What Are All Those Scans, Anyway?
Most of us are familiar with the X-ray and Ultrasound, but there are more imaging scan options that many patients will receive as part of the diagnostic and observational process throughout treatment. A wide variety of letter combinations are tossed about when it comes to diagnostic testing. The jumble of acronyms and initialism can be confusing, with groupings like PET, CT, EKG, MRI, and MUGA, and the occasional long word like echocardiogram thrown in for good measure. Each of these scans serves a distinct purpose, however, and understanding what they are can help a patient to better navigate treatment. Here is an explanation of some of the more common types of imaging scans.
The X-ray is a single photographic or digital image made by passing very short-wavelength electromagnetic radiation through a part of the body. Frequently used to check for broken bones or signs of pneumonia in the lungs, this type of image is also one way that signs of cancer are first discovered.
Using ultrasonic frequencies, an ultrasound scan (also known as a sonogram) is able to create a movie or capture a set of images to a computer file that shows activity within the body. This imaging is used to check on the health of fetuses in the womb, but it is also used to examine veins for signs of blockage and to look at organs or deep tissue. This type of imaging may also be used as a guide during a needle biopsy.
EKG, Echocardiogram, and MUGA
These are all diagnostic tests for the heart. The EKG, or electrocardiogram, is a way of measuring heart function through the use of electrodes attached to the chest that translate electronic activity from different areas of the heart as wavy lines on paper. The echocardiogram is essentially an ultrasound of the heart muscle. In some cases, a transesophageal echocardiogram (TEE) may be necessary for which a small wand is inserted down the esophagus to get an image from the back of the heart. The MUGA, or multigated acquisition scan, allows for the creation of video images that show the lower chambers of the heart. Some or all of these tests may be done prior to cancer treatment to check for pre-existing heart conditions, or to follow up after radiation or chemotherapy.
The MRI, or magnetic resonance imaging, uses a combination of magnets and radio waves to form detailed computer images of tissue and organs. Because it is not a form of nuclear imaging, there is no radiation used during this type of scan, making it appropriate for imaging of the brain or the reproductive system. Often, an MRI requires the patient to lie still within a narrow tube, though there are some less confining MRI machines that have been developed. The MRI process tends to take much longer than scans that use radiation to generate images.
CT and PET
These scans are both forms of computed tomography (the CT). Computed tomography allows for very detailed 3-D images of the inside of the body including organs and tissue by making numerous cross-sectional X-ray pictures in series. Where they differ is that the PET scan, also sometimes referred to as a nuclear medicine scan, shows abnormal metabolic activity. For a PET, or positron emission tomography scan, the patient is injected with a radionuclide tracer that is absorbed by rapidly dividing cells such as cancer cells, which then are highlighted on the scan. While CT scan uses X-rays to take images, the PET scan simply records images based on the low-dose radiation given off from the injected tracer material, which is generally a radioactive sugar. Often the two scans are done simultaneously.
So, where the CT scan shows detail and can clearly display the edges of tumors, it is the PET scan that shows where heightened cellular activity is happening. Combined, these scans are frequently used for staging the level of disease as well as checking progress throughout treatment to measure whether tumors are growing or shrinking, or whether there is any evidence of disease after complete remission.
Of course, scans are only part of the diagnostic process and they do not tell the patient everything about their cancer. Images may reveal infections or inflammation as well as tumors, and they often require professional readings to assess what is actually being shown.1-3
Editor’s Note: We are extremely saddened to say that on October 21, 2018, Jeffrey Poehlmann passed away. Jeffrey’s advocacy efforts and writing continue to reach many. He will be deeply missed.
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