What is MRI (magnetic resonance imaging)?

Magnetic resonance imaging (MRI) uses strong magnetic fields and radio wave energy to take pictures of the inside of an object. This scanning method was developed primarily for use in medicine as a way to take images of structures in a patient's body, but has also been used to study objects such as fossils and historical artifacts. An MRI is capable of providing images that provide information that older scanning technology such as X-rays, computed tomography (CT), and ultrasound cannot.

how is it done

When an MRI is necessary, the patient lies on an imaging table that slides into a large MRI scanner. Powerful magnetic fields are administered to align the nuclei within the atoms of the patient's body. Radiofrequency pulses are then applied. The nuclei release some of the radio frequency energy, and the MRI equipment detects these emissions. With this data, a computer can generate a very detailed view of the tissues inside the body immediately after the scan.


Previous imaging technologies, such as X-rays, could detect dense tissue, particularly bone. Magnetic resonance imaging gives doctors the ability to better see all types of body structures, including soft tissue. MRI is also able to differentiate between different types of soft tissue better than other scanning technologies. The digital images that the computer represents can be two-dimensional or even three-dimensional.


Perhaps the best known use of MRI is in diagnosing injuries to the muscles, ligaments, tendons, or cartilage, such as knee injuries or strained muscles. MRIs are frequently used to detect cancers that are otherwise difficult to diagnose, such as mesothelioma. The ability to detect abnormalities such as cancers in their earliest stages has placed MRI at the forefront of the battle against many diseases. MRIs can also be used to look for a wide range of other conditions, including brain injuries, organ damage in the abdomen, and spinal cord injuries.

Effects in patients

In general, it is believed that patients are not harmed by undergoing an MRI exam, because no radiation is used. There are no known side effects, but patients who have pacemakers or other metal implants are not eligible for these scans. Exams typically last between 30 and 60 minutes. Early models of MRI scanners required patients to be placed in confined positions, but newer versions use an open design that is much more spacious and comfortable. The patient can resume normal activity immediately after the test.

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