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Baseline blood oxygenation modulates response amplitude: Physiologic basis for intersubject variations in functional MRI signals
Author(s) -
Lu Hanzhang,
Zhao Chenguang,
Ge Yulin,
LewisAmezcua Kelly
Publication year - 2008
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21686
Subject(s) - oxygenation , functional magnetic resonance imaging , blood oxygenation , cerebral blood flow , magnetic resonance imaging , medicine , neuroscience , electroencephalography , cardiology , psychology , radiology
Although BOLD functional MRI (fMRI) provides a useful tool for probing neuronal activities, large intersubject variations in signal amplitude are commonly observed. Understanding the physiologic basis for these variations will have a significant impact on many fMRI studies. First, the physiologic modulator can be used as a regressor to reduce variations across subjects, thereby improving statistical power for detecting group differences. Second, if a pathologic condition or a drug treatment is shown to change fMRI responses, monitoring this modulatory parameter is useful in correctly interpreting the fMRI changes to neuronal deficits/recruitments. Here we present evidence that the task‐evoked fMRI signals are modulated by baseline blood oxygenation. To measure global blood oxygenation, we used a recently developed technique, T 2 relaxation under spin‐tagging (TRUST) MRI, which yielded baseline oxygenation of 63.7% ± 7.2% in the sagittal sinus with an estimation error of 1.3%. It was found that individuals with higher baseline oxygenation tend to have a smaller fMRI signal, and vice versa. For every 10% difference in baseline oxygenation across subjects, BOLD and cerebral blood flow (CBF) signals differ by –0.4% and –30.0%, respectively, when using visual stimulation. TRUST MRI is a useful measurement for fMRI studies to control for the modulatory effects of baseline oxygenation that are unique to each subject. Magn Reson Med 60:364–372, 2008. © 2008 Wiley‐Liss, Inc.