Evaluation of Compton scattering sequence reconstruction algorithms for a portable position sensitive radioactivity detector based on pixelated Cd(Zn)Te crystals

We present extensive simulation studies on the performance of algorithms for the Compton sequence reconstruction used for the development of a portable spectroscopic instrument (COCAE), with the capability to localize and identify radioactive sources, by exploiting the Compton scattering imaging. Various Compton Sequence reconstruction algorithms have been compared using a large number of simulated events. These algorithms are based on Compton kinematics, as well as on statistical test criteria that exploit the redundant information of events having two or more photon interactions in the active detector's volume. The efficiency of the best performing technique is estimated for a wide range of incident gamma-ray photons emitted from point-like gamma sources.Comment: 16 pages, 17 figure

Simulated Performance Of Algorithms For The Localization Of Radioactive Sources From A Position Sensitive Radiation Detecting System (COCAE)

Simulation studies are presented regarding the performance of algorithms that localize point-like radioactive sources detected by a position sensitive portable radiation instrument (COCAE). The source direction is estimated by using the List Mode Maximum Likelihood Expectation Maximization (LM-ML-EM) imaging algorithm. Furthermore, the source-to-detector distance is evaluated by three different algorithms based on the photo-peak count information of each detecting layer, on the quality of the reconstructed source image as well as on the triangulation method. These algorithms have been tested on a large number of simulated photons in a wide energy range (from 200keV up to 2MeV) emitted by point-like radioactive sources located at different orientation and source-to-detector distances.Comment: 8 pages, 7 figures, 11th International Conference on Applications of Nuclear Techniques, Crete, Greece, June 12-18, 201

Signal to Noise Ratio optimization for extended sources with a new kind of MURA masks

Using coded aperture, for localization of radioactive hot-spots, results in enhanced efficiency and under certain configurations wide Field of View (FOV). We present a coded aperture assembly technique which can be restructured easily, as well as the reduction of the intrinsic noise of coded apertures constructed with this technique, when they localize spatially extended γ-emitters. Specifically, Modified-Uniformly-Redundant-Array (MURA) coded apertures are structured by embedding lead spheres in a matrix of positions machined inside a transparent medium such as acrylic glass, resulting in an advantageous transparent to opaque area ratio and thus an improved detection efficiency. This configuration also induces a systematic, element-wise, noise on the Point-Spread-Function (PSF) of the correlation matrix. When imaging with these apertures extended hot-spots, a penumbra phenomenon occurrs and reduces this intrinsic noise, in the way a kernel filter does. Fast-Fourier-Transform (FFT) is used to analyze the effect of this phenomenon on the correlation matrix and to explain the maximization of its Signal-to-Noise Ratio (SNR) for certain extent of the hot-spots. Simulations have been used for the detailed study of the SNR dependence on the dimensions of the hot-spot, while experiments with two 99mTc cylindrical sources with 11 mm and 24 mm diameter, respectively and 1.5 MBq activity each, confirm the reduction of the intrinsic noise. The results define the way of optimization of the imaging setup for the detection of extended hot-spots. Such an optimization could be useful for example in the case of lymph nodes or thyroid remnant imaging in nuclear medicine. Finally, we propose a kernel filter, derived by the Auto-Correlation-Function (ACF), to be applied on PSFs with high intrinsic noise, in order to eliminate it. © 2020 IOP Publishing Ltd and Sissa Medialab

Radiological safety and assessment of the performance of X-ray systems in veterinary facilities

This paper concerns an analysis regarding the performance of X-ray equipment as well as the radiological safety in veterinary facilities. Data were collected from 380 X-ray veterinary facilities countrywide during the on-site regulatory inspections carried out by the Greek Atomic Energy Commission. The analysis of the results shows that the majority of the veterinary radiographic systems perform within the acceptable limits; moreover, the design and shielding of X-ray rooms as well as the applied procedures ensure a high level of radiological safety for the practitioners, operators and the members of the public. An issue that requires specific attention in the optimization process for the proper implementation of veterinary radiology practices in terms of radiological safety is the continuous training of the personnel. The above findings and the regulatory experience gained were valuable decision-making elements regarding the type of the regulatory control of veterinary radiology practices in the new radiation protection framework