Uptakes and images of K-38 in rabbit heart, kidney, and brain

The purpose of this study was to evaluate the kinetics and image quality of positron-emitting K-38 (half-life, 7.6 min) and high-resolution small-anim al PET in the heart, kidney, and brain of rabbits. Methods: Studies were pe rformed with 18 closed-chest anesthetized rabbits at baseline and during in fusions of adenosine (0.2 mg/kg/min) and propranolol (0.5-1.0 mg/kg intrave nously) using high-resolution small-animal PET. K-38 was injected intraveno usly and dynamic PET imaging of the heart, kidney, or brain was performed f or 3 min. Colored microspheres were injected into the left ventricle to mea sure organ blood flow. Arterial blood was withdrawn directly from the femor al artery, and, after the animals were killed, K-38 activities in each orga n were measured directly with a well counter. Uptake of K-38 was calculated by dividing the K-38 activities in each organ by the integral of the input function. The extraction fraction of K-38 was estimated by dividing the up take of K-38 in each organ by the organ blood flow, measured by microsphere s. Results: The left ventricular myocardium and kidney were clearly visuali zed, but there was no visual K-38 uptake in the brain. For the heart, kidne y, and brain, respectively, average blood flow was 2.91 +/- 129, 5.49 +/- 0 .71, and 0.57 +/- 0.11 mL/min/g, and the extraction fraction of 38K at base line was 0.55 +/- 0.13, 0.48 +/- 0.13, and 0.022 +/- 0004. The Renkin-Crone model fit the relation between myocardial extraction and flow under a wide range of myocardial blood flow (r = 0.89). Conclusion: K-38 is a suitable tracer for noninvasively showing the potassium kinetics of the heart, kidne y, and brain by PET imaging.