FREQUENCY-FILTERED IMAGE POST-PROCESSING OF DIGITAL LUMINESCENCE RADIOGRAPHS IN PULMONARY NODULE IMAGING

Aim: The aim of the study was to optimize unsharp masking image post-p rocessing of digital luminescence radiographs (DLR) for the representa tion of pulmonary nodules, and to compare DLR to screen-film radiograp hy at two dose levels. Patients and methods: A total of 284 CT-validat ed pulmonary nodules were evaluated. One hundred and forty-nine nodule s were exposed with a 200-speed screen-film combination (SFC) and 135 nodules with a 400-speed SFC, with correspondingly exposed storage pho sphor images. The kernal size in digital post-processing using 'unshar p masking' was varied between S 10 (2.83 mm) and S 70 (19.80 mm). A to tal of 11928 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-a-vis the 400-speed SFC improved significantly (P < 0.05). Smaller filter kernels (S 10; S 20) producing edge-enhance ment processing were significantly inferior to the analog image techni que in both dose ranges (P < 0.05). Conclusions: At speed class 200, l ow-frequency emphasizing digital image post-processing with large filt er kernels are significantly superior to high-frequency emphasizing fi ltrations for the recognition of pulmonary nodules, In the lower dose range DLR with large filter kernel unsharp masking processing showed s ignificantly improved image quality compared to 400 speed SFC for the detection of pulmonary nodules.