Radiology, Vol 140, 213-219, Copyright © 1981 by Radiological Society of North America
Dual energy film subtraction technique for detecting calcification in solitary pulmonary nodules
RA Kruger, JD Armstrong, JA Sorenson and LT Niklason
A simple film subtraction technique has been devised that isolates calcium
image contrast and mutes tissue image contrast. Two exposures are required.
The first is made on XL film using a 65 kVp beam filtered with 2 mm
aluminum. The second is made on OG (high contrast) film using a 130 kVp
beam filtered with 2 mm copper and 2 mm aluminum. The effective energies of
these two beams are approximately 45 keV 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 found to be 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.
