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

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.