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Use your smartphone to scan this QR code and download this article ABSTRACT Nowadays, transillumination imaging is more popular used in the medical field with the development of the vein finder application and also the non-invasive diagnosis applications. The less absorption of those main chromophores (melanin, oxy-hemoglobin, deoxy-hemoglobin, and water) of biological tissue within the near-infrared range (700 1200 nm) causes the relatively high transmission of the near-infrared light through biological tissue. They give us an "optical window" to seethrough the biological tissue non-invasively. Because of the high absorption of oxy-hemoglobin, deoxy-hemoglobin within the near-infrared range in comparison with these other parts in tissue, we can able to obtain a two dimensional (2D) transillumination image of the internal absorption structure such as blood vessel network, liver structure... in the body non-invasively. Using the lightemitting diode (LED)'s array to illuminate the human arm and using a low-cost camera to capture the image, we could obtain the blood vessel network image of the human arm. The captured image is blurred and difficult to distingue the structure inside. Because the camera captured the blood vessel network shadow that diffused on the skin surface. Professor Koichi Shimizu devised thedepth-dependent point spread function (PSF) todescribe the scattering effect froma light point source to the observation surface of a slab diffused medium by applying the diffusion approximation. By suppressing the scattering effect successfully, we could restore the clear image from the blurred image by de-convolution with the appropriated PSF. With our proposed technique, we could reconstruct the absorbing structures such as the kidney and liver in biological tissue. Using the restored images from different angles of view, we could reconstruct the cross-sectional images and three-dimensional image of the absorbing structures in an animal's abdomen. However, the depth information of the absorbing-structure was required in practice to calculate the appropriate PSF. Therefore, in order to make this method more practical, the depth information is crucial. In this paper, we proposed the novel techniques for estimating the parameters of absorbing structure (depth, center location, and width) in the turbid medium by using the convolution and deconvolution operations with the devised PSF. Firstly, by observing images with two-wavelength selected at which the absorption and scattering properties of themedium are different. While changing the depth step-by-step, two convoluted images were compared after convolving the captured image at one of the wavelengths with the PSF calculated by using the absorption and scattering coefficients from another wavelength. We can obtain the correct depth that gives the minimum difference between the two convoluted images. Secondly, we proposed the technique to estimate the depth information from a single transillumination image in order to make this method more practical. Finally, the absorbing structure image can be restored by suppressing the scattering effect. The proposed techniques were validated and examined not only in the simulation but also in the experiment.

Depth estimation of the absorbing structure in a slab turbid medium using point spread function