A CT scan is a painless imaging test that takes detailed cross-sectional pictures of your body using X-rays. The actual scanning typically takes less than a minute for simple studies, though your total time at the facility will be longer if contrast dye is needed. Here’s what to expect from start to finish.
How the Machine Works
A CT scanner looks like a large donut with a flat bed that slides through the center opening. Inside that donut-shaped structure, called a gantry, a motorized X-ray tube rotates around you while digital detectors sit on the opposite side. As the tube completes each full rotation, it shoots narrow beams of X-rays through your body from every angle. A computer then assembles those readings into a detailed two-dimensional “slice” of your anatomy.
Once one slice is complete, the bed moves forward slightly and the process repeats, building a stack of slices that can be viewed individually or reconstructed into three-dimensional images. This is what sets CT apart from a standard X-ray, which captures everything in a single flat image. The rotating approach lets radiologists see organs, bones, and blood vessels in cross-section, making it far easier to spot tumors, bleeding, fractures, and other problems.
Preparing Before Your Appointment
Your preparation depends on whether your scan requires contrast dye. If no contrast is needed, you can eat, drink, and take your medications as normal. If your scan does require contrast, you’ll generally be asked not to eat for three hours beforehand, though clear liquids are fine. If you’re diabetic, the guidance is slightly different: eat a light breakfast or lunch at least three hours before the scan.
You’ll be asked to remove metal jewelry, hairpins, belts, and sometimes your clothing in favor of a hospital gown. Metal objects create bright streaks on the images that can obscure what the radiologist needs to see. Even small items like hair ties with metal clasps or clothing labels with metallic threads can interfere, so it’s easiest to leave accessories at home and wear simple, loose clothes without zippers or snaps.
If you’re receiving IV contrast, the facility may check your kidney function beforehand with a blood test. Contrast dye is filtered through the kidneys, and patients with significantly reduced kidney function may need special precautions or an alternative imaging approach.
What Happens During the Scan
You’ll lie on the scanner bed, usually on your back. A technologist positions you and may place cushions or straps to help you stay still. The bed then slides into the gantry opening, which is wide and shallow, so most of your body remains outside the ring. This is not an enclosed tube like an MRI, and claustrophobia is rarely an issue.
The technologist operates the scanner from an adjacent room with a glass window and can hear you through an intercom the entire time. During the scan, you may hear a soft whirring or humming as the X-ray tube rotates. You’ll likely be asked to hold your breath for a few seconds, particularly for chest or abdominal scans, because breathing motion can blur the images. The scanning portion itself is fast, often finishing in under 30 seconds for a single body region.
Contrast Dye: What It Feels Like
Not every CT scan requires contrast, but when it does, the dye helps certain structures show up more clearly on the images. Contrast can be given in a few ways depending on what part of the body is being examined. Intravenous (IV) contrast is the most common, injected through a small needle in your arm. For scans of the digestive tract, you may be asked to drink an oral contrast solution, which is typically a barium or iodine-based liquid. In some cases, contrast is administered rectally.
IV contrast produces distinctive sensations that catch many people off guard but are completely normal. You may feel a warm flush spreading through your body, notice a metallic taste in your mouth, or experience a brief burning feeling at the injection site. These sensations pass within a few seconds. Some people also feel a sudden warmth in the pelvis that mimics the sensation of urinating, but you haven’t. It’s just the contrast moving through your bloodstream.
Radiation Exposure
CT scans do use ionizing radiation, and the dose varies by body region. A head CT delivers a median dose of about 2 millisieverts (mSv). A chest CT comes in around 4.4 mSv, and an abdominal CT is higher at roughly 6.8 mSv. For context, the average person absorbs about 3 mSv per year from natural background radiation (cosmic rays, radon in soil, and so on), so a single head CT is roughly equivalent to eight months of everyday exposure.
Modern scanners use advanced reconstruction techniques that have steadily reduced doses compared to older machines. Radiologists also tailor the scan settings to use only as much radiation as needed for a diagnostic image. For most patients, the clinical benefit of identifying a serious condition far outweighs the small additional radiation exposure. That said, unnecessary repeat scans should be avoided, and it’s reasonable to keep a personal record of your imaging history.
CT Scans During Pregnancy
CT imaging can be performed during pregnancy when the diagnostic need is clear, but the approach is modified to minimize fetal exposure. For scans outside the abdomen and pelvis, such as a head or chest CT, the fetus receives only scattered radiation, resulting in a very low dose that does not pose a significant risk.
For abdominal or pelvic CTs, the fetal dose from a single-phase scan under well-managed conditions is typically 10 to 25 milligray (mGy), and the American College of Radiology states that doses under 100 mGy do not cause identifiable developmental effects and do not warrant interruption of pregnancy. Radiologists limit the number of scan phases through the abdomen to keep exposure as low as possible. For pregnancies between 3 and 15 weeks that involve multiple abdominal CT scans, a medical physicist may calculate the cumulative fetal dose to guide further decisions.
Getting Your Results
After your scan, a radiologist reviews the images and writes a report that goes to the doctor who ordered the test. How quickly that happens depends on the setting. In emergency departments, the full process from scan order to final radiologist report averages around 4 to 6 hours, though urgent findings are typically communicated faster. For outpatient scans, results are often available within 24 to 48 hours, and your doctor’s office will contact you or make the report accessible through a patient portal.
The images themselves are digital, so they can be shared electronically between providers. If you need a second opinion or see a specialist later, the original scan files can usually be transferred without repeating the test. Many facilities will also give you a CD or digital link with your images if you ask.