Regional myocardial radiotracer kinetics in dogs using miniature radiation detectors

An implantable device for continous 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 thallium-201 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 thallium-201 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 thus possible to measure regional isotope activity without excessive background from the blood pool and opposite heart wall. The probe was found best suited for monitoring activities of isotopes with energies between 60 and 250 keV. With a pair of these devices, dynamic studies of the myocardial kinetics of radioisotopes such as thallium-201 in normal and ischemic myocardium are now possible.