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Comparative Myocardial Uptake and Clearance Characteristics of Potassium and Cesium

Center for Health Sciences, and Laboratory of Nuclear Medicine and Radiation Biology, University of California, Los Angeles, California

Correspondence: For reprints contact: Norman D. Poe, Div. of Nuclear Medicine, UCLA Medical Center, Los Angeles, Calif. 90024.

ABSTRACT

Potassium-43 and its analog, ¹²⁹Cs, have recently been suggested as suitable radiopharmaceuticals for myocardial scanning. Studies with ⁴²K and ¹³¹Cs were undertaken in dogs to determine the myocardial turnover characteristics of these two ions. After simultaneous intravenous injection, potassium clears rapidly from the blood, reaches a plateau in the myocardium within 5–20 min, and then clears with a T_1/2 of 6.5 hr. Initial cesium clearance is slower. A peak is reached gradually in the myocardium within 1–3 hr, and the clearance T_1/2 is 27.3 hr. Following intracoronary injection, potassium is extracted with 71% efficiency on a single circulation, but cesium is extracted with only 22% efficiency. It is concluded that cesium should be used with caution as a substitute for potassium in quantitative myocardial blood flow and function measurements, but that comparable results can be obtained with either radionuclide in localizing ischemic myocardium.