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Positron emission tomography
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'''Positron emission tomography''', commonly referred to as '''PET''', is a method of biomedical imaging. It uses nuclear functional imaging techniques to observe [[metabolic]] processes in the body. In clinical settings, it is predominantly used in oncology for tumor metastasis imaging, neurology, and cardiology.<ref name="pet">{{Cite journal | last = Bar-Shalom | first = Rachel | last2 = Valdivia | first2 = Ana Y. | last3 = Blaufox | first3 = M. Donald | date = 2000-07-01 | title = PET imaging in oncology|url=https://www.sciencedirect.com/science/article/pii/S0001299800800355|journal=Seminars in Nuclear Medicine|series=Entering a New Millennium|language=en|volume=30|issue=3|pages=150–185|doi=10.1053/snuc.2000.7439|issn=0001-2998}}</ref> == How it works == PET uses radioactive tracers (also called radiotracer or radioligand), which are chemical compounds that are biologically active, meaning that the compound functions/reacts/ has a biological purpose in the body. These compounds have been altered such that their structure includes a positron-emitting radioisotope (a radioactive atom). This means that the radiotracer’s movement and activity throughout the body can be detected with a PET machine. Many biological compounds have been made into a radiotracer, which allows for observation of how that compound acts throughout a region of the body.{{Citation needed | date = Mar 2021}} === FDG === For example, fludeoxyglucose (FDG), an analogue of [[glucose]], is a commonly used measure of [[metabolism]]; detection of FDG correlates with regional glucose uptake. Glucose metabolism is an important measure because cancer cells increase their metabolism to support their increased rates of proliferation and distribution throughout the body. Increased metabolic activity is usually accomplished through increased glucose-uptake. Because cancerous tumors have higher levels of metabolic activity, tumors can usually be detected with FDG-PET. In fact, around 90% of clinical PET imaging uses FDG to monitor cancer metastasis.<ref name="Widmann">{{Cite web|url=https://www.ncbi.nlm.nih.gov/pubmed/20473153 | title = Glucose metabolism in cancer cells | first=A. | last = Annibaldi | first2 = C. | last2 = Widmann|journal=Current Opinion in Clinical Nutrition and Metabolic Care | date = July 2010|volume= 13|issue = 4|pages =466-470| doi=10.1097/MCO.0b013e32833a5577}}</ref> == The procedure == A small amount of radiotracer is introduced into the subject’s body via injection, and the subject then enters the PET machine. As the radiotracer breaks down, it emits gamma rays which are picked up by the machine, and then translated into a 3-dimensional image of radiotracer concentration throughout the body. The resulting image can be thought of as a heat map, showing areas of high concentration as more brightly lit.{{Citation needed | date = Mar 2021}} == Clinical reasons for getting a PET scan: == * Generally, to evaluate the function of organs such as the [[heart]] and [[brain]] ** I.e., measuring perfusion of the heart muscle * To diagnose neurological conditions such as [[Alzheimer's disease|Alzheimer’s]], [[Huntington's disease|Huntington’s]], [[Parkinson's disease|Parkinson’s]], [[epilepsy]], and stroke * To detect the spread of cancer * To evaluate cancer treatment efficacy * To locate the specific site for surgery prior to the surgical procedure * To evaluate the brain after [[trauma]]<ref name="jh">{{Cite web|url=https://www.hopkinsmedicine.org/healthlibrary/test_procedures/neurological/positron_emission_tomography_pet_92,p07654 | title = How Does a PET Scan Work?|website=Johns Hopkins Medicine|language=en|access-date=2019-02-27}}</ref> == Risks == The risks for the amount of radiotracer injected into the body is small enough that there is usually no need to take precautions against radioactive exposure. If you are pregnant or breastfeeding, you should notify the doctor/researcher to protect against injury to the fetus or contaminating breastmilk.<ref name="jh" /> == PET research in ME/CFS == PET research in ME has focused on measures of [[neuroinflammation]]. This has been done using a TSPO-binding radioligand to measure [[Microglia|microglial]] activation. [[translocator protein|TSPO]] (translocator protein) is a protein that is produced when [[microglia]], the resident macrophages of the brain, become activated. Microglial activation is a commonly used measure of neuroinflammation. Further research using high-quality PET/TSPO methodology is needed to better understand the pathophysiology of neuroinflammation in ME.<ref name="Mejia2019">{{Cite journal | last = Lara Mejia | first=Paula S. | last2 = Brumfield | first2 = Sydney A. | last3 = VanElzakker | first3 = Michael B.|author-link3 =Michael VanElzakker | date = 2019 | title=Neuroinflammation and Cytokines in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): A Critical Review of Research Methods|url=https://www.frontiersin.org/articles/10.3389/fneur.2018.01033/full#B8|journal=Frontiers in Neurology|language=English|volume=9|doi=10.3389/fneur.2018.01033|issn=1664-2295}}</ref> === Nakatomi et al. 2014 === Nakatomi et al. (2014) was the first case-control study using PET to measure neuroinflammation through TSPO expression in ME. They used [[PK11195]], a first generation TSPO-binding radioligand. They found increased PK11195 in cingulate cortex, [[hippocampus]], [[amygdala]], thalamus, midbrain, and pons. PK11195 concentrations in certain regions were found to have positive correlations with cognitive impairment scores (related to brain fog), [[pain]] scores, and [[depression]] scores. The study concludes that neuroinflammation seems to be present in ME patients and is associated with neuropsychological symptoms.<ref name="Nakatomi2014" /> [[File:PK11195.gif|thumb|312x312px|center|Statistical parametric maps showing areas of significant contrast of PK11195 in brains of ME/CFS patients versus healthy controls.<ref name="Nakatomi2014">{{Cite journal | last = Nakatomi | first = Yasuhito | authorlink = Yasuhito Nakatomi | authorlink2 = Kei Mizuno | authorlink3 = Akira Ishii | authorlink4 = Yasuhiro Wada | authorlink5 = Masaaki Tanaka | authorlink6 = Shusaku Tazawa | authorlink7 = Kayo Onoe | authorlink8 = Sanae Fukuda | authorlink9 = Joji Kawabe | date = Jun 1, 2014|others=Kazuhiro Takahashi; Yosky Kataoka; Susuma Shiomi; Kouzi Yamaguti, Masaaki Inaba; Hirohiko Kuratsune; Yasuyoshi Watanabe | title = Neuroinflammation in Patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis: An 11C-(R)-PK11195 PET Study|url=http://jnm.snmjournals.org/content/55/6/945.full|journal=The Journal of Nuclear Medicine|volume=555|issue=6 | pages = 945-950|quote=|via=SNM Journals}}</ref>''This image was originally published in JNM. Nakatomi, Yasuhito, et al. [https://jnm.snmjournals.org/content/55/6/945 Neuroinflammation in Patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis: An 11C-(R)-PK11195 PET Study]. J Nucl Med. Mar 24, 2014; 55(6):945-950. © SNMMI (non-commercial reuse only)'']] {{See also|Neuroinflammation}} == PET research in [[long COVID]] == Because of the recency of the COVID pandemic, there is a limited amount of PET research in long COVID. Similar to ME, the PET research in long COVID is focused on neurological and brain analysis. === Sollini et al. 2021 === Sollini et al. (2021) compared 13 adult long COVID patients to a group of 26 melanoma patients with a negative PET/CT. COVID patients were matched for sex/age. In 4/13 long COVID patients, CT images showed lung abnormalities presenting mild [18F]FDG uptake. Long COVID patients also had brain hypometabolism in the right parahippocampal gyrus and [[thalamus]] (uncorrected p ≤ 0.001). This study concluded that [18F}FDG PET/CT can be a tool to analyze the multi-organ nature of long COVID.<ref name="Sollini">{{Cite journal | last = Sollini | first = Martina | last2 = Morbelli | first2 = Silvia | last3 = Ciccarelli | first3 = Michele | last4 = Cecconi | first4 = Maurizio | last5 = Aghemo | first5 = Alessio | last6 = Morelli | first6 = Paola | last7 = Chiola | first7 = Silvia | last8 = Gelardi | first8 = Fabrizia | last9 = Chiti | first9 = Arturo | date = 2021-03-07 | title = Long COVID hallmarks on [18F]FDG-PET/CT: a case-control study|url=http://link.springer.com/10.1007/s00259-021-05294-3|journal=European Journal of Nuclear Medicine and Molecular Imaging|language=en|doi=10.1007/s00259-021-05294-3|issn=1619-7070|pmc=PMC7937050|pmid=33677642}}</ref> === Guedj et al. 2021. === Guedj et al. (2021) completed PET scans for 35 long COVID patients which utilized a whole-brain voxel-based analysis. They compared these patients to a local database of 44 health subjects which were controlled by age and sex. Long COVID patients exhibited bilateral hypometabolism compared to health patients. Study supports that PET scans may be valuable for long COVID patients in order to perform a whole-brain voxel-based analysis. Additionally, prevalence of hypometabolism was statistically greater for COVID patients compared to healthy patients.<ref name="Guedj">{{Cite journal | last = Guedj | first = E. | last2 = Campion | first2 = J.Y. | last3 = Dudouet | first3 = P. | last4 = Kaphan | first4 = E. | last5 = Bregeon | first5 = F. | last6 = Tissot-Dupont | first6 = H. | last7 = Guis | first7 = S. | last8 = Barthelemy | first8 = F. | last9 = Habert | first9 = P. | date = 2021-01-26 | title = 18F-FDG brain PET hypometabolism in patients with long COVID|url=http://link.springer.com/10.1007/s00259-021-05215-4|journal=European Journal of Nuclear Medicine and Molecular Imaging|language=en|doi=10.1007/s00259-021-05215-4|issn=1619-7070|pmc=PMC7837643|pmid=33501506}}</ref> ==See also == *[[Brain]] *[[Autopsy]] *[[Long COVID]] == References == {{Reflist}} [[Category:Medical tests]] [[Category:Neurology]]
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