1995 Fiscal Year Final Research Report Summary
Reduction of patient dose by using scattered x-rays
| Project/Area Number |
05680418
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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 |
エネルギー学一般・原子力学
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| Research Institution | Kyoto Institute of Technology |
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Principal Investigator |
KANAMORI Hitoshi Kyoto Inst.Tech., Electronic & Information Science, professor, 工芸学部, 教授 (70027770)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUMOTO Msao Osaka Univ., Faculty of Medicine, associate professor, 医学部, 助教授 (50149944)
NAKAMORI Nobuyuki Kyoto Inst.Tech., Electronic & Information Sciece, associate professor, 工芸学部, 助教授 (20107353)
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| Project Period (FY) |
1993 – 1995
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| Keywords | diagnostic image / scattered x-rays / patient dose |
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| Research Abstract |
(1) Mesurement of scattered x-ray spectra impinged into the pixel of an image plane
A conical collimator of the half angle 45ﾟ was placed in front of a Ge detector. Scatter spectrum was measured by decreasing the diameter of a beam stopper and extrapolated to zero diameter. Primary + Scatter spectrum was obtained by removing the beam stopper. The difference of the above two was the primary spectrum. Thus the separation of the primary and scatter spectra of x-rays impinged into a pixel of an image plane was performed.
(2) Calculation of x-ray spectra emitted from an x-ray tube
The fluctuation of electron energy in the x-ray tube anode was calculated by Monte Carlo method and obtained the Bremsstrahlung crossections by using the quantum theoretical formulas. The results terminated the controversy between Birch and Tucker. We proposed a new theoretical model for characteristic x-ray spectra from tungsten anode.
(3) Calculation of scattered x-ray spectra impinged into the imaging plane
Scattered spectra calculated by using Monte Carlo method were coincided well with the measured spectra. Bucky factors and contrast improvement factors were obtained by the results of the scattered x-ray spectra calculated for various grid ratios and irradiation field sizes. By using these results, it becomes available to select the optimum grid balancing high image quality and low patient dose.
(4) Relation between scatter fraction, image contrast and patient dose
We obtained the scatter fraction by the procedures of (1) and (3) , and took radiographs of an aluminum square-wave chart images for various scatter fractions. We proposed the contrast-dose diagram which indicated the relation between image contrast and patient dose for various scatter fractions. By using this diagram we can find the optimum scatter fraction for minimum dose. This method was applied in a clinical radiograph for Sella Turcica in a head phantom.
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