Physicians usually have a good idea of what they are looking for on the MRI scan before one is performed. The scans are most commonly used for pre-surgical planning, such as for a decompression or a lumbar spinal fusion. MRI scans are extremely sensitive to picking up information about the health of the discs, as well as the presence of any tumors or a lumbar disc herniation (see figure 1) pinching the nerve roots and causing back pain.
In addition to pre-surgical planning, MRI scans are also very useful for the following:
To rule out infection or tumor
For patients who have had surgery, to differentiate scar tissue from a recurrent disc herniation.
Prior to performing an epidural injection to rule out the risk of injecting a steroid into a tumor or infection
An MRI scan is not the best diagnostic study to assess a fracture. A computerized Tomography (CT scan) is generally done for patients who have suffered some trauma (such as a fall) if a fracture is suspected.
The MRI works by rotating a magnet around a patient, which changes the excitation level of hydrogen atoms in the body. When the hydrogen atoms revert back to their normal level of activity, they emit a slight amount of radiation that is then picked up on a scanner.
The developed MRI scan image shows anatomy by differentiating between tissues that have a lot of water (such as fat, cerebrospinal fluid or discs) and tissues that do not have much water (such as bone, cartilage, and nerve roots).
If you have low back pain and/or leg pain and are wondering if you should get an MRI scan to see what is causing the pain, the following general rules explain when a scan is useful and when it is not useful:
By: Peter
F. Ullrich, Jr., MD
October 1999
