Dual energy film subtraction technique for detecting calcification in solitary pulmonary nodules.

Abstract

A simple film subtraction technique was devised that isolates Ca image contrast and mutes tissue image contrast. Two exposures are required. The first is made on XL film using a 65 kVp [kilovolt potential] beam filtered with 2 mm Al. The 2nd is made on OG (high contrast) film using a 130 kVp beam filtered with 2 mm Cu and 2 mm Al. The effective energies of these 2 beams are .apprx. 45 and 83 keV, respectively. A subtraction image is made, using the low energy image for the mask. With this technique it is possible to detect concentrations of 125 mg/cm3 of diffuse calcification in a chest nodule 1 cm in diameter. If the presence of diffuse calcification is an indicator of benignancy in solitary pulmonary nodules, this technique may have diagnostic value for the detection of such calcification. Computerized tomographic findings are discussed and related to this technique.