Uptakes and images of 38K in rabbit heart, kidney, and brain.
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 Arterial blood was withdrawn directly from the femoral artery, and, after the animals were killed, 38K activities in each organ were measured directly with a well counter.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).


CONCLUSIONS
38K is a suitable tracer for noninvasively showing the potassium kinetics of the heart, kidney, and brain by PET imaging.
Takami
A
A
Third Department of Internal Medicine, Chiba University School of Medicine, Japan.
Yoshida
K
K
Tadokoro
H
H
Kitsukawa
S
S
Shimada
K
K
Sato
M
M
Suzuki
K
K
Masuda
Y
Y
Tanada
S
S
D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging*; D006321:Heart / Q000000981:diagnostic imaging*; D007668:Kidney / Q000000981:diagnostic imaging*; D008297:Male; D049268:Positron-Emission Tomography; D011197:Potassium Radioisotopes / Q000493:pharmacokinetics; D011817:Rabbits
D011197:Potassium Radioisotopes