What is a CT or CAT scan?

What is a CT or CAT scan?

A computerized tomography (CT) or computerized axial tomography (CAT) scan integrates data from several X-rays to create a clear image of the body’s internal structures.

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

The CT scans are used worldwide in hospitals.

What is a CT scan?

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

A CT scanner emits a sequence of narrow beams across the human body as it passes through an arc. This is different from an X-ray machine which sends only one beam of radiation. The CT scan provides a more accurate final image compared to an X-ray image.

X-ray detector by the CT scanner can see hundreds of different density levels. It is able to see tissues inside a solid organ.

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

A contrast dye is often used, as it can help to display certain structures more clearly.

For example, if the abdomen needs a 3-D picture, the patient may need to drink a barium meal. On the scan the barium appears white as it passes through the digestive system.

When photos are needed lower down the body, such as the rectum, a barium enema may be given to the patient. If photos of the blood vessel are the target, they can inject a contrast agent into the veins.

With the application of Spiral CT, a fairly new technology, the precision and speed of CT scans can be enhanced. During the scanning the beam follows a spiral path so it gathers continuous data with no image gaps.

CT is a valuable tool in medicine to help in diagnosis but it is a source of ionizing radiation and can potentially cause cancer.

The National Cancer Institute is suggesting that patients address with their doctors the dangers and benefits of CT scans.


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

It is useful for obtaining images of:

  • soft tissues
  • the pelvis
  • blood vessels
  • lungs
  • brain
  • abdomen
  • bones

CT is also the best way to treat other cancers such as liver cancer, lung cancer and pancreatic cancer.

The picture helps a physician to confirm a tumor’s existence and position, its size and how much it has infected surrounding tissue.

For example, a scan of the head may provide valuable brain information when there is bleeding, artery swelling, or a tumor.

A CT scan will show a tumor in the abdomen, and any inflammation or swelling in surrounding internal organs. It may exhibit spleen, kidney, or liver lacerations.

It is useful for preparing areas for radiotherapy and biopsies, since a CT scan identifies irregular tissue, which can provide important data on blood flow and other vascular conditions.

It will help a doctor determine bone disorders, bone density and the patient’s spine condition.

It may also provide the hands, feet, and other structural structures of a patient with essential data about injuries. And small bones, and their underlying tissue, are clearly evident.

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.


The patient may need to abstain from food for a limited duration before the exam, and probably drink.

On the day

The patient will have to undress in most cases, usually down to their panties, and put on a gown that will be issued by the health centre. Do not wear jewellery.

If a gown isn’t issued by the hospital, the patient will wear loose-fitting garments free of metal buttons and zippers.

Some patients will have to drink a contrast dye, or the dye may be given as an enema, or injected. This enhances the appearance of certain blood vessels or tissues.

Any patient with an allergy to the contrast material will inform the doctor in advance. Some medicines can reduce allergic reactions to materials that contrast them.

As metal interferes with the CT scanner’s working, the patient may have to remove all jewelry and metal fastenings.

During the scan

The patient will have to lie on a motorized exam table which slides into a doughnut-shaped CT scanner.

In most cases, the patient lies on the back and faces upwards. But they can need to lie face-down or sideways, often.

The couch will turn slightly after one x-ray image, and then the camera will take another image, and so forth. For the best results the patient requires to lie very still.

All except for the patient will be leaving the room during the exam. An intercom will allow bidirectional communication between the radiograph and the patient.

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


The doctor should explain why the scan is needed, any other options available, and the pros and cons of having a CT scan.
The doctor should explain why the scan is needed, any other options available, and the pros and cons of having a CT scan.

A CT scan will require a low, focused radiation dose.

Such levels of radiation have not proved dangerous, particularly in people who have undergone several scans.

The risk of developing cancer is believed to be less than 1 in 2,000 as a result of a CT scan.

It is calculated that the amount of radiation involved is about the same as a person would be exposed to natural exposure in the atmosphere over a period of between several months and several years.

A scan is only given if the medical reason for doing so is valid. The findings can lead to treatment for otherwise severe conditions. When the decision to conduct a scan is made, doctors must make sure the benefits outweigh the harm.

Problems which may arise from exposure to radiation include cancer and thyroid problems.

This is extremely unlikely in adults, and rare in children too. However, they are more vulnerable to radiation effects. This does not mean that there would be health complications but any CT scans should be noted on the medical record of the infant.

In certain cases, the necessary results can only be seen on a CT scan. An ultrasonic or MRI may be necessary for certain circumstances.

Can I have a CT scan if I am pregnant?

Any woman who thinks that she might be pregnant should inform her doctor in advance, because there is a risk that the x-rays could damage the fetus.

The American Pregnancy Association (APA), citing the American College of Radiography, points out that “No single diagnostic x-ray has a radiation dose sufficiently large to cause adverse effects in a developing embryo or fetus.” However, the APA states that CT scans are not recommended for pregnant women, “Unless the benefits clearly outweigh the risk.”

CT scans and breastfeeding

When, in comparison, a lactating or breastfeeding mother requires an iodinated intravenous dye, she should stop breastfeeding for about 24 hours as the breast milk can pass through.

I have claustrophobia: Can I have a CT scan?

A patient who has claustrophobia should inform their doctor or x-ray in advance. Before the exam, the patient can get an injection or tablet to calm them down.

Finding a radiologist

Your health care professional should usually be able to suggest a appropriate scan location. Through visiting the American College of Radiology website, you can verify if a radiologist is certified.