀ scans (N_b0). MRI measurements were performed on a Siemens Verio 3T system (Siemens Medical Systems, Erlangen, Germany)—gradient coils capable of 45 mT/m and 200 T/m/s slew rate—with a 32-channel phased-array head-coil. Diffusion volumes were acquired using a standard twice-refocused, single-shot EPI pulse sequence: repetition/echo time = 9000/94 ms; matrix, 120 × 120; 63 contiguous slices aligned parallel to the anterior commissure/posterior commissure line; voxel size: 2 × 2 × 2 mm³; 7/8-phase partial Fourier; bandwidth of 1667 Hz/pixel and echo spacing of 0.68 ms. Diffusion gradients were applied along N_d = 30 non-collinear directions (Siemens default vectors) with N_b = 2 non-zero b-values (b = 700 and 1000 s/mm²), and N_b0 = 12 reference scans. Parallel imaging was enabled (GRAPPA, acceleration factor = 2 and 38 reference lines), leading to a total scan time of 11 min and 15 s. DTI maps were computed with standard tools from FSL's diffusion toolbox. (Left to right columns): (i) N_b = 1 (b = 700 s/mm²), N_b0 = 1 (5:06); (ii) N_b = 1 (b = 1000 s/mm²), N_b0 = 1 (5:06); (iii) N_b = 2 (b = 700 and 1000 s/mm²), N_b0 = 1 (9:36); (iv) N_b = 2 (b = 700 and 1000 s/mm²), N_b0 = 12 (11:15).