Radioiodinated hypericin as a tracer for detection of acute myocardial infarction: SPECT-CT imaging in a swine model

Hypericin (Hyp) is a natural compound with a newly discovered necrosis-avidity, which can be exploited as a necrosis-avid tracer once labeled with radioactive iodine as has been tested in rodent models. This study was to evaluate the effect of radioiodinated Hyp ( 131 I-Hyp) for imaging detection of acute myocardial infarction (AMI) in conditions closer to clinical scenarios. We established swine AMI models (n = 6) which were intravenously given 131 I-Hyp and 99m Tc-sestamibi and underwent SPECT-CT imaging with high- and low-energy collimators. The acquired SPECT images were fused with cardiac CT images and correlated with postmortem autoradiography and macro- and microscopic pathology. Tissue γ counting was performed to determine biodistribution of 131 I-Hyp. 131 I-Hyp based SPECT indicated clearly hot regions on ventricular walls which were all histologically proved as AMI. Complementally, the hot AMI regions on 131 I-Hyp SPECT (infarct/myoc ratio of 15.3 ± 7.7) were inversely cold regions on 99m Tc-sestamibi SPECT (infarct/myoc ratio of 0.029 ± 0.021). Autoradiography of heart slices showed 9.8 times higher 131 I-Hyp uptake in infarcted over normal myocardium. With γ counting, the mean 131 I-Hyp uptake in infarcts was 10.69 ID%/g, 12.05 times of that in viable myocardium. 131 I-Hyp shows a potential for clinical detection of AMI once I-131 is substituted by its isotope like I-124 or I-123 for PET or SPECT, respectively.