5 March 2014 Precise spatial co-registration in simultaneous fNIRS and fMRI measurements using markers coaxially fixable to the optodes
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Similar to blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI), functional nearinfrared spectroscopy (fNIRS) observes regional hemodynamic responses associated with neuronal activation. However, the conventional criteria for detecting true positive fNIRS and fMRI signals appear to be based on different understandings of cerebral hemodynamics. Considerable numbers of fNIRS studies have ascribed the increase in oxygenated hemoglobin to a typical sign of functional activation, whereas the corresponding BOLD signal in fMRI directly correlates with a decrease in deoxygenated hemoglobin. This inconsistency requires solution through the simultaneous measurements of fNIRS and fMRI. In practice, however, there remain several technical problems associated with conducting simultaneous measurements with high reproducibility. One issue is the precise spatial registration of NIRS optodes in MR images. We prepared marker containers of an annular shape that can be coaxially fixed to the optode. Liquid paraffin with α-tocopheryl acetate, which exhibits a bright contrast in T1-weighted MR images of human heads, was solidified in each container by adding higher fatty acid. A subject wearing the marker-fixed optodes at parietal area participated in preliminary fNIRS and fMRI experiments; the subject was instructed to execute single-sided hand finger tapping. The positions showed that deoxygenated hemoglobin decreases in fNIRS coincided with the BOLD-positive region in fMRI. The prepared marker is chemically stable and repetitively usable. We believe that this simple method contributes precision to the co-registration of fNIRS and fMRI.
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Toru Yamada, Keiji Matsuda, Takayuki Iwano, Shinji Umeyama, "Precise spatial co-registration in simultaneous fNIRS and fMRI measurements using markers coaxially fixable to the optodes", Proc. SPIE 8928, Optical Techniques in Neurosurgery, Neurophotonics, and Optogenetics, 89280S (5 March 2014); doi: 10.1117/12.2036165; https://doi.org/10.1117/12.2036165

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