| The article aims at constructing protective composite shields for breasts in chest computed tomography and investigating the effects of applying
these new bismuth composites on dose and image quality. Polyurethane and silicon with 5% of bismuth were fabricated as a protective shield.
At first, their efficiency in attenuating the X‑ray beam was investigated by calculating the total attenuation coefficients at diagnostic energy
range. Then, a physical chest phantom was scanned without and with these shields at tube voltage of 120 kVp, and image parameters together
with dose values were studied. The results showed that these two shields have great effects on attenuating the X‑ray beam, especially for
lower energies (<40 kV), and in average, the attenuation coefficients of bismuth‑polyurethane composite are higher in this energy range. The
maximum relative differences between the average Hounsfield units (HUs) and noises of images without and with shield for both composites
in 13 regions of interest were 4.5% and 15.7%, respectively. Moreover, primary investigation confirmed the ability of both shields (especially
polyurethane‑bismuth composite) in dose reduction. Comparing these two composites regarding the amount of dose reduction, the changes in
HU and noise, and attenuation coefficients in diagnostic energy range, it seems that polyurethane composite is more useful for dose reduction,
especially for higher tube voltages. |