A quantitative in-vivo MR imaging study of brain dehydration in diabetic rats and rats treated with peptide hormones

The main aim of the study was to evaluate the combination of quantitative diffusion, T2 and Magnetisation Transfer Imaging of brain water homeostasis using untreated diabetes as an animal model of brain dehydration. In addition, experimental groups of diabetic rats treated with insulin and insulin-like growth factor (IGF-I) and normal rats treated with IGF-I and growth hormone were studied using the same MR imaging protocol. Untreated diabetes caused weight reduction and an increase in water intake, indicating a general body dehydration linked to chronic blood hyperosmolarity. In the investigated cortical gray matter untreated diabetes caused a significant reduction in the apparent diffusion coefficient of water (ADC) and an increase in T2 relaxivity (R2) when compared to a control group. No significant changes were observed for the calculated magnetisation transfer parameters Kfor and T1sat. Both ADC and R2 normalized after appropriate insulin treatment whereas only ADC was normalized after IGF-I treatment. IGF-I treatment of normal rats caused significantly higher rate of increase in body weight compared to normal controls. There were, however, no significant changes in ADC, R2 nor the magnetisation transfer parameters measured in the cortical gray matter of the IGF-I treated normal rats. In conclusion, we found that changes in brain water homeostasis during diabetes were detected by quantitative MR imaging, and that the dehydration induced by diabetes was normalized by insulin treatment but not by IGF-I.