Martin Havlicek1, Dimo Ivanov1, Benedikt A Poser1, and Kamil Uludag1
Adaptation and post-stimulus undershoot observed
in the BOLD signal can originate from both active neuronal and passive vascular
mechanisms. Using a multi-echo GE-EPI functional MRI sequence with two distinct
visual stimuli, we are able to show that not only the BOLD response magnitude
but also its shape is affected by the echo-time (TE). As pure oxygenation
changes predict approximately a linear scaling of the BOLD signal with TE, this
finding indicates that the composition of the underlying physiological
mechanisms contributing to the fMRI signal (i.e. CBF, CBV, and CMRO2) varies
over time.
