Postmortem MR diffusion-weighted imaging of the liver: time-behavior of the hepatic apparent diffusion coefficient in the early death interval

OBJECTIVE: The objective of this study is to assess postmortem changes of the hepatic apparent diffusion coefficient (ADC) at multiple time points in the time interval of 16 hours postmortem in comparison to in vivo controls and to literature data.

MATERIAL AND METHODS: Hepatic diffusion-weighted imaging (DWI) was repeatedly performed at 1.5 Tesla (b values 50, 400, and 800 s/mm2) in 2-hourly steps within 16 hours postmortem in 19 cases (male to female 13:6, mean age 68.5 ± 12.2 years) and 5 in vivo controls. The core body temperature was measured rectally prior to every scan. Mean ADC values were calculated from regions of interest (ROIs) and compared to in vivo healthy controls and to literature data of normal liver parenchyma. Spearman rank correlation and Levenberg-Marquardt algorithm were used to assess a relationship between postmortem core body temperature and ADC values.

RESULTS: Mean hepatic ADC values were significantly lower in postmortem cases than in in vivo controls (52.0 ± 15.0 · 10-5 mm2/s vs. 111.0 ± 15.7 · 10-5 mm2/s, p < 0.0001). The ex vivo liver ADC correlated inversely to calculated liver temperature (-3.5 ± 0.8) · 10-5 mm2/s/°C, r = -0.44, p < 0.0001. At low calculated liver temperature (< 30 °C), the ADC described an average increase of (22 ± 10) · 10-5 mm2/s/°C.

CONCLUSION: Hepatic ADC values show a characteristic change in the immediate 16 hours postmortem, which is influenced by the postmortem liver temperature change. With the knowledge of characteristic postmortem liver changes, diffusion-weighted imaging could be added to conventional postmortem MRI for virtual autopsy.