A CT (computed tomography) scan is a type of imaging test. Like an X-ray, it shows structures inside your body. But instead of creating a flat, 2D image, a CT scan takes dozens to hundreds of images of your body. To get these images, a CT machine takes X-ray pictures as it revolves around you.

Healthcare providers use CT scans to see things that regular X-rays can’t show. For example, body structures overlap on regular X-rays and many things aren’t visible. A CT shows the details of each of your organs for a clearer and more precise view.

Another term for CT scan is CAT scan. CT stands for “computed tomography,” while CAT stands for “computed axial tomography.” But these two terms describe the same imaging test.

Your healthcare provider will tell you everything you need to know about CT scan preparation. Here are some general guidelines:

✔ Plan to arrive early. Your provider will tell you when to come to your appointment.
✔ Don’t eat for four hours before your CT scan.
✔ Drink only clear liquids (like water, juice or tea) in the two hours leading up to your appointment.
✔ Wear comfortable clothes and remove any metal jewelry. You may be given a hospital gown to wear during the scan.

Your provider might use a contrast material to highlight certain areas of your body on the scan. For a CT scan with contrast, your provider will place an IV (intravenous line) and inject a contrast (or dye) into your vein. They may also give you a substance to drink (like a barium swallow) to highlight your intestines. Both improve the visibility of specific tissues, organs or blood vessels and help healthcare providers diagnose several medical conditions. IV contrast agents usually flush from your system (when you pee) within 24 hours.

Here are some additional preparation guidelines for a CT scan with contrast:

✔ Blood test: You might need a blood test before your scheduled CT scan. This will help your healthcare provider ensure the contrast material is safe to use.
✔ Diet restrictions: You’ll 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. You can have broth, tea or black coffee, strained fruit juices, plain gelatin and clear soft drinks (like ginger ale).
✔ Allergy medication: If you’re allergic to the contrast agent used for CT (which contains iodine), you may need to take steroid and antihistamine medications the night before and the morning of your procedure. 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’re allergic to the other.)
✔ Preparation solution: You should drink the oral contrast solution exactly as directed.

During the test, you’ll usually 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 give you a metallic taste in your mouth.

When the scan begins:

✔ The bed slowly moves into the doughnut-shaped scanner. At this point, you’ll need to stay as still as possible because movement can blur the images.
✔ You may also be asked to hold your breath for a short period of time, usually fewer than 15 to 20 seconds.
✔ The scanner takes pictures of the area your healthcare provider needs to see. Unlike an MRI scan (magnetic resonance imaging scan), a CT scan is silent.
✔ When the exam is over, the table moves back out of the scanner.

It usually takes about 24 to 48 hours to get the results of your CT scan. A radiologist (a physician who specializes in reading and interpreting CT scans and other radiologic exams) will review your scan and prepare a report that explains the findings. In an emergency setting, like 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’ll either have another appointment or receive a call. Your healthcare provider will discuss the results with you.