title: Filter wheel equalization in chest radiography: demonstration with a prototype system.
abstract: OBJECTIVE
  To determine the feasibility of using the filter wheel equalization (FWE) technique for radiographic equalization in chest radiography.
  
  
  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.
  
  
  CONCLUSIONS
  The FWE system was shown in the laboratory to be feasible.
authors.affiliation: Department of Radiology, University of California, Davis 95817, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Boone
authors.forename: J
authors.initials: J
authors.lastname: Duryea
authors.forename: E H
authors.initials: EH
authors.lastname: Moore
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D003201:Computers; D003300:Copper; D003964:Diaphragm / Q000000981:diagnostic imaging; D004867:Equipment Design; D005240:Feasibility Studies; D005374:Filtration / Q000295:instrumentation / Q000379:methods; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008297:Male; D008482:Mediastinum / Q000000981:diagnostic imaging; D008961:Models, Structural; D055095:Optics and Photonics; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000295:instrumentation / Q000379:methods*; D013902:Radiography, Thoracic / Q000295:instrumentation / Q000379:methods*; D012272:Ribs / Q000000981:diagnostic imaging; D013997:Time Factors; D014963:X-Ray Intensifying Screens
chemical_list: D003300:Copper