Continuous assessment of regional myocardial perfusion in dogs using krypton-81m.

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Abstract
81mKr was continuously eluted in 5% dextrose from a cyclotron-made 81Rb generator. The unique physical properties of this inert freely diffusible gas (half-life 13 s) have allowed the development of a technique for the constant infusion of this tracer into the aortic sinuses of 25 dogs. Theoretical considerations suggest that an equilibrium of 81mKr activity in the myocardium is principally dependent on blood flow. Experiments have tested the delivery of this indicator and have recorded quantitative high spatial resolution images of the heart with a gamma camera and digital computer. The systematic error was determined by comparing changes in regional blood flow (in ml/g per min, using an electromagnetic flow probe) and changes in calculated flow (mg/g per min) using the regional activity of 81mKr (P < 0.001; r = 0.97; y = 908 X + 0.105; n = 60). The random error and uncertainties concerning mixing and streaming of the indicator were tested by repeating measurements with alterations in heart rate, blood pressure, coronary flow and total myocardial 81mKr activity using different interventions (reproducibility, P = 0.001, r = 0.982; y = 0.982x + -0.257, n = 100 observations). Any quantification of changes in the myocardial activity of 81mKr must consider the stability of the arterial concentration of this indicator and washout of 81mKr at high values of myocardial blood flow. This ultra-short-lived radionuclide will, however, provide an assessment of changes in the distribution of regional myocardial perfusion.