SIMULATION OF SUBTLE LUNG NODULES IN PROJECTION CHEST RADIOGRAPHY

PURPOSE: To measure the radiologic characteristics of subtle lung nodu les and develop nodule phantoms that simulate these characteristics. M ATERIALS AND METHODS: From a database of chest radiographs, 16 radiogr aphs that showed confirmed subtle lung nodules were selected. The opti cal density values surrounding each nodule were obtained, and the radi ologic characteristics of the nodules were evaluated. A set of Teflon nodule phantoms with similar x-ray transmission and variability was de signed and fabricated. The contrast characteristics of the images of t he nodule phantoms were measured. RESULTS: Most of the subtle nodules appeared to have diffuse edges with Gaussian-like contrast profiles. T he contrast and size characteristics of the nodule phantom images fulf illed the design criteria within a 4% deviation. CONCLUSION: The radio logic pattern of subtle lung nodules is poorly simulated by nodule pha ntoms with simple spherical or disk shapes. The nodule phantoms in thi s study produce realistic radiographic patterns with an energy-depende nt attenuation equivalent to that of tissue. The nodule phantoms are i ntended for use in experiments involving human subjects.