We investigated the range of differences in CT values by which radiologists could distinguish among tissues. The contrast discrimination thresholds and contrast discrimination ratios were determined. The test pattern consisted of a square CT film (12 cm in width and 6 cm in length). The film had a circular reference field and a circular test field. Each field was 1 cm in diameter with the distance between the two center being 6.5 cm. The reference fields were set at 60 or 100 H. U.. The test fields were changed and compared with the reference. The window width (WW) and the window level (WL) were set at 400 and 50 H. U. or 250 and 60 H. U.. The contrast dincrimination thresholds for ten observers ranged from 5.9 to 19.3 H. U., and the contrast discrimination ratios were from 11.5 to 21.3%. The effect of WW on contrast discrimination was analyzed for various WWs ranging from 200 to 1000 H. U.. Changes in WW produced no significant difference under the conditions of this investigation.
All Science Journal Classification (ASJC) codes
- Dentistry (miscellaneous)
- Radiology Nuclear Medicine and imaging