The influence of white matter fibre orientation on MR signal phase and decay.

MRI phase images of the brain exhibit excellent contrast and high signal-to-noise ratio. It has been shown recently that the phase contrast not only depends on a tissue's magnetic susceptibility but also on its architecture, which offers new ways of studying biological tissues in vivo. We combined diffusion tensor imaging and multi-echo susceptibility-weighted imaging to investigate the relationship between white matter fibre orientation and gradient-echo phase and magnitude. The local angle between white matter fibres and the main magnetic field was computed from the principal diffusion direction. The phase and signal decay of the gradient-echo images revealed a characteristic relationship with fibre orientation. The phase is in agreement with a recently reported model of cerebral white matter phase contrast in MRI.