Investigation of prolonged hypobaric hypoxia-induced change in rat brain using T2 relaxometry and diffusion tensor imaging at 7T

• The corpus callosum showed early mixed and delayed cytotoxic edema.
• Pathophysiology of the hippocampus involves cytotoxic edema due to hypobaric hypoxia.
• Decrement in T2 gives insights of iron deposition in rat brain.

The present study examines the change in water diffusion properties of the corpus callosum (CC) and the hippocampus, in response to prolonged hypobaric hypoxia (HH) stress, using in vivo magnetic resonance imaging (MRI) modalities such as T2 relaxometry and diffusion tensor imaging (DTI). Three groups of rats (n = 7/group) were exposed to a simulated altitude of 6700 m above sea level for the duration of 7, 14 and 21 days, respectively. Data were acquired pre-exposure, post-exposure and after 1 week of normoxic follow-up in each group. The increment in T2 values with no apparent diffusion coefficient (ADC) change in the CC after 7 and 14 days of HH exposure indicated mixed (vasogenic and cytotoxic) edema formation. After 1 week of normoxia, 7-day HH-exposed rats showed a decrease in ADC values in the CC, probably due to cytotoxic edema. A delayed decrease in ADC values was observed in the hippocampus after 1 week normoxic follow-up in 7- and 14-day HH groups giving an insight of cytotoxic edema formation. Interestingly, 21-day HH-exposed rats did not show change in ADC values. The decrease in T2 values after 14 and 21 days in the hippocampal region depicts iron deposition, which was confirmed by histopathology. This study successfully demonstrated the use of MRI modality to trace water diffusion changes in the brain due to prolonged HH exposure.