You might remember the television show Star Trek.
When Dr. Leonard “Bones” McCoy (the show’s chief medical officer) cared for a sick patient on board the Starship Enterprise, he checked the patient with his scanner in the ship’s sickbay to get a diagnosis instantly. While we aren’t on the Enterprise, advances in medical imaging allow us to receive diagnoses that can seem just as amazing. These science fiction scanners help us to understand CT and PET scans.
CT scans take multiple x-rays and combine them to give cross-sectional views of the body. The process is called tomography and is coordinated by a computer; thus the name Computerized Tomography or CT. PET scans (or Positron Emission Tomography) track the accumulation of certain compounds, tagged with a radioactive marker, in the body. Abnormal activity shows up as color, and then computers turn it into a three dimensional picture, highlighting the problem area.
Understand CT and PET Scans
• Radiation Exposure: Since the scan uses multiple x-rays, there is some exposure. One CT scan of the abdomen is equivalent to three years of natural exposure to the daily background radiation that we all experience. One scan poses very little risk. CT scans are only used when really needed. Pregnant women and children would very rarely be scanned unless the need was absolute.
• Time: CT scans typically take less than five minutes.
• Side Effects: Aside from some radiation exposure, the only risk is a reaction to the intravenous dye that is injected during some scans. Otherwise the test is painless and noninvasive.
• Uses: A CT scan shows bone very well. It is excellent for looking for fractures that cannot be seen on x-ray. But it is also very good at looking at soft tissue bleeding problems and blood clots, such as those that may occur in strokes or trauma. It is also used for evaluating abdominal pain and abnormal chest x-rays, as well as to look for cancer.
• Radiation Exposure: A type of glucose is tagged with a radioactive molecule and injected into your arm intravenously, where the blood carries it to the area of concern. The radioactive part of the molecule does not stay radioactive very long and is quickly excreted from your body.
• Time: PET scans measure metabolic processes and require a lot more time, a portion of which is spent waiting for the radioactive glucose to concentrate in the part of the body being investigated. The time needed for the test is usually between two and four hours.
• Side Effects: Because it requires an injection, there is always the slight risk of a reaction. Otherwise it is also painless and noninvasive.
• Uses: Because the PET scan is spotlighting activity that is happening at a cellular level, it can show abnormalities at a very early stage compared to a CT scan. Therefore PET scans are particularly good at finding early cancers, as well as evaluating the progress of cancer treatments. They are also used by cardiologists to look at heart muscle activity and by neurologists who might be looking for evidence of tumors or Alzheimer’s disease, or investigating severe seizures.