數位放射照相系統的影像接收器所接收到的成像X 光，並非只來自穿透輻射，還包括散射輻射，這 兩者的空間分布以重疊的模式同時進入影像接收器，共同產生最後的輸出影像，但由於散射輻射無法像行 進軌跡為直線的穿透輻射提供直線穿透路徑上的解剖訊息，被視為是雜訊的來源，會降低訊雜比。為了減 少散射輻射對影像的影響，在儀器設備部分是在病人與影像接收器之間安裝柵極，技術層面則是管電壓值 盡量小，本研究使用對比解析板，評估柵極與管電壓對影像品質的影響，實驗結果顯示，管電壓增加，影 像品質上升但存在著極限；有使用柵極的影像對比的確優於沒有使用柵極的，但是在窗值與窗幅的輔助下， 視覺上，沒有使用柵極的影像卻能辨識出較多的方格，影像能否被辨識，對比並非是關鍵性的決定參數， 偏差比值與訊雜比值是較適合作為判斷的參數。數據分析結果亦顯示，在進行數位X 光照相時，在被照體 厚度不大的情況下，柵極的使用可考慮移除。

Image-forming x-rays detected by the image receptor of digital radiographic imaging system consist of primary radiation and scattered radiation. Image information is carried only by the primary radiation, but the spatial distribution of the simultaneously created scattered radiation superimposes the primary radiation and interferes with image quality. On digital radiographic images, scatter acts chiefly as a source of noise, degrading the signal-to-noise ratio. The amount of scatter created diminishes with lower tube voltage, and the intensity of scattered radiation can be reduced by the grid positioned between the patient and the image receptor. In this work, a contrast-detail phantom was used to study the effect of tube voltage and grid on image quality. It was found that the image quality rises with increasing tube voltage, but it has a limit. When using a grid, it is true that the images have better contrast, but the images without grid have more squares which are correctly identified hole-position, by the window level and width. No significant effects were observed that the contrast is the critical decision parameter for image identification, which can be better described by the deviation ratio and signal-to-noise ratio. It was also found that for thin anatomical structures, the use of a grid is not necessary.