Computed radiography excretory urography: can the system sensitivity value be used as an image quality indicator?

The purpose of this study is to determine whether the computed radiography system sensitivity value can be used as an image quality indicator for computed radiography excretory urography with radiation dose reduction. One hundred and twenty-four patients with gynecological malignancies were studied prospectively. Five-minute and 10-minute computed radiographic images of excretory urography were obtained in each patient with different radiation doses (ie, a standard dose image required with screen-film method and a reduced dose one). The images were subjectivity scored by three radiologists without knowledge of the exposure factors or the system sensitivity values. The quality scores of the reduced-dose images used in the five steps were compared with those of the standard dose images (the system sensitivity value was 80 to 120). The images with reduced exposures were arbitrarily divided into five steps according to the system sensitivity value (ie, 150 to 250, 260-400, 410-600, 610-1000, and 1010-1500). There was a gradual degradation of the image quality as the system sensitivity value was increased. In terms of visualization of the bones, the images taken with the system sensitivity values of 150-250 (40%-67% of the standard dose system) showed no statistically significant difference from the standard dose images. As for visualization of the renal pelvic margins, the images taken with the system sensitivity values of 260 to 400 (2%-38% of the standard dose system) showed no statistically significant difference. We conclude that system sensitivity value can be used as a practical though approximate indicator of the image quality.