Track density imaging (TDI) is a technique in diffusion tractography used to create super-resolved maps of white matter in the brain. The trick in TDI is not to image the white matter directly, but rather to reconstruct the likely paths of white matter fibres from diffusion MRI data, and calculate the relative likelihood of white matter at each super-resolved voxel. I personally like how it makes the brain look like a tangled mess of electrical cabling.
Reconstruction and visualisation made with MRtrix3.