To improve the spatial resolution in near-infrared-ray computed tomography (NIR-CT), a first-generation scanner was constructed using the wavelength range of 700–900 nm, called the first living-body window. The NIR photons were produced from an 850-nm-peak light-emitting diode (LED), and the photons penetrating through an object were selected using an infrared filter and detected using a photodiode (PD). The penetrating-photon count rate was regulated by the applied voltage of a DC power supply for the LED. To improve the spatial resolution, we used a polyacetal collimator of 1.0-mm diameter and 5.0-mm length, two Cu pinholes of 1.0-mm diameter, and an Al pinhole of 1.0-mm diameter. The NIR line beam was roughly formed using the collimator, and the beam diameter was reduced using the first pinhole. The second pinhole was set behind the object to detect the primary photons, and the third pinhole was attached to the PD to improve the spatial resolution. The NIR-CT was realized by repeated translations and rotations of the object, the ray-sampling translation step was 0.25 mm, and the rotation step was 1.0°. The scanning time and total rotation angle for the CT were 9.8 min and 180°, respectively. In the NIR-CT of the graphite rods, the spatial resolutions were approximately 1 × 1 mm2, and a 0.5-mm-diam rod was visible. The NIR-CT might be useful for the diagnosis of children’s limbs and small animals.
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