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.

Feasibility of peripheral nerve MR neurography using diffusion tensor imaging adapted to skeletal muscle disease.

Background Diffusion tensor imaging (DTI) of peripheral nerves may provide additional information about nerve involvement in muscular disorders, but is considered difficult due to different optimal scan parameters tailored to magnetic resonance (MR) signal properties of muscle and neural tissues. Purpose To assess the feasibility of sciatic nerve DTI using two different approaches of region of interest (ROI)-localization in DTI scans with b-values 500 s/mm2, in participants with muscular disorders and in controls. Material and Methods DTI of the thigh was conducted on a 3T system in ten patients (6 men, 4 women; mean age =54 ± 15 years) with neuromuscular disorders and ten controls. T1-weighted (T1W) images were co-registered to fractional anisotropy (FA) color-encoded images. The apparent diffusion coefficient (ADC), FA, and fiber track length (FTL) were analyzed by two operators using a freehand ROI and a single-point ROI covering the sciatic nerve. Interclass correlation coefficient (ICC) and Bland-Altman analysis were used for evaluation of inter-operator and inter-technical agreement, respectively. Results Three-dimensional visualization of sciatic nerve fiber was achievable using both techniques. The ICC of DTI metrics showed excellent inter-operator agreement both in patients and controls. Bland-Altman analysis revealed good agreement of both techniques. A maximum FTL was achieved using the single-point ROI technique, but with a lower inter-operator agreement (ICC = 0.99 vs. 0.83). The ADC and maximum FTL were significantly decreased in patients compared to controls. Conclusion Both ROI localization techniques are feasible to analyze the sciatic nerve in the setting of muscular disease. A maximum FTL is reached using the single-point ROI, however, at the cost of lower inter-operator agreement.