Acceptable compression ratio of full-field digital mammography using JPEG 2000

Aim: To estimate the acceptable compression ratio of full-field digital mammography (FFDM) using the Joint Photographic Experts Group (JPEG) 2000 compression algorithm. Materials and methods: Eighty cases that included images of 40 masses (20 benign, 20 malignant) and 40 microcalcifications (20 benign, 20 malignant) were collected. The images were compressed to five different lossy ratios: 20:1, 40:1, 60:1, 80:1, and 100:1, and four radiologists independently determined whether the compressed group was distinguishable from the control group. The ratio of the compressed group that was rated indistinguishable from the control group was compared for each reviewer, and the results were analysed for agreements of three or more reviewers. Results: The ability to distinguish the compressed image from the control group is given as a range across the four reviewers: 0-1.3% (0/80 to 1/80) of the 20:1, 0-2.5% (0/80 to 2/80) of the 40:1, 5-7.5% (4/80 to 6/80) of the 60:1, 10-37.5% (8/80 to 30/80) of the 80:1, and 30-87.5% (24/80 to 70/80) of the 100:1. For three compression groups (20:1, 40:1, and 60:1), three or more reviewers agreed that there was a distinguishable difference for 0/80, 0/80, and 3/80 images, respectively. Thus, the compressed images do not differ significantly from the control group (p > 0.05). However, the 80:1 and 100:1 compressed images were different for 9/80 and 29/80 images, respectively, which is significantly different from the control group (p < 0.05). Conclusion: The lossy 60:1 compression ratio for FFDM is visually identical to the control image and, therefore, potentially acceptable for primary interpretation.