Use of a Non-Fixed Brain Tissue Sample to Examine the Effect of White Matter Orientation to the Magnetic Field on MRI Signals

Christopher John Wiggins¹, Denis Le Bihan¹

It has previously been shown in both human and monkey models that the gradient echo signal of white matter tracts are dependent on their orientation with respect to the applied magnetic field. While in-vivo, both the T2* value and the phase appear to vary with the orientation, ex-vivo studies appear to show only a phase variation. In order both to find a model that allows measurements at multiple orientations, as well as to examine whether the formalin fixation process affects these signals, a sample of non-fixed bovine brain tissue was examined. This showed both T2* and phase variation, similar to in-vivo examinations, indicating that it is the fixation process that alters the T2* behaviour. In addition, T2 (TSE) weighted imaging showed no significant variation with orientation, which thus eliminates a Magic Angle type behaviour.