CT scan or CAT scan: How does it work?

A computerized tomography (CT) or computerized axial tomography (CAT) scan combines data from several X-rays to produce a detailed image of structures inside the body.

CT scans produce 2-dimensional images of a “slice” or section of the body, but the data can also be used to construct 3-dimensional images. A CT scan can be compared to looking at one slice of bread within a whole loaf.

CT scans are used in hospitals worldwide.

What is a CT scan?

CT scan
A CT scan can help diagnose many types of cancer.

A CT scanner emits a series of narrow beams through the human body as it moves through an arc.

This is different from an X-ray machine, which sends just one radiation beam. The CT scan produces a more detailed final picture than an X-ray image.

The CT scanner’s X-ray detector can see hundreds of different levels of density. It can see tissues within a solid organ.

This data is transmitted to a computer, which builds up a 3-D cross-sectional picture of the part of the body and displays it on the screen.

Sometimes, a contrast dye is used because it can help show certain structures more clearly.

For instance, if a 3-D image of the abdomen is required, the patient may have to drink a barium meal. The barium appears white on the scan as it travels through the digestive system.

If images lower down the body are required, such as the rectum, the patient may be given a barium enema. If blood vessel images are the target, a contrast agent will be injected into the veins.

The accuracy and speed of CT scans may be improved with the application of spiral CT, a relatively new technology. The beam takes a spiral path during the scanning, so it gathers continuous data with no gaps between images.

CT is a useful tool for assisting diagnosis in medicine, but it is a source of ionizing radiation, and it can potentially cause cancer.

The National Cancer Institute advise patients to discuss the risks and benefits of CT scans with their doctors.

A CT scan shows
A CT scan can detect abnormalities in the soft tissue.

It is useful for obtaining images of:

soft tissues

the pelvis

blood vessels





CT is often the preferred way of diagnosing many cancers, such as liver, lung, and pancreatic cancers.

The image allows a doctor to confirm the presence and location of a tumor, its size, and how much it has affected nearby tissue.

A scan of the head can provide important information about the brain, for instance, if there is any bleeding, swelling of the arteries, or a tumor.

A CT scan can reveal a tumor in the abdomen, and any swelling or inflammation in nearby internal organs. It can show any lacerations of the spleen, kidneys, or liver.

As a CT scan detects abnormal tissue, it is useful for planning areas for radiotherapy and biopsies, and it can provide valuable data on blood flow and other vascular conditions.

It can help a doctor assess bone diseases, bone density, and the state of the patient’s spine.

It can also provide vital data about injuries to a patient’s hands, feet, and other skeletal structures. Even small bones are clearly visible, as well as their surrounding tissue.

CT versus MRI

The main differences between CT and MRI are:

A CT scan uses X-rays, but an MRI uses magnets and radio waves.

Unlike an MRI, a CT scan does not show tendons and ligaments.

MRI is better for examining the spinal cord.

A CT scan is better suited to cancer, pneumonia, abnormal chest x-rays, bleeding in the brain, especially after an injury.

A brain tumor is more clearly visible on MRI.

A CT scan shows organ tear and organ injury more quickly, so it may be more suitable for trauma cases.

Broken bones and vertebrae are more clearly visible on a CT scan.

CT scans provide a better image of the lungs and organs in the chest cavity between the lungs.

What to know about MRI scansWhat to know about MRI scans
What is an MRI scan and what is it used for? Find out more.
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