These techniques take detailed anatomic pictures of the body. The pictures are acquired by exposing the body to magnetic fields. This causes energy to be released by hydrogen atoms in the body. This emitted energy is detected and a picture of the interior of the body is constructed. Side effects are rare and mild. Sometimes, an intravenous injection of something called gadolinium is also given.

Traditional magnetic resonance imaging (MRI) scanners require that the patient be placed in a small cylindrical tube. This can be somewhat unsettling for claustrophobic patients. Newer scanners are more open but do not produce the high quality pictures that the closed scanners do. Patients can expect to hear loud knocking noises from the scanner as the images are acquired.

Because of the powerful magnets used, patients with pacemakers or certain other metallic substances in their body cannot undergo this procedure. Note that patients with some types of metal, such as artificial heart valves and artificial hips, can undergo this procedure safely. It is important to let the staff of the MRI unit know the patient's complete medical history so that they can determine if the procedure can be safely performed.

In cardiology, MRI scans are primarily used to evaluate the aorta (the main blood vessel that supplies blood to the rest of the body). The chambers of the heart and the strength of the heart muscle can be visualized. Leaky and narrowed heart valves can be evaluated. Tumors in the heart can be detected. MRI is an excellent test to assess congenital heart disease. Stress tests can be performed with MRI also.

Much of the same information can be obtained more conveniently and at lower cost by standard echocardiography or transesophageal echocardiography. However, there are rare situations when MRI scanning is required.

Magnetic Resonance Angiography (MRA) is an MRI scan that essentially produces an angiogram, i.e., pictures of blood vessels. It is quite useful for larger blood vessels such as the aorta and the arteries that go to the brain. It is getting better as time goes on for picturing the small, curving coronary arteries that lie on the surface of the beating heart. It holds promise for the future but at the present time, it cannot replace coronary angiograms.

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