VOL 57 Circu la lion VR 5 APRIL AN OFFICIAL JOURNALo fle AMERICAN HEART ASSOCIATION NO 4 1978 REVIEWS OF CONTEMPORARY LABORATORY METHODS

RADIOACTIVE TRACERS have been used for the evaluation of cardiac structure for over 50 years, since the initial application of Blumgart et al. of Radon' for the measurement of the circulation time in man, using a cloud chamber as the radiation detection device. Many improvements in both instrumentation and radiopharmaceuticals have been introduced to make measurements of regional wall motion and ventricular volumes of both the right and left ventricles, regional myocardial perfusion, and for the detection of acutely damaged tissues in the myocardium. Some of the current clinical applications are summarized in table 1. The function measured with a radioactive tracer procedure will depend on the type of radiopharmaceutical administered, the time of observation, and the type of instrument employed to make the measurement. For example, the initial distribution of a radiolabeled albumin radiopharmaceutical as it courses through the cardiac chambers after intravenous injection is primarily a function of blood flow, while the distribution sometime later is a function of regional blood volume and is unrelated to flow.2 3 If the measurement of initial tracer passage through the heart is made with a device of low frequency response, a radiocardiogram type of curve is recorded. This can be used to determine cardiac output and estimate shunting.4 5 If a high fidelity recording device is employed, then a measurement of ejection fraction can be made at the same time6' 7and a more precise measurement of shunting is possible. There are three classes of nuclear instruments commonly employed to record data from patients undergoing cardiovascular investigation:8 1) a scintillation probe system; 2)