The effect of digitising film prior mammograms on radiologists' performance in breast screening: a JAFROC study

After the introduction of digital mammography the film mammograms from the previous screening round (the prior mammograms) can be displayed in a variety of ways. This paper investigates the performance of radiologists reading digital screening mammograms with the prior mammograms displayed either as film or in digitised format. A set of 162 cases was assembled, each with two view digital mammograms and two view film prior mammograms. Of these cases 66 were malignant as proven by biopsy, and the others were normal or benign. The film prior mammograms were digitised at 75μm. Eight participants, with four to seventeen years experience of reading screening mammograms, each read the mammograms twice; once with the digitised prior mammograms displayed on the digital workstation, and once with the film prior mammograms displayed on an adjacent multi-viewer. The two viewings were at least one month apart. Participants marked the location of abnormalities on a paper copy of the mammograms and rated the probability of malignancy of each abnormality. Participants were video-taped whilst reading the cases to enable analysis of gross eye movements for information regarding the level of use of the prior mammograms. JAFROC analysis showed no difference in performance between the conditions.