What is an MRI?

Sometimes we physicians get very accustomed to ordering a test and assume the patients understand what the test involves.  This blog will attempt to clarify what an MRI is and also a make your experience less scary and more understandable.

While an x-ray is still the mainstay in orthopedics since it looks at the bones for fractures, calcium deposits, loose bodies, and arthritis of the joints, an MRI (or magnetic resonance imaging) is a test that has revolutionized diagnosis and treatment of soft tissue, ligaments, and bone injuries. It has enhanced the diagnosis of many bone conditions in orthopedic surgery.  In the knee, an MRI can look at the tissues in great detail to determine if there are tears of the meniscus, tears of the tendons, and in a higher quality scan even degeneration of the articular cartilage in its early stages.

It is important to know that MRIs do not have any radiation.  Unlike an x-ray which has a very small dose of radiation or a CT scan which has a higher dose of radiation, an MRI has none, and for this reason it is extremely safe.  It is not used in patients that have pacemakers, metal clips, or metal fragments near vital structures.  For example, metal near the brain as in a sheet metal worker could be a contraindication to an MRI.  However, plates, screws, orthopedic hardware, and total joints are not affected by the magnets and MRIs can be safely done in these situations.  The center where the MRI is being ordered will ultimately determine if there are any reasons that your MRI needs to be rescheduled or canceled when you do your scheduling questionnaire.

The quality of the MRI is very important in order to get the best images possible. The strength of the magnet where the MRI is being done will determine the quality of the images that the radiologist and your orthopedic surgeon will see.  The higher the magnet strength, generally the better the pictures.  Some of the newer 3.0 Tesla magnets have incredible detail capabilities. Lower strength magnets such as 0.3 T and 1.0T are older magnets and may have much grainier and not as clear of images.

There are two types of MRIs.  The best quality MRI is a closed MRI, i.e. the patient goes into a tube and the quality of the images from these machines is much better.  An open MRI is often heavily marketed as being “easier, more comfortable”, but as a good consumer you should also know that many times the quality of the MRI in an open scanner can be poor and therefore the level of detail is often not as good. There has been no clinical advantage to a “standing MRI.”

I try to reassure my patients if they have concerns about claustrophobia. For example, if they are having a knee or ankle MRI, their head is not all the way in the tube and therefore it is much more comfortable.  A shoulder MRI, however, is a bit more difficult and less comfortable. Make sure if you are worried about being claustrophobic then consider some sedation first, or if you are sure you cannot tolerate a closed MRI, then an open one would be needed. I have no difficulties giving these patients a sedative such as Valium to make the examination much easier.

Many times the MRI center will have ear plugs or earphones that you can wear while you are having your examination as the machine can be quite loud and depending on your personality some can find the rhythmic sounds pleasing and  fall asleep, while others do get somewhat anxious. Ask for a sedative if your feel like you will be anxious, but just make sure someone drives you home after if you take a sedative.

The test itself takes about 45 minutes.  The cost of the MRIs do vary, so make sure your insurance is covering it. If not, ask your doctor if there is a place to have a “cash pay” for those patient’s that are paying out of pocket since they may work with you on pricing.

MRIs are probably one of the most important medical advances of the 2oth century, but as I always say, it is not the first test. The first “test” is to take a good history and physical exam. Your doctor should actually examine your injured joint. Most of the time that usually gives me the diagnosis, and the MRI is a test to help determine if surgery is necessary.

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Lesley J. Anderson, M.D.

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