A HYPERCAPNIA-BASED NORMALIZATION METHOD FOR IMPROVED SPATIAL LOCALIZATION OF HUMAN BRAIN ACTIVATION WITH FMRI

An issue in blood oxygenation level dependent contrast-based functiona l MRI is the accurate interpretation of the activation-induced signal changes, Hemodynamic factors other than activation-induced changes in blood oxygenation are known to contribute to the signal change magnitu des and dynamics, and therefore need to be accounted for or removed, I n this paper, a general method for removal of effects other than activ ation-induced blood oxygenation changes from fMRI brain activation map s by the use of hypercapnic stress normalization is introduced, First, the effects of resting blood volume distribution across voxels on act ivation-induced BOLD-based fMRI signal changes are shown to be signifi cant, Second, the effects of hypercapnia and hypoxia on resting and ac tivation-induced signal changes are demonstrated, These results sugges t that global hemodynamic stresses may be useful for non-invasive mapp ing of blood volume, Third, the normalization technique is demonstrate d. (C) 1997 John Wiley & Sons, Ltd.