2006 Fiscal Year Final Research Report Summary
High-sensitive X-ray fluoroscopy using chalcogenide glasses: Degradation of X-ray images
| Project/Area Number |
17560279
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Electronic materials/Electric materials
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| Research Institution | Gifu University |
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Principal Investigator |
SHIMAKAWA Koichi Gifu University, Faculty of Engineering, Professor, 工学部, 教授 (60021614)
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| Project Period (FY) |
2005 – 2006
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| Keywords | X-ray direct image for medical use / digital image / chalcogenide glasses / selenium films / X-ray induced carriers / ghost image / image degradation / X-ray photocurrent |
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| Research Abstract |
Amorphous selenium (a-Se) is one of the x-ray photoconductors that is available for use in recently developed direct conversion flat panel x-ray image detectors for medical imaging. To obtain a better understanding of trapping and recombination effects in a-Se, we have studied light and x-ray induced photocurrents in a-Se films. The residual photocurrent, after x-ray exposure, decreases in sandwich cells whereas it increases in coplanar cells. These effects are recovered over a time scale of hours. We show that the results can be interpreted by using VAP (valence alternation pair) type charged defects.
a-Se based x-ray detectors have shown some decrease in the sensitivity (fatigue) as a result of accumulated x-ray exposure. Reduction of sensitivity is one of drawbacks of a-Se detectors, resulting in a ghosting images. The term ghosting means the residual image from previous x-ray exposure. In some explanation of ghosting it has been suggested that x-ray exposure should lead to the gener
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ation of new deep traps.
To get stabilized (and safe) real-time X-ray image (fluoroscopy), the following problems should be overcome :
(1) Degradation of X-ray images with exposing X-ray
(2) Delay of the response time, around several ten seconds, for getting a proper image.
X-ray induced effects on the photocurrent were observed in a-Se. After x-ray exposure, the photocurrent increases in coplanar and decreases in sandwich cells. We have shown that coplanar and sandwich cells have totally different characteristics in terms of x-ray induced effects on the photocurrent. In the coplanar structure, the trapping of x-ray generated holes modifies the quasi-Fermi level and increased the photocurrent. In the sandwich structure, the trapped holes from the photocarriers act as recombination centers, when the x-ray induced electrons are trapped there. It has been turned out that the trapping of X-ray induced charges dominate "ghosting" in the images. It is suggested that new defects are not created by the present x-ray exposure conditions. Less
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Research Products
(10 results)
