Cerebral blood oxygenation in rat brain during hypoxic hypoxia. Quantitative MRI of effective transverse relaxation rates.

Oxygenation-sensitive MRI of respiratory challenges in the brain of experimental animals will considerably benefit from a quantitative relationship between cerebral blood oxygenation and MRI parameters. Here, a multi-echo gradient-echo MRI technique was used to determine effective transverse relaxation rates R2* = 1/T2* of rat brain in vivo during short periods of hypoxia and interleaved normoxic phases. The differential contribution delta R2* observed during hypoxia was found to increase linearly with arterial blood deoxygenation for mild to moderate conditions. Severe deoxygenation resulted in a plateau most likely due to enhanced cerebral blood flow.