Contrast limited adaptive histogram equalization image processing to improve the detection of simulated spiculations in dense mammograms

The purpose of this project was to determine whether Contrast Limited Adapt ive Histogram Equalization (CLAHE) improves detection of simulated spiculat ions in dense mammograms. Lines simulating the appearance of spiculations, a common marker of malignancy when visualized with masses, were embedded in dense mammograms digitized at 50 micron pixels, 12 bits deep. Film images with no CLAHE applied were compared to film images with nine different comb inations of clip levels and region sizes applied. A simulated spiculation w as embedded in a background of dense breast tissue, with the orientation of the spiculation varied. The key variables involved in each trial included the orientation of the spiculation, contrast level of the spiculation and t he CLAHE settings applied to the image. Combining the 10 CLAHE conditions, 4 contrast levels and 4 orientations gave 160 combinations. The trials were constructed by pairing 160 combinations of key variables with 40 backgroun ds. Twenty student observers were asked to detect the orientation of the sp iculation in the image. There was a statistically significant improvement i n detection performance for spiculations with CLAHE over unenhanced images when the region size was set at 32 with a clip level of 2, and when the reg ion size was set at 32 with a clip level of 4. The selected CLAHE settings should be tested in the clinic with digital mammograms to determine whether detection of spiculations associated with masses detected at mammography c an be improved. Copyright (C) 1998 by W.B. Saunders Company.