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Heart MRIDefinition Heart magnetic resonance imaging (MRI) is a non-invasive procedure that uses powerful magnets and radio waves to produce pictures of the heart without exposure to ionizing radiation (X-rays). The heart may be scanned by itself, or a heart MRI may be part of a chest MRI. How the test is performed MRI uses radio waves very close in frequency to those of ordinary FM radio stations, so the scanner must be located within a specially shielded room to avoid outside interference. The patient is lies on a narrow table which slides into a large tunnel-like tube within the scanner. Small devices may be placed around the head, arm, or leg, or adjacent to other areas to be studied. These are special body coils which send and receive the radio wave pulses, and are designed to improve the quality of the images. An IV may be placed in the patient's hand or forearm if contrast medium will be used. A technologist will operate the machine and observe the patient from an adjacent room during the entire study. Several sets of images are usually required, each taking from 2-15 minutes. A complete scan, depending on the sequences performed, and need for contrast enhancement may take 1 hour or more. Newer scanners may complete the process in less time. How to prepare for the test No preparatory tests, diets, or medications are usually needed. An MRI can be performed immediately after other imaging studies. Depending on the area of interest, the patient may be asked to fast for 4 to 6 hours prior to the scan. Certain metallic objects are not allowed into the room. Items such as jewelry, watches, credit cards, and hearing aids can be damaged. Pins, hairpins, metal zippers, and similar metallic items can distort the images. Removable dental work should be taken out just prior to the scan. Pens, pocketknives, and eyeglasses can become dangerous projectiles when the stronge MRI magnet is activated and should not accompany the patient into the scanner area. The MRI's strong magnetic fields can disrupt cardiac pacemakers cannot be scanned and people with them should not be scanned or even enter the MRI area. MRI also should not be used for people with metallic objects in their bodies such as inner ear (cochlear) implants, brain aneurysm clips, some artificial heart valves, older vascular stents, and recently placed artificial joints. Sheet metal workers, or persons with similar potential exposure to small metal fragments, will first be screened for metal shards within the eyes with X-rays of the skull. The patient will be asked to sign a consent form confirming that none of the above apply before the MRI begins. A hospital gown may be recommended, or the patient may be allowed to wear clothing without metal fasteners. How the test will feel There is no pain. The patient cannot feel the magnetic field and radio waves. The primary possible discomfort is the claustrophobic feeling that some experience from being inside the scanner. The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises during normal operation. Ear plugs are usually given to the patient to reduce the noise. A technologist observes the patient during the entire procedure and may be spoken to through an intercom in the scanner. Some MRI scanners are equipped with televisions and special headphones to help the examination time pass. Excessive movement can blur MRI images and cause certain artifacts. If the patient has difficulty lying still or is very anxious, an oral or intravenous sedative may be given. There is no recovery time, unless sedation was necessary. After an MRI scan, you can resume normal diet, activity, and medications. Why the test is performed MRI provides detailed pictures of the heart and blood vessels and can distinguish tissues from moving blood. It can differentiate between heart muscle and surrounding tissues and can clarify the findings from previous x-rays or CT scans. MRI excels at showing the heart from multiple views. MRI is useful in diagnosing congenital abnormalities, abnormal growths, and tumors. MRI is sometimes used to avoid the dangers of angiography, repeated exposure to radiation, or exposure to iodinated contrast dye. It may provide additional information when an echocardiogram is unclear, since bone and air do not interfere with imaging. In addition, heart MRI provides a wider view and better detail than an echocardiogram. What abnormal results mean The sensitivity of MRI depends, in part, on the experience of the radiologist. A heart MRI may reveal the following disorders:
What the risks are There is no ionizing radiation involved in MRI, and there are no known side effects of the magnetic fields and radio waves on the human body. However, because the effects of strong magnetic fields on a fetus are not well known, pregnant women are usually advised to avoid MRI scans. MRI is usually not recommended for traumatic injuries, because traction and life-support equipment cannot safely enter the scanner area, and scan times are relatively lengthy. Gadolinium, the most commonly used intravenous contrast agent, is very safe. There have been documented allergic reactions to it, but this is extremely rare. If sedation is used, there are associated risks of oversedation. The technologist will monitor the patient's vital signs, including heart rate and respiration, as needed. Special considerations MRI is more accurate than CT scan or other tests for certain conditions, but less accurate for others. Disadvantages include the high cost, long duration of the scan, and sensitivity to movement. People with claustrophobia or who are confused or anxious may have difficulty lying still for the relatively long scan times. MRI is not portable and is incompatible with some metallic implants, life support devices, traction, apparatus, and similar equipment. MRI is superior in most cases in which differentiation of soft tissues is necessary. It can view organs without obstruction by bone and foreign bodies. It is capable of showing the tissues from multiple viewpoints and is a non invasive way to evaluate blood flow. Illustrations
Page Content: Magnetic resonance imaging - cardiac; NMR - cardiac; Nuclear magnetic resonance - cardiac; MRI of the heart ; heart mri; cardiac imaging magnetic resonance |
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