Magnetic resonance imaging (MRI) is a noninvasive medical test that helps physicians diagnose and treat medical conditions.
MR imaging uses a powerful magnetic field, radio frequency pulses and a computer to produce detailed pictures of organs, soft tissues, bone and virtually all other internal body structures. The images can then be examined on a computer monitor, printed or copied to CD. MRI does not use ionizing radiation (x-rays).
Detailed MR images allow physicians to better evaluate parts of the body and certain diseases that may not be assessed adequately with other imaging methods such as x-ray, ultrasound or computed tomography (also called CT or CAT scanning).
What are some common uses of the procedure ?
Cardiac MRI imaging is performed to help : -
evaluate the structures and function of the heart, valves, major vessels, and surrounding structures (such as the pericardium).
diagnose and manage coronary heart disease and a variety of cardiovascular problems.
detect and evaluate coronary artery disease.
plan a patient's treatment for cardiovascular problems and monitor patient's progress.
Using cardiac MRI, physicians can : -
examine the size and thickness of the chambers of the heart.
determine the extent of damage caused by a heart attack or progressive heart disease.
detect the buildup of plaque and blockages in the blood vessels.
assess a patient's recovery following treatment.
How should I prepare ?
You may be asked to wear a gown during the exam or you may be allowed to wear your own clothing if it is loose-fitting and has no metal fasteners.
Guidelines about eating and drinking before an MRI exam vary with the specific exam and also with the facility. Unless you are told otherwise, you may follow your regular daily routine and take medications as usual.
Some MRI examinations may require the patient to swallow contrast material or receive an injection of contrast into the bloodstream. The radiologist or technologist may ask if you have allergies of any kind, such as allergy to iodine or x-ray contrast material, drugs, food, the environment, or asthma. However, the contrast material used for an MRI exam, called gadolinium, does not contain iodine and is less likely to cause an allergic reaction.
The radiologist should also know if you have any serious health problems and what surgeries you have undergone. Some conditions, such as severe kidney disease may prevent you from having an MRI with contrast material.
Women should always inform their physician or technologist if there is any possibility that they are pregnant. MRI has been used for scanning patients since the 1980's with no reports of any ill effects on pregnant women or their babies. However, because the baby will be in a strong magnetic field, pregnant women should not have this exam unless the potential benefit from the MRI is assumed to outweigh the potential risks.
If you have claustrophobia (fear of enclosed spaces) or anxiety, you may want to ask your physician for a prescription for a mild sedative. Jewelry and other accessories should be left at home if possible, or removed prior to the MRI scan. Because they can interfere with the magnetic field of the MRI unit, metal and electronic objects are not allowed in the exam room.
These items include : -
jewelry, watches, credit cards and hearing aids, all of which can be damaged.
pins, hairpins, metal zippers and similar metallic items, which can distort MRI images.
removable dental work.
pens, pocketknives and eyeglasses.
body piercings.
In most cases, an MRI exam is safe for patients with metal implants, except for a few types. People with the following implants cannot be scanned and should not enter the MRI scanning area unless explicitly instructed to do so by a radiologist or technologist who is aware of the presence of any of the following:
internal (implanted) defibrillator or pacemaker
cochlear (ear) implant
some types of clips used on brain aneurysms
You should tell the technologist if you have medical or electronic devices in your body, because they may interfere with the exam or potentially pose a risk.
Examples include but are not limited to : -
artificial heart valves
implanted drug infusion ports
implanted electronic device, including a cardiac pacemaker
artificial limbs or metallic joint prostheses
implanted nerve stimulators
metal pins, screws, plates or surgical staples.
In general, metal objects used in orthopedic surgery pose no risk during MRI. However, a recently placed artificial joint may require the use of another imaging procedure. If there is any question of their presence, an x-ray may be taken to detect the presence of any metal objects.
Patients who might have metal objects in certain parts of their bodies may also require an x-ray prior to an MRI. Dyes used in tattoos may contain iron and could heat up during MRI, but this is rarely a problem. Tooth fillings and braces usually are not affected by the magnetic field but they may distort images of the facial area or brain, so the radiologist should be aware of them.
How does the procedure work ?
Unlike conventional x-ray examinations and computed tomography (CT) scans, MRI does not depend on radiation. Instead, while in the magnet, radio waves redirect the axes of spinning protons, which are the nuclei of hydrogen atoms, in a strong magnetic field.
The magnetic field is produced by passing an electric current through wire coils in most MRI units. Other coils, located in the machine and in some cases, placed around the part of the body being imaged, send and receive radio waves, producing signals that are detected by the coils.
A computer then processes the signals and generates a series of images each of which shows a thin slice of the body. The images can then be studied from different angles by the interpreting physician.
Overall, the differentiation of abnormal (diseased) tissue from normal tissues is often easier with MRI than with other imaging modalities such as x-ray, CT and ultrasound.
How is the procedure performed ?
MRI examinations may be performed on outpatients or inpatients. You will be positioned on the moveable examination table. Straps and bolsters may be used to help you stay still and maintain the correct position during imaging.
Small devices that contain coils capable of sending and receiving radio waves may be placed around or adjacent to the area of the body being studied.
If a contrast material will be used in the MRI exam, a nurse or technologist will insert an intravenous (IV) line into a vein in your hand or arm. A saline solution will drip through the IV to prevent blockage of the IV line until the contrast material is injected. You will be moved into the magnet of the MRI unit and the radiologist and technologist will leave the room while the MRI examination is performed.
If a contrast material is used during the examination, it will be injected into the intravenous line (IV) after an initial series of scans. Additional series of images will be taken following the injection. When the examination is completed, you may be asked to wait until the technologist checks the images in case additional images are needed.
Your intravenous line will be removed.
MRI exams generally include multiple runs (sequences), some of which may last several minutes.
The entire examination is usually completed within 30 minutes.
MR spectroscopy, which provides additional information on the chemicals present in the body's cells, may also be performed during the MRI exam and may add approximately 15 minutes to the exam time.
What will I experience during and after the procedure ?
Most MRI exams are painless.
Some patients, however, find it uncomfortable to remain still during MR imaging. Others experience a sense of being closed-in (claustrophobia). Therefore, sedation can be arranged for those patients who anticipate anxiety, but fewer than one in 20 require it.
It is normal for the area of your body being imaged to feel slightly warm, but if it bothers you, notify the radiologist or technologist. It is important that you remain perfectly still while the images are being recorded, which is typically only a few seconds to a few minutes at a time. For some types of exams, you may be asked to hold your breath. You will know when images are being recorded because you will hear tapping or thumping sounds when the coils that generate the radiofrequency pulses are activated.
You will be able to relax between imaging sequences, but will be asked to maintain your position as much as possible.
You will be alone in the exam room during the MR imaging, however, the technologist will be able to see, hear and speak with you at all times using a two-way intercom. Many MRI centers allow a friend or parent to stay in the room.
You may be offered or you may request earplugs to reduce the noise of the MRI scanner, which produces loud thumping and humming noises during imaging. MRI scanners are air-conditioned and well-lit. Some scanners have music to help you pass the time.
When the contrast material is injected, it is normal to feel coolness and a flushing for a minute or two. The intravenous needle may cause you some discomfort when it is inserted and once it is removed, you may experience some bruising. There is also a very small chance of irritation of your skin at the site of the IV tube insertion.
If you have not been sedated, no recovery period is necessary. You may resume your usual activities and normal diet immediately after the exam. A few patients experience side effects from the contrast material, including nausea and local pain. Very rarely, patients are allergic to the contrast material and experience hives, itchy eyes or other reactions.
It is recommended that nursing mothers not breastfeed for 36 to 48 hours after an MRI with a contrast material.
Who interprets the results and how do I get them ?
A radiologist, a physician specifically trained to supervise and interpret radiology examinations, will analyze the images and send a signed report to your primary care or referring physician, who will share the results with you. Your physician will be providing you with the results. This may take up to one day. However, if it is considered an emergency or if you are taking a flight back, there are ways for physicians to get results more quickly
What are the benefits vs. risks ?
Benefits : -
MRI is a noninvasive imaging technique that does not involve exposure to radiation.
MRI images of the heart are generally clearer and more detailed than with some other imaging methods. This detail makes MRI an invaluable tool in early diagnosis and evaluation of cardiac abnormalities, especially those involving the heart muscle.
MRI has proven valuable in diagnosing a broad range of conditions, including cardiac anatomical anomalies (congenital defects, etc.), functional abnormalities (valve failure, etc.), tumors and ischemic and degenerative conditions.
MRI can help physicians evaluate both the structure of an organ and how it is working.
MRI enables the detection of abnormalities that might be obscured by bone with other imaging methods.
The contrast material used in MRI exams is less likely to produce an allergic reaction than the iodine-based materials used for conventional x-rays and CT scanning.
Cardiac MRI allows physicians to quickly examine the structures and function of the heart and major vessels, without the risks associated with traditional, more invasive procedures.
Cardiac MRI can help in the diagnosis and treatment of patients with following conditions : -
Coronary artery disease
Congestive heart failure and cardiomyopathy
Congenital heart disease
Pericardial disease
Cardiac masses and thrombi
Arrhythmia
Aortic disease
Peripheral vascular disease
Valve disease
Risks : -
The MRI examination poses almost no risk to the average patient when appropriate safety guidelines are followed.
If sedation is used there are risks of excessive sedation. The technologist or nurse monitors your vital signs to minimize this risk.
Although the strong magnetic field is not harmful in itself, medical devices that contain metal may malfunction or cause problems during an MRI exam.
There is a very slight risk of an allergic reaction if contrast material is injected. Such reactions usually are mild and easily controlled by medication.
Nephrogenic systemic fibrosis is currently a recognized, but rare, complication of MRI believed to be caused by the injection of high doses of MRI contrast material in patients with poor kidney function.
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