Detection of clusters of simulated calcifications in lumpy noise backgrounds
Philip F. Judy · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1996
The effect of the lump amplitude of lumpy backgrounds on human observers' ability to find clusters of simulated calcifications was measured. Clusters of simulated calcifications were randomly located in 56-pixel-radius circular areas of lumpy backgrounds to which Gaussian noise was added. The clusters of simulated calcifications were projections of five 2.5 pixel- radius spheres randomly located less than 10 pixels of its center. The lumpy backgrounds were produced by adding to the circular areas at random locations, 50 Gaussian lumps of a standard deviation of 7 pixels. Stimulus sets were rendered on the gray-scale monitor of a computer workstation. Three observers searched each area for the cluster. They indicated the location most likely to contain a cluster with a mouse pointer and rated the likelihood that the indicated location actually contained a cluster. The Gaussian noise was adjusted so that the fraction of clusters found was approximately 0.5 for the three levels of amplitude of the lumpy backgrounds and the uniform backgrounds. The detectability, d', was calculated from the fraction of clusters found using an M-alternative forced choice model. A cluster was scored as found (a hit) if the center of the cluster was contained within a specified area surrounding the observer indicated location. The observer detection loss ratio, the ratio of d' to SNR-SKE, decreased from 0.6 for the uniform noise background to 0.25 for the lumpy backgrounds. Observers' ability to find clusters of simulated calcifications is significantly decreased by lumpy backgrounds.