Health Vocabulary: X-rays and CT/CAT Scans

An inside look at looking inside the body.

An X-ray scan is a painless diagnostic imaging technique that looks inside the body using focused beams of electromagnetic radiation. The CT/CAT scan is a more complex version of the X-ray that compiles many images to create cross-sections and 3D models of body structures.

As X-ray particles pass through body tissue, some particles are blocked or absorbed depending on the structure’s density. Bone, which is dense, appears white in the resulting image because it blocks most of the X-ray particles. Muscle, fat, and fluid appear in shades of gray, and any structure containing air (like the lungs) will appear black because the particles can pass through easily.

Both x-ray particles and visible light are electromagnetic radiation, of similar but different types. During either an X-ray or a CT/CAT scan, radiation exposure is kept to a minimum. Have you ever had to wear a lead apron during an X-ray? That’s to shield the parts of your body that aren’t being scanned.

If they’re made of electromagnetic radiation, why are they called X-rays and not E-rays?

When German scientist Wilhelm Roentgen discovered X-rays in 1895, he didn’t know the source of the radiation. He named his discovery after the mathematical symbol for something unknown – X.

So what makes a CT/CAT scan special?

CT/CAT scans use a mobile X-ray unit that circles the body to create cross-sectional images, called slices. In fact, the “T” of both CT and CAT stands for tomography, which comes from the Greek tomos, or slice. When the slices are stacked together, they can create a 3D image of your insides in high detail.

Which is it – CT or CAT scan?

Both! They’re the same thing. CT stands for computed (or computerized) tomography. CAT stands for computed axial tomography, where axial refers to the axis around which the mobile X-ray unit rotates. Modern advances in CT have added a spiral  scan to the axial scan, which means more of the body can be scanned in less time.

Are they safe?

X-rays are very common, used everywhere from the dentist’s office to your family practice. Generally your radiation exposure is low. Since X-rays use radiation, though, it’s always a good idea to limit your exposure to only what’s medically necessary. Talk to your doctor if you’re concerned about radiation exposure, and don’t pressure your doctor to order an X-ray. X-ray scans are great tools for doctors, but they will only prescribe them if the benefits outweigh any potential risks.

CT/CAT scans use slightly more radiation than standard X-rays, but newer CT machines are faster and require less radiation than in the past, and doctors use the lowest possible dose of radiation.
If you’re pregnant or think you might be, tell your doctor before having either an X-ray or a CT scan.

Sources:

http://www.fda.gov/Radiation-EmittingProducts/ResourcesforYouRadiationEmittingProducts/ucm252766.htm

http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/MedicalX-Rays/ucm115318.htm

http://www.mayoclinic.org/tests-procedures/x-ray/basics/risks/prc-20009519