| Budget Amount *help |
¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 1988: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1987: ¥900,000 (Direct Cost: ¥900,000)
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| Research Abstract |
In order to measure X-ray spectra of scattered radiation together with primary beam by using a planar Ge detector, we have confirmed that the active area of a 10mm x 7mm detector is 7mm in diameter and the available incident angle is within 20 . We prepared conic Pb collimators of various maximum incident angles of up to 20 . Scatter rejection effects of the air-gap method and angular distributions of the scattered radiation were analyzed by experiments and computer simulation techniques. Variables were 70 kV of tube voltage, an object of 20-cm acrylic resin, 2-cm and 30-cm fields, and object-detector distances of 1 to 50 cm. The results show that scatter fractions do not decrease prominently by the air-gap method for the 30-cm field, but they decrease noticeably for the 2-cm field. For the 30-cm field we have obtained angular dependence relations by attaching beam stoppers of various diameters to the exit surface of the object. It was confirmed that the larger scatter angle yielded the lower mean energy and the lower exposure. These phenomena are caused by the Compton effect.
The information spectrum given by us in 1984 is modified by the effect of scatter which decreases the contrast of radiographs. The modification is simply that the signal Wiener spectrum is multiplied by (1-s)^2, where s is the scatter rate. Also the effects of blurs due to object motion are inserted in the information spectrum, by inserting the MTF caused by the blur into the signal Wiener spectrum. Examples are demonstrated, where the detectability of low-contrast objects and resolution of highcontrast objects are successfully explained by information spectral values in low- and high-frequency ranges, respectively.
The scatter degrades the image quality but decreases the patient dose. These two competitive effects should be investigated, and the best scatter ratio for each object should be found.
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