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Diagnostic Study - Description & Definition


Positron emission tomography (PET) scanning is a noninvasive nuclear medicine diagnostic tool that is used for quantifying regional blood flow and tissue glucose metabolism in vivo. In a PET scan, radiotracers like 2-deoxy-2-[18F] fluoro-D-glucose (FDG) emit positrons—positive antiparticles of electrons—which then undergo radioactive decay. They collide with electrons to produce 2 photons, which are emitted at 180° angles. The PET scanner then detects these photons and reconstructs an image of spatial density that highlights the functional data and reveals blood flow changes. PET scans are particularly useful for studying normal versus abnormal brain activity and are most commonly used for diagnosing and monitoring neurologic disorders, certain cancers, and heart disease; however, research suggests that they may also serve a role in assessing skeletal muscle activity and identifying articular conditions like rheumatoid arthritis and osteoarthritis affecting the hand and/or wrist.1-3

Historical Overview

PET imaging was based on discoveries dating back to the late 1800s, when the physiology of brain circulation first became appreciated. The evolution from theory to medical practice did not occur until the 1950s, when modern radiotracers and technologically advanced scanning devices were introduced. After World War II, nuclear research transitioned from the Manhattan Project to scientific particle pursuits, which led to the development of safe radioisotopes and brought PET imaging closer to fruition. In 1961, Lassen and Ingvar utilized radiotracer 133 Xe to localize sensory, motor, and mental functions in a human brain. Color-coded patterns tracked brain blood flow as it related to function, which became the standard visual representation of cerebral PET images. The first large-scale use of a human positron-imaging device was developed in the 1950s to detect brain tumors with sodium iodide. Refinements led to increased sensitivity and to multiple detectors, and in 1972, one of the first PET imaging devices called PC-I was unveiled. Then, in 1975, Phelps and Hoffman constructed and introduced an improved PET scanner with hexagonal detectors. A ring-shaped PCR-I (1985) and a cylindrical shaped PCR-II (1988) detector eventually provided even better resolution and sensitivity for PET scanning.1


Before the PET scan is performed, the patient is given a tracer that has been tagged with a radioactive atom that breaks down quickly to release positrons. The most commonly used tracer is FDG, which is injected, inhaled, or swallowed. Approximately 30-60 minutes after the tracer is administered, the patient is asked to lie on the scanner table that moves into the scanning ring. The PET scan may take anywhere from 30 minutes to 2 hours, during which time the patient must remain still to ensure that the images produced are clear.2,3

Normal Study Findings - Video
Diagnoses Where These Studies May Be Used In Work-Up (with abnormal findings images)
Comments and Pearls
  • Continued advancements in both PET/CT and PET-MRI hybrids will improve the understanding of cerebral processes, and may help to better track treatment outcomes and disease-modifying therapies.1
  • Although FDG PET imaging has been employed in several settings to evaluate muscle tissue metabolism and perfusion, the application of PET to study exercising skeletal muscle remains limited. FDG PET provides tomographic spatial information and allows exercise to be performed conveniently before imaging, the combination of which is not available with other techniques used for measuring muscle activity.4
  • One study has suggested that PET scanning may also be used to detect rheumatoid arthritis with a newly invented agent called F-FEDAC for targeting activated macrophages. Though additional research is needed, this finding hold promise and may lead to additional functions of PET scanning for identifying articular conditions like osteoarthritis in the future.5
  1. Portnow, LH, Vaillancourt, DE and Okun, MS. The history of cerebral PET scanning: from physiology to cutting-edge technology. Neurology 2013;80(10):952-6.PMID: 23460618
  2. Omi, R, Sano, H, Ohnuma, M, et al. Function of the shoulder muscles during arm elevation: an assessment using positron emission tomography. J Anat 2010;216(5):643-9.PMID: 20298439
  3. Watad, A, Eshed, I and McGonagle, D. Lessons Learned from Imaging on Enthesitis in Psoriatic Arthritis. Isr Med Assoc J 2017;19(11):708-711. PMID: 29185286
  4. Pappas, GP, Olcott, EW and Drace, JE. Imaging of skeletal muscle function using (18)FDG PET: force production, activation, and metabolism. J Appl Physiol (1985) 2001;90(1):329-37.PMID: 11133926
  5. Chung, SJ, Yoon, HJ, Youn, H, et al. (18)F-FEDAC as a Targeting Agent for Activated Macrophages in DBA/1 Mice with Collagen-Induced Arthritis: Comparison with (18)F-FDG. J Nucl Med 2018;59(5):839-845. PMID: 29326355
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