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

Summary 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 (P et CO 2 ). 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. P et CO 2 was altered to stimulate changes in cerebral vascular reactivity ( CVR ), while P et O 2 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 P et CO 2 are reproducible both within‐ and between‐visit MRI scans.