Differential registration of two types of radionuclides on macroautoradiograms for studying coronary circulation:...

Double-radionuclide autoradiography proved to be feasible using combinations of Tc-99m and I-125, or Tc-99m and C-14. Because of the short half-life of Tc-99m (6 hr), we first registered Tc-99m on x-ray film. Given an adequate Tc-99m:I-125 activity ratio of 20:1, the exposure duration for Tc-99m was still too short for I-125 to blacken the x-ray film. The pure emission from C-14 is completely absorbed by a thin aluminum sheet--hence no problem there. After the decay of Tc-99m, therefore, it was entirely feasible to continue autoradiography with I-125 (T1/2 = 60.2 days) or C-14 (T1/2 = 5730 yr). Based on these conditions, we applied (a) tracer microspheres labeled with I-125 and Tc-99m to define the respective perfusion areas of the left anterior descending, septal, and left circumflex coronary arteries of the beating heart, and (b) Tc-99m pyrophosphate and C-14 antipyrine to demarcate respectively the localization of the infarct-avid substance and the regional blood flow. We verified the first procedure with postmortem angiography and the second with histochemistry.