Dual-energy digital radiographic quantification of calcium in simulated pulmonary nodules

The presence or absence of calcium in solitary pulmonary nodules may indicate whether a nodule is benign or malignant. Because current techniques for measuring the amount of calcium in these nodules are unsatisfactory, a study was carried out to assess the capability of dual-energy digital chest radiography to identify and quantify the calcium content of simulated pulmonary nodules of known calcium content. Measurements were carried out on 280 nodules of various sizes and calcium content that were placed within the lungs of a frozen human-chest phantom. A new calcium quantification technique that uses a parallelogram was developed to eliminate the problem of nodule superimposition over ribs. Nodules containing more than 35 mg of calcium per square centimeter (i.e., 7, 30, 60, and 110 mg of calcium for spherical nodules 0.5, 1.0, 1.5, and 2.0 cm in diameter) were measured with a high degree of accuracy and reasonable precision. Dual-energy digital radiography is a simple and accurate method of measuring the calcium content of solitary pulmonary nodules in humans.