Overview
Cardiac Magnetic Resonance Imaging (Cardiac MRI)
This cardiac MRI picture shows the 4 chambers of the heart using what is called a "bright blood" technique. Blood within the heart shows up as white, and the heart muscle shows up as dark gray. The 4 chambers of the heart are the left ventricle (LV), the right ventricle (RV), the left atrium (LA), and the right atrium (RA).
MRI is a scan that lets doctors see inside the body without having to perform surgery. The test is painless, and uses no radiation. Cardiac MRI is a test that gives doctors a detailed picture of the heart, including the chambers and valves, without patients having to undergo cardiac catheterization.
What is Cardiac MRI ? 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).
How does it work? The MRI machine looks like a long, narrow tube. When you are placed inside of the tube, you are surrounded by a magnetic field. The human body is made up of different elements, most of which are also magnetic.
The magnetic field surrounding your body reacts with the magnetic elements within your body to transmit a faint radio signal. For example, your body contains a large amount of hydrogen atoms, and those atoms are very magnetic. The MRI machine's magnetic field excites the hydrogen atoms in your body, which in turn creates a small radio signal. A computer reads the radio signal and turns it into an image that can be seen on a computer monitor.
What should I expect? No special preparation is needed before you have an MRI. The MRI machine will surround you during the test, and some people may feel closed in or claustrophobic. You will have to lie still, and you may be asked to hold your breath briefly while the technician takes pictures of your heart.
An MRI is a completely painless test, and because the MRI machine uses magnetism, you are not exposed to any radiation like you would be with an x-ray machine. MRI cannot be done if you have a pacemaker.
Magnetic Resonance Angiography (MRA) :-
When doctors use an MRI machine to study the blood vessels leading to the brain, heart, kidneys, and legs, it is called magnetic resonance angiography (MRA). MRA uses the same technology as MRI, but technicians use special settings on the machine to detect and diagnose blood vessel diseases. MRA can usually give doctors very clear images of the blood vessels without exposing the patient to radiation. In some cases, a harmless dye may be used to make the images even clearer. The MRA dye highlights the blood vessels, making them stand out from the tissues around them.
If you are having an MRA procedure that does not require a contrast dye, the procedure will be just like an MRI procedure. If a contrast dye is needed, it will be injected (usually in your arm) over 1 to 2 minutes, and then more scans will be done. The dye used for the test is harmless.
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 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.
Lumbar spine trauma. Drawing of the mechanism of injury of the lumbar spine burst injury is compared with an axial CT image. The centrally applied vertical force results in radial expansion of the vertebral body endplate. The posterior margin of the endplate may be displaced into the spinal canal (arrow).
