What to Expect When Undergoing a CT Scan (2024)

Computed tomography—also called a CT scan, CAT scan, or computerized axial tomography—relies on multiple X-rays to create a 3-D image. It allows healthcare providers to look at organs and helps them to diagnose an injury, such as a fracture, or a condition like cancer.

A CT scan provides more information than some other imaging tests without the need for invasive techniques. For example, it can sometimes be used to complete a biopsy. It may be done with contrast, an ingestible or injectable dye that allows technicians to visualize a body process better.

This article explains how a CT scan works, why you might need one, and how to prepare. It also discusses what results mean and the overall safety of a CT scan for most (but not all) people.

What Is a CT Scan?

A CT scan is a painless, non-invasive procedure that can be used to visualize nearly every part of the body. Since the introduction of CT technology in 1967, the imaging procedure first used in diagnosis has advanced with applications in disease prevention, screening, and management.

A CT scan is typically used when an X-ray cannot provide enough detail of an injury or disorder, especially in emergencies where time is of the essence.

What Can CT Scans Detect?

Among the many uses of a CT scan are:

• CT scanning of the abdomen may be used to identify masses in the liver, kidney, or pancreas or to search for causes of bleeding in the urinary tract (hematuria).
• CT scanning of the cardiovascular system can map blood flow (CT angiography) and help diagnose kidney disorders, aortic aneurysms, atherosclerosis, or pulmonary edema.
• CT scanning of the heart can help diagnose and monitor coronary artery disease (CAD) or aid in valve replacement surgery.
• CT scanning of the head and brain may be used to look for tumors, hemorrhage, bone trauma, blood flow obstruction, and brain calcification (commonly seen in people with Parkinson's disease and dementia).
• CT scanning of the lungs can help detect changes in the lung architecture due to fibrosis (scarring), emphysema, tumors, atelectasis (collapsed lung), and pleural effusion.
• CT scanning of the skeletal system can aid in diagnosing a spinal cord injury, pathologic fractures, bone tumors, or lesions and help evaluate a complex fracture, osteoporosis, or joint damage caused by arthritis.

Given this, your healthcare provider may order this test for several reasons, including monitoring an already-diagnosed condition.

What Is a CT Scan With Contrast?

Contrastagents, or radiocontrast agents or contrast dyes, are used in CT scans to highlight structures that are difficultto differentiate from their surroundings, such as the brain, spine, liver, or kidneys. Most are iodine-based and are injected intravenously (into a vein) before the scan.

For specific gastrointestinal investigations, an oral or enema solution may be needed. Barium sulfate and agents like Omnipaque (iohexol) are most commonly used.

Side effects can range from mild to life-threatening and develop anywhere from one hour to seven days after the dose. They include:

• Flushing
• Rash
• Itching
• Runny nose
• Coughing
• Dizziness
• Abdominal cramps
• Constipation
• Nausea
• Vomiting

Diabetes, asthma, heart disease, thyroid disorders, and kidney impairment may increase your risk of side effects.

Those with a known allergy to a radiocontrast agent should be pre-treated with antihistamines and steroids before receiving contrast.

What Is the Procedure for a CT Scan?

A CT scan is generally quick and painless. Knowing what to expect during the procedure can help make the process as smooth as possible.

Before the Test

The preparations for a CT scan can vary based on the diagnosed condition and whether a contrast agent is used. Your healthcare provider will provide specific instructions based on the aims of the test.

Location

The test is typically conducted in a hospital or an independent radiology facility. Newer CT imaging systems comprise a large, donut-shaped unit and a motorized scanning table that passes through the scanner.

A series of X-ray emitters and detectors are in the tunnel's center (gantry). These are far less claustrophobic and loud compared to older systems.

The radiographer will conduct the CT scan from a radiation-safe control room adjacent to the scanning room.

How Do I Prepare for a CT Scan?

• Dress appropriately: Depending on the part of your body being scanned, some or all of your clothing may need to be removed.Wear comfortable clothing without zippers, buttons, rivets, or snaps (such as a sweatsuit).
• Remove jewelry: Anything made of metal must be removed from the scanning site (including eyeglasses, jewelry, and piercings). It is best to leave any non-essential accessories at home.
• Ask about food restrictions: Food and drink restrictions may be needed for some CT procedures, especially those involving contrast agents. In such cases, you may be asked to stop eating or drinking six to eight hours beforehand.
• Ask about your medications: Certain medications may also need to be temporarily stopped. Advise your healthcare provider about any drugs you may be taking, whether prescription, over-the-counter, or recreational.

How Much Does a CT Scan Cost?

The CT scan costs between $600 and $1,500 when no contrast is used, but it depends on your state and the chosen facility. A more extensive evaluation with a contrast agent may be as high as $5,000.

As a rule, CT scans will require some form of insurance pre-authorization. Your healthcare provider can submit this request on your behalf. If approved, be sure to find out what your out-of-pocket expenses will be. If you are uninsured or underinsured, shop around for the best prices.

By and large, hospital radiology units are more expensive than independent ones. You can also ask if the lab offers flexible payment options. If you are uninsured, ask if they have a patient assistance program with a tiered price structure.

During the Test

On the day of the test, after signing in and confirming your insurance information, you may be asked to sign a consent form stating that you understand the purpose and risks of the procedure. You will then be led to a changing room to change out of your clothes.

Pre-Test

If you are having a conventional CT, you are now ready to get into position in the scanning room. But if your healthcare provider has ordered that your test be done with a contrast agent, you will need to undergo some additional preparations:

• If an IV contrast agent is ordered, you will be positioned on the table in the scanning room, and an IV line will be inserted into a vein in the arm, after which a contrast agent is injected. Sometimes, the agent may be injected directly into the joint (arthrogram) or lower spine (myelogram). You may experience brief flushing or a metallic taste in your mouth.Depending on the body part being scanned, you may need to wait in a reclined or prone position for several minutes or more. The IV line is kept in place until the end of the scan.
• If an oral contrast agent is ordered, you will be asked to drink a contrast solution before entering the scanning room. Depending on the part of the body being assessed, you may need to wait 30 to 60 minutes before the scan can be performed. Let the nurse or radiographer know if you experience nausea or distress.
• If a rectal contrast agent is ordered, you will be positioned on the table in the scanning room, and your rectum will be lubricated. An enema tube will be inserted to gradually fill your colon with the contrast agent (and sometimes air). You may be given a shot of Buscopan (butylscopolamine) to ease muscle spasms. A balloon at the tip of the tube is then inflated to prevent leakage and kept there until the scan is complete.

Depending on the investigation, you may be asked to lie on your back, side, or stomach. The table can be raised or lowered, and straps and pillows may keep you in position and help you stay still during the test.

Throughout the Test

When it is time to begin, the technician will inform you by communicating with you through the speaker. At first, the motorized table will move in and out of the scanner quickly.

This ensures that the table is in the correct starting position and that the scan will cover the entire body part being investigated. You will also see light lines projected onto your body to ensure you are in the correct position.

From there on, the table will move slowly through the scanner. The gantry will spin around you as the X-ray emitters produce an array of beams. The beams will pass through your body and be received by corresponding detectors.

During each scan, remember to remain still. In some cases, you may be asked to hold your breath. Your position may also be altered to obtain different views. Unlike CT scanners of old, newer units only emit slight buzzing, whirring, or clicking sounds. You will feel no pain from the scan.

A computer will then translate the signals into a series of cross-sectional (tomographic) images called slices. The two-dimensional slices can be converted into the final 3D image using geometric digital processing.

Post-Test

The radiographer will double-check once the scans are completed to ensure the images are clearly visualized.

• If an IV contrast agent was used, the IV line would be removed and the puncture wound bandaged.
• If an oral contrast agent is used, you will be given a glass of water and encouraged to drink plenty of fluids.
• If a rectal contrast agent is used, the solution will be extracted from the colon through the enema tube. Once the tube is removed, you will be led to the restroom to expel the rest into the toilet. A sanitary pad may be provided to protect your clothing from leakage. A laxative may also help clear the bowel and prevent constipation.

You can usually drive yourself home or to work.

After the Test

Most iodine-based contrast agents have a half-life of two to four hours, meaning they are fully cleared from your body in a day or two. Much of the solution will be excreted in the urine, so drink plenty of fluids.

If given a barium solution, you may experience short-term constipation, and your stools may be chalky for a day or two. Call a healthcare provider if you don’t have a bowel movement after two days.

Regardless of the type of CT done, call your healthcare provider if you experience any unusual symptoms, including:

• Fever
• Chills
• Vomiting
• Shortness of breath
• Rapid heartbeat

The radiation from the CT scan will not remain in the body, and you will be of no harm to anyone you touch, kiss, or stand close to.

Interpreting the Results

After a CT scan, you should get results from your healthcare provider within a day or two. In addition to the images, the radiologist will prepare a detailed report outlining the normal and abnormal findings.

A CT scan can sometimes provide definitive evidence of a disorder, particularly:

• Fractures
• Kidney stones
• Clots
• Narrowing (stenosis) of blood vessels
• Air passages
• Intestines

At other times, a scan can only suggest what is happening. This is especially true with abnormal growths, lesions, and tumors. Further investigation is often needed to determine whether the growth is benign or malignant and what types of cells may be involved.

In some cases, no problem may be found. This doesn't mean that you are necessarily in the clear. It simply indicates that nothing was detected based on the limitations of the CT technology.

Based on the results, your healthcare provider may offer a treatment plan or recommend further testing.

Follow-Up

If further investigation is needed, the diagnosis may involve the following:

• Blood tests
• Urine tests
• Cultures
• Tissue biopsies
• Imaging tests
• Exploratory surgery

If cancer is suspected, a combination PET-CT scan may provide more definitive evidence of a malignancy alongside a biopsy of the growth itself.

A CT scan is fast and accurate. But if your symptoms continue despite a "normal" result, speak with your healthcare provider about other test options or ask for a referral to a specialist who can expand the investigation.

What Are the Risks of a CT Scan?

Despite being a valuable tool for diagnosis and screening, a CT scan does carry risks, which relate to increasing your risk of cancer and reacting to contrast agents.

Cancer Risk

With CT scans, the main concern is the exposure to "high" radiation levels and the potential risk of cancer. While it is true that CT scans expose you to anywhere from 100 to 1,000 times more radiation than a conventional X-ray, that doesn't necessarily translate into a proportional increase in cancer risk.

According to the National Cancer Institute (NCI), the cancer risk from a single CT scan is small.

Compared to the average lifetime risk of cancer among Americans (one in five), the risk from a CT scan is more or less in the range of one in 2,000. The additive impact translates to a lifetime risk of roughly 20.05% compared to the general average of 20%.

Children may be at the highest risk because they have more years to live following the procedure compared to, say, someone in their 50s, 60s, or 70s. However, studies have found no clear association between medical radiation and cancer risk in children.

Allergic Reactions

Life-threatening allergic reactions—known as anaphylaxis—to CT contrast is extremely rare. Symptoms include shortness of breath, hives, facial swelling, rapid heart breath, impaired breathing, abdominal cramps, and a feeling of impending doom. If not treated immediately, anaphylaxis can lead to seizures, coma, shock, and even death.

Can I Have a CT Scan If I'm Pregnant?

CT scans may pose some risks if you are pregnant. If you suspect you may be pregnant or have been trying to get pregnant, advise your healthcare provider.

Generally speaking, the risk to your fetus is negligible if the abdomen or pelvis is not being scanned. If the CT scan involves the abdomen or pelvis, the risk to your baby is still considered minor.

Similarly, oral and rectal contrast agents are not absorbed in the bloodstream and cannot harm the fetus. While intravenous agents can cross the placenta and enter the fetal circulation, animal studies to date have not shown any evidence of harm.

If breastfeeding, it's essential to know that barium is not absorbed into the bloodstream and will not be passed to your baby in breast milk.

While less than 1% of an iodine-based solution may be transmitted in breast milk, this amount cannot cause harm to a baby and does not warrant the interruption of breastfeeding.

However, some mothers may prefer a more conservative approach and avoid breastfeeding for 24 to 48 hours after the test. (In such cases, pumping a couple of days' supply beforehand can tide you over.)

Can I Have a CT Scan if I’m Claustrophobic?

While not moving as the scan is being performed is imperative, newer multi-detector CT systems are fast and easy, reducing the amount of time you need to hold your position. In fact, in a study examining the conmfort of patients undergoing a CT scan, 33% indicated they suffer from some degree of clausprophobia, but 99.1% of patients stated they didn't have claustrophobic feelings during their CT scan. Patients who are anxious about their test can speak to a healthcare provider in advance about their concerns.

Pediatric Considerations

According to the NCI, between 5 million and 9 million CT scans are performed annually on children in the United States, including infants and toddlers.

While the lifetime risk of cancer in children from a single CT scan is low, the NCI recommends adjusting the procedure so that the lowest possible radiation dose is delivered to achieve a clear imaging result.

This would involve:

• Performing CT scans only when needed
• Considering other options that do not emit radiation, such as MRI and ultrasound
• Adjusting the radiation level based on the child's size and weight
• Narrowing the scan to the smallest necessary area
• Reducing the scan resolution if high-quality images are not necessary

If more than one CT scan is recommended, discuss the benefits and risks with your healthcare provider, and do not hesitate to ask if there are other means to achieve a reliable diagnosis.

Contraindications

CT scans are almost always avoided during pregnancy unless the benefits of the test outweigh the potential risks.

Other contraindications may include:

• A known iodine allergy
• Planned radioiodine treatment of thyroid cancer
• Gastrointestinal perforation (for oral or rectal solutions)

From a practical standpoint, high body weight may exclude using a CT scan, given that most machines can only accommodate weights of less than 425 to 450 pounds and a back-to-belly measurement of fewer than 28 inches.

Summary