MRI - Magnetic Resonance Imaging

MRI uses magnetic fields and radio waves to produce high-quality two- or three-dimensional images of body structures without injecting radioactive tracers. MRI also produces images of the internal organs of the body but without exposing the patient to ionizing radiation as x-rays and CT scans do. (Read about "X-rays" "CT Scan - Computerized Tomography")

A large cylindrical magnet creates a magnetic field around the patient, and radio waves are sent through the magnetic field. Sensors read the signals and a computer uses the information to construct an image.

In the procedure, a patient lies on a table and the table passes through a large tube. Depending on what part of the body is being examined, a contrast material may be used to highlight specific areas inside the body. The patient is asked to lie very still. They may hear whirring and thumping as the magnets are activated. The technician is able to talk to the patient and the patient can talk to the technician.

MRI scans are non-invasive. If confined spaces create anxiety for you, you can ask to come out of the tube. You will be asked to remove all metal from your body, such as jewelry. You should inform the imaging facility if you have any metal inside your body, such as plates, pins or a pacemaker. You should also let them know about any tattoos. People may have swelling or burning in the tattoo when they have magnetic resonance imaging done, according to the Food and Drug Administration.

Using MRI, scientists can image both surface and deep body structures with a high degree of anatomical detail, and they can detect minute changes in these structures that occur over time. These pictures can show the difference between normal and diseased tissue.

MRI is especially useful for imaging many organs including, but not limited to, the following:

• brain (Read about "The Brain")
• spine (Read about "The Spine")
• knee (Read about "The Knee")
• shoulder (Read about "The Shoulder")
• soft tissue of joints and the inside of bones (Read about "Orthopedics")
• heart problems (Read about "The Heart & Cardiovascular System")
• liver (Read about "The Liver")
• spleen (Read about "The Spleen")

They also are helpful for diagnosing particular conditions such as:

• stroke (Read about "Stroke")
• multiple sclerosis (Read about "Multiple Sclerosis")
• coronary heart disease (Read about "Coronary Heart Disease")

MRI's can also be used to get information about tumors and cancer (Read about "Cancer: What It Is") in many parts of the body, including but not limited to:

• brain (Read about "Brain Tumors")
• spinal cord (Read about "Nervous System")
• lung (Read about "Lung Cancer")
• liver (Read about "Liver Cancer")
• bone (Read about "Skeletal System")
• prostate (Read about "The Prostate")
• uterus (Read about "Uterine Cancer")

The National Cancer Institute says MRI makes better images of organs and soft tissue than other scanning techniques, such as CT or x-ray. MRI can also be helpful in differentiating between noncancerous fibrocystic disease and breast cancer. (Read about "Breast Diseases & Conditions" "Breast Cancer") It also is helpful in spotting tumors when the breast tissue is very dense or a woman has breast implants.

Functional MRI (fMRI)

Functional MRI (fMRI) relies on the magnetic properties of blood to enable scientists to see images of blood flow, particularly in the brain, as it is occurring. (Read about "The Brain") Thus doctors and researchers can make "movies" of changes in brain activity as patients perform various tasks or are exposed to various stimuli.

An fMRI scan can produce images of brain activity as fast as every second. Thus, with fMRI, it can be determined with greater precision when brain regions become active and how long they remain active. As a result, fMRI can help the physician see whether brain activity occurs simultaneously or sequentially in different brain regions as a patient thinks, feels, or reacts to conditions.

An fMRI scan can also produce high-quality images that can pinpoint exactly which areas of the brain are being activated. For example, fMRI can produce an image that distinguishes structures less than a millimeter apart.

Magnetic Resonance Angiography (MRA)

Magnetic resonance angiography (MRA) is a special type of MRI that can be used to see the blood vessels in your neck or brain. This test can detect a variety of brain and blood vessel abnormalities, such as aneurysms. It can also be used to determine risk of stroke or the extent of damage caused by a stroke (Read about "Aneurysms" "Stroke")

Intraoperative MRI (iMRI)

Intraoperative MRI (iMRI) refers to the use of computer-assisted imagery during surgeries. An iMRI system uses a strong magnetic field, radio-frequency signals and advanced computer systems to create images of an area while it is being operated on. This can help the surgeon pinpoint the location of tumors and/or diseased tissue and monitor the surgery as it is progressing. iMRI can be used during procedures such as surgery for brain tumors. (Read about "Brain Tumors" "Neurosurgery")

Nuclear Magnetic Resonance Imaging (NMRI)

The term Nuclear Magnetic Resonance Imaging (NMRI) is seldom used anymore. It referred to the fact that the magnets act on the nucleus of cells, not that radioactive material is used.