Magnetic Resonance Imaging (MRI) of the Bones, Joints, and Soft Tissues
(MRI Scan of the Bones, Joints, and Soft Tissue)
What is magnetic resonance imaging (MRI)?
Magnetic resonance imaging (MRI) is a diagnostic procedure that uses a combination of a large magnet, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.
How does an MRI scan work?
The MRI machine is a large, cylindrical (tube-shaped) machine that creates a strong magnetic field around the patient. The magnetic field, along with a radiofrequency, alters the hydrogen atoms' natural alignment in the body. Computers are then used to form a two-dimensional (2D) image of a body structure or organ based on the activity of the hydrogen atoms. Cross-sectional views can be obtained to reveal further details. MRI does not use ionizing radiation, as do X-rays or computed tomography (CT scans).
A magnetic field is created and pulses of radio waves are sent from a scanner. The magnetic field aligns the hydrogen protons in your body along the same vector. The radio waves then knock the particles out of this aligned position. As the nuclei realign into proper position, the nuclei send out radio signals. These signals are received by a computer that analyzes and converts them into an image of the part of the body being examined. This image appears on a viewing monitor. Some MRI machines look like narrow tunnels, while others are more open.
Magnetic resonance imaging (MRI) may be used instead of computed tomography (CT) in situations where organs or soft tissue are being studied, because with MRI scanning bones do not obscure the images of organs and soft tissues, as does CT scanning.
Reasons for the procedure
In orthopedics, an MRI may be used to examine bones, joints, and soft tissues such as cartilage, muscles, and tendons for injuries or the presence of structural abnormalities or certain other conditions, such as tumors, inflammatory disease, congenital abnormalities, osteonecrosis, bone marrow disease, and herniation or degeneration of discs of the spinal cord. MRI may be used to assess the results of corrective orthopedic procedures. Joint deterioration resulting from arthritis may be monitored by using magnetic resonance imaging.
There may be other reasons for your physician to recommend an MRI of the bones, joints, or soft tissue.
Risks of the procedure
Because radiation is not used, there is no risk of exposure to ionizing radiation during an MRI procedure.
Due to the use of the strong magnet, MRI cannot be performed on patients with implanted pacemakers, some older intracranial aneurysm clips, cochlear implants, certain prosthetic devices, implanted drug infusion pumps, neurostimulators, bone-growth stimulators, certain intrauterine contraceptive devices, or any other type of iron-based metal implants. MRI is also contraindicated in the presence of some internal metallic objects such as bullets or shrapnel, as well as surgical clips, pins, plates, screws, metal sutures, or wire mesh.
If you are pregnant or suspect that you may be pregnant, you should notify your physician. In general, there is no known risk of MRI in pregnancy. However, particularly in the first trimester, MRI should be reserved for use only to address very important problems or suspected abnormalities.
If contrast dye is used, there is a risk for allergic reaction to the dye. Patients who are allergic to or sensitive to medications should notify their physician.
MRI contrast may have an effect on other conditions such as allergies, asthma, anemia, hypotension (low blood pressure), kidney disease, and sickle cell disease.
Nephrogenic systemic fibrosis (NSF) is a very rare but serious complication of MRI contrast use in patients with kidney disease or kidney failure. If you have a history of kidney disease, kidney failure, kidney transplant, liver disease or are on dialysis, you must inform the MRI technologist or radiologist prior to receiving contrast.
There may be other risks depending upon your specific medical condition. Be sure to discuss any concerns with your physician prior to the procedure.
Before the procedure
Your physician will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
If your procedure involves the use of contrast dye, you will be asked to sign a consent form that gives permission to do the procedure. Read the form carefully and ask questions if something is not clear.
Generally, there is no special restriction on diet or activity prior to an MRI procedure.
Before the examination, it is extremely important that you inform the technologist if any of the following apply to you:
You are claustrophobic and think that you will be unable to lie still while inside the scanning machine, in which case you may be given a sedative
You have a pacemaker or have had heart valves replaced
You have any type of implanted pump, such as an insulin pump
You have metal plates, pins, metal implants, surgical staples, or aneurysm clips
You have any metallic fragments anywhere in the body
You have permanent eyeliner or tattoos
You are pregnant or suspect you may be pregnant
You ever had a bullet wound
You have ever worked with metal (e.g., a metal grinder or welder)
You have any body piercing
You have an intrauterine device (IUD)
You are wearing a medication patch
As there is a possibility that you may receive a sedative before the procedure, you should plan to have someone drive you home afterward.
Based upon your medical condition, your physician may require other specific preparation.
During the procedure
MRI may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your physician's practices.
Generally, MRI of the bones, joints, or soft tissue follows this process:
You will be asked to remove any clothing, jewelry, eyeglasses, hearing aids, hairpins, removable dental work, or other objects that may interfere with the procedure.
If you are asked to remove clothing, you will be given a gown to wear.
If you are to have a procedure done with contrast, an intravenous (IV) line will be started in the hand or arm for injection of the contrast dye.
You will lie on a scan table that slides into a large circular opening of the scanning machine. Pillows and straps may be used to prevent movement during the procedure.
The technologist will be in another room where the scanner controls are located. However, you will be in constant sight of the technologist through a window. Speakers inside the scanner will enable the technologist to communicate with and hear you. You will have a call button so that you can let the technologist know if you have any problems during the procedure. The technologist will be watching you at all times and will be in constant communication.
A surface coil may be placed over the area to be examined if it is a relatively small area, such as a joint.
You will be given earplugs or a headset to wear to help block out the noise from the scanner. Some headsets may provide music for you to listen to.
During the scanning process, a clicking noise will sound as the magnetic field is created and pulses of radio waves are sent from the scanner.
It will be important for you to remain very still during the examination, as any movement could cause distortion and affect the quality of the scan.
At intervals, you may be instructed to hold your breath, or to not breathe, for a few seconds, depending on the body part being examined. You will then be told when you can breathe. You should not have to hold your breath for longer than a few seconds.
If contrast dye is used for your procedure, you may feel some effects when the dye is injected into the IV line. These effects include a flushing sensation or a feeling of coldness, a salty or metallic taste in the mouth, a brief headache, itching, or nausea and/or vomiting. These effects usually last for a few moments.
You should notify the technologist if you feel any breathing difficulties, sweating, numbness, or heart palpitations.
Once the scan has been completed, the table will slide out of the scanner and you will be assisted off the table.
If an IV line was inserted for contrast administration, the line will be removed.
While the MRI procedure itself causes no pain, having to lie still for the length of the procedure might cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure such as surgery. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.
On occasion, some patients with metal fillings in their teeth may experience some slight tingling of the teeth during the procedure.
After the procedure
You should move slowly when getting up from the scanner table to avoid any dizziness or lightheadedness from lying flat for the length of the procedure.
If any sedatives were taken for the procedure, you may be required to rest until the sedatives have worn off. You will also need to avoid driving.
If contrast dye is used during your procedure, you may be monitored for a period of time for any side effects or reactions to the contrast dye, such as itching, swelling, rash, or difficulty breathing.
If you notice any pain, redness, and/or swelling at the IV site after you return home following your procedure, you should notify your physician as this could indicate an infection or other type of reaction.
Otherwise, there is no special type of care required after a MRI scan of the bones, joints, and soft tissues. You may resume your usual diet and activities, unless your physician advises you differently.
Your physician may give you additional or alternate instructions after the procedure, depending on your particular situation.