Purpose: Signal intensity (SI) and image contrast on postmortem magnetic resonance (MR) imaging are different from those of imaging of living bodies. We sought to suppress the SI of cerebrospinal fluid (CSF) sufficiently for fluid-attenuated inversion recovery (FLAIR) sequence in postmortem MR (PMMR) imaging by optimizing inversion time (TI).
Materials and Methods: We subject 28 deceased patients to PMMR imaging 3 to 113 hours after confirmation of death (mean, 27.4 hrs.). PMMR imaging was performed at 1.5 tesla, and T₁ values of CSF were measured with maps of relaxation time. Rectal temperatures (RT) measured immediately after PMMR imaging ranged from 6 to 32°C (mean, 15.4°C). We analyzed the relationship between T₁ and RT statistically using Pearson’s correlation coefficient. We obtained FLAIR images from one cadaver using both a TI routinely used for living bodies and an optimized TI calculated from the RT.
Results: T₁ values of CSF ranged from 2159 to 4063 ms (mean 2962.4), and there was a significantly positive correlation between T₁ and RT (r = 0.96, P < 0.0001). The regression expression for the relationship was T₁ = 74.4 * RT + 1813 for a magnetic field strength of 1.5T. The SI of CSF was effectively suppressed with the optimized TI (0.693 * T₁), namely, TI = 0.693 * (77.4 * RT + 1813).
Conclusion: Use of the TI calculated from the linear regression of the T₁ and RT optimizes the FLAIR sequence of PMMR imaging.