What is Magnetic
MRI technology was developed from Nuclear Magnetic Resonance or NMR by
Raymond Damadian, a former State University of New York researcher in 1977.
Damadian himself was the first human being ever tested and led the way for
the technology to be used diagnostically on patients ever since.
While the physics involved in describing the precise mechanics of MRI are
extremely complicated and beyond the scope or interest of this page, the
basic idea of how a MRI works is fairly easy to understand.
MRI is a noninvasive imaging technique that does not use x-rays (unlike CAT scan). The process involves passing a strong magnetic field through the head. The magnetic field used is 30,000 + times that of the earth's magnetic field. It's effect on the body, however, is harmless and temporary. The MRI scanner can detect radiation from certain molecules, which are present in different concentrations in different tissues. The fluid contrast between structures in the brain can then be visualized. The goal of MRI is to produce cross-sectional imaging in which there is significant contrast between tissues of interest.
MRI is used as an imaging technique because of the very detailed pictures of anatomy that can be achieved. It is especially helpful in diagnosing tumors or other abnormalities of the tissue in the brain and spinal cord. It may also be used to diagnose diseases and disorders of the eyes and ears, joints and soft tissues.
The equipment involved will surround a patient that is lying still on a table in a enclosed tunnel. The tunnel is what contains the magnet and the radio-wave source (the detection device). This equipment sends its signals to a connected computer and display screen and the images can then be pieced together. It is very important that the patient lie very still, as the clarity of the images achieved depend on absolute motionlessness. This may be difficult for patients who feel claustrophobic or for children, even though the entire procedure usually takes only 30 minutes--15 minutes per anatomic or technical sequence.
The potential risks involved with having a MRI are minimal. However, there are some things that any patient undergoing this procedure should be aware of. The most important of these is the danger of having any metal object that contains iron and is easily magnetized, or ferromagnetic, in the room or, especially, in the body. This is a special concern to anyone who has had a surgical clip inserted, such as an aneurysm clip placed in the head from pervious treatment. Any patient with this concern should talk to their doctor about the type of metal used in the clip before consenting to a MRI. In previous cases, ferromagnetic aneurysm clips have caused injury and even death. The room should also be cleared of any ferromagnetic material because the magnetic field can turn these objects into potentially dangerous projectiles.
Other potential risks to consider include magnetic field interference with biomedical implants, such as a pacemaker, cochlear implants and ocular prostheses. The magnetic field could affect the functioning of the device or cause it to dislodge within the tissue. People carrying these devices should not expose themselves to the field of a MR scanner unless specific permission is given by a doctor or until the ferromagnetic quality of the metal can be determined.
The above risks may be considered greater with the higher field models (stronger magnet). These models have their own special risks as well as their own benefits. Depending on the type of field that is used during the imaging, the patient may experience a tingling in the skin or involuntary muscle contractions due to temporary nerve and muscle stimulation. A patient also should be forewarned about the noise generated by a MR scanner and should be offered earplugs, unless they are beforehand assured the machine is equipped with noise cancellation technology.