The field of medical imaging has made great strides with advances in technology. Scans are vital in identifying certain disease processes and abnormalities in a quick and noninvasive manner. The first magnetic resonance imaging, or MRI, scan was completed in 1946, and MRIs have since become one of the most widely used imaging techniques.
Uses
MRI scanning is used in diagnosing, visualizing and evaluating a broad range of medical diseases and conditions. MRI scans are used to diagnose degenerative diseases such as multiple sclerosis as well as strokes, tumors of the pituitary gland and brain and infections or inflammation in the brain and spine. They also can visualize torn ligaments, shoulder injuries and bone fractures. In the cardiovascular system, MRIs can detect plaque buildup in the arteries, structural problems of the heart and damage from a heart attack.
Equipment
MRI scans involve large, expensive machines most often found in hospitals or clinical settings. The machine is cylindrical in shape and completely surrounded by a large magnet, and it has a hollow tube through the center where the movable scanning table slides. Some machines are open on the sides, reducing the feeling of being closed in, which is especially useful for claustrophobic patients. The computers and imaging screens are in an adjacent room, where technicians monitor the imaging process.
Procedure
Before imaging begins, patients are asked to remove all jewelry and accessories, as they can obstruct the resulting images. Depending on the type and reason for the MRI scan, a patient may also receive contrast material administered orally or injected into an arm vein. After preparation, the patient is asked to lie on the MRI table, which slowly slides into the machine. During the procedure, the patient must lie still as the machine makes several passes over the body, some lasting several minutes. The machine is equipped with a speaker system so the radiologist and patient can communicate.
How it Works
During an MRI scan, a magnetic field is generated that polarizes the water molecules of the body, meaning it forces them into a specific orientation. A radiofrequency pulse at a specific frequency is then applied across the body, causing the water molecules to change orientation, also called spin transition. The spin transitions of the water molecules create a signal that's detected by computers, and a resulting cross-sectional image of the body is generated. The image slices are compiled to create a three-dimensional image of the body.
Benefits
Magnetic resonance imaging is a safe, painless and noninvasive medical imaging technique with multiple benefits and few risks. The technique uses nonionizing radiation to generate images, which is generally harmless to body tissues, as opposed to ionizing radiation, like that in CT scans, which can damage cells. MRI scans have high-contrast resolution that's sensitive to tissue morphology and pathology, allowing detection of abnormalities that otherwise might not be found. Also, the contrast material, if used, does not contain iodine, decreasing the likelihood of an allergic reaction.
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