Nuclear Medicine

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Introduction[edit | edit source]

PET scan brain.png

Nuclear medicine imaging uses small amounts of radioactive materials called radiotracers (typically injected into the bloodstream, inhaled or swallowed). The radiotracer travels through the area being examined and gives off energy in the form of gamma rays which are detected by a special camera and a computer to create images of the inside of your body. Nuclear medicine imaging provides unique information that often cannot be obtained using other imaging procedures and offers the potential to identify disease in its earliest stages.[1]

Image 1: PET scan brain

  • Nuclear medicine scans differ from radiology, as the emphasis is not on imaging anatomy, but on the function. For such reason, it is called a physiological imaging modality.
  • Single photon emission computed tomography (SPECT) and positron emission tomography (PET) scans are the two most common imaging modalities in nuclear medicine[2]

Diagnostic Use[edit | edit source]

PET scan image.jpeg

Nuclear medicine imaging uses small amounts of radioactive material to diagnose, evaluate or treat a variety of diseases. These include many types of cancers, heart disease, gastrointestinal, endocrine or neurological disorders and other abnormalities. Because nuclear medicine exams can pinpoint molecular activity, they have the potential to identify disease in its earliest stages. They can also show whether a patient is responding to treatment.

Image 2: Pathology image revealing lymph node metastasis resulting from positron emission tomography (application in oncology).

Nuclear medicine imaging procedures are noninvasive. With the exception of intravenous injections, they are usually painless. These tests use radioactive materials, called radiopharmaceuticals or radiotracers, help diagnose and evaluate medical conditions.

  • Radiotracers are molecules linked to, or "labeled" with, a small amount of radioactive material that can be detected on the PET scan. Radiotracers accumulate in tumors or regions of inflammation. They can also bind to specific proteins in the body.
  • The most commonly used radiotracer is F-18 fluorodeoxyglucose, or FDG, a molecule similar to glucose. Cancer cells are more metabolically active and may absorb glucose at a higher rate. This higher rate can be seen on PET scans. This allows diagnosis of a disease before it may be seen on other imaging tests. FDG is just one of many radiotracers in use or in development.

Depending on the type of exam, the radiotracer is injected, swallowed or inhaled as a gas. It eventually accumulates in the area of the body under examination. A special camera or imaging device detects radioactive emissions from the radiotracer. The camera or device produces pictures and provides molecular information[1].

Test Types[edit | edit source]

Bone Scan Distal Fibula.jpg

Scans are used to diagnose many medical conditions and diseases. Some of the more common tests include the following:

  • Renal scans. These are used to examine the kidneys and to find any abnormalities. These include abnormal function or obstruction of the renal blood flow.
  • Thyroid scans. These are used to evaluate thyroid function or to better evaluate a thyroid nodule or mass.
  • Bone scans. These are used to evaluate any degenerative and/or arthritic changes in the joints, to find bone diseases and tumors, and/or to determine the cause of bone pain or inflammation.
  • Gallium scans. These are used to diagnose active infectious and/or inflammatory diseases, tumors, and abscesses.
  • Cardiac MRI flow.gif
    Heart scans. These are used to identify abnormal blood flow to the heart, to determine the extent of the damage of the heart muscle after a heart attack, and/or to measure heart function.
  • Brain scans. These are used to investigate problems within the brain and/or in the blood circulation to the brain.
  • Breast scans. These are often used in conjunction with mammograms to locate cancerous tissue in the breast[3].

Examples of Nuclear Scans[edit | edit source]

Positron Emission Tomography (PET)

  • Primarily used to detect diseases of the brain and heart. A short-lived isotope, such as 18F, is incorporated into a substance used by the body such as glucose which is absorbed by the tumor of interest. PET scans are often viewed alongside computed tomography scans, which can be performed on the same equipment without moving the patient. This allows the tumors detected by the PET scan to be viewed next to the rest of the patient's anatomy detected by the CT scan.

Single Photon Emission Computed Tomography (SPECT)

  • SPECT scans are primarily used to diagnose and track the progression of heart disease, such as blocked coronary arteries. There are also radiotracers to detect disorders in bone, gall bladder disease and intestinal bleeding. SPECT agents have recently become available for aiding in the diagnosis of Parkinson's disease in the brain, and distinguishing this malady from other anatomically-related movement disorders and dementias.
  • SPECT imaging instruments provide three-dimensional (tomographic) images of the distribution of radioactive tracer molecules that have been introduced into the patient’s body. The 3D images are computer generated from a large number of projection images of the body recorded at different angles. SPECT imagers have gamma camera detectors that can detect the [null gamma ray] emissions from the tracers that have been injected into the patient. Gamma rays are a form of light that moves at a different wavelength than visible light. The cameras are mounted on a rotating gantry that allows the detectors to be moved in a tight circle around a patient who is lying motionless on a pallet[4].

[5]

The main difference between SPECT and PET scans is the type of radiotracers used. While SPECT scans measure gamma rays - gamma ray is a packet of electromagnetic energy (photon). In a PET scan the decay of the radiotracers used produce small particles called positrons. A positron is a particle with roughly the same mass as an electron but oppositely charged. These react with 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 shoot off in opposite directions. The detectors in the PET scanner measure these photons and use this information to create images of internal organs.[4]

Bone Scan 

Imaging technique that uses a radioactive compound to identify areas of healing within the bone. Bone scans work by drawing blood from the patient and tagging it with a bone seeking radiopharmaceutical. This radioactive compound emits gamma radiation. The blood is then returned to the patient intravenously. As the body begins its metabolic activity at the site of the injury, the blood tagged by the radioactive compound is absorbed at the bone and the gamma radiation at the site of the injury can be detected with an external gamma camera. A bone scan can be beneficial in determining injury to the bone within the first 24-48 hours of injury or when the displacement is too small to be detected by an x-ray or CT scan[6][7]

References[edit | edit source]

  1. 1.0 1.1 Radiologyinfo Nuclear Medicine Available from: https://www.radiologyinfo.org/en/info.cfm?pg=gennuclear(accessed 7.4.2021)
  2. St Petershcs Nuclear Medicine Available from:https://web.archive.org/web/20150227082414/http://www.saintpetershcs.com/Nuclear-Medicine/ (accessed 7.4.2021)
  3. John Hopkins Nuclear Medicine Available from:https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/nuclear-medicine (accessed 7.4.2021)
  4. 4.0 4.1 NIH Gov. Nuclear medicine Available from: https://www.nibib.nih.gov/science-education/science-topics/nuclear-medicine ( accessed 8.4.2021)
  5. Andrew B. Newberg, Abass Alavi, Single Photon Emission Computed Tomography☆, Reference Module in Neuroscience and Biobehavioral Psychology, Elsevier, 2017, ISBN 9780128093245, obtained from
  6. Swain J, Bush K. Diagnostic Imaging for Physical Therapists. St. Louis: Saunders Elsevier; 2009
  7. College A. ACR Practice Guideline For The Performance Of Adult and Pediatric Skeletal Scintigraphy ( Bone Scan ). North. 2007:1-5.