Near-infrared (NIR) topography has been applied to the measurement of brain activation. However the position
resolution of optical topography is not sufficient to measure focal brain activation. Since the localization of the brain
activation in visual cortex depends on the visual stimuli position, it is difficult to resolve the localized brain activation in
the visual cortex by NIR topography. In this study, we measured the localised brain activation evoked by visual
stimulation to evaluate the position resolution of NIR topography with the high-density probe arrangement. The
topographic image is obtained without solving inverse problem to investigate the effect of the high-density probe
arrangement on improvement of the position resolution of NIR topography. When the brain activations evoked by the
broad visual stimuli such as the whole checker boards, the topographic image measured with the single-density
arrangement is almost the same as that with the double-density arrangement. The double-density arrangement effectively
improves the topographic image when the brain activations were evoked by the localized visual stimuli such as the fanshaped
checker boards.
In near-infrared topography, the topographic images of the brain activation considerably depend on the relative position
between the probe arrangement and brain activation. The variance of topographic image due to the relative position
between the brain activation and the probe arrangement is evaluated by the phantom experiment and simulation. We
examined five types of probe arrangements. The variation of the topographic images measured by 15-mm probe
arrangements is considerably improved in comparison with the image measured by the 30-mm probe arrangements. The
images are almost independent of the relative position in case where the diameter of the brain activation is greater than
30mm.
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