计算机X线摄影系统中总威纳频谱测试的探讨

Investigation of overall Wiener spectrum measurement in a computed radiography system

目的 研究计算机X线摄影 (computedradiography,CR)系统中总威纳频谱 (Wienerspectrum ,WS)随影像处理的变化。方法 利用常规X线机对成像板 (imagingplate,IP)曝光 ,改变空间频率处理的参数频率等级 (frequencyrank ,RN)、频率类型 (frequencytype,RT)、增强强度 (degreeofenhancement,RE)以及谐调处理参数旋转量 (rotationamount,GA)来制作总的WS抽样照片 ,用显微密度计扫描 ,通过快速傅立叶变换来计算总的WS。结果 (1)当空间频率为 1 0LP/mm时 ,副扫描方向上的总WS值为 7 2 6× 10 -5mm2 ,是主扫描方向上总WS值的 1 5 7倍 ,在高空间频率范围内出现峰值。(2 )当空间频率为 1 0LP/mm时 ,主扫描方向上RN =0的总WS值为 7 90× 10 -5mm2 ,是RN =5的WS值的 1 70倍 ,是RN =9的WS值的 3 30倍。 (3)当空间频率为 1 0LP/mm时 ,主扫描方向上RE =1 5的总WS值为 1 0 5× 10 -4 mm2 ,是RE =1 0的WS值的 2 2 7倍 ,是RE =0 5的WS值的 2 92倍。 (4 )当空间频率为 1 0LP/mm时 ,主扫描方向上GA =1 5的总WS值为 1 2 5× 10 -4 mm2 ,是GA =0 8的WS值的 2 70倍。 (5 )当空间频率为 1 0LP/mm时 ,副扫描方向上RT =T的总WS值为 9 80×10 -5mm2 ,是RT =F的WS值的 1 0 2倍 ,是RT =R的WS值的 1 35倍 ,是RT =P的WS值的 1

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.