Magnetic resonance imaging (MRI) is a medical imaging technique used to look at the internal structure and function of the body. MRI provides much greater contrast between the different soft tissues of the body than computed tomography (CT) does. It is especially useful in showing changes in the brain and musculoskeletal system.
MRI does not use radiation. Instead, a powerful magnetic field constructs an image of the body. MRIs of the spine are viewed by the reader in three ways. First, the level of involvement. In the lumbar spine, most disc problems occur at the L5S1 level, but L1-2, L2-3, L3-4, or L4-5 vertebral segments can also be affected.
Second, they look at the morphology of the disc. Morphology refers to the extent of disc damage. This ranges from mild bulge (inner disc material pushes against its own outer covering) to protrusion (inner disc material pushing into the outer covering of the disc). More progressive damage leads to extrusion (inner disc material pushing through the outer disc covering) and finally, sequestration. Sequestration refers to disc fragment that breaks off and becomes a free-floating loose body in the spinal canal.
Location is the third assessment of the problem. The location of most disc problems is usually posterolateral. This means the disc pushes back toward the spinal canal and off to one side or the other. Disc protrusion can be central (straight back), lateral (just to one side), or foraminal. Foraminal describes a disc that has moved into the space where the spinal nerve root exits the spine. Lateral and foraminal discs can occur on the right or left side.
Specialists trained to read and interpret MRIs can make sense of what looks like modern art to most patients. MRIs are the gold standard in diagnosing disc problems. Studies show they are both reliable and valid. Of course, human error can occur and the person reading and interpreting the study can be wrong. This doesn’t happen very often and is usually quickly corrected when a second look is requested.