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Uptakes and Images of ³⁸K in Rabbit Heart, Kidney, and Brain

Third Department of Internal Medicine, Chiba University School of Medicine, Chiba
Division of Advanced Technology for Medical Imaging, National Institute of Radiological Sciences, Chiba, Japan

Correspondence: For correspondence or reprints contact: Katsuya Yoshida, MD, Third Department of Internal Medicine, Chiba University School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba, 260-8677, Japan.

ABSTRACT

The purpose of this study was to evaluate the kinetics and image quality of positron-emitting ³⁸K (half-life, 7.6 min) and high-resolution small-animal PET in the heart, kidney, and brain of rabbits. Methods: Studies were performed with 18 closed-chest anesthetized rabbits at baseline and during infusions of adenosine (0.2 mg/kg/min) and propranolol (0.5–1.0 mg/kg intravenously) using high-resolution small-animal PET. ³⁸K was injected intravenously and dynamic PET imaging of the heart, kidney, or brain was performed for 3 min. Colored microspheres were injected into the left ventricle to measure organ blood flow. Arterial blood was withdrawn directly from the femoral artery, and, after the animals were killed, ³⁸K activities in each organ were measured directly with a well counter. Uptake of ³⁸K was calculated by dividing the ³⁸K activities in each organ by the integral of the input function. The extraction fraction of ³⁸K was estimated by dividing the uptake of ³⁸K in each organ by the organ blood flow, measured by microspheres. Results: The left ventricular myocardium and kidney were clearly visualized, but there was no visual ³⁸K uptake in the brain. For the heart, kidney, and brain, respectively, average blood flow was 2.91 ± 1.29, 5.49 ± 0.71, and 0.57 ±0.11 mL/min/g, and the extraction fraction of ³⁸K at baseline 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: ³⁸K is a suitable tracer for noninvasively showing the potassium kinetics of the heart, kidney, and brain by PET imaging.

Key Words: ³⁸K • PET • myocardium • kidney • brain