Postmortem MRI of the brain in all cases showed characteristic common SI changes. Global cerebral ischemia without following reperfusion and low body temperature explain these changes.

In Japan, the medical examiner system is not widespread, the rate of autopsy is low, and many medical institutions therefore perform postmortem imaging using clinical equipment. Postmortem imaging is performed to clarify cause of death, select candidates for autopsy, make a guide map for autopsy, or provide additional information for autopsy. Findings are classiˆed into 3 categories: cause of death and associated changes, changes induced by cardiopulmonary resuscitation, and postmortem changes. Postmortem magnetic resonance imaging shows characteristic changes in signal intensity related to low body temperature after death; they are low temperature images.

Purpose: We measured T 1 and T 2 values of cerebral postmortem magnetic resonance (PMMR) imaging and compared the data of cadavers with that of living human subjects.Materials and Methods: We performed PMMR imaging of the brains of 30 adults (22 men, 8 women; mean age, 58.2 years) whose deaths were for reasons other than brain injury or disease at a mean of 29.4 hours after death. Before imaging, the bodies were kept in cold storage at 4°C (mean rectal temperature, 15.6°C). We measured T 1 and T 2 values in the brain bilaterally at 5 sites (bilateral caudate nucleus, putamen, thalamus and gray matter and white matter of the frontal lobe) and compared the data of PMMR imaging with that from MR imaging of the corresponding sites in 24 healthy volunteers (9 men, 15 women; mean age, 51.8 years). We also investigated the influence of body temperature on T 1 and T 2 values.Results: Compared with MR imaging findings in the living subjects, PMMR imaging showed significantly shorter T 1 values in the caudate nucleus, putamen, thalamus and gray matter and white matter of the frontal lobe and significantly longer T 2 values in the gray matter and white matter of the frontal lobe; T 2 values in the caudate nucleus, putamen, and thalamus showed no such differences. T 1 values correlated significantly with body temperature in all 5 brain sites measured, but T 2 values did not.Conclusion: Compared with findings of cerebral MR imaging in living adult subjects, those of PMMR imaging tended to demonstrate shorter T 1 values and longer T 2 values. We attribute this to increased water content of tissue, reduced pH, and reduced body temperature after death.

Purpose: Signal intensity and image contrast differ between postmortem magnetic resonance (PMMR) images and images acquired from the living body. We sought to achieve sufficient fat suppression with short-tau inversion recovery (STIR) PMMR imaging by optimizing inversion time (TI).Material and Methods: We subjected 37 deceased adult patients to PMMR imaging at 1.5 tesla 8 to 60 hours after confirmation of death and measured T 1 values of areas of subcutaneous fat with relaxation time maps. Rectal temperature (RT) measured immediately after PMMR ranged from 6 to 31°C. We used Pearson's correlation coefficient to analyze the relationship between T 1 and relaxation time (RT). We compared STIR images from 4 cadavers acquired with a TI commonly used in the living body and another TI calculated from the linear regression of T 1 and RT.Results: T 1 values of subcutaneous fat ranged from 89.4 to 182.2 ms. There was a strong, positive, and significant correlation between T 1 and RT (r = 0.91, P < 0.0001). The regression expression for the relationship was T 1 = 2.6*RT + 90 at a field strength of 1.5T. The subcutaneous fat signal was suppressed more effectively with the optimized TI.Conclusion: The T 1 value of subcutaneous fat in PMMR correlates linearly with body temperature. Using this correlation to determine TI, fat suppression with PMMR STIR imaging can be easily improved.

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