Positron Emission Tomographic Imaging of the Myocardium with 81Rb

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Abstract
An approach to the assessment of regional myocardial perfusion has been developed utilizing positron emission tomographic imaging of the heart after intravenous administration of 18Rb (T1/2 = 4.6 hr) and a multicrystal positron camera. In five intact anesthetized dogs, 1.0 to 2.0 mCi of 81RbCl was administered and imaging begun 5 min later. A total of 7 to 9 transverse section images of the heart (1 cm thick) were obtained by the computer reconstruction of 208 images taken at uniformly spaced angles as the camera was rotated 180° around the animal. Collection time was 18 min. Emission images of 81Rb activity were corrected for attenuation by first obtaining transmission data using a planar positron-emitting source. Transverse section images through the apex of the heart showed uniform uptake of 81Rb+ activity below the left ventricular (LV) cavity. Tomographic images through the midventricular level showed myocardial 81Rb+ distribution in an annular pattern around the LV cavity, and tomographic cuts through the base of the heart showed a horseshoe appearance of activity anteriorly and diminished tracer uptake posteriorly in the region of the left atrial wall. These studies demonstrate the feasibility of three-dimensional myocardial imaging by using the 33% positron emission of 81Rb+ and a positron camera.