PET tomography in studies of distributions of 7.6-min potassium 38 in the dog heart.

Potassium 38 emits a 2.68-MeV (max) positron, followed promptly by a 2.17-MeV gamma-ray in 99.8% of its disintegrations. A positron is emitted also, followed by a 3.94-MeV gamma-ray, in 0.2% of the decays. The pairs of 511-keV PET +/- gamma-quanta, which are emitted at 180 +/- 0.3 degrees to each other, are in true coincidence with the prompt gamma-rays emitted by the daughter nucleus, within the resolving time of PET instrumentation. Studies made with phantoms by means of a commercial version of the MGH PET camera demonstrated that quantitatively satisfactory images are derived, despite the presence of the prompt gamma-rays. Two-dimensional (2-D) focal-plane images reveal high uptake of 38K promptly in the myocardium of dogs, under barbiturate sedation. Third-dimensional (3-D) transverse section PET tomographic images, through four 1.0-cm-thick heart "slices" orthogonal to the plane of the 2-D images and with 1.4-cm sequential spacing, show 38K uptake to be concentrated especially highly in the left ventricle, as expected. Peak levels of activity were observed over the myocardium at 12 s after intravenous bolus injection of ionic 38K. Dynamic mode 2-D images were taken at intervals as short as 0.5 s and extending to 1 h.