A method to evaluate tracer kinetics in small laboratory animals using a series of thermoluminescent dosimeters

Miniature detector probes have previously been used in large animal models to investigate myocardial 201Tl clearance kinetics. The results of these studies helped develop clinical imaging protocols that greatly improved the accuracy of thallium scintigraphy. However, miniature detector probes are too large to be used in small animals. Thus, if a method could be developed to measure regional time activity curves in small animals, it would provide a cost-effective alternative to both experiments in large animals and/or multiple experiments at varying time points that can produce results only by postmortem analysis of several animals. Accordingly, we developed a method to measure a regional time activity curve of a tracer in rabbits by using a series of thin thermoluminescent dosimeters [CaF2 (dopant) TLDs, 1 mm thick] placed on the surface of the myocardium. Background contributions associated with high blood pool activity are modeled and then subtracted from the initial TLD response. To validate and illustrate this method, thallium kinetics were determined for nonischemic rabbit myocardium (n = 6). Myocardial thallium concentration decreased monoexponentially with a mean half-time equal to 396 +/- 141 min. Arterial blood activity decreased triexponentially with a final half-time of 243 +/- 73 min. No significant difference was found when the myocardial half-time was compared to the final arterial half-time. These findings are consistent with previous work using a cadmium telluride probe in a canine model. Therefore, TLD analysis can provide a cost-effective, reliable, and reproducible method to measure regional myocardial clearance kinetics.