Comparison of CO₂ in Air Versus Carbogen for the Measurement of Cerebrovascular Reactivity with Magnetic Resonance Imaging

Abstract

Measurement of cerebrovascular reactivity (CVR) can give valuable information about existing pathology and the risk of adverse events, such as stroke. A common method of obtaining regional CVR values is by measuring the blood flow response to carbon dioxide (CO 2 )-enriched air using arterial spin labeling (ASL) or blood oxygen level-dependent (BOLD) imaging. Recently, several studies have used carbogen gas (containing only CO 2 and oxygen) as an alternative stimulus. A direct comparison was performed between CVR values acquired by ASL and BOLD imaging using stimuli of (1) 5% CO 2 in air and (2) 5% CO 2 in oxygen (carbogen-5). Although BOLD and ASL CVR values are shown to be correlated for CO 2 in air (mean response 0.11 ± 0.03% BOLD, 4.46 ± 1.80% ASL, n ¼ 16 hemispheres), this correlation disappears during a carbogen stimulus (0.36±0.06% BOLD, 4.97±1.30% ASL). It is concluded that BOLD imaging should generally not be used in conjunction with a carbogen stimulus when measuring CVR, and that care must be taken when interpreting CVR as measured by ASL, as values obtained from different stimuli (CO 2 in air versus carbogen) are not directly comparable.

Magnetic resonance imaging for assessment of cerebrovascular reactivity in cerebral small vessel disease: A systematic review

“…25 Additionally the high oxygen concentrations used in some gas mixtures may cause further complex changes to the BOLD contrast. 26 One study has suggested that there is little difference between breath holding and CO 2 inhalation, although this study used ASL rather than BOLD to assess CVR. 27 This study also found bigger differences between the vasodilatory stimuli it assessed when absolute change rather than percentage change CVR measures were used.…”

The Vascular Steal Phenomenon is an Incomplete Contributor to Negative Cerebrovascular Reactivity in Patients with Symptomatic Intracranial Stenosis

“…Pseudocontinuous arterial spin labeling data were pairwise subtracted and normalized by M 0 to generate CBF-weighted maps, spatially smoothed to match the BOLD postprocessing (full-width-half-maximum ¼ 3 mm), and CBF was quantified upon application of the solution of the flow-modified Bloch equation assuming a blood-water T 1 reduction from 1.6 seconds to 1.4 seconds (effect of hyperoxia). 26,27 To enable comparison of negative regions between all subjects, BOLD and CBF-weighted maps were co-registered to a 4 mm isotropic Montreal Neurological Institute (MNI) T 1 -weighted atlas.…”

BOLD fMRI of cerebrovascular reactivity in the middle cerebral artery territory: A 100 volunteers’ study

“…Because of the more complex and equivocal nature of BOLD signal changes during hyperoxic hypercapnia, it is advocated to perform BOLD CVR mapping using normoxic hypercapnia [40]. However, some ethical committees could be reluctant to allow normoxic hypercapnic challenge rather than hyperoxic hypercapnic challenge, especially in patients referred for stroke and steno-occlusive disease.…”