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Jpn J Physiol. 2004 Feb;54(1):79-86.

Absorber's effect projected directly above improves spatial resolution in near infrared backscattered imaging.

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Department of Biophysical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, 560-8531 Japan.


The spatial resolution of near infrared spectroscopic imaging in brain function mapping studies needs to be improved. Most near infrared spectroscopic imaging systems use optical fibers that are arranged like a lattice. The light source and the detector have one-on-one correspondence at intervals of about 3 cm. In this study, we apply several detectors against one source to improve spatial resolution. We assume that a local absorber within a strong scattering medium is a model for local cerebral activation. When we calculate absorbance, which is used to spectroscopically calculate hemoglobin concentration, the peak position shifts away from above the position where an absorber is located. As far as absorbance is calculated, we cannot obtain spatial information about the absorber even if many detectors are used against one source. When we calculate the difference between detected light intensities, however, we demonstrate that an absorber projected onto the measuring surface has an influence directly above it. We predict this property from a light diffusion equation and also prove it experimentally through measurements of a uniform resinous phantom with an absorber. This is one of the basic principles supporting the achievement of higher spatial resolutions with near infrared spectroscopic imaging.

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