Magnetic resonance imaging (MRI) uses powerful magnetic fields and radio wave energy to take pictures of the inside of an object. This method of scanning was developed primarily for use in medicine as a way to take images of structures in a patient's body, but it also has been used to study objects such as fossils and historical artifacts. An MRI is able to provide images that give information that previous scanning technology, such as X-ray, computed tomography (CT) and ultrasound cannot.
How It is 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. Next, radio frequency pulses are applied. The nuclei release some of the radio frequency energy, and these emissions are detected by the MRI equipment. With this data, a computer can generate a highly detailed view of tissues within the body immediately after the scan.
Earlier imaging technologies, such as X-rays, were able to detect dense tissues, particularly bones. MRI scans give doctors the ability to better view all sorts of body structures, including soft tissues. Magnetic resonance imaging also is able to differentiate between different types of soft tissues better than other scanning technologies. The digital images that are rendered by the computer can be two-dimensional or even three-dimensional.
Perhaps the most well-known use of magnetic resonance imaging is in the diagnosis of injuries to muscles, ligaments, tendons or cartilage, such as knee injuries or pulled muscles. MRIs are frequently used to detect cancers that would otherwise be difficult to diagnose, such as mesothelioma. The ability to detect abnormalities, such as cancers at their early stages, has put magnetic resonance imaging at the forefront of the battle against many diseases. MRIs also can be used to look for a wide range of other conditions, including brain injuries, damage to organs in the abdomen and spinal injuries.
Effects on Patients
It generally is believed that patients are not harmed by undergoing an MRI exam, because radiation is not used. There are no known side effects, but patients who have pacemakers or certain other metallic implants are not eligible for these scans. Exams typically take 30 to 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 is able to resume normal activity immediately after the test.