Origin of Phase Contrast

Measurement of the NMR frequency of water protons is one of the most sensitive ways to quantify magnetic fields. Small susceptibility differences within tissue placed in a strong magnetic field give rise to effects which are measurable by NMR and visualised in MR phase images.The information contained in the phase contrast between different tissue types is being increasingly used, for example to enhance visualisation of the vasculature in magnitude images [Haacke 2004], or to visualise subcortical structures with higher CNR than in magnitude images [Duyn 2007]. However, the microscopic origin of the susceptibility contrast between tissue types is not entirely understood yet Work is in progress [Oros 2009] on the investigation of the origin of phase contrast in fixed and fresh tissue, starting with the rat brain. To this aim, complementary MRI parameters as proton density, T2* and field maps are compared and their correlation with histology and chemical composition of the tissue is investigated.