Three SKE-BKE detection tasks. In the first two cases, the task is to discriminate a solid tumor (elliptical shape with major radius 1.0 mm, minor radius 0.6 mm, and contrast 2:1) from a tumor consisting of two hot spots (0.6 mm in diameter, 1.2 mm center-to-center spacing, and contrast 3:1). In case #3, the task is to distinguish a single sold tumor of diameter 2.0 mm (contrast 2:1) from a tumor (diameter 2.0 mm, contrast 3:1) with necrotic core (cold spot of diameter 0.6 mm).