What is a CT or CAT scan and 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 trusted 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?

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 information is sent to a computer, which creates a 3-D cross-sectional image of the bodily component and presents it on the screen. A contrast dye is occasionally used to assist in revealing particular structures more clearly.

If 3-D imaging of the abdomen is needed, the patient may be required to consume a barium meal. On the scan, the barium appears white as it passes through the digestive system.

If images of the lower body, such as the rectum, are needed, the patient may be given a barium enema. A contrast agent will be injected into the veins if blood vessel pictures are the goal.

The use of spiral CT, a relatively recent technique, may increase the accuracy and speed of CT scans. During scanning, the beam follows a spiral route, collecting continuous data with no pauses between images.

CT is a vital tool for assisting in medical diagnosis. However, it emits ionizing radiation that has the potential to cause cancer.

Patients should discuss the risks and advantages of CT scans with their doctors, according to the National Cancer Institute.


It is useful for obtaining images of:

  • Soft tissues
  • The pelvis
  • Blood vessels
  • lungs
  • Brain
  • abdomen
  • bones

CT is often the preferred method of diagnosis for many cancers, such as liver, lung, and pancreatic cancers.

A clinician can use the image to confirm the presence and location of a tumor, as well as its size and the extent to which it has damaged neighboring tissue.

A head scan can reveal critical information about the brain, such as whether there is any bleeding, artery swelling, or a tumor.

A CT scan of the abdomen can identify a tumor as well as any swelling or inflammation in the internal organs surrounding it. It can reveal any spleen, kidney, or liver lacerations.

A CT scan is useful for planning locations for radiotherapy and biopsies because it detects abnormal tissue, and it can also provide significant data on blood flow and other vascular issues.

It can assist a doctor in determining bone disorders, bone density, and the condition of the bones.

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:

  • An MRI, on the other hand, uses magnets and radio waves instead of X-rays.
  • A CT scan, unlike an MRI, does not reveal tendons and ligaments.
  • For studying the spinal cord, an MRI is preferable.
  • Cancer, pneumonia, abnormal chest x-rays, and bleeding in the brain, especially after an injury, are better candidates for a CT scan.
  • On an MRI, a brain tumor can be seen more clearly.
  • Because a CT scan may detect organ rupture and injury more immediately, it may be more suited to trauma patients.
  • On a CT scan, broken bones and vertebrae are more obvious.
  • CT scans give a clearer picture of the lungs and the organs in the chest cavity between them.


The patient may need to abstain from food, and possibly drink, for a specific period before the scan.

On the day

In most places, the patient will need to undress, usually down to their underwear, and put on a gown that the health center will provide. Avoid wearing jewelry.

If the hospital does not provide a gown, the patient should wear loose-fitting clothes free of metal buttons and zippers.

Some patients may have to drink a contrast dye, or the dye may be given as an enema or injected. This improves the picture of some blood vessels or tissues.

Any patient who has an allergy to contrast material should tell the doctor beforehand. Some medications can reduce allergic reactions to contrast materials.

As metal interferes with the workings of the CT scanner, the patient will need to remove all jewelry and metal fastenings.

During the scan

The patient will need to lie down on a motorized examination table that slides into a doughnut-shaped CT scanner machine.

In most cases, the patient will lie on their back, facing up. But, sometimes, they may need to lie facedown or sideways.

After one x-ray picture, the couch will move slightly, and then the machine will take another image, and so on. The patient needs to lie very still for the best results.

During the scan, everybody except for the patient will leave the room. An intercom will enable two-way communication between the radiographer and the patient.

If the patient is a child, a parent or adult might be allowed to stand or sit nearby, but they will have to wear a lead apron to prevent radiation exposure.


A CT scan involves a small, targeted dose of radiation. These levels of radiation, even in people who have undergone several scans, have not been proven to be harmful. The likelihood of developing cancer as a result of a CT scan is estimated to be less than one in 2,000.

The level of radiation involved is considered to be similar to what a person might be exposed to in the environment over a period of a few months to several years.

A scan is only performed if there is a compelling medical reason. The findings may lead to treatment for diseases that might otherwise be fatal. When deciding whether or not to get a scan, doctors will make sure that the advantages outweigh the risks.

Cancer and thyroid problems are two disorders that could emerge as a result of radiation exposure.

This is extremely unlikely in adults, and also unlikely in children. However, are more susceptible to the effects of radiation. This does not mean that health issues will result, but any CT scans should be noted on the child’s medical record.

In some cases, only a CT scan can show the required results. For some conditions, an ultrasound or MRI might be possible.

Can I have a CT scan if I am pregnant?

Any woman who suspects she may be pregnant should tell her doctor beforehand because there is a risk that the x-rays could harm the fetus.

Citing the American College of Radiography, the American Pregnancy Association (APA) points out that “No single diagnostic x-ray has a radiation dose significant enough to cause adverse effects on a developing embryo or fetus.”

However, the APA notes that CT scans are not recommended for pregnant women “unless the benefits clearly outweigh the risk.”

CT scans and breastfeeding

If a lactating or breastfeeding mother needs an iodinated intravenous dye for contrast, she should avoid breastfeeding for about 24 hours as the dye may pass into the breast milk.

I have claustrophobia: Can I have a CT scan?

A patient who has claustrophobia should tell their doctor or radiographer beforehand. The patient may be given an injection or tablet to calm them down before the scan.

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