Size Discrimination Of Features On CT Images
Philip F. Judy, Richard G. Swensson · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1986
Observers rated the likelihood that two circular features on a CT image differed in size, or the likelihood that a ring was present on a CT image. The ring features were produced by subtracting the image profiles of the two disks that had to be distinguished. Since a physical cross-correlator used the same formal calculations on the image pixel values in both tasks, the signal-to-noise ratio (SNR) for the size discrimination task could be predicted from the values of SNR in the ring discrimination task. The 15 sets of images in both tasks studied three levels of feature contrast for discrimination with the relative difference in the disks' diameters adjusted to vary observers' performance over a measureable range. Indices of performance accuracy, as estimated from observers' ROC curves, were well predicted by assuming that they were proportional to the calculated values of Task SNR. The fitted constants of proportionality were similiar in both the size-discrimination (0.470) and ring-detection (0.556) tasks. Thus the human. observer's processing of image information in both the size-discrimination and ring-detection tasks was similar to, but less efficient than, that of the physical cross-correlator.