Optimized soft-copy display of digitized mammograms

Digitization and CRT display reduce sharpness of mammograms. To ensure image quality on a CRT, comparable to the quality of original films, a modified unsharp-masking (USM) algorithm is proposed to correct for this reduction. This study evaluates the clinical value of this algorithm and determines the optimal setting of its parameters. Eight complete mammographic cases were processed by a modified USM algorithm with 19 settings for three parameters, resulting in 152 stimuli. All cases showed a clearly visible mass; five also contained microcalcifications. The modification of the standard USM algorithm consisted of selectively improving low contrasts. Moreover, the USM enhancement was made grey value dependent to avoid clipping. Four experienced screening radiologists and four physicists (having experience with mammography imaging) rated all mammograms on a 1-10 point scale, according to image quality and suitability for diagnosis. The images were randomly presented. Before the experiment started, a subset of the images was shown to familiarize the observers to the range of images and parameter settings. For a contrast enhancement factor of about 0.4, the processed mammograms appeared to be significantly better than the original digitized mammograms (P<.001). Differences in the results for the radiologists and the physicists were small.