Monte Carlo assessment of coded aperture tool for breast imaging: a Mura-mask case study

The main purpose of this work was to perform a rigorous computational study on scintimammography with a Mura-mask based on Monte Carlo simulation of voxelized breast phantoms. Three main objectives were addressed:(1) verification of Geant4 version 10.4,(2)optimization of the imaging setup, and(3) small tumor detection and localization. We successfully verified the Geant4-based imaging of a commonly used phantom in the field. We used a Mura-mask with a 41× 41 array pattern with adjustable thickness, material, and hole shape(box and cylinder);a low-energy high-resolution collimator with different hole shapes(cylinder and hexagon);and a voxelized breast phantom with different sizes(small, medium,and large) and glandularity percentages(low, medium, and high). We also compared the detector crystal outputs of CdZnTe and NaI(Tl). The simulation was followed by a deconvolution procedure, and the data(images) were statistically emphasized. Statistical metrics indicate that the Mura-mask(W material with 1.5 mm thickness and box holes) combined with a CdZnTe detector leads to the optimum point spread function. Finally, a preliminary study on small-sized tumor detection and localization was conducted with different tumor-to-background ratios(from2 to 12). Tumors with diameters of 5 and 8 mm could be detected, while those of 2 mm were undetectable. Nevertheless, this study enhances our understanding of the early detection of tumors in the field of scintimammography.

Photon energy absorption and exposure buildup factors for deep penetration in human tissues

Using photons in therapeutic and diagnostic medicine requires accurate computation of their attenuation coefficients in human tissues.The buildup factor,a multiplicative coefficient quantifying the ratio of scattered to primary photons,measures the degree of violation of the Beer-Lambert law.In this study,the gamma-ray isotropic point source buildup factors,specifically,the energy absorption buildup factor(EABF)and exposure buildup factor,are estimated.The computational methods used include the geometric progression fitting method and simulation using the Geant4(version 10.4)Monte Carlo simulation toolkit.The buildup factors of 30 human tissues were evaluated in an energy range of 0.015-15 MeV for penetration depths up to 100 mean free paths(mfp).At all penetration depths,it was observed that the EABF seems to be independent of the mfp at a photon energy of 1.5 MeV and also independent of the equivalent atomic number(Zeq)in the photon energy range of 1.5-15 MeV.However,the buildup factors were inversely proportional to Zeq for energies below 1.5 MeV.Moreover,the Geant4 simulations of the EABF of water were in agreement with the available standard data.(The deviations were less than 5%.)The buildup factors evaluated in the present study could be useful for controlling human exposure to radiation.

Investigation of SPECT/CT cardiac imaging using Geant4

The purpose of this paper is to propose a friendly computational framework able to investigate particles tracking through different compartments of the human being using dedicated numerical techniques.The main building blocks of this framework are:(i) convenient X-ray spectra calculator for different filter/anode combination,(ii) realistic voxelized computational human phantom,(iii)validated Geant4-based Monte Carlo simulation,and(iv)extendable and free image processing software.We studied the multimodality SPECT/CT cardiac imaging using specific spectrum of the ^(99m)Tc and 120 kVp X-ray beam,for internal and external exposure,respectively.The application of the framework to quantify the loss of information between combined and simultaneous coregistration was carried out.Two main objectives were addressed:(i) an ideal geometry was simulated for educational purposes(ii) a realistic case study was carried out,for research purposes,concerning the modeling of the GE Infinia II 3/800 Gamma Camera.We compared the effect of using a Na I(Tl) and CZT crystal detector,and a LEHR and MEGP collimator with different uptake values of the heart organ(1:1,5:1 and 50:1) for both simultaneous andcombined SPECT/CT images.We confirmed the usefulness of the Na I(Tl) crystal with the LEHR collimator for such kind of study.