New articles published in 12(3) and 12(3A)
Abstract:
Introduction: PET/CT and PET/MRI are valuable multimodality imaging techniques for visualizing both functional and anatomical information. The most used PET reconstruction algorithm is Ordered Subset Expectation Maximization (OSEM). In OSEM, the image noise increases with increased number of iterations, and the reconstruction needs to be stopped before complete convergence. The Bayesian penalized likelihood (BPL) algorithm, recently introduced, uses a noise penalty factor (β) to achieve full convergence while controlling noise. This study aims to evaluate how reconstruction algorithms and lesion radioactivity levels affect PET image quality and quantitative accuracy across three different PET systems. Materials and Methods: A NEMA phantom was filled with 18F and scanned by one PET/MRI and two PET/CT systems with sphere-to-background concentration ratio (SBR) of 2:1, 4:1, or 10:1. PET images were reconstructed with OSEM or BPL with TOF. The number of iterations and β-values were varied, while the matrix size, number of subsets, and filter size remained constant. Contrast recovery (CR) and background variability (BV) were measured in images. Results: CR increased with increased sphere size and SBR. CR and BV decreased with increased β for the 10mm sphere. Increased number of iterations in OSEM showed increased BV with limited variation in CR. BPL gave higher CR and lower BV values than OSEM. The optimal reconstruction was BPL with β between 150 and 350, where BPL was available, and OSEM with two iterations and 21 subsets for the PET/CT without BPL. Conclusion: BPL outperforms OSEM, and SBR significantly influences tracer uptake quantification in small lesions. Future studies should explore the clinical implications of these findings on diagnosis, staging, prognosis, and treatment follow-up.
12(3): Decommissioning and demolition of a dicalcium phosphate plant: aspects of radiological protection and safety
Abstract:
The detection of ionising radiation in materials from the decommissioning of a dicalcium phosphate plant meant that this whole operation had to be overhauled in terms of radiological protection and safety. Thus, an operations plan was drawn up that included: initial training for all workers involved, measurements of dose rates and a set of analyses by gamma and alpha spectrometry. Samples of "dry sludge" and debris were analysed for the identification and quantification of the radionuclides present, samples of workers' urine were analysed for the detection of any internal contamination, samples of washing water and air filters were analysed for the detection and control of any radioactive atmospheric contamination. In addition, individual dosimeters were distributed to workers. The extent of contamination was identified and the areas where higher values were detected were properly marked. From the results obtained (radiation dose rates and activity concentrations), it was possible to establish categories and separate the contaminated materials according to their physical characteristics. After the plant decommissioning, the resulting waste with dose rates higher than the effective dose limits for the public was packed in big bags. These bags were divided in 3 groups according to the external radiation dose rates at contact. This segregation allowed the competent authority to release a significant number of big bags from regulatory control. The remaining big bags are stored in two metal containers subject to regular radiological monitoring. The objective of this work is the presentation of a factual article where the methodology implemented to deal with this situation, which had never occurred in Portugal, is described, having only the Portuguese legislation as a reference.
12(3): Decommissioning and demolition of a dicalcium phosphate plant: aspects of radiological protection and safety
Abstract:
The mine decommissioning process is associated to the mitigation of environmental impacts and recovery of degraded areas during the useful life of the unit. In the case of uranium mining, aspects concerning environmental radioprotection are necessary, thus avoiding increased human exposure to radiation and undesirable effects on the ecosystem. In order to adequately treat impacted areas, the possible form of management for environmental remediation will depend on the conditions of the particular mine. In the case of the Caldas Decommissioning Unit (UDC), mine acidity is a relevant issue, and the control of chemical elements in order to maintain the parameters defined by legislation must be continuously observed. Aiming to study strategic elements for the treatment of acid drainage water in the Caldas region, simulated solutions prepared in the laboratory, composed of Fe, Al and Mn, were proposed. It was possible to prepare a mixed solution with a concentration of these elements close to that found in the UDC, and representative of the acidity condition of the mine. The removal of elements by adsorption was also evaluated separately and together, verifying the influence of ions on the process. It was observed that the adsorbent material (RT) has a high adsorption power for iron, the ability to also adsorb manganese in concentrations close to those found in UDC, being influenced by the high aluminum content, which reduces its removal efficiency due to previous saturation. However, even in this case, the effectiveness of RT in treating acidic drainage waters is still evident, which can be enhanced by the combination of treatment methods. The study presented is especially relevant due to the conduct of activities that are representative of a real solution, but carried out in a controlled and simplified environment.
