VASCULAR TRANSIT TIMES IN CALCARINE CORTEX - KINETIC-ANALYSIS OF R2-ASTERISK CHANGES OBSERVED USING LOCALIZED H-1 SPECTROSCOPY

A kinetic analysis of water signal intensity changes measured in human visual cortex by PRESS localized H-1 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.