Delineation of hypoxia in canine myocardium using PET and copper(II)-diacetyl-bis(N(4)-methylthiosemicarbazone).

Unlabelled: Copper(II)-diacetyl-bis(N(4)-methylthiosemicarbazone) (copper-ATSM) is a hypoxia-avid tracer for the selective identification of hypoxic tissue. Using canine models of hypoxic myocardium, we report our findings on *Cu-ATSM PET (*Cu is defined as either (60)Cu, (61)Cu, or (64)Cu) for the delineation of ischemic and hypoxic myocardium.

Methods: In protocol I, myocardial hypoxia was induced by global hypoxia (n = 3). In protocol II, myocardial ischemia was generated by occlusion of the left anterior descending coronary artery (n = 9). In protocol III, coronary artery stenosis was induced by a stenosis in the left anterior descending coronary artery (n = 4). PET dynamic data were acquired immediately after tracer injection. Tracer retention kinetics were analyzed using either monoexponential analysis (1/k(mono)) or a simple 2-compartment model (1/k(4)).

Results: In protocol I, tracer retention in hypoxic myocardium was 2-fold greater than in normal myocardium, despite a 7-fold increase in blood flow (normal, 0.70 +/- 0.42 mL.min(-1).g(-1); hypoxic, 4.94 +/- 3.00 mL.min(-1).g(-1) [P < 0.005]). In protocol II, approximately 3 h after occlusion, retention of *Cu-ATSM within 20 min was greater in ischemic regions (myocardial blood flow, 0.28 +/- 0.26 mL.min(-1).g(-1)) than in normal tissue (myocardial blood flow, 0.52 +/- 0.19 mL.min(-1).g(-1)) (1/k(mono), 40.72 +/- 39.0 min vs. 26.69 +/- 22.29 min [P < 0.05]; 1/k(4), 6.85 +/- 4.90 min vs. 3.51 +/- 1.97 min [P < 0.05]). In selected dogs, tracer retention decreased at 24 h, suggesting the development of necrosis with no subsequent retention of *Cu-ATSM. In protocol III, dobutamine infusion after stenosis placement resulted in increased tracer retention consistent with hypoxia in the damaged regions.

Conclusion: *Cu-ATSM PET has shown quantitative selective uptake in hypoxic myocardium within 20 min of tracer administration in 3 canine models of hypoxia.