In vivo 31P-MR spectroscopic studies of hamster liver after irradiation

Acute radiation effects on liver tissue were examined experimentally by using phosphorus-31 magnetic resonance spectroscopy (P-31 MRS). Thirty hamsters received a single electron irradiation of 40 Gy to the left hepatic lobe; and each 5 were examined on Day 1, Day 2, Day 3, Week 1, Week 4, and Week 8 after irradiation. Five other animals not exposed to irradiation were selected as the control group. The peak intensities of phosphodiester (PDE) and γ-ATP in all the irradiated groups were lower than those in the control group. Phosphomonoester (PME) tended to be lower in the Day 1, Day 2, and Day 3 groups than the control group. α-ATP was the lowest in the Week 8 group. There was no significant difference between the irradiated and control groups regarding peak intensities of PME and PDE. Intracellular pH values for the Day 1, Day 2, and Day 3 groups tended to be decreased, and to be increased in the Week 1 and Week 4 groups. However, the Week 8 group showed a tendency for a decreased pH. A decrease in intracellular pH reflected metabolic acidosis with increasing lactic acid caused by enhanced anaerobic glycolytic activity. Histological examination showed congestion with focal loss of hepatocyte that surrounded the sublobular vein, as found in the Day 3 and Week 1 groups. Fatty degeneration and spotty necrosis of liver cells were noted in the Week 8 group. These findings were similar to those in the clinical setting, as shown in patients with acute radiation hepatitis. The results obtained from P-31 MRS indicated the metabolic changes in the liver after irradiation, suggesting a correlation with histological findings. P-31 MRS may have considerable potential for the evaluation of acute hepatic injury after irradiation. (N.K.)