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Reproducibility of blood oxygen level‐dependent signal changes with end‐tidal carbon dioxide alterations

Hypercapnia has been utilized as a stimulus to elicit changes in cerebral blood flow (CBF). However, in many instances it has been delivered in a non‐controlled method that is often difficult to reproduce. The purpose of this study was to examine the within‐ and between‐visit reproducibility of blood oxygen level‐dependent (BOLD) signal changes to an iso‐oxic square wave alteration in end‐tidal carbon dioxide partial pressure (PetCO2). Two 3‐Tesla (3T) MRI scans were performed on the same visit, with two square wave alterations administered per scan. The protocol was repeated on a separate visit with minimum of 3 days between scanning sessions. PetCO2 was altered to stimulate changes in cerebral vascular reactivity (CVR), while PetO2 was held constant. Eleven subjects (six females; mean age 26·5 ± 5·7 years) completed the full testing protocol. Excellent within‐visit square wave reproducibility (ICC > 0·75) was observed. Similarly, square waves were reproducible between scanning sessions (ICC > 0·7). This study demonstrates BOLD signal changes in response to alterations in PetCO2 are reproducible both within‐ and between‐visit MRI scans.