Figure 8. Comparison of single-core CPU and GPU execution times (in log scale) running the Levenberg-Marquardt algorithm with speed gains over two orders of magnitude: (a) As the number of Levenberg-Marquardt iterations are increased, and (b) as the number of voxels per slice are increased.

The execution times for (a) are for a slice of 4804 voxels, with the convergence criterion of the algorithm decreased to allow more iterations. For each case, results are shown for different number K of gradient directions (64, 128 and 256) and for estimating fibres.