1997 Fiscal Year Final Research Report Summary
Reduction of patient dose at medical x-ray diagnosis using scattered x rays.
| Project/Area Number |
08680524
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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 |
エネルギー学一般・原子力学
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| Research Institution | Fukui University of Technology |
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Principal Investigator |
KANAMORI Hitoshi Fukui University of Technology, Electrical Engineering, professor, 工学部, 教授 (70027770)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUMOTO Masao Osaka University, Faculty of Medicine, associate professor, 医学部, 助教授 (50149944)
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| Project Period (FY) |
1996 – 1997
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| Keywords | medical x-ray image / image quality / patient dose / granularity / scattered x rays |
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| Research Abstract |
(1)Measurement of x-ray spectra
We have attempted to perform the direct measurement of x-ray spectra using low-cost CdTe and CdZnTe detectors, which have been developed recently. The results obtained with CdTe detector were less exact than those with a Ge detector, but those with CdZnTe detector agreed with it.
(2)Effects of anti-scatter grids on x-ray spectra and radiographic image quality
By using a conical collimator and a lead beam stopper, primary and scattered x-ray photon spectra through an object and an anti-scatter grid (addreviated as grid, hereafter) were measured separately, varying the irradiation field area. From these results, we obtained the grid ratio, scatter ratio and Bucky factors. The scatter ratio varied with tube voltage but Bucky factors did not. At any spatial frequency, the effects of grids for removing scattered x-rays were almost constant for the tube voltage.
(3)Optimum tube voltage of radiographs obtained by psychophysical analysis
We proposed a new method for
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determining the optimum tube voltage of a chest radiograph using psychophysical analysis. The optimum density range of screen-film system was obtained from gradient curve and minimum perceptible contrasts. An optimum tube voltage, by which the highest density in the lung-field and the lowest density in the mediastinum just covered the optimum density range, was obtained using x-ray photon spectrum and sensitivity spectrum of the screen.
(4)Modulation transfer function and Wiener spectra for a screen-film system
We have obtained the tube voltage dependence of the modulation transfer function (MTF) of a rare-earth screen-film system. The values of the MTFs for the front and back sides at spatial frequencies of less than 3mm^<-1> decreased with the tube voltage. We showed that to explain this phenomenon, not only K-x rays but coherent and incoherent scattered x-ray photons yielded in the screens had to be taken into consideration.
The influence of the crossover effect on the tube voltage dependence of the Wiener spectrum of the quantum mottle for the front and back emulsion has been investigated. It was found that if the crossover effect was appropriately included in the radiographs, the patient exposure and the Wiener spectrum of the quantum mottle could be reduced. Less
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