Table of ContentsView AllTable of ContentsWhat Is a CT Scan?PurposeContrastProcedureInterpreting the ResultsRisks
Table of ContentsView All
View All
Table of Contents
What Is a CT Scan?
Purpose
Contrast
Procedure
Interpreting the Results
Risks
Computed tomography—also called a CT scan, CAT scan, orcomputerized 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 abiopsy. It may be done withcontrast, 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.
Verywell / Emily Roberts
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:
Given this, your healthcare provider may order this test for several reasons, including monitoring an already-diagnosed condition.
CT Scan vs. MRICT scans are fast, widely available, and versatile. However, for some conditions, doctors may order magnetic resonance imaging (MRI) for its improved ability to see soft tissues such as muscles, joints, ligaments, and spinal discs.Because of the strong magnetic waves, it may not be appropriate for people with implants likepacemakers, artificial joints orcochlear implants.
CT Scan vs. MRI
CT scans are fast, widely available, and versatile. However, for some conditions, doctors may order magnetic resonance imaging (MRI) for its improved ability to see soft tissues such as muscles, joints, ligaments, and spinal discs.Because of the strong magnetic waves, it may not be appropriate for people with implants likepacemakers, artificial joints orcochlear implants.
CT scans are fast, widely available, and versatile. However, for some conditions, doctors may order magnetic resonance imaging (MRI) for its improved ability to see soft tissues such as muscles, joints, ligaments, and spinal discs.
Because of the strong magnetic waves, it may not be appropriate for people with implants likepacemakers, artificial joints orcochlear implants.
What Is a PET Scan?
What Is a CT Scan With Contrast?
Contrast agents, or radiocontrast agents or contrast dyes, are used in CT scans to highlight structures that are difficult to 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 sulfateand 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:
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?
How long does a CT scan take?From arrival to completion, the appointment should take around one to two hours. The scan itself without a contrast agent should take around three to five minutes to perform. If a contrast agent is used, it can take anywhere from several minutes to an hour for the solution to fully circulate through the bloodstream or gastrointestinal tract.
How long does a CT scan take?
From arrival to completion, the appointment should take around one to two hours. The scan itself without a contrast agent should take around three to five minutes to perform. If a contrast agent is used, it can take anywhere from several minutes to an hour for the solution to fully circulate through the bloodstream or gastrointestinal tract.
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 yourout-of-pocket expenseswill 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:
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
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.
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.
If you need to sneeze or itch during a CT scan, or you are cramping up, let the technician know. There is no problem with stopping the test momentarily. In some cases, the technician may be able to make you more comfortable without obstructing the imaging.
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.
You can usually drive yourself home or to work.
After the Test
Most iodine-based contrast agents have ahalf-lifeof 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:
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.
After a CT scan, you should get results from your healthcare provider within a day or two. In addition to the images, theradiologistwill prepare a detailed report outlining the normal and abnormal findings.
A CT scan can sometimes provide definitive evidence of a disorder, particularly:
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 isbenign or malignantand 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.
If further investigation is needed, the diagnosis may involve the following:
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.
When used appropriately, the benefits of a CT scan will almost always outweigh the possible risks. If you’ve had one or more CT scans in the past, it is important to advise your healthcare provider if a new one is ordered.
Allergic Reactions
Life-threatening allergic reactions—known asanaphylaxis—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.
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.
However small the risk may be, it’s always best to speak with your healthcare provider about any procedure performed during pregnancy so that you can make an informed choice.
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:
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:
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
CT scans are generally safe, well-tolerated, and helpful for diagnosing various conditions. They can be performed quickly, and thus are an invaluable tool for diagnosing time-sensitive injuries and diseases. Although there is some potential risk from radiation or possible side effects of contrast solution, a healthcare provider will weigh these risks against the potential benefits when recommending whether someone should undergo a CT scan.
4 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Johns Hopkins Medicine.Computed tomography (CT) scan.National Cancer Institute.Computed tomography (CT) scans and cancer.American College of Obstetricians and Gynecologists.Guidelines for diagnostic imaging during pregnancy and lactation [ACOG committee opinion number 723].Niehoff JH, Heuser A, Michael AE, Lennartz S, Borggrefe J, Kroeger JR.Patient comfort in modern computed tomography: what really counts.Tomography. 2022;8(3):1401-1412. doi:10.3390/tomography8030113
4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Johns Hopkins Medicine.Computed tomography (CT) scan.National Cancer Institute.Computed tomography (CT) scans and cancer.American College of Obstetricians and Gynecologists.Guidelines for diagnostic imaging during pregnancy and lactation [ACOG committee opinion number 723].Niehoff JH, Heuser A, Michael AE, Lennartz S, Borggrefe J, Kroeger JR.Patient comfort in modern computed tomography: what really counts.Tomography. 2022;8(3):1401-1412. doi:10.3390/tomography8030113
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Johns Hopkins Medicine.Computed tomography (CT) scan.National Cancer Institute.Computed tomography (CT) scans and cancer.American College of Obstetricians and Gynecologists.Guidelines for diagnostic imaging during pregnancy and lactation [ACOG committee opinion number 723].Niehoff JH, Heuser A, Michael AE, Lennartz S, Borggrefe J, Kroeger JR.Patient comfort in modern computed tomography: what really counts.Tomography. 2022;8(3):1401-1412. doi:10.3390/tomography8030113
Johns Hopkins Medicine.Computed tomography (CT) scan.
National Cancer Institute.Computed tomography (CT) scans and cancer.
American College of Obstetricians and Gynecologists.Guidelines for diagnostic imaging during pregnancy and lactation [ACOG committee opinion number 723].
Niehoff JH, Heuser A, Michael AE, Lennartz S, Borggrefe J, Kroeger JR.Patient comfort in modern computed tomography: what really counts.Tomography. 2022;8(3):1401-1412. doi:10.3390/tomography8030113
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