Here are definitions of medical terms related to MRI.
Echocardiogram: A method of obtaining an image of the heart structure by using ultrasound (inaudible, high-frequency, sound waves). The sound is reflected differently by each part of the heart. The result is a complex series of echoes that are recorded and analyzed.
Electrocardiogram (ECG, or EKG): A record of the electrical impulses that immediately precede contraction of the heart muscle. The waves produced are known as the P, Q, R, S, and T waves. The EKG is used to diagnose heart disorders, many of which produce deviations from normal electrical patterns.
Ischemia: Insufficient blood supply to a specific organ or tissue, usually caused by a blood vessel disease, but can also result from vessel injury, constriction, or inadequate blood flow due to inefficient action of the heart.
Radio waves (MRI): The "radio wave signals" used in MRI are actually a changing magnetic field that is much weaker than the strong magnetic field of the main magnet in the machine.
Stroke: Damage to part of the brain caused by the interruption of the blood supply, or by leakage of blood outside the vessel walls. Stroke can cause damage to sensation, movement, or function, depending on which area of the brain is affected.
Thallium stress test: A specialized kind of exercise stress test which is done after the patient receives a injection of a harmless radioactive substance (thallium) into the bloodstream. Its purpose is to show how well blood flows to the heart muscle during exercise. The source of exercise can be either a treadmill or a stationary bicycle.
Ventricle: There are two ventricles in the heart, the right and the left ventricle. They are the lower, pumping chambers, which receive blood from the upper heart chambers (atria) and pump it to the lungs and the rest of the body.