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Computed Tomography: Complete Overview

If your doctor has ordered you to get a computed tomography (CT) scan, you might have some questions. Read on to get a complete overview of this imaging technique, including how it works and how it compares to magnetic resonance imaging (MRI).

What is computed tomography (CT)?

Computed tomography, also called a CT or CAT scan, is a vital tool used to diagnose injuries and illnesses. Its sophisticated imaging system uses X-rays to create detailed pictures of the inside of the body. With greater precision than traditional X-rays, computed tomography can be used for adults and children. 

CT’s sophisticated imaging system uses X-rays to create detailed pictures of the inside of the body.

Tomography, which comes from the Greek tomos (to slice or cut) and graphein (to record), is different from a regular X-ray. In a traditional X-ray procedure, a fixed X-ray tube directs one X-ray beam through your body. The resulting image can only show a two-dimensional image. Bones appear white and muscle and fat tissue appear grey. Tomography, on the other hand, uses an X-ray tube that rotates around the body, creating “slices” of cross-sectional images. These images are more detailed. They can be looked at two-dimensionally or made into three-dimensional images. 

What is computed tomography used for?

In addition to injuries, computed tomography is used to detect cancer, heart disease, blood diseases, spinal problems, blood clots, and bladder or kidney stones.

CT scans are considered to be one of the best ways to detect cancer in the pelvis, abdomen, and chest. The exact tumor size, location, and impact on other tissues in the body can be determined. CT scans can also be used to see how cancer is responding to treatment and detect any recurrence.

While they are widely used in cancer treatment and prevention, CT scans are also used for many other reasons. They can be used to detect internal injury following a car accident or to assess, diagnose, and treat vascular diseases such as stroke or blood clots.

In children, computed tomography can be used to detect a variety of conditions:

How does computed tomography work?

CT scans work by using continuously moving X-ray beams that center around the exact part of the body where an image is needed.

The machine itself, which is large and shaped like a doughnut, houses an X-ray tube that emits X-ray beams to a specific section of the body. This tube can be placed to scan any portion of the body, from a very small area to a full body scan. 

The machine itself, which is large and shaped like a doughnut, houses an X-ray tube that emits X-ray beams to a specific section of the body.

At the start of the procedure, you’ll lie down on a motorized table that faces the machine. When the procedure begins, the table moves into the center of the scanner (the “O” of the doughnut). Next, the X-ray tube moves in a circle around your body, emitting X-rays. These X-rays move through your body and to the scanner, which is directly opposite the X-ray tube. The scanner then captures and transmits the cross-sectional image and the process continues. 

The images are taken from a variety of different angles and sent to a computer. There, they are reassembled to create either a two-dimensional or three-dimensional image. Three-dimensional images are particularly useful to see interior parts of the body from different angles, taking apart the image into smaller slices to look at in greater detail.

The images are taken from a variety of different angles and sent to a computer. There, they are reassembled to create either a two-dimensional or three-dimensional image.

While they already deliver significantly more detail than traditional X-rays, CT scans have continued to improve. Newer models are faster and can capture small abnormalities better than ever before.

CT scan procedure

Getting a CT scan is a simple and painless procedure that typically lasts 30 minutes or less. 

When you go for your CT scan, you’ll want to wear comfortable clothing and leave any jewelry at home. You may also be asked to fast before the procedure. Contrast material is a fluid dye that doctors sometimes use to accentuate certain areas in the body. The doctor will insert the dye before a procedure, either through an intravenous line or (more rarely) an enema.

Getting a CT scan is a simple and painless procedure that typically lasts 30 minutes or less.

The radiology technician, who administers the scan, will have you lie down on the motorized table, with either your head or your feet facing the machine. The position will depend on which part of your body needs to be scanned. You will be asked to lie very still in order for the machine to capture accurate images. Then the technician will leave the room but will be able to communicate with you through a microphone that transmits their voice directly into the machine. 

The table will move slowly into the center of the machine. When the actual scan begins, the table will move slowly back and forth, capturing slices or images that are sent to the computer. You will hear the whirring of the machinery during this time, and you may hear the technician speaking with you as well. The length of the procedure depends on the size of the area being scanned but is usually not longer than 30 minutes.

Following the scan, it may take a few minutes while the technician confirms that the captured images are clear enough to be used. Then they will come back into the room and remove any intravenous line, if used, and bandage the area. After this, you’re all done and free to go about your day.          

Side effects of computed tomography

If you’re scared that getting a CT scan could make you feel claustrophobic, try not to worry. The machine is open on both ends, so you’re never in a tight or enclosed space.

While the CT procedure does not produce any side effects, the contrast agents that are sometimes used can cause side effects.

If you’re scared that getting a CT scan could make you feel claustrophobic, try not to worry. The machine is open on both ends, so you’re never in a tight or enclosed space.

Two of the most common dyes used as contrast agents are iodine and barium. In rare circumstances, these dyes can cause a reaction. Mild reactions include hives or itching, and more serious reactions involve swelling and shortness of breath. In very rare situations, contrast dyes can cause kidney issues. If you have diabetes, for example, you could be at a higher risk of developing kidney problems and should speak with your doctor. If you experience any of these symptoms, tell the radiology technologist immediately to get them treated quickly.  

Who should undergo computed tomography?

If you or your doctor suspects something is seriously wrong with you, a CT scan may be needed. Some of the common reasons for getting a CT scan include:

1. You have sustained a severe physical injury.

In serious injuries, when unknown damage including internal bleeding may have occurred, CT scans can detect these problems quickly so they can be treated.

2. You need blood vessels inspected.

By being able to detect any blockages or issues with blood vessels, CT scans can help you avoid exploratory surgery or a biopsy. Any vascular diseases can also be identified using tomography. 

3. You need a scan done on very small bones.

Because it produces a much greater level of detail than a traditional X-ray, a CT scan is great for examining areas that contain small bones, like the back, feet, or hands.

4. You are undergoing cancer treatment.

CT scans can be a great help for doctors planning cancer treatments or checking for cancer recurrence.

5. You need surgery done on a tumor.

With a CT scan, doctors can pinpoint exactly where a tumor is located and its size. This helps them determine exactly where to operate, and they can do further scans to confirm the cancer has been successfully treated.

6. You can’t have an MRI.

MRIs take much longer than CT scans, anywhere from 30 minutes to an hour. If a patient, such as a child, has trouble lying still for that long, a CT scan may be a better option. Computed tomography is also an alternative for people with metal implants who cannot get an MRI.

Who should not undergo computed tomography?

While it’s not a dangerous procedure, it’s good to inform yourself about your options. 

The X-rays used in tomography emit radiation, which can damage DNA and increase the chance that they’ll turn cancerous. Your chances of getting a lethal cancer from a CT scan are 1 in 2,000. 

Children, whose bodies are still growing, are more susceptible to the harmful effects of radiation. To help counteract this, tomography devices can be set to child-appropriate dosages. 

In general, most doctors agree that CT scans should not be used to diagnose someone who has no symptoms.

If you are pregnant and considering a CT scan, your doctor can help you decide whether the benefits from the scan outweigh its risks. The American College of Radiology has emphasized that the chances of a CT scan harming a fetus are negligible. In general, CT scans are not recommended during pregnancy unless the benefits of the CT scan clearly outweigh the potential risk. 

Some doctors recommend that breastfeeding moms wait 24–48 hours before nursing if a contrast agent has been used during the scan, but research reports say that no delay is necessary. This is because the amount of dye transferred through breast milk is very small and much less of a risk than switching to formula.   

In general, most doctors agree that CT scans should not be used to diagnose someone who has no symptoms.  

MRI vs CT scan: What’s the difference?

How does a CT scan compare to an MRI? Both are used to capture images in your body. The difference is what they use and how they use it to capture those images.

Because MRIs use strong magnets, people who have certain types of metal in their body cannot use an MRI.

MRIs use radio waves instead of X-rays. For this reason, there is no radiation in an MRI procedure. While you still go into a tube-like entrance during an MRI, different versions, including an upright version, exist. A coil is placed on an area of your body that helps the radio waves gather the information they need. MRI machines, unlike computed tomography, are also very loud, and you may be asked to wear headphones to help soften the sound. Because MRIs use strong magnets, people who have certain types of metal in their body cannot use an MRI. 

Conclusion

A CT scan can provide very important, even life-saving, information. Its widespread use and ability to help doctors and patients make informed decisions make it one of the most valuable imaging methods available. 

https://www.fda.gov/radiation-emitting-products/medical-x-ray-imaging/what-computed-tomography

https://www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct

https://www.radiologyinfo.org/en/info.cfm?pg=bodyct

https://www.cancer.gov/about-cancer/diagnosis-staging/ct-scans-fact-sheet

https://www.mayoclinic.org/tests-procedures/ct-scan/about/pac-20393675

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1952588/

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