Cerebrovascular MRI in the mouse without an exogenous contrast agent

To assess the effect of a variety of anesthetic regimes on $$ -weighted MRI of the mouse brain and to determine the optimal regimes to perform $$ -weighted MRI of the mouse cerebrovasculature without a contrast agent.

Twenty mice were imaged with a 3D $$ -weighted sequence under isoflurane, dexmedetomidine, or ketamine-xylazine anesthesia with a fraction of inspired oxygen varied between 10% and 95% + 5% CO₂ . Some mice were also imaged after an injection of an iron oxide contrast agent as a positive control. For every regime, whole brain vessel conspicuity was visually assessed and the apparent vessel density in the cortex was quantified and compared.

The commonly used isoflurane anesthetic leads to poor vessel conspicuity for fraction of inspired oxygen higher or equal to 21%. Dexmedetomidine and ketamine-xylazine enable the visualization of a significantly larger portion of the vasculature for the same breathing gas. Under isoflurane anesthesia, the fraction of inspired oxygen must be lowered to between 10% and 14% to obtain similar vessel conspicuity. Initial results on automatic segmentation of veins and arteries using the iron oxide positive control are also reported.

$$ -weighted MRI in combination with an appropriate anesthetic regime can be used to visualize the mouse cerebrovasculature without a contrast agent. The differences observed between regimes are most likely caused by blood-oxygen level dependent effects, highlighting the important impact of the anesthetic regimes on cerebral blood oxygenation of the mouse brain at rest.