Figure 1

Schematic of basic principles underlying DSI tractography. (A) Schematic of a voxel with 2 fiber populations. Water diffuses primarily parallel to the direction of fiber orientation (arrows). (B) Each point in q-space corresponds to the signal intensity in the voxel resulting from the application of that diffusion-encoding vector. Vector length and orientation (location from the origin in q-space) are determined by the diffusion field gradient strength (intensity-time product) and the gradient direction, respectively. Signal intensity is lowest when the diffusion gradient is strongest and aligned with the fiber orientation. (C) Fourier transformation of q-space produces a probability distribution function (PDF) in which the local maxima indicate the axes of fiber orientation in that voxel (blue and red lines). Radial integration reduces the PDF to an orientation density function (ODF), which still contains the directional information needed to produce the fiber tractograms. Connection of the local maxima in the ODF of each voxel by integration into multivoxel streamlines produces the 3D myofiber tractograms.