Search Results (2)

This study aims to obtain uniform and homogeneous bismuth germanate oxides thin films by spin coating and using the sol-gel technique with different precursors, followed by low-temperature annealing at 560 °C. By using Bi(NO₃)₃ precursors, we have obtained transparent, yellowish thin films with a 200 nm thickness. The structural analysis of the initial sol-gel powder has shown the presence of two crystalline structures, the cubic Bi₄Ge₃O₁₂ (BGO) and monoclinic Bi₂GeO₅ crystallites, which evolves towards the BGO structure after annealing. The elemental analysis confirmed the composition of the desired compound Bi₄Ge₃O₁₂ with 60 wt % GeO₂ and 40 wt % Bi₂O₅. On the other hand, by changing the precursor to (Bi(CH₃COO)₂, the film thickness increased to 500 nm thicker due to the high viscosity of the sol, and a dominant monoclinic Bi₂GeO₅ crystalline structure appeared. The elemental analysis revealed a nonstoichiometric composition with 38 wt % GeO₂ and 62 wt % Bi₂O₃. Due to the low GeO₂ phase content that reacted with metastable Bi₂GeO₅, we obtained cubic Bi₄Ge₃O₁₂ as a secondary phase, with Bi₂GeO₅ as a dominant crystalline phase. The redshifts of both absorptions and emissions spectra peaks confirmed a different disorder structure as an interplay between the cubic Bi₄Ge₃O₁₂ (BGO) and monoclinic Bi₂GeO₅ phases. Full article

Background: The aim of the present study was to assess the upper information content bound of positron emission tomography (PET) images, by means of the information capacity (IC). Methods: The Geant4 Application for the Tomographic Emission (GATE) Monte Carlo (MC) package was used, and reconstructed images were obtained by using the software for tomographic image reconstruction (STIR). The case study for the assessment of the information content was the General Electric (GE) Discovery-ST PET scanner. A thin-film plane source aluminum (Al) foil, coated with a thin layer of silica and with a 18F-fludeoxyglucose (FDG) bath distribution of 1 MBq was used. The influence of the (a) maximum likelihood estimation-ordered subsets-maximum a posteriori probability-one step late (MLE-OS-MAP-OSL) algorithm, using various subsets (1 to 21) and iterations (1 to 20) and (b) different scintillating crystals on PET scanner’s performance, was examined. The study was focused on the noise equivalent quanta (NEQ) and on the single index IC. Images of configurations by using different crystals were obtained after the commonly used 2-dimensional filtered back projection (FBP2D), 3-dimensional filtered back projection re-projection (FPB3DRP) and the (MLE)-OS-MAP-OSL algorithms. Results: Results shown that the images obtained with one subset and various iterations provided maximum NEQ values, however with a steep drop-off after 0.045 cycles/mm. The single index IC data were maximized for the range of 8–20 iterations and three subsets. The PET scanner configuration incorporating lutetium orthoaluminate perovskite (LuAP) crystals provided the highest NEQ values in 2D FBP for spatial frequencies higher than 0.028 cycles/mm. Bismuth germanium oxide (BGO) shows clear dominance against all other examined crystals across the spatial frequency range, in both 3D FBP and OS-MAP-OSL. The particular PET scanner provided optimum IC values using FBP3DRP and BGO crystals (2.4829 bits/mm²). Conclusions: The upper bound of the image information content of PET scanners can be fully characterized and further improved by investigating the imaging chain components through MC methods. Full article