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The purpose of this study was to quantitatively evaluate the compression ratios using JPEG2000 on CR images. The high compression ratios for large size images may be needed for efficient and economic data transfer within a digital environment. CR chest images of 11 patients with abnormal lesions and 13 patients without abnormal lesions were obtained using FUJI CR system and were converted into portable graymap (PGM) and bitmap (BMP) file format by Analyze software prior to compression. JPEG 2000 compression algorithms were JJ2000 and Jasper. The compression ratios applied to all images were from
10:1 to 100:1 with every increment of 5. The compressed images were quantitatively evaluated by computing peak signal-to-noise ratio and by scoring lesion detect ability by radiologists. The criteria for scoring lesion detect ability of compressed images were 5 levels: 5=lesion is certainly present, 4=lesion is probably present, 3=equivocal, 2=lesion is probably not present, 1=lesion is certainly not present.
The results of PSNR were 44dB for 10:1 ratio, 42dB for 20:1 ratios, 41dB for 40:1, 40dB for 100:1, which may be acceptable ranges. The average scores of lesion detect ability for abnormal data and normal data were 4.3 and 1.4, respectively. The result showed that the CR chest images of 1760 x 2140 resolution may be compressed as much as 100:1 without affecting clinical diagnostic performance. The JPEG2000 compression technique to be adopted for DICOM 3.0 was appeared to be used for very high compression ratios, which will be resulting in efficient transfer and economic storage.