Evaluation of scatter-to-primary ratio, grid performance and normalized average glandular dose in mammography by Monte Carlo simulation including interference and energy broadening effects

Abstract

In this work, a computational code for the study of imaging systems and dosimetry in conventional and digital mammography through Monte Carlo simulations is described. The developed code includes interference and Doppler energy broadening for simulation of elastic and inelastic photon scattering, respectively. The code estimates the contribution of scattered radiation to image quality through the spatial distribution of the scatter-to-primary ratio (S/P). It allows the inclusion of different designs of anti-scatter grids (linear or cellular), for evaluation of contrast improvement factor (CIF), Bucky factor (BF) and signal difference-to-noise ratio improvement factor (SIF). It also allows the computation of the normalized average glandular dose, D(g).(N). These quantities were studied for different breast thicknesses and compositions, anode/filter combinations and tube potentials. Results showed that the S/P increases linearly with breast thickness, varying slightly with breast composition or the spectrum used. Evaluation of grid performance showed that the cellular grid provides the highest CIF with smaller BF. The SIF was also greater for the cellular grid, although both grids showed SIF < 1 for thin breasts. Results for D(g).(N) showed that it increases with the half-value layer (HVL) of the spectrum, decreases considerably with breast thickness and has a small dependence on the anode/filter combination. Inclusion of interference effects of breast tissues affected the values of S/P obtained with the grid up to 25%, while the energy broadening effect produced smaller variations on the evaluated quantities.

Monte Carlo study of the effects of system geometry and antiscatter grids on cone‐beam CT scatter distributions

“…IAA is commonly assumed in MC simulations of x-ray transport, but it neglects interference effects in the Rayleigh form factor, 72 which can lead to overestimation of the intensity of coherent scatter, especially at lower x-ray energies. [73][74][75] To obtain initial insight into the possible effect of such IAA bias on our results, a series of preliminary simulations was carried out. The interference effects were included in the Rayleigh form factor following Refs.…”

Simulação de mamografia digital por dupla energia para imagens quantitativas

“…O modelo mais simples para a determinação daD g em mamografia, relaciona esta grandeza com a medida do kerma de entrada na mama, utilizando apenas um parâmetro, conforme mostrado na equação a seguir [52,55,56,57]:…”

“…A figura 4.2 mostra os resultados obtidos para o estudo da razão espalhado-primário, levando em consideração a energia total transmitida dos feixes primário e espalhado, SP R e , para um feixe polienergético de 28 kVp em função da espessura da mama e comparado com os resultados obtidos por Cunha [57].…”

“…Os resultados de DgN em função da espessura da mama, utilizando um feixe polienergético de 28 kVp(Mo/Mo), são mostrados na figura 4.4, juntamente aos resultados obtidos por Cunha [57] e Boone [56]. A figura mostra uma boa aproximação entre os resultados obtidos e as referências, estando abaixo dos 2% em ambos os casos.…”

Desenvolvimento e aplicação de um sistema de raios X dispersivo em energia para determinação do coeficiente de atenuação linear e do perfil de espalhamento de neoplasias mamárias

“…Este fato ocorre principalmente, devido à pequena diferença nas propriedades de atenuação dos tecidos mamários e à ocorrência de efeitos de espalhamento (inelástico e elástico), fatores esses que degradam o contraste da imagem, diminuindo a eficácia de detecção desse exame (Koch et al 1996;Barnes, 1991, Poletti, 1997. No intervalo de energia usado em mamografia, 50% da radiação transmitida pela mama é devido aos fótons espalhados (Cunha et al 2010). Dessa forma, surgiram muitos estudos a respeito das propriedades de atenuação e espalhamento dos tecidos humanos.…”