COMPARISON OF 3 TISSUE COMPOSITION MEASUREMENT TECHNIQUES USING DIGITAL MAMMOGRAMS - A SIGNAL-TO-NOISE STUDY

Tissue composition measurement may provide a quantitatively and physic ally meaningful method to objectively determine the ''mammographic den sity'' linked to breast cancer risk. A single energy hybrid (SEH) tech nique is described for measuring the tissue composition on a pixel-by- pixel basis with a single digital mammogram. Theoretical models were d erived and used to compute signal-to-noise ratios (SNRs) in tissue com position measurement using the SEH method. The results were compared w ith those computed for measurements using the dual kVp and dual screen methods. SNRs were theoretically related to the pixel area, total una ttenuated detector exposure and fluence spectra of the incident X-rays . SNRs were computed for measurement of the adipose tissue thickness f or a 6 cm thick breast, consisting of 50% of adipose tissue and 50% of glandular tissue. Effects of kVp and prepatient filtration were studi ed by computing the SNRs for various kVps and filters and optimal kVps and filters are determined. The results showed that the SNRs obtained with the SEH method is an order of magnitude better than the dual kVp method, which, in turn, is an order of magnitude better than the dual screen method. When using the optimal kVp's and no prepatient filtrat ion, the SNRs were computed to be 84.2, 13.2, and 2.0 for the SEH, dua l kVp, and dual screen methods, respectively. Prepatient filtration ca n improve the SNR by as much as 35% for the dual kVp and dual screen t echniques with reasonable tube loading factors(8-10). Copyright (C) 19 98 by W.B. Saunders Company.