Regional myocardial radiotracer kinetics in dogs using miniature radiation detectors

Abstract

An implantable device for continuous measurement of regional myocardial radioisotope activity was designed and validated. The probe consists of a 2-mm3 cadmium telluride crystal surrounded by lead foil housed in a 4.5-mm-outer-diameter steel cylinder. Activity in serial dilutions of 201Tl measured by this miniature .gamma. detector correlated well with activity measured in the well counter (r = 0.99). In vivo probe measurements of regional myocardial 201Tl activity in a canine model were compared with activity in punch biopsies, again with excellent correlation (r = 0.90). The crystal was mounted on a modified arterial clamp, which was inserted into the left ventricle through the apex and situated on the endocardial surface of the anterior or posterior wall. It was possible to measure regional isotope activity without excessive background from the blood pool and opposite heart wall. The probe was best suited for monitoring activities of isotopes with energies between 60-250 keV. With a pair of these devices, dynamic studies of the myocardial kinetics of radioisotopes such as 201Tl in normal and ischemic myocardium are now possible.