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| Fig. 1: Illustration of the basic structure of the head of the Anger Scintillation Camera. This outlines the basic structure of the gamma camera and how the sections work. [2,5] (Source: Wikimedia Commons) |
Many types of imaging are used for diagnosis and treatment in the medical field. From MRI to CT Scans, technology enables medical professionals to find out what is wrong with a patient and move forward to treat the issue. Although many imaging methods exist, this report will focus on the medical imaging technique of nuclear medical imaging.
The first nuclear medical imaging technique that became widespread and prevalent in the medical field is called the rectilinear scanner. This technique was prevalent in the 1950's and 60's. The rectilinear scanner plots the image one plane at a time. Later, a large area position sensitive detector was developed and replaced the rectilinear scanner because the large area position detector was ale to look at the photons more holistically. The most common version of this type of imaging device is called the Anger scintillation method, and is also known as the gamma camera (see Fig. 1). [1]
The Anger scintillation camera uses radioactivity and scintillations (flashes of UV light emitted when a high-energy photon hits a particle) to determine the spread of a radioisotope throughout a person's body. Gamma rays are emitted in a person's body via a chemical tracer to determine where the radioactive particles are moving. The most common tracer used is called Technetium-99m, which is ideal because of its relatively short half-life and its pure gamma emissions. [2] Additionally, its ability to interact with multiple different body systems, and thus be tracked throughout the majority of the body is one of the benefits of technetium as a tracer. Next, the tracer then emits radiation and this can be tracked by the gamma rays being shot into the body. This technique is utilized to "map the function and processes of the body," which differentiates this process from some other imaging techniques that simply track anatomy and structure of the body. [1]
Due to its ability to track functions and processes of the body, Anger scintillation imaging is often used in detecting processes of the body, such as examining the function of the thyroid as well as providing medical professionals with detailed images of other body systems, which gives medical professionals the capability to find tumors and perform other related diagnostic exams on patients. [3] Anger scintillation imaging is ideal for retrieving real time pictures of what is occurring in a bodily system.
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| Fig. 2: This is an example of the type of image that SPECT imaging technology produces. SPECT imaging uses the technique of "tomography" to create an image like the one shown here by taking multiple images and synthesizing them. This is a synthesized photo taken of a thyroid using this procedure. (Source: Wikimedia Commons) |
While newer and slightly more complex methods of gamma camera imaging technology have appeared, such as the PET and SPECT scanners, Anger imaging is still the most frequently utilized method for medical scans, and although efficiency and ease for imaging techniques have improved slightly, the actual technological method for nuclear medical imaging has not changed drastically since the invention of the gamma camera- specifically the Anger technique. [1] While newer, more comfortable, and more modern methods have come to be, the instruments for medical nuclear imaging remain more or less similar to a decade ago. In an Anger scintillation camera, the individual scintillator is generally a large Chrystal, compared to many small individual scintillators in more modern techniques. Thus, an advantage of the Anger scintillation method specifically is that it is able to work continuously and requires less equipment and is easier and cheaper to set up and deconstruct than other medical imaging devices such as the PET scan (Fig. 1). [2] Furthermore, the Anger scintillation method produces less statistical noise and can be used with higher resolution collimators, thereby producing images of better spatial resolution. [1] Finally, another major advantage of the Anger method is that the scintillation camera is more flexible in its positioning, permitting images to be obtained from almost any angle. [1]
The process of nuclear medical imaging requires that a microscopically small dose of nuclear radioactive material be injected into a patient's body. While this amount is quite insignificant, there is sometimes concern for the accumulation of harmful amounts of radioactive material in patients who receive many nuclear image treatments. One association called the NHS Foundation Trust advises that pregnant women and people who need to be extra cautious for some reason about "ionizing radiation" avoid the test, as it may not be suitable. [3] Additionally, the Society of Nuclear Medicine explains how the type of radiation created in medical imaging (through gamma rays or X-rays) is called "ionizing radiation" and has the potential to damage tissues if too much exposure occurs. The dosage of radiation varies depending on location and imaging technique used in diagnosis. While many nuclear imaging tests only incur a minor amount or radiation, some tests actually expose a person to a significant amount of radiation if they were to receive this treatment multiple times. For example, a study performed by JAMA Internal Medicine revealed that a single CT scan can deliver a similar amount of radiation, approximately 10 to 100 mSv, as the survivors of the atomic bombings in Hiroshima and Nagasaki that have been correlated to increased risk of cancer in these long term survivors. [4] Thus, although many argue that the threat of side effects from nuclear radiation is insignificant compared to the threat of allowing a devastating disease/condition to develop and spread, there is still reason to use caution when exposing patients to nuclear radiation in medical imaging. [3]
Nuclear medical imaging is an important field that plays a key role in diagnosing many detrimental conditions and diseases, including cancer and thyroid issues. While nuclear radiation is somewhat of a concern, the overwhelming majority of research reveals that the minor amount of radiation one is exposed to is worth the potential diagnosis of serious, life threatening conditions.
© Serena Harber. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J. T. Bushberg et al., The Essential Physics of Medical Imaging, 3rd Ed. (Lippincott Williams and Wilkins, 2011).
[2] M. K. Loken, G. T. Telander, and R. J. Salmon, "Technetium-99m Compounds for Visualization of Body Organs," J. Amer. Med. Assoc. 194, 152 (1965).
[3] "Your Nuclear Medicine (Gamma Camera) Scan," NHS Foundation Trust, October 2011.
[4] R. Smith-Bindman et al., "Radiation Dose Associated with Common Computed Tomography Examinations and the Lifetime Attributable Risk of Cancer," Arch. Intern. Med. 169, 2078 (2009).
[5] H. O. Anger, "Scintillation Camera with Multichannel Collimators," J. Nucl. Med. 5, 515 (1964).
