Magnetic Resonance Imaging (MRI)
What is MRI?
MRI is a diagnostic procedure that uses a combination of a large magnet, radiofrequency pulses, and a computer to produce detailed images of organs and structures within the body. MRI does not use ionizing radiation, as do X-rays and computed tomography (CT scans). Because ionizing radiation is not used, there is no risk of exposure to ionizing radiation during an MRI procedure.
Magnetic resonance imaging (MRI) may be used instead of computed tomography (CT) in situations where organs or soft tissue are being studied, since MRI is generally better in differentiating between types of soft tissues. This feature makes MRI ideal for imaging the musculoskeletal system, brain, spine, internal organs and heart.
Newer uses and indications for MRI have contributed to the development of additional magnetic resonance technology. Magnetic resonance angiography (MRA) is a procedure used to evaluate blood flow through arteries in a noninvasive manner. MRA can also be used to detect aneurysms, vascular malformations and other vascular pathology within the brain, spinal cord, or other parts of the body).
Magnetic resonance spectroscopy (MRS) is another noninvasive procedure used to assess chemical abnormalities in body tissues. MRS may be used to assess disorders in the brain and other organs of the body.
Functional magnetic resonance imaging of the brain (fMRI) is used to determine the specific location within the brain where a certain function occurs. The general areas of the brain in which such functions occur are known, but the exact location may vary from person to person. During functional resonance imaging of the brain, you will be asked to perform a specific task while the scan is being done. By pinpointing the exact location of the functional center in the brain, doctors can plan surgery or other treatments for a particular disorder of the brain.
Another advance in MRI technology is the "open" MRI. Standard MRI units have a closed cylinder-shaped tunnel into which the patient is placed for the procedure. Open MRI units do not completely surround the patient, and some units may be open on all sides. Open MRI units are particularly useful for procedures involving:
- Claustrophobia. Before the development of open MRI units, patients with severe claustrophobia often required a sedative medication prior to the procedure.
- Very large or obese persons. Almost anyone patient can be accommodated in most open MRI units.
How is an MRI performed?
Although each facility may have specific protocols in place, an MRI procedure generally follows this process:
- Because of the strong magnetic field, the patient must remove all jewelry and metal objects, such as hairpins or barrettes, hearing aids, eyeglasses, and dental pieces.
- If a contrast medication and/or sedative are to be given by an intravenous line (IV), an IV line will be started in the hand or arm.
- The patient will lie on a table that slides into the scanner.
- The MRI staff will be in another room where the scanner controls are located. However, the patient will be in constant sight of the staff through a window. Speakers inside the scanner will enable the staff to communicate with and hear the patient. The patient will have a call bell so that he or she can let the staff know if he or she has any problems during the procedure.
- During the scanning process, a clicking noise will sound as the magnetic field is created and pulses of radio waves are sent from the scanner. The patient may be given headphones to wear to help reduce the noises from the MRI scanner and hear any messages or instructions from the technologist.