Magnetic Resonance Imaging
(MRI Scan)
Medical Reviewer:
What is an MRI scan?
An MRI (or magnetic resonance imaging) scan is a radiology technique that uses magnetism, radio waves, and a computer to produce images of body structures. The MRI scanner is a tube surrounded by a giant circular magnet. The patient is placed on a moveable bed that is inserted into the magnet. The magnet creates a strong magnetic field that aligns the protons of hydrogen atoms, which are then exposed to a beam of radio waves. This spins the various protons of the body, and they produce a faint signal that is detected by the receiver portion of the MRI scanner. The receiver information is processed by a computer, and an image is produced.
The image and resolution produced by MRI is quite detailed and can detect tiny changes of structures within the body. For some procedures, contrast agents, such as gadolinium, are used to increase the accuracy of the images.
When are MRI scans used?
An MRI scan can be used as an extremely accurate method of disease detection throughout the body. In the head, trauma to the brain can be seen as bleeding or swelling. Other abnormalities often found include brain aneurysms, stroke, tumors of the brain, as well as tumors or inflammation of the spine.
Neurosurgeons use an MRI scan not only in defining brain anatomy but in evaluating the integrity of the spinal cord after trauma. It is also used when considering problems associated with the vertebrae or intervertebral discs of the spine. An MRI scan can evaluate the structure of the heart and aorta, where it can detect aneurysms or tears.
It provides valuable information on glands and organs within the abdomen, and accurate information about the structure of the joints, soft tissues, and bones of the body. Often, surgery can be deferred or more accurately directed after knowing the results of an MRI scan
What are the risks of an MRI scan?
An MRI scan is a painless radiology technique that has the advantage of avoiding x-ray radiation exposure. There are no known side effects of an MRI scan. The benefits of an MRI scan relate to its precise accuracy in detecting structural abnormalities of the body.
Patients who have any metallic materials within the body must notify their physician prior to the examination or inform the MRI staff. Metallic chips, materials, surgical clips, or foreign material (artificial joints, metallic bone plates, or prosthetic devices, etc.) can significantly distort the images obtained by the MRI scanner. Patients who have heart pacemakers, metal implants, or metal chips or clips in or around the eyeballs cannot be scanned with an MRI because of the risk that the magnet may move the metal in these areas. Similarly, patients with artificial heart valves, metallic ear implants, bullet fragments, and chemotherapy or insulin pumps should not have MRI scanning.
During the MRI scan, patient lies in a closed area inside the magnetic tube. Some patients can experience a claustrophobic sensation during the procedure. Therefore, patients with any history of claustrophobia should relate this to the practitioner who is requesting the test, as well as the radiology staff. A mild sedative can be given prior to the MRI scan to help alleviate this feeling. It is customary that the MRI staff will be nearby during MRI scan. Furthermore, there is usually a means of communication with the staff (such as a buzzer held by the patient) which can be used for contact if the patient cannot tolerate the scan.
How does a patient prepare for an MRI scan and how is it performed?
All metallic objects on the body are removed prior to obtaining an MRI scan. Occasionally, patients will be given a sedative medication to decrease anxiety and relax the patient during the MRI scan. MRI scanning requires that the patient lie still for best accuracy. Patients lie within a closed environment inside the magnetic machine. Relaxation is important during the procedure and patients are asked to breathe normally. Interaction with the MRI technologist is maintained throughout the test. There are loud, repetitive clicking noises which occur during the test as the scanning proceeds.
Occasionally, patients require injections of liquid intravenously to enhance the images which are obtained. The MRI scanning time depends on the exact area of the body studied, but ranges from half an hour to an hour and a half.
How does a patient obtain the results of the MRI scan?
After the MRI scanning is completed, the computer generates visual images of the area of the body that was scanned. These images can be transferred to film (hard copy). A radiologist is a physician who is specially trained to interpret images of the body. The interpretation is transmitted in the form of a report to the practitioner who requested the MRI scan. The practitioner can then discuss the results with the patient and/or family.
Future
Scientists are developing newer MRI scanners that are smaller, portable devices. These new scanners apparently can be most useful in detecting infections and tumors of the soft tissues of the hands, feet, elbows, and knees. The application of these scanners to medical practice is now being tested.
Pictures of an MRI of the spine
This patient had a herniated disc between vertebrae L4 and L5. The resulting surgery was a discectomy
Picture of herniated disc between L4 and L5
Cross-section picture of herniated disc between L4 and L5
MRI Scan At A Glance
- MRI scanning uses magnetism, radio waves, and a computer to produce images of body structures.
- MRI scanning is painless and does not involve x-ray radiation.
- Patients with heart pacemakers, metal implants, or metal chips or clips in or around the eyes cannot be scanned with MRI because of the effect of the magnet.
- Claustrophobic sensation can occur with MRI scanning.
Last Editorial Review: 4/5/2007
http://www.medicinenet.com/mri_scan/article.htm
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