MRI is the most recently developed diagnostic imaging technique for the evaluation of spinal conditions. Through the use of radio waves and strong magnets with some 3 times the magnetic force of the Earth, this noninvasive technique visualizes the component parts of the spine from multiple directions. Under the influence of the strong magnet, the hydrogen atoms in water in the body line up like compass needles. These hydrogen atoms are exposed to radio signals that cause them to momentarily change their spinning axis. In the process of returning to their orientation under the influence of the magnet, they release a small, brief radio signal. A radio receiver computes all these radio signals. A computer generates the image of the organs and skeletal structures based on the pattern of these hydrogen ion radio waves.
Magnetic Resonance Imaging (MRI)
What is a MRI scan?
MRI is an imaging technique that does not use radiation for the generation of the images. Strong magnets, radio wave generator and receiver, and a powerful computer are used to generate images. MR scans are most successful using the hydrogen atoms in water to generate images. All structures of the spine can be delineated by MR including areas of inflammation. Soft tissues are most easily imaged.
How is a MRI scan taken?
The MRI is a painless procedure, but may be uncomfortable if you are experiencing spine pain. You are positioned on your back on a sliding table. The table is positioned inside the magnet that is open on both ends. The top of the tube is about 2 inches from your face. Frequently you are given earphones to listen to other sounds than the clicking of the radio wave generator. The duration of the test correlates with the number of structures to be examined.
Closed versus Open MRI scans?
In a closed MR scanner, you are on your back in a confining oval tube. The tube is open on both ends. The top of the tube is 2 to 3 inches from your face. Depending on the number of images needed, the test lasts between 20 to 60 minutes. Also during the procedure, a ticking sound is produced. For those who are scared of closed spaces (claustrophobics), an open MR scanner is an alternative. The open machine consists of a round magnet supported by 4 columns. The scanner is open on all sides. The concern about open scanners is that the images are less sharp than closed scanner images. For claustrophobic patients, oral sedation prior to a closed machine procedure is usually adequate to calm anxieties.
Lying, Sitting, Standing scanners?
You have spine pain that occurs frequently in a certain position, standing, sitting, or lying. Lying is the position least frequently associated with spine pain, but is the position most frequently used for MR scanning. Sitting and standing MRI scanners are available but in fewer numbers than standard machines. Also the quality of these sitting and standing scans are less than usual MR scans. Individuals have much greater difficulty sitting or standing in exactly the same place for periods of time when the scans are produced. Therefore, more likely than not, your scan will be done in a lying position. You will need to ask your physician if a sitting or standing study is appropriate for you and if that scanner is available in your community.
Contrast or No Contrast?
Gadolinium is a chemical that has magnetic properties. In areas where the integrity of the blood vessels has been damaged (cancer, infection, inflammation) gadolinium injected into a vein will escape from blood vessels into damaged tissues. These tissues look the same in regular MR scans, but stand out on contrast MR. Contrast MR scans are ordered after spine operations to identify scar tissue and when tumors or inflammation are suspected. Gadolinium should not be used in individuals with compromised kidney function. The contrast can cause unusual scarring in a variety of tissues when used in people with kidney failure.
People who have pacemakers, or have ferrous-based metal clips should not come close to the MR magnet. Pacemakers may misfire and metal clips may move around. Severely claustrophobic patients may be unable to tolerate the scanner in any form.