Example: Reusable DTI-Volume Tracking

This example exercises the complete reusable DTI tractography boundary. It fits a known prolate tensor for eight image-axis voxels and a low-anisotropy tensor for four voxels, places those maps in a DtiVolume, selects seeds by an inclusive FA threshold, and tracks through the validated volume.

The first panel plots the fitted FA for every voxel. Blue bars are the values returned by DiffusionMaps::fractional_anisotropy; the red line is the seed threshold. The orange points are the seeds returned by dti_volume_seed_points, not hand-selected coordinates. The second panel plots the streamlines returned by dti_volume_tractography; its boundary marks the first low-anisotropy voxel where DtiVolume stops the field.

The example asserts before writing the SVG that:

• the fitted high- and low-anisotropy regimes lie on the expected sides of the seed and tracking thresholds;
• the tracking result attempted and generated exactly the computed seed count;
• every generated line terminates at a field boundary or the configured step limit; and
• the SVG contains exactly one bar, seed marker, and streamline primitive for each corresponding computed value.

Source and command

Source: crates/ritk-tractography/examples/book_dti_volume_tractography.rs

cargo run --locked -p ritk-tractography --example book_dti_volume_tractography -- \
  docs/book/figures/dti_volume_tractography.svg

The output is deterministic because the gradient scheme, tensor values, and rendering coordinates are fixed. This is a code and numerical-contract verification example. It is not anatomical or clinical validation.