Myocardial and blood kinetics of thallium-201 (201T1) and potassium42 (42K) were studied in five patients with normal coronary angiography. A mixture of 400 oCi of 201TI, 400 μCi of 42K, 50 μCi ofiodine-125 radioiodinated human serum albumin as intravascular indicator, and 400 μCi of tritiated water (THO) as extravascular indicator was injected as a bolus into the pulmonary artery, and blood timeconcentration curves were obtained from the aortic root and coronary sinus. These curves were numerically deconvoluted to obtain the frequency function of transit times (FFTT) of the four isotopes through the coronary system.
Initial maximal myocardial extraction of the two tracers were similar. The net maximal myocardial uptake of 201TI per 100 g of tissue ranged from 1.0-2.7% of the injected dose and was positively related to myocardial blood flow (MBF) calculated from THO and to the ratio MBF/cardiac output (CO), while net uptake of 42K ranged from 1.4-2.4%, but was not correlated with MBF nor with MBF/CO.
The analysis of the FFTT indicates that 42K, but not 201TI, is washed out from the myocardium more rapidly when MBF and the heart rate are higher. Thus, thallium appears to be a much more suitable agent than potassium isotopes for myocardial perfusion studies.