Investigation of overall wiener spectrum measurement in a computed radiography system

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 to 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 x 10-5 mm2 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 sun-scan direction. (2) The WS value of RN with 0 at scan direction was 7.90 x 10-5 mm2 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 x 10-'4 mm2 when 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 x 10-4 mm2 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 x 10-5 mm2 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