| Ghosting caused by bulk charge trapping in direct conversion flat-panel detectors using amorphous selenium. | |
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MedLine Citation:
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PMID: 15789596 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Direct flat-panel detectors using amorphous selenium (a-Se) x-ray photoconductors are gaining wide-spread clinical use. The goal of our investigation is to understand the physical mechanisms responsible for ghosting, i.e., x-ray induced change in sensitivity that results in image persistence, so that the knowledge can be used to consistently minimize ghosting artifacts in a-Se flat-panel detectors. In this paper we will discuss the effect on x-ray sensitivity of charge trapping in a-Se, which is the dominant source for ghosting in a-Se flat-panel detectors. Our approach is to correlate ghosting in electroded a-Se detectors with the trapped charge concentration measured by the "time-of-flight" (TOF) method. All measurements were performed as a function of radiation exposure X of up to approximately 20 R at electric field strength's of E(Se)=5 and 10 V/microm. The results showed that the x-ray sensitivity decreased as a function of X and the amount of ghosting decreased with increasing E(Se). The shape of the TOF curves changed as a result of irradiation in a manner indicating trapped electrons in the bulk of a-Se. The density of trapped electrons n(t) increases as a function of X. A method was developed to determine the values of n(t) in the bulk of a-Se from the TOF measurements, and to predict the corresponding change in x-ray sensitivity. Our results showed that a recombination coefficient consistent with that predicted by Langevin produced good agreement between calculated and measured x-ray sensitivity changes. Thus it can be concluded that the trapping of electrons in the bulk of a-Se and their subsequent recombination with x-ray generated free holes is the dominant mechanism for ghosting in a-Se. |
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Authors:
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Wei Zhao; G DeCrescenzo; Safa O Kasap; J A Rowlands |
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Publication Detail:
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Type: Comparative Study; Evaluation Studies; Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.; Validation Studies |
Journal Detail:
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Title: Medical physics Volume: 32 ISSN: 0094-2405 ISO Abbreviation: Med Phys Publication Date: 2005 Feb |
Date Detail:
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Created Date: 2005-03-25 Completed Date: 2005-06-28 Revised Date: 2008-11-21 |
Medline Journal Info:
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Nlm Unique ID: 0425746 Medline TA: Med Phys Country: United States |
Other Details:
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Languages: eng Pagination: 488-500 Citation Subset: IM |
Affiliation:
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Department of Radiology, State University of New York at Stony Brook, L-4 Health Sciences Center, Stony Brook, New York 11794-8460, USA. wei.zhao@sunysb.edu |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Artifacts* Computer Simulation Equipment Design Equipment Failure Analysis Models, Theoretical* Radiation Dosage Radiographic Image Enhancement / instrumentation*, methods Radiometry / instrumentation*, methods Selenium / chemistry*, radiation effects* Static Electricity Transducers X-Ray Intensifying Screens* |
| Grant Support | |
ID/Acronym/Agency:
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CA84439-03/CA/NCI NIH HHS |
| Chemical | |
Reg. No./Substance:
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7782-49-2/Selenium |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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