Craniofacial Regeneration—Bone
Vincenzo Guarino, Marco Antonio Alvarez-Pérez in Current Advances in Oral and Craniofacial Tissue Engineering, 2020
PET scans also use radiopharmaceuticals to create three-dimensional images. The main difference between SPECT and PET scans is the type of radiotracers used. While SPECT scans measure gamma rays, the decomposition of radiotracers used with PET scans produces small particles called positrons. A positron is a particle with approximately the same mass as an electron, but with an opposite charge. These react with the electrons in the body and when these two particles combine they annihilate each other. This annihilation produces a small amount of energy in the form of two photons that fire in opposite directions. The PET scanner detectors measure these photons and use this information to create images of the internal organs. With this non-invasive technique, quantitative information on biological processes at the molecular level is obtained through tomographic images that reflect the concentration of activity of a radiopharmaceutical administered to a patient. The information obtained depends on the metabolic pathway, the targeted target receptor, the biodistribution and the rates of accumulation and elimination of the radiopharmaceutical. This makes it possible to perform an early detection of pathological processes with PET (Phelps 2000).
Neuroimaging in the Evaluation of Neurogenic Bladder Dysfunction
Jacques Corcos, Gilles Karsenty, Thomas Kessler, David Ginsberg in Essentials of the Adult Neurogenic Bladder, 2020
For PET imaging, a positron emitting radionuclide on a tracer molecule is intravenously applied prior to the PET scan.39 When the emitted positrons collide with electrons within the tissue of the investigated body area, annihilation (= γ-) radiation emits in 180° opposite directions and can be detected as coincidences by the PET scanner. There are different radionuclides available, which are chosen based on their specific characteristics and the purpose of investigation. For PET investigation of supraspinal LUT control, mainly the 15O radionuclide in conjunction with hydrogen (= H215O) is used due to its short half-life of about 2 minutes. This allows for repetitive scans of different or similar conditions (e.g., empty bladder, full bladder, micturition) within a shorter time span. The accumulation of the applied radionuclide and amount of recorded annihilations correspond to the blood flow to the brain tissue.
Photon Interactions with Matter
Eric Ford in Primer on Radiation Oncology Physics, 2020
The final photon–matter interaction that we consider is pair production which happens at the highest energies. This is a quantum mechanical interaction of the photon in the field of the nucleus (Figure 5.2.4). The photon is converted to a pair of particles: one electron (e−) and one positron (e+). Recall that the positron is the positively charged antiparticle of the electron. Because of conservation of energy, the total energy of the pair that is created is equal to the energy before (i.e. the energy of the incident photon). This means that the energy of the incident photon must be at least twice the rest mass energy of the electron (E0 > 1.022 MeV). If it is not then there will not be enough energy to create the electron/positron pair. The total kinetic energy of the pair that is created is E0 – 1.022 MeV. The probability of pair production increases rapidly with energy above 1.02 MeV and is also larger for higher Z nuclei.
Vacancy-induced toxicity of CoSe2 nanomaterials in rat lung macrophages
Published in Nanotoxicology, 2020
Guizhu Wu, Xue Chen, Ze Zhang, Nali Zhu, Qilin Yu, Huajie Liu, Lu Liu
The positron lifetime experiments were measured with a fast-slow coincidence ORTEC system with a time resolution of ∼230 ps full width at half-maximum. A 5 mCi source of 22Na was sandwiched between two identical samples, with a total count of 1 million. Positron lifetime calculations were performed with the atomic superposition (ATSUP) method (Robles, Ogando, and Plazaola 2007), in which the electron density and the positron crystalline Coulomb potential were constructed by the non-self-consistent superposition of free atom electron density and Coulomb potential in the absence of the positron. The calculations of the positron lifetime were conducted with the electron-positron enhancement factor according to Barbiellini’s generalized gradient approximation (Barbiellini et al. 1996). Positron lifetime calculations were performed for unrelaxed structure monovacancy defects and vacancy associates in CoSe2 using 3 × 3 × 2 supercells.
Advantages and limitations of amino acid PET for tracking therapy response in glioma patients
Published in Expert Review of Neurotherapeutics, 2020
Karl-Josef Langen, Alexander Heinzel, Philipp Lohmann, Felix M. Mottaghy, Norbert Galldiks
Therefore, a number of diagnostic approaches with a focus on metabolic and functional imaging methods are under investigation [3]. Positron emission tomography (PET) is a well-established method in nuclear medicine that is able to detect the distribution of radiolabelled molecules in the human body with high sensitivity and a spatial resolution of 3–5 mm. Since numerous metabolic substrates, receptor ligands or pharmaceuticals can be labeled with positron-emitting isotopes such as carbon-11, nitrogen-13 or fluorine-18, PET offers great potential for the assessment of metabolic and physiological processes. However, radiolabelling of the molecules with short-lived positron emitters is a rather sophisticated procedure. In addition, the tracers must meet a number of conditions such as high in vivo stability, high specificity and a sufficient residence time in the target tissue in order to be clinically useful.
Primary pulmonary schwannoma presenting as a massive cystic lesion
Published in Canadian Journal of Respiratory, Critical Care, and Sleep Medicine, 2018
A previously healthy 50-year-old Caucasian female presented to hospital with right-sided chest discomfort, radiating to the ipsilateral shoulder, and dry cough. She had no other complaints. The patient was a lifelong nonsmoker and denied recent travel history. Vital signs and physical examination were unremarkable, aside for decreased breath sounds over the right upper lobe area on respiratory auscultation. Chest radiograph performed showed a large right upper lobe (RUL) opacity (Figure 1); no prior chest imaging was available for this patient. Chest computed tomography (CT) with intravenous contrast revealed a thin-walled well-defined 13 × 12 × 8.5 cm cystic RUL mass, causing contralateral shifting and narrowing of the trachea and right mainstem bronchus (Figures 2 and 3). The lesion showed CT attenuation of approximately 10 to 15 Hounsfield units. No other pertinent finding was identified on chest imaging. On positron emission tomography (PET) scan, this strictly parenchymal mass appeared heterogeneous with some areas displaying no uptake and others achieving up to a standardized uptake value of 10.0. No other abnormality was seen on PET scan. Thoracic surgery assessment was requested, and excision of the lesion was performed. Histologic examination showed a mass with both solid and cystic areas, filled with serous fluid, mucus and a tan-beige friable material. The morphology and immunohistochemical profile was in keeping with a diagnosis of an intrapulmonary schwannoma.
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