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Frequently Asked Questions

MRI (Magnetic Resonance Imaging)

Is MRI safe?

MRI does not use any x-rays or ionizing radiation, nor does it require any invasive techniques. However, because of the use of strong magnetic fields, there are safety concerns if you have a pacemaker, an aneurysm clip, or if you have a history of eye injury involving metal fragments. It is important that you accurately complete the MRI Screening form, so that our staff can determine whether it is safe for you to have an MRI.

How does MRI work?

MRI uses a powerful magnetic field and radio waves to make detailed maps of hydrogen protons in the body. In areas of disease there is often a change in the concentration or behavior of hydrogen and this is reflected in the MR image as areas of brighter or darker signal intensity. A radiologist trained to interpret these complex maps will review your MR examination and provide a report to your doctor.

Why does the scan take so long?

MR images can be acquired in a number of different ways. Some techniques are better at defining anatomical detail while others are better at highlighting specific disease processes. Each individual technique takes about 5 minutes, and a MR exam may employ three to ten of these techniques.

How long do I have to hold still?

You will be asked to keep very still for the duration of each individual scanning technique. Your MR exam is comprised of a series of scans lasting about 5 minutes each. If you move during a scan, the images will be blurry and not useful in your diagnosis.

What about my dental fillings?

Dental work may cause some image distortion if we are imaging the mouth area, but there is no risk of your fillings becoming dislodged.

What about my artificial knee or hip?

There is no risk to you or your implant. Unless we are imaging directly in the area of your orthopedic implant (screws, pins, or plates) your MRI exam should be fine.

Why do you ask so many questions about my past surgeries?

We must ensure that you have no implants that can be affected by a strong magnetic field. Some implants that are of particular concern to us are pacemakers and aneurysm clips.

Why does the scanner make so much noise?

MR imaging employs magnetic fields called gradient fields that are used to determine the location of signals generated in the MRI process. These powerful gradient fields are switched on and off at a very fast rate and the result are a banging sound. You will be given hearing protection to dampen the noise.

Can I have other body parts scanned while I am in there?

No. A request for an MRI exam is like a prescription for medication. Each exam requires a specific request from your doctor. Our scanner focuses on one body part at a time, even though your whole body may be positioned in the scanner.

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

CT and MRI provide different kinds of information. Your doctor determines which is the most appropriate test for you, and sometimes both are necessary. CT scanners make images by using x-rays to plot the difference in electron density of adjacent tissues, and MR scanners make images based on differences in the density and behavior of hydrogen protons.

What if I am claustrophobic?

Claustrophobia is the fear of small spaces. MR imaging takes place inside a large magnet, and this may make some people feel concerned about being in a confined space. Patients may feel a bit nervous at first, but they generally settle down, and some even find it relaxing. The scanner is open at both ends, has lights inside it, and air circulating through it. The MRI technologist will be in communication with you throughout your examination and you will have a call button in your hand. If you do feel anxious you will be removed from the scanner immediately.

Should I take sedation?

Normally sedation is not necessary, but if you know that you suffer from claustrophobia, e.g., you cannot ride in airplanes or elevators, you may prefer to take some mild sedation before your MRI examination. Please let your doctor know before you come for your MRI, so he/she can prescribe a medication that relieves anxiety. The medication must be obtained from a pharmacy well in advance of the MRI appointment time, and brought with you to the MRI department. Medication cannot be obtained from the MRI department. Please remember that you cannot drive after taking this kind of medication, and will need to bring someone with you to drive you home after the test.

What about general anesthetic?

General anesthetic is rarely used for MRI and requires specialized MRI-compatible equipment. This equipment is available at St Paul’s Hospital, but an anesthetic will only be booked for a patient once they have attempted the exam with mild sedation first.

Will I be having any injections?

If the radiologist reviewing your images thinks that it is necessary, then we will give you an injection of a contrast agent to help with your diagnosis. This contrast agent is sometimes referred to as a ‘dye’.

Is the MRI dye the same as CT or X-ray dye?

No, MRI uses gadolinium. The risk of reaction to this dye is much lower than to X-ray dye. It is not iodine-based, so if you have had a serious reaction to X-ray dye, it is still safe for you to have MRI dye.

What is Nephrogenic Systemic Fibrosis?

NSF is a disease process that produces progressive fibrosis. Most commonly it involves the skin in which it produces sites of skin thickening that can be painful or itchy.  If it occurs around the joints it can cause joint stiffening, which can be disabling.  In some cases, the fibrosis can involve the internal organs. There is a possible association between the MRI contrast agent and the incidence of this rare disease in patients with kidney disease. Therefore if you are scheduled for an MRI with a contrast injection, and your kidneys do not work well, you must have a recent (within 3 months) eGFR value available. This is a measure of your kidney function. If you have not had recent blood work done, your test will be rebooked while we wait for the blood test to be done. You will need to see your doctor to have the blood test arranged. Depending on your eGFR level, you may not have the contrast injection done at all.


When will I get the results?

Your doctor should receive a report within about 10 days of your MRI appointment. To obtain results please make an appointment with your doctor, do not contact the MRI department.

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