Technical note: Quantitative optimization of the FLAIR sequence in post mortem magnetic resonance imaging

The fluid attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) sequence aims at suppressing the signal of the cerebrospinal fluid (CSF) by acquiring images at the time point at which the longitudinal magnetization and therefore the signal of CSF is zero. This time point is also called the null point inversion time (TI_null). However, the FLAIR sequence is impaired by the temperature dependency of TI_null in post mortem MRI due to the lower body temperature of the deceased subject. Therefore, the temperature correction of TI_null is crucial for correctly suppressing the CSF signal in post mortem FLAIR imaging. Thus, the goal of this study was to determine the temperature effect on post mortem TI_null for achieving a robust suppression of the CSF signal in in situ post mortem MRI using the FLAIR sequence. For this purpose, nine deceased subjects underwent an in situ MRI brain examination on a 3 T MRI scanner. TI_null of CSF was determined quantitatively based on different FLAIR acquisitions using varying inversion times. The brain and rectal temperatures were determined prior to the MRI scan. A significant positive linear relation was found between TI_null of CSF and the brain temperature, as well as between TI_null of CSF and the rectal temperature. The found linear relations between TI_null and both brain and rectal temperatures allow correcting TI_null for varying temperatures of the deceased. This in turn enables an optimal suppression of the CSF signal in future post mortem FLAIR MRI acquisitions.