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:

  1. 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.
  2. The scanner takes pictures of the area the healthcare provider needs to see. Unlike an MRI scan, a CT scan is silent.
  3. 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.

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