Filter wheel equalization in chest radiography: Demonstration with a prototype system

PURPOSE: To determine the feasibility of using the filter wheel equalization (FWE) technique for radiographic equalization in chest radiography. MATERIALS AND METHODS: An FWE system with two rotating wheels (one for each lung) with 25 lung-shaped, 1.0-mm-thick copper templates was constructed, Preexposure images were acquired; the computer used these images to select and position templates for each lung. An equalized radiograph was then produced. Radiographs were acquired in two male volunteers (both 33 years of age) and in a phantom. RESULTS: Optical densities in the lungs and nonlung areas on a conventional phantom radiograph were 2.07 and 0.55, respectively; after equalization, the corresponding optical densities were 2.06 and 1.42. Outside the lungs, radiographic contrast (difference in optical density) increased threefold; in the lungs, there was a very small decrease in radiographic contrast due to beam hardening. Well-equalized and relatively artifact-free radiographs were obtained with a 20-msec exposure time. CONCLUSION: The FWE system was shown in the laboratory to be feasible.