Magnetic resonance imaging (MRI) has become a very valuable tool in diagnostic orthopaedics and other fields of medicine and surgery. It allows the ability to see tissues in far more detail than CT scans or x-rays. It basically allows doctors to take a cross section of any part of the body and look critically at the anatomy and possible pathology or problems within it.
The MRI machine does not expose the patient to radiation. This is a very large advantage over traditional imaging such as x-ray and CT scan (computed tomography, which utilizes much more radiation than plain x-rays). The mechanism is very complex by which the images are generated but the key is using a very strong magnet to pass a force through the molecules of the body and causing an "excited" stage that, when the molecules finish reacting, generates a very detailed image. There are patients that cannot use the MRI. Any patient with a pace-maker for their heart, clips at the base of the brain (from an aneurysm repair), or have metal implant are not able to utilize the MRI. So be sure to tell your doctor if there are any implants in your body. In addition, it is important to share if there has ever been metal debris that has entered your eye. Some modern orthopaedic implants are inert and do not react with the magnetic strength or field of the MRI. The MRI uses a super cooled coil to be able to generate a superconductor field strength.
Typically, the patient is placed into a tube-like cylinder while lying on a mobile bed. Usually, the fit is quite tight and being placed in such a confined area is difficult for all patients to handle. For that reason, it is important to know if there is any history of claustrophobia (fear on confined, small places). In such cases, sedation is sometimes used for relaxation. Patient size can also limit the efficiency of the MRI and patients over 275 pounds may have difficulty fitting in the scanner.
Newer technology has permitted the construction of MRI machines that are not tube-like in shape and actually, have an open, exposed aspect. This can make the exam far more comfortable and can accommodate larger patients as well. The drawback can be inferior quality images. The closer the recording coil to the body, the better the images generated.
The MRI has become an integral part of some evaluations. It can detect very subtle changes that are not evident on plain x-rays or even CT scans. It can also critically evaluate the condition of ligaments and tendons. The MRI, though, can be so sensitive to minor changes that the findings need to be correlated with the clinical exam (what the patient's complaints are). For instance, the disks in the spine of the lower back are very often abnormal in subjects that are completely normal and painfree (they just volunteered for the study). This is why it very important to discuss with your doctor whether the MRI will help diagnose and plan treatment. In addition, the exam is very expensive and can take up to 45 minutes to complete. In the correct setting, the MRI is an invaluable tool in treating the knee.
Last updated: 26-Oct-01