Evaluation of optical unsharp masking and contrast enhancement of low-scatter chest radiographs

Conventional chest radiography poses a challenging technical problem because of its requirement for simultaneous high-contrast display and wide-latitude recording across the entire image. We developed and evaluated a method of producing chest radiographs by using a tantalum air-interspace grid for highly efficient scatter rejection, wide-latitude X-ray film for recording the low-scatter image, and a LogEtronics printer for optical unsharp masking and contrast enhancement of the recorded image (TWL technique). TWL images can be readily obtained and have excellent contrast and detail across the entire image. In comparison with a conventional technique, the TWL technique provides about a 15% improvement in image contrast in well-penetrated areas and a threefold to tenfold improvement in poorly penetrated areas. A detection study using simulated lung nodules and a chest phantom showed about 10% overall improvement in nodule detection with the TWL technique (51% vs 42%), most of which was due to improvement in detection rates in poorly penetrated areas of the chest (62% vs 26%). In well-penetrated areas, there was a decrease in detection rates (52% vs 44%) using TWL images despite measured improvements in image contrast in these areas. Possibly this was due to the observers' unfamiliarity with the reversed-contrast TWL images. Our results show the TWL technique to be valuable for improving image quality and diagnostic accuracy in chest radiography.
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