A comparison between the electronic magnification (EM) and true magnification (TM) of breast phantom images using a CDMAM phantom

Purpose

To provide a comparison between the image quality of electronically magnified (EM) and geometric, or true, magnification (TM) mammographic images.

Materials and methods

One Computed Radiography (CR), one Digital Radiography (DR) and two screen–film (S–F) imaging systems were investigated. A Contrast-Detail Mammography (CDMAM) phantom was used as a test object. Three contact images and three sets of TM images with a magnification factor of 1.8 were taken on all systems. Software was used to zoom the contact images by a factor of 1.8 to produce EM images. Two observers evaluated all of the images. An Image Quality Figure and contrast detail curve were used to analyze the observer data and Mann–Whitney U-tests were performed to determine the statistical significance of the results.

Results

No significant differences were found between soft copy and hard copy for any imaging modality. No significant difference in contrast detail detectability (CDD) was seen between EM images from the two digital systems and TM images on S–F systems. The results for the DR EM images and S–F TM images also showed no differences. The CDD of DR TM images was significantly better than both EM and S–F TM images.

Conclusion

Digitally zoomed images offer the same level of CDD as S–F TM images, and so may be viably used in their place. DR systems offer greater CDD than conventional S–F images, when comparing the TM images. This implies that doses can be greatly reduced for TM views using DR systems, while maintaining acceptable image quality.