MRI uses a large magnet, radio frequencies and a computer to produce its images. As the patient enters an MRI scanner, his body is surrounded by a magnetic field up to 8,000 times stronger than that of the earth.
The human body is made of tiny particles called atoms. At the center of all atoms are spinning particles called nuclei. Normally, nuclei spin at many different angles. The magnetic field of the MRI scanner makes the nuclei spin at the same angle.
The scanner then subjects the nuclei to a radio signal, temporarily knocking them out of alignment. When the signal stops, the nuclei return to the aligned position, releasing their own faint radio frequencies. A part of the scanner known as the coil, working like a radio antenna, receives these frequencies. The data is then computer processed to produce very detailed images of the human anatomy.
With MRI technology it is possible to see, with unparalleled clarity, the brain and the tiny nerves that make up the spinal cord. Understandably, MRI has become the technology of choice for examining the brain, neck and spinal cord.
There are some patients who cannot undergo an MRI examination. They are those dependent upon cardiac pacemakers, those with metallic clips previously placed to stop or prevent bleeding into the brain or those with metallic foreign bodies in or around the eyes.
Because MRI uses no ionizing radiation and presents no apparent risk to patients, it is replacing more painful and risky examinations.
In children, it is being used to look for congenital or post surgical changes in the spinal cord as well as tumors of the spinal cord and brain. In adults, it rapidly displays degenerative disease of the spinal disks. In the past, these patients could be studied only by myelography, a painful procedure that requires an injection of dye into the spine. The dye causes terrible headaches and a hospital stay of at least 24 hours.
In its few years in clinical use, MRI has proven a valuable addition to previously available imaging techniques.