Observer performance and dose efficiency of mammographic scanning equalization radiography

The detection of fibrils, microcalcifications, and low contrast lesions is vital to the detection of early breast cancer. It has been shown through sensitometric measures and anthropomorphic phantom images that mammographic scanning equalization radiography (MSER) overcomes the latitude limitations of conventional mammographic techniques. MSER increases image quality by regional modulation of the entrance exposure to suit the local variations in x-ray transmission within the patient. In order to assess the effect of equalization on the detection of breast lesions, we have compared observer performance in MSER and conventional imaging techniques. The observation tasks were the threshold visualization of fibrils, microcalcifications, and low contrast discs (simulating lesions), located on a uniform background. The performance of the observers was determined for a range of background x-ray transmission simulating the range of transmission generated by variations in breast composition and thickness. For the conventional images, the threshold visible diameter of the fibrils, microcalcifications, and low contrast discs, increased as the x-ray transmission of the phantom changed from that for which the film was optimally exposed. For the MSER images, the performance of the observers was almost independent of the background transmission of the object since MSER ensures that the film is optimally exposed for a large range of object transmission. Even with significant changes in object x-ray transmission, only minor changes in fibril, microcalcification, and disc detection were observed. Utilizing the results of the contrast-detail experiment, a dose efficiency comparison of conventional and MSER imaging techniques was performed. The dose efficiency analysis showed that MSER varied the incident exposure so as to maintain consistent performance of the observer, over the entire breast. These results suggest that MSER would improve the ability of radiologists to detect early breast cancer in women presenting with mammographically dense breasts, in a very dose efficient manner.