Magnetic Resonance Imaging (MRI) Scan

January 15, 2026

This page was reviewed under our medical and editorial policy by Henry Krebs, M.D., associate clinical professor, Department of Diagnostic Radiology, City of Hope^® Cancer Center Atlanta 

A medical team may schedule an MRI for a patient as part of his or her cancer care and treatment. MRI, which stands for magnetic resonance imaging, is a type of imaging scan that allows doctors to create detailed pictures of structures in the body. It may also be referred to as nuclear magnetic resonance (NMR) imaging.

This guide to MRI scans is designed to help patients understand what to expect from the procedure.

What Is an MRI?

An MRI uses strong magnets to help take pictures of different layers (cross sections) of soft tissues within the body. The images, taken from multiple angles, are then combined to create 3D pictures. These allow doctors to have a clear view of internal structures.

The technology that underlies MRI scans is complex. It relies on high-energy radio waves that, when combined with the machine’s powerful magnetic force, cause hydrogen atoms in the body to send out signals, creating tiny electromagnetic signals. A receiver in the MRI machine converts these signals into images.

An MRI may be recommended for cancer patients during diagnosis, staging and treatment.

Diagnosis: During diagnosis, an MRI may help doctors see tumors in the body, although additional testing may be required before a diagnosis is made.

Staging: When staging a cancer, to determine its size and location, MRIs help determine where in the body cancer is found. The results of an MRI may also help doctors predict which forms of treatment may be most appropriate.

Treatment: Once treatment is underway, additional MRI testing may be used to check how well the patient is responding.

MRI With Contrast

In some instances, a doctor may recommend an MRI with contrast. This provides clearer images of the area being examined and is used on certain tumor types, including those in the spinal cord and brain. It may also be used to detect small tumors in the early stages.

Contrast is a safe chemical substance, or dye. Most often, this is made using a chemical element called gadolinium. This dye is either injected into the bloodstream or the patient may be asked to swallow contrast liquid. Once absorbed, the dye affects how the body’s tissue responds to the MRI. This increases the detail detected by the machine and improves the quality of the resulting images.

Does an MRI Show Cancer?

An MRI scan may indicate if a tumor is present and where it is located, but this alone generally is not enough to confirm a cancer diagnosis. In most cases, additional testing is needed, with a biopsy being the most common way to confirm the presence of cancer cells.

Once cancer has been diagnosed, MRIs are helpful tools for checking if and where the cancer has metastasized, or spread to other areas of the body.

MRI Versus CT Scan

MRIs and computed tomography (CT) scans are imaging tools used in the care of cancer patients, but they work differently.

A CT scan uses X-rays to produce images, while MRIs make images using magnets and radio waves. CT scans also use small, safe amounts of radiation, while MRIs do not.

In addition to helping doctors with cancer staging, as an MRI does, CT scans have additional purposes. They may be used to help accurately guide a biopsy and to aid in the planning of radiation therapy.

MRI Preparation

For patients scheduled to have an MRI, the health care team will explain how to prepare and will be able to answer any questions.

An MRI machine is an enclosed space, so some patients may feel nervous or claustrophobic. If that is a concern, patients should let their care team know in advance. The team may be able to assist by playing soft music or talking patients through everything they will see and hear to ease their nerves. Medication to help patients relax may also be an option.

If an MRI with contrast is being performed, patients should let their doctor know if they have any allergies, in case materials in the dye could cause a reaction.

The MRI is an outpatient procedure, so for most patients, it will not require any special preparation.

What Not to Do Before an MRI

Before an MRI, patients must remove anything metal from their person or clothing and should let the medical team know if they have any metal implants or prohibited items, including:

• Implanted devices with electrical currents, including pacemakers and related cardiac devices
• Cochlear (hearing) implants
• Any metal inside the body from past accidents, injuries or surgery
• Clips used for brain aneurysms
• Artificial joints
• Certain types of piercings

Patients should also remember not to bring any magnetized items with them into the MRI room. These include:

• Credit or debit cards
• Eyeglasses
• Pens
• Clothing with zippers
• Watches, jewelry and metal hair clips or accessories

Safe places are available to keep these items before entering the MRI area.

Due to the powerful pull of the magnets used in MRI machines, bringing certain types of metal into the MRI room may have serious consequences and may result in injury.

MRI Procedure

During an MRI, the patient may first change into a medical gown. If an MRI with contrast is being performed, the dye will first be entered into the bloodstream via an intravenous line or consumed orally.

Then, the patient will lie flat on his or her back on an exam table that moves into the MRI machine. The machine itself is a long, tube-shaped structure. The patient will be positioned so that clear images of the area may be taken. The MRI technologist will be in an adjacent room with a view of the machine and will be in constant communication with the patient.

The technologist will then begin taking images. While each image is taken, the patient must remain still. He or she will hear loud sounds that resemble banging or knocking and may feel temporarily warm. A series of pictures will be taken until the technician has all of the images needed.

While some patients may dislike the confined feeling of being in an MRI machine, the process is completely painless, and the patient will not feel anything during the procedure.

If a patient has had an MRI with contrast, it is recommended to drink lots of water after the procedure. This will help flush the contrast dye from the body.

How Long Does an MRI Take?

The length of time an MRI takes may vary, depending on the number of images needed and the part of the body being examined. On average, the MRI process lasts about 30 to 60 minutes, but sometimes it may take longer.

MRI Side Effects

An MRI is a very well-tolerated procedure that should not cause discomfort or side effects. However, some patients may feel temporarily claustrophobic or nervous when entering the MRI machine’s tube.

If patients are having an MRI with contrast, they may have mild side effects from the contrast dye. These may include:

• Headache
• A cold feeling moving through the body
• Feeling sick to the stomach
• Pain where dye was injected
• A metallic taste in the mouth

Most side effects do not last long. The chemical used in contrast dye is known to have negative effects on patients who have kidney problems or are on dialysis, so it is usually not used on anyone with kidney damage.

If patients feel unwell or notice any side effects during their MRI, they should let their imaging technician know right away.

How Long Do MRI Results Take?

Each patient’s doctor will let him or her know when to expect MRI results. This may take anywhere from a few days to a week or more. After the results are ready, a doctor will explain to the patient what the MRI results mean and whether additional tests are needed.