CT (Computed Tomography) Scan
What is a CT scan?
Medical professionals use computed tomography, also known as CT scan, to examine structures inside your body. A CT scan uses X-rays and computers to produce images of a cross-section of your body. It takes pictures that show very thin “slices” of your bones, muscles, organs and blood vessels so that healthcare providers can see your body in great detail.
Traditional X-ray machines use a fixed tube to point X-rays at a single spot. As X-rays travel through the body, they are absorbed in different amounts by different tissues. Higher density tissue create a whiter image than other tissues against the black background of the film. X-rays produce 2D images. CT scans have a doughnut-shaped tube that rotates the X-ray 360 degrees around you. The data captured provides a detailed 3D view of the inside of your body.
Are a CT scan and CAT scan the same thing?
CT scans and CAT scans describe the same imaging test. CAT scan stands for computed axial tomography.
What is a CT scan with contrast?
Sometimes, your scan uses a contrast agent. This contrast agent, sometimes called a dye, improves the images by highlighting certain features. Your healthcare provider will either have you drink a special liquid containing the contrast agent or give you an IV injection with the contrast or both depending on the type of CT scan and the reason for the scan. The contrast agent is cleared from your body through your urine, first rapidly then more slowly over the next 24 hours.
How do I prepare for a CT scan?
Your healthcare provider will give you instructions on how to prepare for your CT scan. On the day of the exam, you should pay attention to:
- Arrival: You should plan to arrive early, depending on your healthcare provider’s instructions. Arriving early helps the testing stay on schedule.
- Diet: Avoid eating and drinking for four hours before your exam.
- Medications: Ask your healthcare provider if you should take your regular medicines before the CT scan.
- Comfort: You should wear comfortable clothes. You may need to change into a gown before the exam and remove your watch and jewelry, including any piercings you can remove. You may need to remove dentures and hearing aids, too. Zippers and metal objects can obstruct the scan.
If your CT scan uses dye or contrast, your provider may give you some specific preparation guidelines:
- Blood test: You may need a blood test before your scheduled CT scan. The blood test will make sure the healthcare provider chooses the right dye.
- Diet restrictions: You will need to watch what you eat and drink for the four hours before your CT scan. Consuming only clear liquids helps prevent nausea when you receive the contrast dye. You can generally have broth, tea or black coffee, strained fruit juices, plain gelatin and soft drinks, like ginger ale.
- Allergy medication: If you are allergic to the contrast agent used for CT (which contains iodine), you may need to take a steroid medication the night before and morning of your procedure along with an antihistamine, such as benedryl, before the exam. Be sure to check with your healthcare provider and have them order these medications for you if needed. Contrast agents for MRI and CT are different; being allergic to one doesn't mean you are allergic to the other.
- Preparation solution: You should drink the oral contrast solution as instructed by your technologist or nurse.
What happens during the test?
During the test, you will lie on your back on a table (like a bed). If your test requires it, a healthcare provider may inject the contrast dye intravenously (into your vein). This dye can make you feel flushed or have a metallic taste in your mouth.
When the scan begins:
- The bed slowly moves into the doughnut-shaped scanner. At this point, you will need to stay as still as possible because movement can create blurry images.
- The scanner takes pictures of the area the healthcare provider needs to see. Unlike an MRI scan, a CT scan is silent.
- When the exam is over, the table moves back out of the scanner.
How long does the test take?
Typically, you should plan for an hour for a CT scan. Most of that time is for preparation. The scan itself takes between 10 and 30 minutes or less. Generally, you can resume your activities after a healthcare provider says it is safe to do so — usually after they complete the scan and verify clear images.
Results and Follow-Up
How long does it take to get results?
The results of the scan usually take 24 hours. A radiologist, a physician who specializes in reading and interpreting CT scan and other radiologic images, will review your scan and prepare a report that explains them. In an emergency setting, such as a hospital or emergency room, healthcare providers often receive results within an hour.
Once a radiologist and your healthcare provider have reviewed the results, you will either have another appointment or receive a call. Your healthcare provider will discuss the results with you.
What does a CT scan show?
Your healthcare provider will order a CT scan to help make a diagnosis of your health. The scan enables providers to closely examine bones, organs and other soft tissues, blood vessels and suspicious growths. Things that a CT scan can find include:
- Certain types of cancer and benign (noncancerous) tumors.
- Fractures (broken bones).
- Heart disease.
- Blood clots.
- Bowel disorders (blockages, Crohn's disease).
- Brain and spinal cord diseases or injuries.
- Internal bleeding.
Healthcare providers can also see organs and tissues on X-rays. But on X-rays, body structures appear to overlap, making it difficult to see everything. The CT scan shows spaces between organs for a clearer view.
Are CT scans safe?
Healthcare providers consider CT scans generally safe. CT scans for children are safe, too. For children, your CT technician may use machines adjusted for children to reduce their radiation exposure.
CT scans, like other diagnostics, use a small amount of ionizing radiation to capture the image. Some risks associated with CT scans include:
- Cancer risk: All types of imaging using radiation, such as X-rays, cause a small increase in your risk of developing cancer. The difference is too tiny to measure effectively.
- Allergic reactions: Occasionally, people have a minor or more serious allergic reaction to the contrast agent.
If you have concerns about the health risks of CT scans, talk to your healthcare provider. They will discuss your concerns and help you make an informed decision about the scan.
Can I have a CT scan if I’m pregnant?
If you are or might be pregnant, you should tell the CT technician. CT scans of the pelvis and abdomen can subject the unborn baby to radiation, but it’s not enough to cause actual harm. CT scans in other parts of the body don’t put your baby at any risk.
A note from Cleveland Clinic
CT scans are an excellent diagnostic tool. You may have worries when your provider orders a CT scan. But this safe, painless test is noninvasive and has very little risk. The reward is that a CT scan can help your providers accurately diagnose a health concern and provide the right treatment for you. Talk to your healthcare provider about any concerns you may have, including other options for testing.
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