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ABSTRACFMass lesion detection perfomiance of a LoRad Digital Spot Mammography (DSM) system was compared with a KOdak Miii R screen-film combination exposed either in front ofthe DSM, or in the Buoky of a GE 600T mammography unit. Low.confrast objects siniulaling small masses were superimposed on anRME 165 anthropomorphic breast phantom and radiographs obtained at 28 kVp and anmAsvalue, whichresulted in a mean film density of-'1.l. DSM images were obtained at the same radiation exposure as used with screen-film. Fully masked radiographs were viewed on a mammography light box, and the DSM images were viewed on the DSM monitor in a darkened room. Ofthe 64 regions ofinterest (ROl) in each type ofimage, 28 (44%) contained the test object. For each imaging modality, six radiologists and six scientists assessed the probability of a simulated mass being present in each ROl. The resultant data were used to plot Receiver Operating Characteristic (ROC) curves of twelve readers for each of the three imaging modalities investigated.There was no significant difference inreaderperfonnance between the screen-film combination exposed in front ofthe DSM system and exposed in the GE 600T system. Both screen-film imaging systems resulted in the same average area under the ROC curve, A, ofO.78. At the same levelofradiation exposure, the DSM had an average ROC area, A, ofO.71 which was significantly inferior to the average ormance achieved using screen4ilm (p < 0.005). For this detection task, there were no significant differences in performance between the radiologists and scientists. Reader performance was found to improve with the number of images read, demonstrating an observer learning curve for this specific detection task. INTRODUCHONIn comparison to conventional screen-film systems, digital mammography systems may enhance lesion detection because of the ability to independently optimize the acquisition and display of medical images.' Previous studies have shown that digital mammography systems peiform much better than screen-film combinations when the imaging performance is measured using contrastdetail phantoms."3In ibis study, low-contrast objects simulating small masses were imaged with an anthropomorphic breast phantom developed by Caldweil eta!4 and now commercially available (RAIl 165; Middleton, WI). Three imaging modalities, two screen-film and one digital, were investigated. Low-contrast detection performance of each imaging modality was measured using a Receiver Operating Characteristic (ROC) methodology, with the area under the ROC curve (A7) used to measure imaging performance.5 2. METHOD 2.1. Phantoms Digital and film images were generated of the central region of an RMI 165 anthropomorphic phantom A 1 mm thick acrylic base was positioned on top of the RMI 165 phantom containing a 4 x 4 array of 1cm x 1cm regions of interest (ROl). Radiopaque markers were located in the four corners of each ROl to permit these regions to be identified in the resultant radiographic images. Each image was 5 cmx 5cm in size and conta...

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