We have developed and evaluated a prototype optical computed tomography (CT) system
for gel dosimetry that measures the amount of irradiation in three dimensions. The major
advantage of this CT is that the light source color can be changed as required. The
projection data are obtained using a color camera. The images of the red, green, and blue
components can be extracted separately from the color images. Black and white images
(brightness values) can also be synthesized from color images. Although optical CT using a
color camera has been reported previously, there have been no reports of optical CT with
a variable light source color. In this study, we investigated the influence of light source
color and each color component obtained by the camera on measurements of samples. The
radiochromic dye hydrogel dosimeter has different colors depending on its composition,
and its color changes over time. Therefore, we used a sample of blue ink instead of a
dosimeter in this study. First, the light transmission spectrum of the blue ink samples used
was investigated. Next, we investigated the relationship between the pixel values of the
reconstructed image and the light source color. The blue ink sample showed a large change
in transmitted light in the wavelength band of 500 to 700 nm corresponding to colors
mainly in the red region. Next, by changing the color of the light source, we investigated
which color component obtained by the color camera was suitable for measurement. The
results indicated that the red component was suitable for this purpose. When a different
radiochromic dye hydrogel dosimeter is used, it is possible to select a suitable light source
color and a suitable camera color component by measuring the transmitted light spectrum
of the gel dosimeter.
ゲル線量計用光CT 装置の光源色依存性について
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