1991 Fiscal Year Final Research Report Summary
Quality Assurance Device for Dental X-rayEquipment
| Project/Area Number |
63570945
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
外科・放射線系歯学
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| Research Institution | Showa University |
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Principal Investigator |
HARATA Yasuo Showa Univ., School of Dentistry Assistant Professor, 歯学部, 助教授 (30119250)
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| Co-Investigator(Kenkyū-buntansha) |
NISHIKAWA Keiichi Tokyo Dental College, Assistant, 歯学部, 助手 (30180590)
SAKAINO Rie Showa Univ., School of Dentistry, Assistant, 歯学部, 助手 (50153862)
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| Project Period (FY) |
1988 – 1990
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| Keywords | Quality assurance device / Noninvasive measurement / Dental X-ray unit / Tube potential / Half value layer / Total filtration / Exposure rate / Voltage waveform |
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| Research Abstract |
In X-ray examination it is important to know the beam quality for maximum image quality and minimum dose to the patient. To design a low-priced device measuring beam quality with high perormance we developed the method of measurement of a tube potential. a half value layer(HVL) and total filtration and evaluated the hardware and the software of the trial quality assurance (QA) system. From a computer simulation and an experiment using calibrated ionization chamber these parameters of beam quality can be estimated by the method matching the measured exposure ratio of different filtered beams and the calculated database of theoretical attenuation of X-ray beam. In practice their waveforms as well as the tube potentials are also important for beam characteristics. Ionization chambers are not satisfactory for this purpose because its sensitivity is too low to detect a instantaneous exposure rate and its response is too slow to follow transients. A photodiode detector combined with phosphor
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has a sensitivity sufficiently high to detect the exposure rate and a potential fast enough response to follow the transients. We studied the characteristics of a photodiode with phosphor as a detector of the QA device. The the combination of an intensifying screen made of rare earth and a silicon photodiode for visible to infrared rays seems to be best for QA detector in sensitivity and response. The X-ray beams different filtration were measured with the photodiode detector and the signal from the detector was amplified. analog-to-digital converted. stored in the RAM disk of a portable personal computer. From the analysis of the measured data it was found that in the range from 50kV to 80kV the logarithmic ratio of signal intensities of the different filtered beams has a linear relationship with the tube potential calibrated by the voltage divider and the relationship was almost independent from tube filtration. With and without the filter of HVL calibrated by the ionization chamber the obtained signal rations gave approximately constant values independent form the beam quality. We implemented the program to correct the small effects of beam filtration and of beam quality by the iterative method using the database of the theoretical attenuation curves. The estimated values of beam quality showed within 3% of true values by the correction. Less
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