Influence of breast characteristics in myocardial scintigraphy through the Monte Carlo method.

BACKGROUND By reducing the specificity associated with loss of information, the influence of attenuation of the breasts is very important in myocardial perfusion studies. However, although several studies have been conducted over the past years, little has been developed to determine accurately the influence of the characteristics of the breasts on the quality of myocardial scintigraphy, avoiding additional exposure to radiation. OBJECTIVE The purpose of this study is to quantify the attenuation of photons by the breasts, in myocardial perfusion studies with (99m)Tc according to different sizes and compositions. METHODS Each breast was assumed to be a cube composed of fibroglandular and adipose tissue. The data related to (99m)Tc photons were analyzed in a Monte Carlo model. We varied the thickness and composition of breasts and analyzed the interference in attenuation. The EGS 4 software was used in the simulations. RESULTS Setting the thickness of a breast, the variation of its composition causes a maximum increase of 2.3% in the number of photons attenuated. By contrast, maintaining a fixed composition of breast tissue, the difference in photon attenuation was 45.0%, averaging 6.0% for each additional centimeter in the breast thickness. CONCLUSION Monte Carlo simulation showed that the influence of the thickness of the breasts in the attenuation of photons in myocardial scintigraphy with (99m)Tc is much greater than the influence of their compositions.