CAT scan
Meaning of CAT scan: The older name survives in speech, though modern scanners sweep in a spiral and the axial part of it no longer describes them.
Definition of CAT scan
A CAT scan is an X-ray examination that builds cross-sectional pictures of the inside of the body. The tube and detectors rotate around the person, recording images from many angles, and a computer combines them into slices that can be viewed one at a time or reassembled into three-dimensional views. The same test is now more often called a CT scan.
Why is it called a CAT scan?
The letters stand for computerized axial tomography. Axial referred to the way the earliest machines worked, taking one flat slice across the body at a time before moving on to the next. Scanners have since changed. The table now glides through the opening while the tube circles continuously, tracing a spiral through the body and gathering one unbroken block of data that the computer can slice afterward in any plane. Because the acquisition is no longer axial, the middle letter has quietly dropped out of professional use, and CT scan is the name found in most reports today. Both names describe the same examination, and the older one persists mainly in conversation.
What does contrast material add?
X-rays distinguish tissues by density, and many soft tissues are close enough in density to look alike. An iodine-based contrast material given into a vein briefly brightens the blood, so vessels stand out, organs show their blood supply, and areas of inflammation or tumor that draw more blood separate from their surroundings. Timing decides what is seen: images taken seconds after injection show arteries, and later images show veins and the kidneys clearing the agent. A different preparation swallowed beforehand outlines the stomach and bowel. Not every study uses contrast, and kidney function and previous reactions govern whether it is given.
How does it compare with other scans?
| Test | What makes the image | What it shows best |
|---|---|---|
| Plain X-ray | A single burst of X-rays through the body onto a detector | Bone, and large changes in the chest or abdomen |
| CAT or CT scan | X-rays from many angles, reassembled by computer | Detailed anatomy of bone, organs, vessels, and fresh bleeding |
| MRI | Strong magnetic fields and radio waves, with no X-rays at all | Soft tissue such as brain, spinal cord, muscle, and joints |
| PET scan | A radioactive tracer marking where cells are most active | Metabolic activity, often paired with CT in one machine |
The trade-off with CT is radiation. A scan delivers considerably more than a plain X-ray of the same region, which is why the question of whether the information will change what happens next is weighed each time one is requested.
Also known as
Used in a sentence
A CAT scan of the abdomen was ordered to further evaluate the patient's persistent pain.
Good to know
A CAT scan uses X-rays and involves radiation exposure, which distinguishes it from magnetic resonance imaging, a different technique that uses magnetic fields rather than radiation to produce detailed images.
Word origin
Where “CAT scan” comes from
Tomography is formed from Greek tomos, meaning a slice or section, and graphein, meaning to write, describing an image assembled as a series of slices.