Frequency-filtered image post-processing of digital luminescence radiographs in pulmonary nodule imaging

Abstract

Aim: The aim of the study was to optimize unsharp masking image post-processing of digital luminescence radiographs (DLR) for the representation of pulmonary nodules, and to compare DLR to screen-film radiography at two dose levels. Patients and methods: A total of 284 CT-validated pulmonary nodules were evaluated. One hundred and forty-nine nodules were exposed with a 200-speed screen-film combination (SFC) and 135 nodules with a 400-speed SFC, with correspondingly exposed storage phosphor images. The kernal size in digital post-processing using ‘unsharp masking’ was varied between S 10 (2.83mm) and S 70 (19.80mm). A total of 11 928 individual assessments were obtained from six independent observers and evaluated in multifactorial variance analyses. Results: The large filter kernels of S 40 and S 70 were on a par with the 200-speed SFC ( P > 0.05). As the exposure dose was reduced, the quality of the digital image vis-à-vis the 400-speed SFC improved significantly ( P < 0.05). Smaller filter kernels (S 10; S 20) producing edge-enhancement processing were significantly inferior to the analog image technique in both dose ranges ( P < 0.05). Conclusions: At speed class 200, low-frequency emphasizing digital image post-processing with large filter kernels are significantly superior to high-frequency emphasizing filtrations for the recognition of pulmonary nodules. In the lower dose range DLR with large filter kernel unsharp masking processing showed significantly improved image quality compared to 400 speed SFC for the detection of pulmonary nodules.