Magnetic Resonance Imaging of the spine
MRI (magnetic resonance imaging) is an imaging technique used to get cross-sectional images using strong magnetic field and radio waves (radio frequency pulses) instead of X-rays.
In MRI scanning, patients are placed inside a very large and strong magnet, so that all the protons in the atoms of the patient's body can be aligned to a magnetic field. Then, radio waves (called radio frequency pulses) are directed at the protons -- i.e., the nuclei of hydrogen atoms -- to excite the protons. Once the radio waves are stopped, excited atoms emit radio signals received by an antenna (i.e., a surface coil in the MRI machine), which are then measured and processed to form an image using a computer.
In the human body, protons are most abundant in the hydrogen atoms of water. Thus, MRI images represent the water content in the area of the exam. The more water present, the more radio signals emitted, and the whiter the image.
MRI is usually the best choice for examination of the spine.
Types of spine MRI:
- Cervical spine MRI
- Thoracic spine MRI
- Lumbosacral spine MRI
It provides cross-sectional images in any anatomical plane (upper to lower, right to left, front to back, oblique).
It provides clear, detailed images of various soft tissues, such as gray and white matter of the brain, meninges, nerves, inner ear, eyes, blood vessels, temporomandibular joints, tumors, and fluids.
It is excellent in evaluating tumors of the brain, meninges, pituitary gland, and vascular or brain stem abnormality.
Compared to the iodine-based contrast medium in X-ray or CAT scan, MRI dye is relatively safe.
Provides angiographic images without being invasive
MRI can evaluate organ function as well as structure.
Pain in the neck, mid back, and lower back
Pain/numbness in the extremities that may be caused by spinal nerve/cord conditions
Swelling in the neck, mid back, and lower back
In case of spine injuries -- to detect spinal cord/nerve injury, fracture, and hemorrhage.
Disc herniation -- to evaluate disc disease and to plan surgery
Spinal stenosis, radiculopathy
Tumors and cancer of the vertebrae, soft tissue, and spinal cord
Infections -- spondylitis, osteomyelitis, diskitis, abscesses
Spinal cord diseases, such as multiple sclerosis, etc.
Follow up of tumors, infection, and surgery
You will be asked to lie on the scan table. After proper positioning, the exam table will slide into the center of the magnet.
During the scan you will be alone in the exam room, but you can talk to and listen to the technologist using an intercom, who will watch you through a glass window and video camera.
During actual scanning, you will hear loud tapping noises, but you are required to remain still until it's done (to get clear pictures).
In the event that a contrast medium is needed to make organs and blood vessels stand out, it will be injected into your vein during the exam.
The exam usually takes from 15 minutes to an hour and a half.
Wear comfortable, loose-fitting clothing.
Take off your clothes in the examining area and put on a hospital gown.
Remove any metal objects such as watches, car keys, wallets, beepers, cellular phones, zippers, snaps, hairpins, jewelry, accessories, eyeglasses, hearing aids and any removable dental work, because they can be affected by the huge magnet and degrade the quality of the imaging.
The information on credit cards can be erased by this strong magnetic field.
Let your radiologist or technologist know when you have a metal object in your body, such as a cardiac pacemaker, prosthetic heart valve, prosthetic hip or knee joint, implanted infusion pump, intrauterine device (IUD), cochlear implant, aneurysm clip or vascular clips, hearing aid, metal monitoring device, surgical staples, metal plates, pins, screws, bullets, shrapnel or any metal fragments. This is because the strong magnetic fields can cause these ferromagnetic metal objects to move, dislodge, cause burns, or electrical currents.
Tooth fillings can distort images.
Tattoos may degrade image quality.
For contrast-enhanced MRI, you will be asked if you have any drug allergies.
If you are pregnant or suspect pregnancy, you should inform your technologist or radiologist.
If you have any history of claustrophobia, you should inform your radiologist or technologist of it. Sedatives can be given before scanning.
Earplugs can be used to protect your ear from loud repetitive noises during scanning.
A radiologist (a physician specialist trained to interpret MRI images or other radiology exams, such as CAT scans, X-ray, mammography, etc.) reviews the body MRI and reports the results to your personal doctor.
The physician's office informs patients when the results are in, and what the results are. The office uses the results as a reference in evaluating and treating patients.
The strong magnetic field can cause metal implants to dislodge, burn, and cause additional injuries. When you have any metal implant in your body, such as a pacemaker, prosthetic valves, or clips, you should let your radiologist or technologist know its brand name and model. If it is not confirmed to be compatible with the magnet, you should not take the MRI. If you have had bullet injuries or possible metal fragments in your body, X-rays can be taken instead for detection of metal objects.
Metallic implants/fragments that might be affected by magnet:
Women in the first 12 weeks of pregnancy should avoid MRI and the contrast medium. There are no known harmful effects to pregnant women and unborn babies. However, because it is a recently-developed technology, the long term effects of MRI are not known.
Allergic reactions to the contrast medium are possible, but very rare.
Claustrophobia. Lying alone inside the tunnel of huge magnet may provoke intense fear of confinement. If you have any history of claustrophobia, you should inform your radiologist or technologist. Sedatives can be given before scanning.
- Cardiac pacemakers
- Artificial cardiac valves
- Cerebral aneurysm clips, vascular clips
- Epidural electrodes
- Prosthetic hip
- Prosthetic knee
- Implanted port (brand names: Port-o-cath, Infusaport, Lifeport)
- Chemotherapy or insulin pumps
- Intrauterine device (IUD)
- Metallic bone plates, pins, screws, surgical staples, especially within 4-6 weeks after surgery.
- Bullets, shrapnel, possible metal fragments, especially in and around eyes
- Metallic ear implants
Limited ability in imaging bone -- conventional X-ray or CT scan is better in demonstrating bone details.
Compared to CT scanning, MRI is less sensitive in demonstrating acute hemorrhage.
Hard to depict calcifications
MRI does not always distinguish tumor tissue from edema fluid
Less sensitive in detecting small abnormalities compared to CT scans (poor spatial resolution)
Inability to scan critically-ill patients requiring life support systems and monitoring devices that employ ferromagnetic materials.
May be dangerous in scanning patients with metal implants and other metal objects
May provoke claustrophobia
Longer exam time compared to CT scans
Safety in scanning pregnant women is not known.