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X-ray Interactions in Matter
Published in Ken Holmes, Marcus Elkington, Phil Harris, Clark's Essential Physics in Imaging for Radiographers, 2021
This process does not occur in diagnostic X-ray beams. The process only occurs with a photon energy of 1.02 MeV and above. The photon interacts with the nucleus of an atom and produces a positron and an electron. Positron annihilation is the basis of positron emission tomography (PET) scanning.
Effective Brain Computer Interface Based on the Adaptive-Rate Processing and Classification of Motor Imagery Tasks
Published in Mridu Sahu, G. R. Sinha, Brain and Behavior Computing, 2021
Saeed Mian Qaisar, Reem Ramadan, Humaira Nisar
The EEG is a test used to detect the electrical waves of the brain by sending the electrical impulses absorbed via the transducing electrodes. These electrodes are commonly placed on the scalp of the head via a headset; however, there are other methods which can be partially or fully invasive through surgery implants of such electrodes inside the human skull. The reason why other tests are not as popular as the EEG is due to their high sensitivity to the surrounding environment, lack of portability, bulkiness in size, as well as their high cost. Additionally, the EEG allows one to explore the electrical activity of the brain directly. It rapidly diagnoses any abnormalities in the functionality of the cerebral system. This feature is not available in the blood flow estimation based techniques. Positron emission tomography measures metabolic activities. These are implicit pieces of information about the electrical activity of the brain and can result in a relatively slower identification of changes in the neural activity of the brain in contrast to the EEG-based approach.
Positron Emission Tomography
Published in George C. Kagadis, Nancy L. Ford, Dimitrios N. Karnabatidis, George K. Loudos, Handbook of Small Animal Imaging, 2018
Positron emission is a nuclear decay process with three decay products (daughter nucleus, positron, and neutrino), which allows the positron (antimatter equivalent of the electron) to be emitted with a range of possible energies. After emission, the positron travels through its surrounding medium undergoing a series of collisions with nearby electrons; these collisions change the direction of the positron and decelerate it, until the positron has lost sufficient energy for a positron–electron annihilation to take place (Figure 8.1). The annihilation process produces a pair of 511 keV annihilation photons that travel in almost opposite directions. The distance (range) traveled by the positron prior to its annihilation depends on the material density and its effective atomic number and on the positron’s initial kinetic energy, which is radionuclide dependent (Levin and Hoffman 1999). As an example, among all useful positron emitters, 18F nuclei emit positrons with the smallest initial maximum kinetic energy of 0.63 MeV resulting into a range of less than 1 mm in tissues (Levin and Hoffman 1999). The range of positrons emitted from 82Rb, on the other hand, is approximately 3.5 mm. As the PET scanner effectively measures the distribution of positron–electron annihilations and not positron emissions, which originate at the radiotracer location, the positron range negatively affects the PET spatial resolution in a radionuclide-dependent manner.
Application of molecular imaging technology in neurotoxicology research
Published in Journal of Environmental Science and Health, Part C, 2018
Xuan Zhang, Qi Yin, Marc Berridge, Che Wang
Positron emission tomography imaging requires tracers that are radiolabeled with positron-emitting radionuclides. Common nuclides in use are 11 C, 13 N, 15 O, 18 F, 22Na, 52Fe, 64Cu, 89Zr, 124I. The positron-emitter decays by emitting a positively charged positron. The emitted positron annihilates with an electron in surrounding tissue. The annihilation produces two 511 keV γ rays that simultaneously travel in precisely opposite directions and are detected in coincidence by an array of photon detectors in the PET instrument. The physics associated with the pair of annihilation photons is the one that provides PET’s spatial resolution and quantitative accuracy. The image data of PET is acquired by detecting and processing millions of such coincidence events to reconstruct an image of the quantitative spatial distribution of the radioactivity within the field of view of the PET camera.[7,12]
Development of Tracer Particles for Positron Emission Particle Tracking
Published in Nuclear Science and Engineering, 2023
Thomas Leadbeater, Andy Buffler, Michael van Heerden, Ameerah Camroodien, Deon Steyn
Fluorine-18 has a 109.8-min half-life decaying by positron emission at 97% intensity with no associated gamma photon emissions.50 It forms very strong covalent bonds with carbon compounds and can be incorporated into a wide variety of organic molecules. The most widely used radiotracer in medical PET by far is 18FDG, having proven to be of great utility in the rate measurement of glycolytic metabolism.48 A different set of ion exchange reactions from those used for 68Ga enables different materials to be labeled with positron activity such that both the range of possible tracer particles and the useful lifetime are extended.
New Compact Neutron Generator System for Multiple Applications
Published in Nuclear Technology, 2020
For the production of the 6-MeV D-10B neutrons, pure 10B or its compound should be used as a thick target for the D− ion beam. The natural abundance of 10B is only 20%. For this reason, an efficient scheme such as the multi E × B filter system5 can be employed to produce enriched 10B for the target of the neutron generator. In the 10B(d,n)11C reaction, both the 6-MeV neutrons and the radioisotope 11C are produced simultaneously. The latter is commonly used in positron emission tomography (PET) imaging. Application of the 6-MeV neutrons is discussed in Sec. VI.