Post Mortem Temperature and its Effect on Quantitative Magnetic Resonance Imaging

The purpose of this study was to determine the post mortem temperature effect on the magnetic resonance (MR) parameters T1, T2, T2*, MD, and FA. The relations between the temperature and the magnetic resonance parameters allow the correction for the temperature in post mortem magnetic resonance imaging (PMMR), thus, a tissue contrast loss due to post mortem temperature changes can be avoided. Further, the profiles of the forehead, brain, and rectal temperature were recorded in order to find a correlation that would allow a non-invasive determination of the brain temperature. The temperature effect was computed by fitting the post mortem MRI parameters in situ of eight different regions of interest in the brains of nine deceased and the corresponding brain temperatures. The temperature profiles were recorded in situ with temperature probes placed on the forehead, in the rectum, and in the brain (via the os ethmoidale), while the corpses were stored in the cooling chamber. In this thesis, a significant linear correlation was observed between the brain and the forehead temperature, while the brain and the core temperature revealed no linear correlation. Further, a significant linear relation between the brain temperature and the relaxation parameter T1 of the gray matter was observed, while T2 did not correlate with temperature. T2*, on the other hand, could be shown to depend on the brain temperature in deep gray matter and occipital white matter. Additionally, a temperature effect on the mean diffusivity was observed, while the fractional anisotropy showed no direct temperature dependence.
As a conclusion, the measured temperatures propose that the brain’s tissue magnetic resonance imaging parameters correlate with the brain temperature, more precisely in a linear relation. Furthermore, the observed results suggest the need for correction regarding different brain temperatures, particularly that of T1 in order to avoid brain tissue contrast loss caused by post mortem temperature decreases.