Cerebrovascular MRI in the mouse without an exogenous contrast agent.

Jérémie P Fouquet,Luc Tremblay,John G Sled,Martin Lepage,Lindsay S Cahill,Réjean Lebel

doi:10.1002/mrm.28129

Abstract

PurposeTo assess the effect of a variety of anesthetic regimes on T2∗‐weighted MRI of the mouse brain and to determine the optimal regimes to perform T2∗‐weighted MRI of the mouse cerebrovasculature without a contrast agent.MethodsTwenty mice were imaged with a 3D T2∗‐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.ResultsThe 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.Conclusion T2∗‐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.

Highlights

The critical role of the vasculature in both the normal and pathological brain is increasingly drawn to our attention
We demonstrated that it is possible to image a significant fraction of the mouse cerebrovasculature using T∗2-weighted MRI (T∗2 MRI) without contrast agent by choosing an appropriate anesthetic regime
As opposed to results obtained in the rat, the widely used ISO anesthetic generates a poor vessel conspicuity when administered with 100% O2 or medical air

Summary

| INTRODUCTION

The critical role of the vasculature in both the normal and pathological brain is increasingly drawn to our attention. We directly compare the cerebrovascular trees obtained under ISO, KX, and DEX and assess how modifying the breathing gases modulates image contrast and vessel conspicuity. These 3 anesthetics are already used extensively for mouse imaging studies because of practical aspects such as ease of use, the possibility of repeated use, and the quick recovery of the animals (especially for ISO and DEX).[13,14,15,16,17] We acquire T∗2-weighted images after an injection of an iron oxide contrast agent (Resovist) as a positive control and explore its capacity to differentiate veins and arteries in the cerebral cortex. The results provide information on the effects of different anesthetics on the cerebral blood oxygenation of the mouse at rest

| METHODS

| RESULTS

Findings

| DISCUSSION

| CONCLUSIONS