Mr. Shohei Okubo Profile

Shohei Okubo

at Nagoya Univ Graduate School of Medicine

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Proceedings Article | 18 March 2015 Paper

Statistical estimation of the directional dependency of subject in visibility-contrast imaging with the x-ray Talbot-Lau interferometer

Takayuki Shibata, Shohei Okubo, Yoshie Kodera

Proceedings Volume 9412, 941255 (2015) https://doi.org/10.1117/12.2081769

KEYWORDS: X-rays, Interferometers, X-ray imaging, Glasses, Aluminum, Visibility, Statistical analysis, Phase shifts, Refraction, Absorption

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Conventional x-ray image is formed by absorption contrast due to attenuation of x-ray intensity. In recent years, the phase-contrast method has highlighted, in which image contrast is decided according to phase shift of x-rays transmitted through an object. The phase-contrast method is excellent for visualization of soft tissue, which is difficult to visualize using conventional x-ray imaging. The Talbot-Lau interferometer using phase-contrast method was developed by Konica Minolta, Inc. There are images of three types can be obtained in the Talbot-Lau interferometer, i.e. absorption image, differential phase-contrast image, and visibility-contrast image. Visibility-contrast image reflects reduction of coherence due to the object’s structures. Its well-known feature is the contrast due to the x-ray small-angle scattering. In addition, in the visibility-contrast image, the relationship between the signal intensity and the direction of the subject’s structure has been analyzed. Talbot-Lau interferometer only detected the phase shift along the periodic direction of grating due to use the one-dimensional grating. In this study, we focused on how the signal intensity was affected by the direction of the subject structure, and analyzed the edge signal of the subject. We imaged acrylic, glass and aluminum cylinder with the Talbot-Lau interferometer by rotating from 0 degree to 90 degrees with respect to the periodic direction of the grating, and measured their edge signal. Moreover, we statistically estimated the angular function from edge signals of cylinder and compared with our previous study’s method. They correspond with high accuracy and this study warrant accuracy of our previous study’s method.

Proceedings Article | 18 March 2015 Paper

The quantitative evaluation of the correlation between the magnification and the visibility-contrast value

Shohei Okubo, Takayuki Shibata, Yoshie Kodera

Proceedings Volume 9412, 941256 (2015) https://doi.org/10.1117/12.2082453

KEYWORDS: Visibility, X-rays, Optical spheres, X-ray imaging, Interferometers, Glasses, Scattering, Diffraction gratings, Absorption, X-ray detectors

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Talbot-Lau interferometer, which consists of a conventional x-ray tube, an x-ray detector, and three gratings arranged between them, is a new x-ray imaging system using phase-contrast method for excellent visualization of soft tissue. So, it is expected to be applied to an imaging method for soft tissue in the medical field, such as mammograms. The visibility-contrast image, which is one of the reconstruction images using Talbot-Lau interferometer, is known that the visibility-contrast reflects reduction of coherence that is caused from the x-ray small-angle scattering and the x-ray refraction due to the object’s structures. Both phenomena were not distinguished when we evaluated the visibility signal quantitatively before. However, we consider that we should distinguish both phenomena to evaluate it quantitatively. In this study, to evaluate how much the magnification affect the visibility signal, we investigated the variability rate of the visibility signal between the object-position in the height of 0 cm to 50 cm from the diffraction grating in each case of examining the scattering signal and the refraction signal. We measured the edge signal of glass sphere to examine the scattering signal and the internal signal of glass sphere and some kinds of sheet to examine the refraction signal. We can indicate the difference of the variability rate between the edge signal and the internal signal. We tried to propose the estimation method using magnification.

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