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Abstract #3727

The dependence of the BOLD response transients on stimulus type and echo time

Martin Havlicek1, Dimo Ivanov1, Benedikt A Poser1, and Kamil Uludag1

1Cognitive Neuroscience, Maastricht University, Maastricht, Netherlands

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.

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