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A Radiologist’s Guide to Getting a CT Scan

How long does a CT scan take

Wondering how long your CT scan will take or when you’ll get your CT scan results? Radiologist Dr. Ania Kielar answers these questions and more.

Computed tomography (better known as a CT scan) is a medical imaging procedure that uses X-rays to create cross-sectional images of different parts of the body. Those images, called ‘slices’, are digitally compiled together into a single image.

Dr. Ania Kielar, President of the Canadian Association of Radiologists and Vice Chair of Radiology at the University of Toronto explains how CT scans work, when and why they’re used and how long it takes to get your results back.

What’s a CT scan and how does it work?

According to Dr. Kielar, CT scans are “the bread and butter of radiology” because of the clear, detailed images the procedure provides. During a CT scan, a patient lies on a table, which is slowly threaded through a doughnut-shaped machine that rotates around them to take a series of X-rays. A computer then digitally combines those ‘slices’ into a detailed 3D image.

In a CT scan, the X-ray images are typically taken from different angles to capture a complete 360° view, including:

  • Coronal: the front view, showcasing the front and back sides of the body
  • Sagittal: the side view, dividing the body into left and right sections
  • Axial: the cross-sectional view, presenting the top and bottom halves of the body

After your scan, the images are sent to a radiologist who reads and interprets them and creates a report about the findings.

What is the difference between a CT scan and an MRI?

Both CT scans and MRIs provide clear images of the inner workings of the body to help doctors diagnose conditions or monitor treatment, but they use different methods to create those images. A CT uses multiple X-rays combined together by computer to create a single, highly-detailed image. An MRI captures images using powerful magnets and radio waves.

MRI scans can provide very clear images of soft tissues like ligaments, muscles or tendons, while CT scans of skeletal structures can be more distinct and defined. In terms of procedure length, a CT scan does not take as long as an MRI. In addition, CT scans are generally less expensive to produce, and the equipment is more widely available.

Your doctor will choose the kind of imaging procedure that is best for your particular circumstances and needs.

What does a CT scan show?

What a CT scan shows depends on what is being imaged. “We use CT scans for a lot of reasons,” says Dr. Kielar. In the head, for instance, “we look at the bones in the skull, sinuses, the brain.”

Radiologists also use CT scans to examine the internal organs and structures to identify many illnesses and injuries, such as:

  • Blood clots and diseases
  • Bone or joint fractures or deterioration
  • Brain bleeds or clots
  • Cancer and other tumors
  • Heart abnormalities
  • Inflammatory diseases
  • Kidney or bladder stones
  • Lung issues
  • Spinal injuries or irregularities

Dr. Kielar explains that CT scans provide valuable information so doctors can properly assess what’s going on inside the body. “We would look at the legs for a complicated fracture of, say, the knee or the lower leg or ankle. We would also scan the lower leg to look at the vessels to see if they’ve got flow going in them or if they need bypass surgery.”

What is a contrast agent and when is it used?

Depending on the situation, patients may be given a contrast agent, which is a kind of dye, to improve the quality of the images produced. “The contrast agent helps the radiologist see all the organs and be able to identify what is happening inside of them,” says Dr. Kielar. “It doesn’t happen with all patients, it depends on the reason we’re imaging the patient.”

The dye, which might be administered either orally, rectally or through an IV, helps doctors better pinpoint and identify many issues, including:

  • Abscesses
  • Fluid build-up in the lungs or other organs
  • Hemorrhages
  • Lesions
  • Ulcers or ulcerative colitis

How long does a CT scan take?

The CT scan itself does not usually take very long, but preparation for the exam and getting into the right position can take time, anywhere from 30-60 minutes. According to Dr. Kielar, “Once they have you on the table in the right spot, it takes less than a minute.”

The exact length of your CT scan appointment will depend on what part is being scanned and why, and whether or not a contrast agent is being used. “If you have to drink the oral contrast for a CT scan, that adds an extra half an hour,” Dr. Kielar explains. “It’s not like you just shoot it back, you have to drink the agent slowly over about half an hour. Then they take you over to the CT scanner and image you.”

How can patients prepare for a CT scan?

Your CT scan provides your medical team with information to help them diagnose or assess your condition. There are several steps you can take to prepare for your appointment:

  • Bring your requisition. Your requisition has important information for the imaging clinic, describing the area to be scanned. Having it on hand will make the check-in process much easier.
  • Wear comfortable clothing. Wear loose clothing so you can easily change into a gown if required. Remove all jewelry and metal items, as they might interfere with the scan.
  • Refrain from eating (in some cases). Some CT scans require patients to arrive with an empty stomach, but not all. “It really depends on the body part,” Dr. Kielar says. “The imaging clinic will give you instructions. If you’re doing a CT scan of the abdomen, we don’t want the stomach to be full.” You may be required to fast for 4-6 hours before some CT scans. Check with the clinic when you make your appointment for any preparation instructions.
  • Have bloodwork completed if necessary. If a contrast agent will be used, a blood test may be required to ensure a patient’s kidneys are functioning properly and will be able to clear the agent from their system following the scan. “If we’re giving you intravenous contrast, we don’t want the stomach to be full because some people feel unwell after getting the contrast agent,” says Dr. Kielar. “Not most, but sometimes.”
  • Drink only clear fluids. Even if you don’t have to fast for your appointment, you should drink only clear fluids (water, tea, black coffee, juice) in the two hours before your scan. If your CT scan requires a contrast agent, it is best to avoid caffeine for 24 hours before your scan.
  • Ask about your medications ahead of time. While regular medications can generally be taken before a CT scan, Dr. Kielar encourages you to disclose any other necessary medications when making an appointment. “Whenever you go to the hospital, I strongly recommend that you have a list of your past medical history and your medications.”
  • Let the clinic know if you have anxiety. While CT scanners are open machines, some people might still experience anxiety or claustrophobia. Don’t hesitate to mention any concerns with your doctor or radiologist. If you are anxious about the procedure, you can be provided with a short-term, fast-acting relaxant.

Are there any other concerns or risks that accompany a CT scan?

CT scans are considered low-risk imaging procedures. X-rays use very low-dose ionizing radiation in the safest possible quantity. Dr. Kielar describes the dosage as “ALARA – As Low As Reasonably Achievable.” But it is helpful to know all the possibilities so you can make informed decisions.

  • Allergies. Some patients may feel a little flushed after being administered contrast dye. According to Dr. Kielar, there is also a very small chance, less than 1%, of having an allergic reaction that may require medical attention. “Any time we give a contrast agent there are risks but they are extremely low. It’s a risk that can be discussed with your doctor but it’s one that we’re generally willing to take because otherwise we can’t tell what’s happening.”
  • Pregnancy. It is vital to inform the radiologist if you are pregnant. ”We try not to scan people who are pregnant,” says Dr. Kielar. ”If we can avoid it until later, we will.” However, a CT scan can be performed on a pregnant patient under specific circumstances. According to the Radiological Society of North America (RSNA), missing or delaying a diagnosis may be more dangerous than a low dose of ionizing radiation. If a CT scan is deemed necessary for the health of the mother, the radiologist and CT technician can also adjust the dosage parameters for peace of mind.

What should patients do after a CT scan?

CT scans are non-invasive and do not typically require a recovery period. You can resume your regular activities right away after the procedure. That includes taking pain medications if you have any discomfort.

“If we use the contrast agent, we usually recommend people drink a reasonable amount of fluids after the scan,” Dr. Kielar says. “Even if the kidneys are working very well, we don’t want that contrast to be inside of their veins for very long.” If you drink plenty of water, 6-8 glasses, the contrast will be quickly flushed from your system.

How much time does it take to get your CT scan results back?

If your CT scan is taken in a hospital, your results may be available the same day. For outpatient scans, the radiologist will read and interpret the scans, and send the results to your referring physician, typically within a week. Your doctor will then make a follow-up appointment with you to discuss your results.

With PocketHealth, you can have early access to your CT scan images and reports, often as soon as they are released by the radiologist. PocketHealth is a secure platform where you can see, share and store your all your medical images and information in one place. Access your records today.

How to understand your CT scan results

Your CT scan report will discuss your images from three views: coronal, sagittal, and axial, mentioning any abnormalities and highlighting any findings.

The radiologist interprets your images using the Hounsfield scale. This common scale expresses how much X-ray radiation is absorbed by your body in Hounsfield Units (HU). High numbers on the Hounsfield scale represent dense tissue, which appears light or white in CT scan images. Low numbers represent non-dense tissue, which appears darker. Blood, for instance, is 60-90 HU, while bone is 300-1000 HU.

PocketHealth’s Report Reader provides definitions of complex medical terms to help you better understand your CT scan results. Report Reader also highlights any follow-up recommendations in the report, so you’ll always be fully informed about the next steps to take.

What does unremarkable mean on a CT scan?

In CT scan results, ‘unremarkable’ is actually a good thing. It means nothing unusual was found during your scan.

Confidently advocate for your health

A CT scan compiles multiple X-ray images into a detailed 3D view of your body. CT scan images help your medical team diagnose illnesses and injuries and to monitor the progress of treatment.

PocketHealth is here to support you, to help you access and understand your CT results so you can feel confidently prepared to advocate for your health.

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Learn more about how to use PocketHealth to access and share your CT scan records.

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