DETECTION OF SUBTLE ABNORMALITIES ON CHEST RADIOGRAPHS AFTER IRREVERSIBLE COMPRESSION

PURPOSE: To assess the effect of wavelet-based compression of posteroa nterior chest radiographs on detection of small uncalcified pulmonary nodules and fibrosis. MATERIALS AND METHODS: Computed tomography (CT) of the chest was used to identify 20 patients with normal posteroanter ior chest radiographs, 20 with a solitary uncalcified pulmonary nodule 1-2 cm in diameter, and 20 with fibrotic disease. A double-blind prot ocol for readings of original images and images compressed at 40:1 and 80:1 was analyzed by using the nonparametric receiver operating chara cteristic to measure differences in diagnostic accuracy and their stat istical significance. RESULTS: There was no substantial differences in the overall diagnostic accuracy (measured by the area under the curve index) for both nodules and fibrosis between images compressed at 40: 1 and 80:1 and uncompressed images. Readers tended to perform better o n images compressed at 40:1 compared with uncompressed images. The ''h igh-sensitivity'' portion of the 80:1 compression curve for nodules wa s below that for the uncompressed curve, although this was not statist ically significant. CONCLUSION: Lossy compression of chest radiographs at 40:1 can be used without decreased diagnostic accuracy for detecti on of pulmonary nodules and fibrosis. There is no statistically signif icant difference in diagnostic accuracy at 80:1 compression, but detec tion ability is decreased.