Abstract #1713

Breaking β: Understanding the β-Value in Calibrated Functional MRI

Avery J.L. Berman^1,2 and Bruce Pike²

¹Montreal Neurological Institute, McGill University, Montreal, QC, Canada, ²Department of Radiology and Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada

In calibrated functional MRI (fMRI), the parameter β is used to describe the non-linear dependence of the change in the transverse relaxation rate on the susceptibility offset (Δχ) of blood relative to tissue. Estimates of β at high field strengths have generally been assumed or obtained in post-hoc analyses. Using simulations from vessel networks, we present here a detailed description of β’s dependence on vessel radius. We show that the estimate of β is highly dependent on the range of Δχ used in the fit. This could have important implications for methods that propose to measure β-values in vivo using a contrast agent to alter Δχ.

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