We assessed the repeatability of fMRI Cerebrovascular Reactivity (CVR) estimates using CO2 sinusoidal stimuli. We estimated BOLD-CVR amplitude and phase using a fast Fourier transform (FFT) analysis and a cross-correlation analysis (Rapidtide). Amplitude and delay maps showed sensible regional variations for both time-points, but participant variability was notable. CVR spatial correlations between time-points were higher after averaging within cortical parcels, compared to weak voxel-wise correlations. Qualitatively, Rapidtide achieved higher between-session correlations than FFT. GM average amplitudes agreed between time-points. At the correct spatial scale, with careful consideration of parameter scaling, this short stimulus is a viable CVR mapping option.
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