Medical imaging prep: how to prepare for your imaging scan

MRI & CT scan prep

What is an MRI?

MRI (short for magnetic resonance imaging) is a medical imaging technique that uses a magnetic field and radio waves to produce highly detailed images of your body’s organs and tissues.1 The MRI machine is essentially a large, cylindrical magnet, with a board you lay on in the middle. The scan process can take about 15 to 60 minutes, and the duration of the test depends largely on whether your scan is one with or without contrast dye.

What is a CT scan?

A CT (computerized tomography) scan is a medical imaging test that uses ionizing radiation to create multi-slice X-ray images of the inside of your body. It’s more detailed than a single X-ray because it takes pictures from different angles all around you. This type of scan is especially useful for assessing trauma injuries and guiding surgeries. You can expect it to take anywhere from a few minutes to half an hour.

So how can you prepare for these tests before they start?

Regarding food and medications:

• For MRIs, unless told otherwise, continue to eat, drink, and take your medications as normal.
• For CT scans, you may be asked to hold off on drinking or eating for a few hours before your exam. Be sure to check with your imaging center ahead of time if there are limitations like these.

Tell your doctor:

• If you have any metal in your body (think IUD, metal pins, cochlear implants, nerve stimulators, infusion pumps, bullets, etc.).
  • Most metal devices are not safe for MRIs. They can also distort CT scan results.
  • If you have a dark ink tattoo, as some contain trace metals.
• If you’re pregnant or breastfeeding. 
  • MRIs are not recommended during pregnancy, and you may need to take certain precautions if your scan calls for contrast dye and you’re breastfeeding.
  • CTs might not be ideal during pregnancy either, and your doctor may be able to recommend a safer alternative for your medical imaging test.
• If you have liver or kidney problems (some contrast dye agents might not be safe).

When you arrive:

• You’ll likely be asked to change out of your clothes and into a medical gown (women especially should be sure to remove underwire bras). When you’re changing, remove any jewelry, bobby pins, glasses, hearing aids, wigs, or dentures. You should be able to lock all of your belongings into a secure locker and retrieve them after your test is over.

Ultrasound prep

What is an ultrasound?

Ultrasounds are medical imaging tests that use sound waves from transducers and gel to produce images of your body’s organs, tissues, and vessels. They don’t use or give off any radiation. Diagnostic ultrasounds are commonly ordered on the heart, liver, blood vessels, kidneys, and reproductive organs. They allow doctors to watch pregnancies progress, visualize pathologies and injuries, and even administer noninvasive treatment (dissolving blood clots, destroying tissue, etc.). Ultrasounds generally take 30 to 90 minutes.²

Though most ultrasounds do not require preparation, there are some exceptions.

Regarding food and medications:

• For pelvic ultrasounds: unless told otherwise by your doctor, you should be able to eat and take your medication as normal. For some pregnancy scans, you may be asked to drink a large amount of water an hour beforehand (having a full bladder puts your uterus into clearer view for the ultrasound technician).
• For abdominal ultrasounds: it is advised that adults do not eat or drink for 8 hours before their exam. For children, 4 hours.
• For transrectal ultrasounds (to examine the prostate): your doctor may instruct you to do an enema 2 hours prior to your exam.
• For biopsies: you will need to discontinue the use of any blood thinners, vitamin E, or aspirin for several days before your ultrasound.
  • Many biopsies require that you do not eat or drink anything after midnight the night prior to your exam. Be sure to check with your doctor if this applies to you.

Tell your doctor:

• All the medications you’re regularly taking, including vitamins and supplements. They will be able to tell you which, if any, should be discontinued ahead of your exam. Blood thinners in particular are important to stop because they increase your risk of excessive bleeding during a therapeutic ultrasound.

When you arrive:

• You may be asked to remove some or all of your clothing and wear a paper or medical gown. This varies based on the type of ultrasound.

Nuclear scan prep

What is a nuclear scan?

Nuclear scans are medical imaging tests that evaluate how organs are working in real time (as opposed to their anatomy).³ Nuclear medicine scans use radiotracers and a small amount of radiation to analyze functioning and disease in the body’s organs and tissues. Nuclear scans include tests like PET, SPECT, bone density, biliary, and cardiological scans.

Because there are so many types of nuclear scans, exam time and preparation for each type is a little different. Here are some general tips for what to do before your nuclear scan.

Regarding food and medications:

• These guidelines will vary based on the type of nuclear scan you’re getting.
  • For PET scans: no caffeine, gum, mints, sugar, or carbs for 12 hours before the scan; no food or drink besides water for six hours beforehand. Medications can be taken as prescribed unless your doctor tells you otherwise. It’s also advised that you refrain from exercise for about one to two days before your scan.
  • For nuclear stress tests: the radiology center should contact you if any special prep is required.
  • For biliary scans: no food or drink for four hours before the scan.
  • For cisternograms: no food or drink for eight hours before the scan.
  • For gastric emptying: no food or drink for 12 hours before the scan.

Tell your doctor:

• All the medications you’re regularly taking, including vitamins and supplements. They will be able to tell you which, if any, should be discontinued ahead of your exam. Over-the-counter medications that contain caffeine like Excedrin cannot be taken before certain nuclear scans. If you’re diabetic, be sure to check about insulin management with your doctor.
• If you’re pregnant or breastfeeding.
  • PET scans are not recommended during pregnancy, and your doctor may be able to recommend a safer alternative for your medical imaging test. You may also need to refrain from breastfeeding for about 24 hours after your scan to allow the radiotracer to clear your system.⁴

When you arrive:

• You might be asked to change out of your clothes and into a medical gown, and to remove any jewelry, bobby pins, glasses, hearing aids, wigs, or dentures. You should be able to lock all of your belongings into a secure locker and retrieve them after your test is over.

Booking your scan

If you’re ready to schedule your medical imaging scan, head over to scan.com’s easy-to-use scan search tool to find a reputable imaging center near you.

Resources: 

1. mayoclinic.org: Tests and Procedures - Mayo Clinic

2. cedars-sinai.org: Preparing for Your Exam | Cedars-Sinai

3. clevelandclinic.org: Nuclear Medicine Imaging: What It Is & How It's Done

4. hopkinsmedicine.org: Radiology Exams and Procedures | Johns Hopkins Medical Imaging