MRI (Magnetic Resonance Imaging)

Last updated October 2009
Edited by: Guy Slowik, FRCS

When Is An MRI Requested?

MRI is used for a variety of diagnostic purposes. It is most often used to obtain information that hasn't been provided by other imaging techniques, including ultrasound, conventional x-ray, or computed tomography.

In general, MRI is used to:

  • Determine exactly what the problem is inside the body

  • Show exactly where the problem is

  • Rule out certain diseases

Because MRI produces images in any plane, it is particularly valuable in studying the brain and spinal cord and pinpointing even the smallest abnormality there. Because the water and fat content of tumors is different from surrounding normal tissue, MRI can reveal the precise location and size of tumors.

MRI also:

  • Provides images of the internal structure of the eye and ear

  • Produces detailed images of the heart and major blood vessels

  • Provides images of blood flow in the circulatory system

  • Produces detailed images of joints and soft tissues, particularly of cartilage, ligaments and tendons within joints such as the knee

Some additional diseases and medical conditions identified by MRI include:

  • Disorders of chest and lungs

  • Disorders of abdominal organs and the digestive tract

  • Disorders of the kidneys, urinary tract and pelvic organs

  • Infections

  • Inflammatory conditions

  • Trauma and other injury

Nice To Know:

MRI in the Diagnosis of Stroke Damage to part of the brain caused by the interruption of the blood supply, or by leakage of blood outside the vessel walls. Stroke can cause damage to sensation, movement, or function, depending on which area of the brain is affected.

One of the most recent and valuable uses for the MRI is in the diagnosis of strokesDamage to part of the brain caused by the interruption of the blood supply, or by leakage of blood outside the vessel walls. Stroke can cause damage to sensation, movement, or function, depending on which area of the brain is affected..

A new kind of MRI machine can pinpoint spots of dying tissue deep within the brain during the first hours of a stroke, when a blood clot in the head is choking off the oxygen supply.

This new technology comes in two varieties:

  1. "Diffusion-weighted" imaging shows exactly which brain tissue is already dead

  2. "Perfusion-weighted" imaging shows the parts of the brain that are still alive but starved of blood.

Both these technologies work by measuring how easily water flows through the brain.

Both of these MRI procedures take just a few minutes and cost about the same as "ordinary" MRI scans, although the machines capable of taking these enhanced images are more expensive.

Nice To Know:

"Real Time" Stress MRI - Pictures of the Heart in Motion

Fast cine magnetic resonance imaging is a new type of "stress" test that offers an alternative for diagnosing coronary (heart) artery disease. For those patients whose poor health precludes the standard stress tests, such as stress echocardiography A method of obtaining an image of the heart structure by using ultrasound (inaudible, high-frequency, sound waves). The sound is reflected differently by each part of the heart. The result is a complex series of echoes that are recorded and analyzed., treadmill exercise tests, or thallium stress testsA specialized kind of exercise stress test which is done after the patient receives a injection of a harmless radioactive substance (thallium) into the bloodstream. Its purpose is to show how well blood flows to the heart muscle during exercise. The source of exercise can be either a treadmill or a stationary bicycle., fast cine MRI can prove invaluable for finding problems with the heart in such patients.

Fast cine MRI utilizes a new technology that allows imaging of the heart in "real time," This means that the imaging process is synchronized with the heart's cycle so that images are taken over numerous heartbeats in a 5- to 10-minute interval. Fast cine MRI captures the heart's movement at almost the same time that the heart is contracting and relaxing-close to "real time."

  • For this test, the patient receives a drug called dobutamine, which increases heart rate and the speed at which the heart contracts and relaxes, thus mimicking the effects of exercise on the heart. Dobutamine also induces cardiac ischemia Insufficient blood supply to a specific organ or tissue, usually caused by a blood vessel disease, but can also result from vessel injury, constriction, or inadequate blood flow due to inefficient action of the heart.Insufficient blood supply to a specific organ or tissue, usually caused by a blood vessel disease, but can also result from vessel injury, constriction, or inadequate blood flow due to inefficient action of the heart., a reduction in the blood supply to the heart.

  • After receiving the drug, the patient is placed in the MRI machine and high-speed imaging begins. These images allow the physician to evaluate the ability of the left ventricularThere are two ventricles in the heart, the right and the left ventricle. They are the lower, pumping chambers, which receive blood from the upper heart chambers (atria) and pump it to the lungs and the rest of the body. wall of the heart to move during physical stress. The imaging uses the highest speed available to visualize the rapid movements of the heart and obtain an immediate image of the heart in motion.

The MRI stress tests takes approximately 35 minutes, and most patients tolerate the procedure well. The test has proved to be an accurate predictor of heart disease. Among those who had a negative MRI stress tests, 97 percent were free of heart disease during the first year following testing.

The test has advantages for those who aren't suited for the standard stress tests, such as:

  • Obese patients

  • Those who have had previous cardiothoracic (heart or chest) surgery

  • Those who have lung disease

The test should not be used in people who have:

  • Pacemakers

  • Cochlear implants (ear implants)

  • Metal clips, especially in the eyes

  • Defribillators (a device used to deliver a brief electric shock to the heart to treat an irregular or rapid heart beat)

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