THE DETECTABILITY OF SIMULATED LOW-CONTRAST OBJECTS IN THE CT IMAGES ON A CRT

The detectability of simulated low-contrast objects in CT images on a CRT were investigated. The limits of the detection of a signal (i. e., a disease) were discussed in terms of CRT diagnosis. Assuming that the CT images were observed on a CRT exposed with an abdominal condition, this experiment was performed. The 16-alternative forced-choice (16-AFC) experiments was employed to study the dependence of the detectability of test objects regarding objects size (0.25〜9cm^2), background noise level (RMS=20.6, 10.3, 5.7) and objects contrast (-1〜-16CT numbers). The CT images were displayed on a 735-line CRT (12-inch, interlaced, 256 gray levels). The results indicate that the detectability of low-contrast objects in the CT images on a CRT depends strongly on the background noise level and object size. When the RMS noise level was higher than 10 or the object size smaller than 1cm^2, the detectability decreased sharply. Through these results the limits of the detection of a signal in terms of CRT diagnosis could be observed.