Magnetic resonance imaging (MRI) is a unique and versatile medical imaging modality. Doctors can obtain highly refined images of the body's interior using MRI. By using strong magnetic fields and pulses of radio waves to manipulate the natural magnetic properties in the body, this technique produces images not possible with other diagnostic imaging methods. MRI is particularly useful for imaging the brain and spine, as well as the soft tissues of joints and the interior structure of bones. The entire body can be imaged using MRI, and the technology poses few known health risks.
Purpose
MRI was developed in the 1980s. The latest additions to MRI technology are angiography (MRA) and spectroscopy (MRS). MRA was developed to study blood flow, while MRS can identify the chemical composition of diseased tissue and produce color images of brain function. The many advantages of MRI include:
Detail. MRI creates precise images of the body based on the varying proportions of magnetically polarizable elements in different tissues. Very minor fluctuations in chemical composition can be determined. MRI images have greater subject contrast than those produced with standard x rays, computed tomography (CT), or ultra-sound, all of which depend on the differing physical properties of tissues. This contrast sensitivity lets MRI distinguish fine variations in tissues deep within the body. It also is particularly useful for spotting and distinguishing diseased tissues (tumors and other lesions) early in their development. Often, doctors prescribe an MRI scan to more fully investigate earlier findings of the other imaging techniques.
Scope. The entire body can be scanned, from head to toe and from the skin to the deepest recesses of the brain. Moreover, MRI scans are not adversely affected by bone, gas, or body waste, which can hinder other imaging techniques. (Although the scans can be degraded by motion such as breathing, heartbeat, and normal bowel activity.) MRI process produces cross-sectional images of the body that are as sharp in the middle as on the edges, even of the brain through the skull. A close series of these two-dimensional images can provide a three-dimensional view of a targeted area.
Safety. MRI does not depend on potentially harmful ionizing radiation, as do standard x-ray and CT scans. There are no known risks specific to the procedure, other than for people who might have metal objects in their bodies.
Given all the advantages, doctors would undoubtedly prescribe MRI as frequently as ultrasound scanning, but the MRI process is complex and costly. The process requires large, expensive, and complicated equipment; a highly trained operator; and a doctor specializing in radiology. Generally, MRI is prescribed only when serious symptoms and/or negative results from other tests indicate a need. Many times an alternative imaging procedure is more appropriate for the type of diagnosis needed.
Doctors may prescribe an MRI scan of different areas of the body.
Brain and head. MRI technology was developed because of the need for brain imaging. It is one of the few imaging tools that can see through bone (the skull) and deliver high quality pictures of the brain's delicate soft tissue structures. MRI may be needed for patients with symptoms of a brain tumor, stroke, or infection (like meningitis). MRI also may be needed when cognitive and/or psychological symptoms suggest brain disease (like Alzheimer's or Huntington's diseases, or multiple sclerosis), or when developmental retardation suggests a birth defect. MRI can also provide pictures of the sinuses and other areas of the head beneath the face.
Spine. Spinal problems can create a host of seemingly unrelated symptoms. MRI is particularly useful for identifying and evaluating degenerated or herniated intervertebral discs. It can also be used to determine the condition of nerve tissue within the spinal cord.
Joint. MRI scanning is often used to diagnose and assess joint problems. MRI can provide clear images of the bone, cartilage, ligaments, and tendons that comprise a joint. MRI can be used to diagnose joint injuries due to sports, advancing age, or arthritis. It can also be used to diagnose shoulder problems, like a torn rotator cuff. MRI can detect the presence of an otherwise hidden tumor or infection in a joint, and can be used to diagnose the nature of developmental joint abnormalities in children.
Skeleton. The properties of MRI that allow it to see though the skull also allow it to view the interior of bones. It can be used to detect bone cancer, inspect the marrow for leukemia and other diseases, assess bone loss (osteoporosis), and examine complex fractures.
The rest of the body. While CT and ultrasound satisfy most chest, abdominal, and general body imaging needs, MRI may be needed in certain circumstances to provide more detailed images or when repeated scanning is required. The progress of some therapies, like liver cancer therapy, need to be monitored, and the effect of repeated x-ray exposure is a concern.
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