Cerebrovascular reactivity mapping without gas inhalation: signal characterization with multi-echo BOLD

Motivation: Cerebrovascular reactivity (CVR) has shown strong promise in large-vessel stenotic diseases and small-vessel-related cognitive impairment and dementia. Conventional CVR MRI requires CO2 inhalation inside the scanner. Recently, a gas-free technique was proposed based on breath modulations. Goal(s): To characterize the signal underpinnings of breath-modulation CVR MRI using multi-echo BOLD acquisition. Approach: We examined the relationships among multi-echo CVR, end-tidal (Et) CO2, and a gold-standard blood flow response to CO2 inhalation. Results: T2* changes measured with multi-echo showed strong correlation with EtCO2, and were highly correlated with the gold-standard CO2-inhalation CVR. Breath-modulation data can be used to estimate a bolus-arrival-time map. Impact: Breath-modulation resulted in an EtCO2 reduction by ~2.5mmHg. In terms of the BOLD acquisition sequences, ME-BOLD T2* CVR yielded a similar precision as the SG-BOLD, but with higher accuracy. Breath-modulation MRI can also yield reliable bolus arrival time maps.