Cerebrovascular MRI in the mouse without an exogenous contrast agent

Abstract

Purpose To 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. Methods Twenty 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. Results 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. 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.

Non-invasive in situ visualization of the murine cranial vasculature

“…achieves velocity-based measurements of directionality of blood flow allowing the determination of artery or vein ( Tang et al., 2020 ). There are also many contrast-based and time-of-flight (TOF) MRI methods that enable visualization of the cerebrovasculature in mice ( Fouquet et al., 2020 ; Pastor et al., 2017 ). Both in vivo and ex vivo methods have limitations on quantitative evaluation of vasculature such as measurement of vessel diameter.…”

A protocol for visualization of murine in situ neurovascular interfaces

“…Recent studies have used ultrasound (US) or contrasted or time-of-flight MRI methods for such purposes like velocity-based measurements of directionality of blood flow which help determine vessel type. 11 , 12 , 13 While our ex vivo imaging method does not allow for assessment of blood flow, it does provide a uniform effect on vessel diameter through the use of sodium nitroprusside alone. The provision of anesthetics for in vivo methods, in comparison, may have complicated, unpredictable combinatorial effects on vasoconstriction and vasodilation.…”