IMAGING MODALITIES
High-Field MRI
About
Magnetic Resonance Imaging (MRI) does not use ionizing radiation (x-rays). It is capable of producing multiple views, providing the radiologist with a better picture of a specific area. The procedure offers improved images of soft tissue like the brain, spinal cord, muscle and certain internal organs.
MR images are formed with the use of computers, a powerful magnet, and radio waves interacting with the magnetic properties of naturally present atoms within the body. The MRI machine looks much like a large cube with a hole in the middle. This structure houses a super-conducting magnet capable of producing a magnetic field that is about 20,000 times that of the earth’s.
At Great Basin Imaging we have two MRI’s machines. One is a 1.5 high field MRI and one is a .7 high field OPEN MRI. The open MRI is used for patients who find the 1.5 MRI claustrophic.
What To Expect
During an MRI scan, you will normally lie comfortably on your back on a table that is moved inside a large magnet. A piece of equipment called a “coil,” which sends and receives the radio frequency waves used in this technology, will be placed around the area being examined. During the scan, as with all MRI exams, you will hear various noises, ranging from a buzzing to a loud knocking. You will be given earplugs to diminish the noise.
Because an MRI exam can take images or “slices” from various angles, several sequences or sets of images will be taken. Each sequence will last from one to 10 minutes, and the technologist will inform you before the scanning noise begins. The total exam time for a scan can range from 30 to 60 minutes. You must lie very still during each sequence, in order to produce clear, diagnostic images.
Depending on your symptoms or prior medical history you may be given an intravenous contrast medium for your scan. The technologist will explain this procedure to you if necessary.
Patient Preparation
Because of the magnetic power of this equipment, patients are asked to remove all metal objects that might be affected or attracted by the magnet. Metal objects have an adverse effect on the images and could cause damage to the machine. Patients with pacemakers, surgical clips, a prosthesis, or any other metal objects on the body should tell the technologist prior to entering the examination room. The exam is completed within 30 minutes to an hour. Normally there is no preparation needed. The exception is MRCP, which require the patient to not eat for 2 hours prior to the exam.
Common Uses for the Test
Because MRI can give such clear pictures of soft-tissue structures near and around bones, it is the most sensitive exam for spinal and joint problems. MRI is widely used to diagnose sports-related injuries, especially those affecting the knee, shoulder, hip, elbow and wrist. The images allow the physician to see even very small tears and injuries to ligaments and muscles.
In addition, MRI of the heart, aorta, coronary arteries and blood vessels is a fast, noninvasive tool for diagnosing coronary artery disease and heart problems. Physicians can examine the size and thickness of the chambers of the heart and determine the extent of damage caused by a heart attack or progressive heart disease.
MRI is the sensitive exam for brain tumors, strokes and certain chronic disorders of the nervous system such as multiple sclerosis. In addition, it is a useful means of documenting brain abnormalities in patients with dementia and it is commonly used for patients with disease of the pituitary gland. MRI can detect tiny areas of tissue abnormality in patients with disease of the eyes or the inner ear.
Organs of the chest and abdomen—including the lungs, liver, kidney, spleen, pancreas and abdominal vessels—can also be examined in high detail with MRI, enabling the diagnosis and evaluation of tumors and functional disorders. MRI is growing in popularity as an addition to traditional mammography in the early diagnosis of breast cancer. Because no radiation exposure is involved, MRI is often the preferred diagnostic tool for examination of the male and female reproductive systems, pelvis and hips and the bladder.
MRI’s of the spine or back can be used to detect a bulging, degenerated or herniated intervertebral disk—a frequent cause of severe lower back pain and sciatica. Compressed (or pinched) and inflamed nerves are visible on MRI. In some cases the cause of nerve compression, whether from a herniated disk, arthritis or some other abnormality, also is demonstrated. MRI generally is the next non-invasive imaging examination used after x-rays of the lower spine; however, in cases of suspected disk herniation, MR may be the first study ordered. MRI is frequently done to help plan surgeries on the spine such as the decompression of a pinched nerve or spinal fusion. MRI performed after spinal surgery will show whether anything has changed and whether post-operative scarring or infection is present. If a patient has failed to improve as expected, MRI may show why. The exam can help to diagnose—or rule out—spinal infection or tumors that arise in, or have spread to, the spine; the common tumors include prostate, lung and breast cancers.
Risks and Benefits
Benefits:
The detail makes MRI an invaluable tool in early diagnosis and evaluation of tumors.
MRI contrast material is less likely to produce an allergic reaction than the iodine-based materials used for conventional x-rays and CT scanning.
MRI enables the detection of abnormalities that might be obscured by bone with other imaging methods.
MRI provides a fast, noninvasive alternative to x-ray angiography for diagnosing problems of the heart and cardiovascular system.
Exposure to radiation is avoided.
Risks:
MRI is generally not used in the first 12 weeks of pregnancy. Doctors usually use other methods of imaging, such as ultrasound, unless there is a strong medical reason to use MRI.
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