What is an MRI?

A magnetic resonance imaging (MRI) scan uses a very strong magnetic field, as well as radio waves, to create a detailed image of your organs and tissues.

MRIs are a good choice when doctors need to look at a particular area, especially soft tissues (tissue that surrounds your internal organs and bones). These scans are able to pick up smaller lesions in the liver and pelvic region that might be missed on CT scans. They can also show more detail than a CT scan. MRIs are also the most common choice for brain scans.

MRIs may not be the best choice for someone who is very claustrophobic, as they take much longer than CT scans. MRIs might also be a problem for people with metal implants in their bodies, as they can heat up and cause discomfort during scans. This is mainly a problem for older devices, as newer ones are designed to be compatible with MRI technology.

Here’s what an MRI machine looks like:

What do I need to do before the scan?

You probably won’t need to prepare much for an MRI — but chat with your doctor about any specific instructions they might have. In most cases, you will be able to take all your medications and eat and drink as usual. If you are sensitive to loud noises, bring a pair of earplugs!

What happens on scan day?

Arrive at the test center a bit early. When you get there, you’ll register with the front desk. Then you’ll be taken to a dressing area, where you should remove all jewelry and clothing, and put on a hospital gown. You will be asked to sign some consent forms outlining the minimal risks of MRI scans.

Then, the technician will explain the procedure. If you’re having a contrast MRI, they will place an IV. The IV will typically be put in your arm, but in some cases they will use your port, if you have one.

The technician will ask you if you’ve ever had an allergic reaction to the contrast dye used. It’s important to let them know if you have any metal implants in your body.

What happens during the scan?

An MRI takes between 20 and 90 minutes, and is completely painless.

During an MRI, you’ll lie flat on a narrow table sticking out of a doughnut-shaped machine. The table will move, sliding you through the machine.

If you receive IV contrast, you will likely feel a warm flush sensation in your groin area. It’s possible the technician will place a hard white plastic coil around the part of your body being scanned. The coil works as a radio receiver to help improve the images. They may also use molds or immobilization devices to keep certain parts of your body still. These devices should not feel uncomfortable! Let the technician know if they are.

The technician will give you directions from a cubicle next to the scan room — such as when to hold your breath or stay completely still. You will be able to hear the technician, and the technician will be able to hear you. If you need help with anything, just ask!

Some patients find it helpful to close their eyes when going into the machine. If you are feeling claustrophobic, you can request a sedative — but this is usually not needed.

You’ll likely feel air from the fans as the table moves. The MRI machine often makes thumping noises. This is caused by the magnetic fields the machine uses. If the technician approves them, you can use earplugs to muffle the sound. 

What happens after the scan?

It’s a good idea to drink plenty of water following a scan with contrast, to help your body get rid of the dye. 

Your MRI scan report should be available within a few days. It will be sent to your oncologist and uploaded to your patient portal, if you have one. Your oncologist will discuss the results with you at your next appointment.

You should also request a CD copy of your scan photos for your records. Place this copy in a safe space. Some hospitals have a $5 charge for them, but they are legally obligated to provide you with a copy.

How often do I need to get an MRI?

It depends on your individual circumstances. MRIs are not routinely used in the US, but they are sometimes ordered if your oncologist wants to take a closer look at a concerning area found on a CT scan.

Oncologists will use different types of surveillance scans (CT, MRI or PET) depending on what they think is the best way to monitor your cancer. So you’ll likely get a variety of scans at different points in your treatment. 

How useful are MRIs?

MRIs are considered very good imaging tools to look at soft tissue. Most CRC patients will get a pelvic MRI at diagnosis to rule out metastases in the pelvis. For rectal cancer, MRIs are very useful for staging and to assess how the cancer has affected lymph nodes. MRIs are also very useful for looking at liver metastases. Although an MRI shows more detail than a CT scan, peritoneal metastases can be very difficult to detect with most imaging techniques.

If your doctor is unsure of the results of an MRI, they’ll likely order another test to get a better look.

Should I be concerned about radiation exposure?

No. MRI scans do not use ionizing radiation like CT scans. Instead, they use magnetic fields and radio waves to take pictures of your body.