Cardiac Magnetic Resonance Imaging
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 a unique method of imaging blood vessels and heart without the need of a contrast medium. MRI can evaluate functions of the heart and vessels.
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 flowing blood and various soft tissues, such as cardiac muscles, blood vessels, atherosclerotic plaque
Compared to the iodine-based contrast medium in X-rays or CT scans, MRI dye is relatively safe.
It provides angiographic images without being invasive.
MRI can evaluate the functions of the heart, cardiac valves, and vessels, as well as the structures.
When you suspect other heart conditions, aortic and vascular diseases
When you have uncertain abnormalities in your chest x-ray, echocardiography or chest CT that need to be evaluated.
Old myocardial infarctions
Acute myocardial infarctions
Evaluation of cardiac function: myocardial contraction, valvular motion
Pericarditis, pericardial diseases
Congenital heart diseases
Cardiac mass, tumor, cancer
Aortic diseases: aneurysm, tear, dissection
Pulmonary artery diseases
Vascular diseases: blockage, atherosclerotic plaque
You will be asked to lie down on the scan table. After proper positioning, the examining 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. He 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 the procedure is done, in order to get clear pictures.
In the event a contrast medium is required to make the 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, wallet, beepers, cellular phones, zippers, snaps, hairpins, jewelry, accessories, eyeglasses, hearing aid, and any removable dental work, because they can be affected and degrade the quality of imaging.
The information on credit cards can be erased by strong magnetic field.
Let your radiologist or technologist know when you have a metal object implanted or imbedded 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 generated by MRI can cause these ferromagnetic metal objects to move, dislodge, or cause burns and electrical currents.
Tattoos and permanent eyeliner 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 applied to protect your ear from the loud repetitive noises typically emitted by the MRI appliance during scanning.
A radiologist (a physician specialist trained to interpret MRI images or other radiology exams, such as CAT scans, X-rays, mammography, etc.) reviews your cardiovascular MRI and reports the results to your personal doctor.
Your doctor's office will inform you when the results are in, and what they mean. The doctor's office uses the results as a reference in evaluating and treating patients.
The strong magnetic field generated by this procedure can cause metal implants to dislodge, burn, and cause additional injuries. If you have any metal implants in your body (such as a pacemaker, prosthetic valves, clips, etc.), you should let your radiologist or technologist know its brand name and model. If it is not confirmed to be compatible with MRI magnetic fields, you should not take 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 the MRI magnet:
Women in the first 12 weeks of pregnancy should avoid MRI and contrast medium. There are no known harmful effects to pregnant women and unborn babies as of this writing. 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 this huge magnet may provoke 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 devices (IUDs)
- Metallic bone plates, pins, screws, surgical staples, especially within 4-6 weeks after surgery.
- Bullets, shrapnel, possible metal fragments, especially in and around the eyes
- Metallic ear implants
Less sensitive in demonstrating acute hemorrhage compared to CT scan.
Hard to depict calcifications
Less sensitive in detecting small abnormalities compared to CT scan (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 with CT
Safety in scanning pregnant women is not known.