Objective To test the overall characteristic curve on a computed radiography system. Methods Imaging plate was exposed by scale-time expose using conventional X-ray equipment. It was processed by CR system. Density of different optical density wedge on CR film was measured by using densimeter. Then, characteristic curve was plotted. Results (1) Overall characteristic curve of CR system was affected by gradation processing. (2) Average gradient of overall characteristic curve was 1.98, 3.10, and 3.75 when GA was 0.8,1.4, and 2.4. (3) Overall characteristic curve rotated around rotation center when rotation amount was changed. Conclusion According to the diagnostic purpose and different body position, rotation amount can be selected, and different contrast imaging can be acquired.

Objective To study the effect of image processing on overall Wiener spectrum (WS) in a computed radiography system. Methods Imaging plate was exposed using conventional X-ray equipment. Overall WS sampling films were made by changing 3 parameters of spatial frequency processing, including frequency rang(RN), frequency type(RT), and degree of enhancement(RE), and by changing 1 of 4 parameters of gradation processing(rotation amount,GA).WS values were calculated by scanning on micro-densimeter for every film proceeded as discrete signal using fast Fourier transform. Results (1) The WS value of subscan direction was 7.26?10 -5 mm 2 when the spatial frequency was 1.0 LP/mm, it was 1.57 times larger than that of scan direction. The WS had peaks under high spatial frequency at sunscan direction. (2) The WS value of RN with 0 at scan direction was 7.90?10 -5 mm 2 when the spatial frequency was 1.0 LP/mm, it was 1.70 times larger than that of RN with 5, and 3.30 times larger than that of RN with 9. (3) The WS value of RE with 1.5 at scan direction was 1.05?10 -4 mm 2when the spatial frequency was 1.0 LP/mm, it was 2.27 times larger than that of RE with 1.0, and 2.92 times larger than that of RE with 0.5. (4) The WS value of GA with 1.5 at scan direction was 1.25?10 -4 mm 2 when the spatial frequency is 1.0 LP/mm, it was 2.70 times larger than that of GA with 0.8. (5) The WS value of RT with T at subscan direction was 9.80?10 -5 mm 2 when the spatial frequency was 1.0 LP/mm, it was 1.02 times larger than that of RT with F, and 1.35 times larger than that of RT with R, and also 1.55 times larger than that of RT with P. Conclusions RN, RE, and GA contributed strongly to Wiener spectra, but the contribution of RT was small. When processing the clinical images, adequate processing parameters should be chosen to reduce the image noise, so as to meet the clinical diagnostic need.