The change in cerebrovascular reactivity between 3 T and 7 T measured using graded hypercapnia

Mapping cerebrovascular reactivity (CVR) to hypercapnia is important both clinically and for improved understanding of the haemodynamic properties of the BOLD effect. In this work, BOLD/R2⁎ CVR was investigated by using a device which provided small, repeatable and stable steps in PETCO2, whilst maintaining a steady PETO2 level. Significant CVR was observed in both grey and white matter at both 3 and 7 T, whilst an approximately linear relationship found between R2⁎ CVR and field strength has implications for BOLD models and calibration. Grey matter R2⁎ CVR was 0.066 ± 0.004 s−1 mm Hg−1 at 3 T and 0.141 ± 0.008 s−1 mm Hg−1 at 7 T. White matter R2⁎ CVR was 0.021 ± 0.003 s−1 mm Hg−1 at 3 T and 0.040 ± 0.007 s−1 mm Hg−1 at 7 T.