The physical basis of application of positron emission tomography and modern radiopharms

This article provides a review of the literature on the history, physical and technical foundations and features of the application of positron emission tomography (PET), which came into practice in the 1970s. PET is a method of visualizing the space-time distribution of a positron-emitting radiopharmaceutical (RP) in the patient‘s body by annihilation radiation. The classification of radiopharmaceuticals that are used in clinical and diagnostic practice is considered.

Baryonic effects on the detectability of annihilation radiation from dark matter subhaloes around the Milky Way

We use six, high-resolution ΛCDM simulations of galaxy formation to study how emission from dark matter annihilation is affected by baryonic processes. These simulations produce isolated, disc-dominated galaxies with structure, stellar populations, and stellar and halo masses comparable to those of the Milky Way. They resolve dark matter structures with mass above ∼106 $\rm M_{\odot }$ and are each available in both full-physics and dark-matter-only versions. In the full-physics case, formation of the stellar galaxy enhances annihilation radiation from the dominant smooth component of the galactic halo by a factor of three, and its central concentration increases substantially. In contrast, subhalo fluxes are reduced by almost an order of magnitude, partly because of changes in internal structure, partly because of increased tidal effects; they drop relative to the flux from the smooth halo by 1.5 orders of magnitude. The expected flux from the brightest Milky Way subhalo is four orders of magnitude below that from the smooth halo, making it very unlikely that any subhalo will be detected before robust detection of the inner Galaxy. We use recent simulations of halo structure across the full ΛCDM mass range to extrapolate to the smallest (Earth-mass) subhaloes, concluding, in contrast to earlier work, that the total annihilation flux from Milky Way subhaloes will be less than that from the smooth halo, as viewed both from the Sun and by a distant observer. Fermi-LAT may marginally resolve annihilation radiation from the very brightest subhaloes, which, typically, will contain stars.

Evaluation of the shielding parameters implemented in the PET-CT facility at the National Institute of Nuclear Medicine & Allied Sciences (NINMAS), Dhaka

Positron Emission Tomography (PET) combined with Computed Tomography (CT) is a very sensitive diagnostic imaging modality that consists of both functional and anatomical imaging into one combined scanning system. Because of the high energy of annihilation radiation (511 keV) for PET tracers, shielding requirements are an important consideration in the design of a PET/CT facility. The shielding evaluation for adequate radiation protection of a PET/CT facility consists of the assessment of annual effective dose both to occupational workers and to members of the public’s. The overall shielding assessment takes into account the radionuclides activity involved, the facility design, the scanning procedures, the expected number of patients per year and so on. The evaluation also depends upon the size of the PET/CT imaging room and patient’s uptake rooms, the thickness and the physical materials of walls, floors and ceilings. In this work we verified the adequacy of shielding installed in the PET/CT facility at the National Institute of Nuclear Medicine & Allied Sciences (NINMAS), Dhaka. The assessment results were compared to the provided shielding which was the design requirements. Bangladesh Journal of Physics, 26(2), 51-59, December 2019

Crystallization pathways, morphologies and structural defects of α-MnO2 nanomaterial synthesized under annealed temperatures

Manganese dioxide, in particular α-MnO2, is one of the advanced inorganic nanomaterials having wide applications in many areas. Hence, understanding the crystallization pathways, morphologies, and formation mechanism of defects in its structure is of particular importance, not only for fundamental science but also for practical applications. Herein, different physically and chemically based methods, such as Neutron Diffraction (ND), XRD, SEM, TPR- H2, TGA-DSC, FT-IR, Positron Annihilation Lifetime (PAL), Doppler Broadening (DB) of positron annihilation radiation, and Electron-Momentum Distribution (EMD) measurements combined with theoretical calculations, were utilized to systematically investigate the composition, structure, and morphology of α-MnO2 nanomaterial under different annealed temperatures. The investigated material was synthesized at room temperature using a facile chemical method with potassium permanganate (KMnO4) and ethanol (C2H5OH), prior to being treated by temperatures of 100 oC – 800 oC. Results demonstrated, for the first time, that the α-MnO2 nucleation can be formed even at room temperature and gradually developed to α-MnO2 nanorods at 600 oC. This novel finding, which cannot be explored by conventional XRD, was confirmed by ND analysis. In addition, PAL analysis combined with theoretical ab initio calculations indicated the existence of H+ ions in the tunnel [1x1] of α-MnO2. At the same time, DB and EMD measurements explored the presence of Mn and O vacancies in α-MnO2 crystals at low temperatures. Finally, the present study reported a remarkable finding that organic molecules may act as reactants as well as templates, which are entirely decomposed and disappeared at highly annealed temperatures.

Estimating the Shielding Requirements for a Newly Planned PET-CT Facility

Positron Emission Tomography (PET) combined with Computed Tomography (CT) is a powerful and very sensitive diagnostic tool that integrates functional and anatomical imaging into one combined scanning system. Positron emission tomography is based on the characteristic way in which positrons annihilate by combining with an electron. This process usually results in the emission of two 511 KeV photons which travel in opposite directions. These 511 KeV annihilation photons are much higher energy than other diagnostic radiations. Because of this high energy of the annihilation radiation, shielding requirements for a PET facility are different from most of the other diagnostic imaging facilities and it’s a very important consideration in the design of a PET or PET-CT imaging facility. As a result, significant shielding may be required in floors and ceilings as well as adjacent walls in a PET-CT facility. In this work we present the estimation of the shielding requirements for a newly planned PET-CT facility. Shielding calculations of adjacent walls were presented for both controlled and uncontrolled areas. Formulas were used to calculate the shielding materials following the basic AAPM (American Association of Physicists in Medicine) guidelines. This mathematical analysis of the shielding estimation is very important for a newly planned PET-CT facility. Adequate safe planning with vendor, facility architect and a qualified medical physicist are essential to make a cost effective and safe design while maintaining radiation safety standards with regulatory limits. Bangladesh J. Nuclear Med. 21(2): 102-107, July 2018