A total of 120 screening mammograms were selected from the Dutch breast cancer screening program and were digitized by using a laser digitizer suitable for medical applications (Lumiscan 85, Lumisys, Sunnyvale, CA, USA) at a pixel resolution of 50 µm. The mammograms were averaged down to a resolution of 100 µm, maintaining a gray-level resolution of 12 bits. From these cases, 40 had a biopsy-proven malignant mass, and 80 were cancer-free. As a result of the Dutch screening protocol, the majority of the cases had only mediolateral oblique (MLO) views available. Of the 120 cases only 25 had additional CC views. All cancer cases selected were subtle cancers that were missed at the original screening and were retrospectively identified as visible. We chose to use cases with missed cancers to maximize the power of our observer experiment. Cases with only microcalcifications were excluded. Each mammogram was presented with the corresponding prior screening mammogram, as is common in screening practice to allow detection of temporal changes. The study is summarized in Table 1.
Table 1 Study overview
Total cases 120
  Normal cases 80
  Cancer cases 40
  Cancer cases detected by CADa 33
Available CAD regionsb 587
  Available true-positive CAD regions 41
  Available false-positive CAD regions 546
aCancers hit in at least one view by the CAD system at an operating level of 2.0 false-positive markings per image
bRegions that could be queried at the operating level of 2.0 false-positives markings per image