This study was undertaken to further investigate recent reports of unusual contrast-detail (CD) behavior in images with mammographic backgrounds, namely threshold contrast for detection increased with nodule size for Gaussian nodules. In this work we investigated the effects on the CD curve of allowing differently shaped nodules, in particular nodules with sharper edges. The following types of nodules/disks were studied: Gaussian shaped nodules and blurred disks, the latter characterized by a radius and an independent edge sharpness parameter. In a second type of disk the edge blur was held proportional to the disk radius. Ideal Observer detection thresholds were calculated for different nodule/disk radii ranging from 1.5 to 15 mm and observer performance studies were conducted. Noise power spectra (NPS) measurements confirmed the frequency dependence previously reported, NPS (alpha) 1/f3.1. For the Gaussian nodules we confirmed the reported CD behavior, with threshold contrast (alpha) radius0.2. However, for the disk nodules with fixed blur edges we observed different behavior (larger objects required less contrast), with threshold proportional to radius-0.28. For the disk nodules with variable blur the threshold contrast was almost independent of radius. In summary while we duplicated the reported CD diagrams for Gaussian nodules, different behavior was observed for nodules with edges. We conclude that in addition to considering the details of the noise, it is necessary to consider the signal properties in more detail.