Vascular transit times in calcarine cortex: Kinetic analysis of R2* changes observed using localized 1H spectroscopy

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Abstract
A kinetic analysis of water signal intensity changes measured in human visual cortex by PRESS localized 1H spectroscopy at 500 ms resolution with light‐emitting diode (LED) goggle stimulation was used to determine vascular transit times for transitions between rest and activation. Monoexponential curve fitting was used to determine both R2* values for each free induction decay and the time constants for R2* changes with activation and deactivation. Measured transit time values were in general agreement with the literature, and were significantly shorter for “Off→On” than for “On→Off” transitions, consistent with known alterations in blood flow with activation and deactivation. The differences in transit times between “Off→On” and “On→Off” also varied with stimulus frequency in accordance with known physiology. This type of analysis may provide a useful means of analyzing functional activation data and for quantitatively comparing functional activation results from differing subjects and imaging sessions.