MRI Mapping of Cerebrovascular Reactivity via Gas Inhalation Challenges

Abstract

The brain is a spatially heterogeneous and temporally dynamic organ, with different regions requiring different amount of blood supply at different time. Therefore, the ability of the blood vessels to dilate or constrict, known as Cerebral-Vascular-Reactivity (CVR), represents an important domain of vascular function. An imaging marker representing this dynamic property will provide new information of cerebral vessels under normal and diseased conditions such as stroke, dementia, atherosclerosis, small vessel diseases, brain tumor, traumatic brain injury, and multiple sclerosis. In order to perform this type of measurement in humans, it is necessary to deliver a vasoactive stimulus such as CO 2 and/or O 2 gas mixture while quantitative brain magnetic resonance images (MRI) are being collected. In this work, we presented a MR compatible gas-delivery system and the associated protocol that allow the delivery of special gas mixtures (e.g., O 2 , CO 2 , N 2 , and their combinations) while the subject is lying inside the MRI scanner. This system is relatively simple, economical, and easy to use, and the experimental protocol allows accurate mapping of CVR in both healthy volunteers and patients with neurological disorders. This approach has the potential to be used in broad clinical applications and in better understanding of brain vascular pathophysiology. In the video, we demonstrate how to set up the system inside an MRI suite and how to perform a complete experiment on a human participant.

Cerebrovascular reactivity mapping without gas challenges

“…However, despite its potential, CVR mapping has not been used in large-scale clinical trials or routine clinical practice. One of the most important limitations of this method is that CVR mapping using gas-inhalation is typically viewed as cumbersome (although recent development in breathing apparatus (Lu et al, 2014; Tancredi et al, 2014) has begun to address these issues) and thus cannot be applied routinely. There are additional concerns of using gas challenges in acute or severely ill patients, as they may not tolerate or report their intolerance of hypercapnia.…”

“…A regression analysis between EtCO 2 and the MRI time course yielded the gas-inhalation-based CVR map (Lu et al, 2014; Yezhuvath et al, 2009). The resting-state CVR map (in relative units) was obtained following the procedures developed in Study 2 (Figure 1).…”

“…At present, CVR mapping is typically performed using hypercapnic gas inhalation as a vasoactive challenge while collecting perfusion sensitive MRI images (Lu et al, 2014; Spano et al, 2013; Wise et al, 2007; Yezhuvath et al, 2009). Hypercapnic gas inhalation increases the blood concentration of CO 2 , which, as a potent vasodilator, dilates blood vessels and increases cerebral perfusion (Brian, 1998).…”

Multiparametric imaging of brain hemodynamics and function using gas-inhalation MRI

“…The MRI-compatible gas delivery system has been described previously (Lu et al, 2014; Yezhuvath et al, 2009). Briefly, prior to the breathing task, the subject was fitted with a nose clip, so that they can breathe room air and prepared gases through a mouthpiece (Figure 1b).…”

Time delay processing of hypercapnic fMRI allows quantitative parameterization of cerebrovascular reactivity and blood flow delays

“…First, the only additional supplies required are gases and MR compatible gas administration equipment, which are easily utilized in clinical neurovascular imaging suites. 19,20 Second, the oxygenation change that can be induced with alternating normoxic and hypercarbic gas is large compared to endogenous fluctuations, so the amplitude of the hemodynamic signal used for time delay estimation is even higher, leading to more stable measurement. The changes in endogenous blood oxygenation may additionally be amplified by adding a hyperoxic component to the hypercarbic gas mixture, as in the case of carbogen.…”