Magnetic Resonance Imaging (MRI)
What is MRI?
MR or MRI stands for Magnetic Resonance Imaging. This is a technique that allows cross sectional pictures of the body. The test is ordered when your doctor suspects a specific disease process that might be seen on such images. MRI uses a magnetic field and radio waves to generate these images and has essentially no risk to the patient.
How does MRI make images?
Your body is composed primarily of water. Within each water molecule there are two hydrogen atoms. These hydrogen atoms have a neat property that allows them to align with the magnetic field. By applying energy from a surrounding antenna a weak signal can be collected from these hydrogen nuclei which can be made into pictures which demonstrate their location and provide some information with regard to the nature of the tissue they composed.
How does this compare to other imaging techniques?
While CT or Computerized Tomography is another cross sectional technique, there are some important differences between the two. CT imaging uses ionizing radiation or x-rays to make a pictures. While as the doses commonly used for imaging poses very little risk to the patient, it is generally accepted that no ionizing radiation is better than even a little ionizing radiation.
While both CT and MR may use contrast to better demonstrate abnormal tissue such as a tumor, the contrast used in MR is relatively safer in that there are fewer risks to the patient.
What are some typical uses for MRI imaging?
- Brain and Spine: MR has effectively replaced CT for the diagnosis of most diseases of the brain and spine. Some outstanding exceptions include patients with spine fractures and acute head trauma.
- Vascular System: MR is currently being used for the diagnosis of carotid artery disease, screening for intracranial aneurysms, and screening for renal artery stenosis. For patients who may be at increased risk for conventional radiographic contrast, MR angiography of the lower extremities is an elegant means of demonstrating blockage of arteries and may allow for surgical planning or limitation of exposure to conventional contrast by streamlining the conventional angiographic exam.
- Musculo-Skeletal System: MR imaging of the knee and shoulder are routinely performed in patients with suspected meniscal tear and rotator cuff injuries.
Is there any reason why I cannot have an MR study?
There are certain patients who should not have an MR examination. Patients with cardiac pacemakers and cochlear implants currently could not have MR imaging. Certain electrical devices such as vagal neuro stimulators can be imaged but you should ask your physician or call the MR center if you have a question regarding an implanted electrical device.
Patients who have previous aneurysm clips should not have an MR study unless the aneurysm clip is known to be compatible with the scanner and you should ask your doctor or check with the MR center prior to imaging. There are varieties of surgically implanted metallic devices such as hip prostheses and intramedullary rods which are generally compatible with MR imaging but if you have a question check with you doctor.
What about pregnancy?
We recommend that patients do not have an MR scan during their pregnancy unless it is medically indicated. These cases should be handled on an individual basis and while there is no known risk to MR imaging it is considered prudent to wait until after the pregnancy if possible.
Does it hurt to have an MR scan?
The process of having an MR scan requires lying quietly within the scanner. During the course of the scan you will be instructed when the scans begin and be asked to hold as still as possible during that time. The scanner makes a rhythmic knocking sound, which is muted for the patient by wearing earplugs. You may need to have an injection of contrast during the course of the exam, which would require the usual discomfort of a small needle placed in a vein. If you get uncomfortable or anxious during the course of an examination, you can be taken out of the scanner instantly at any time during the examination. You can communicate with the technologist during this scan. We recommend the patients bring along any music that they think would help them relax during the course of the examination and there are earphones that allow you to listen to CDs or tapes during the course of the examination. At the end of the examination you are free to go without any necessary recovery time.
Who will look at the images?
The MRI scans are reviewed by a radiologist who is trained in the interpretation of these images. A report will be dictated and then transcribed and sent to your referring physician. If you have any questions, ask your provider.
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