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

Purpose: 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 (¹³¹I-Hyp) for imaging detection of acute myocardial infarction (AMI) in conditions closer to clinical scenarios.

Methods: We established swine AMI models (n = 6) which were intravenously given ¹³¹I-Hyp and ^99mTc-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 ¹³¹I-Hyp.

Results: ¹³¹I-Hyp based SPECT indicated clearly hot regions on ventricular walls which were all histologically proved as AMI. Complementally, the hot AMI regions on ¹³¹I-Hyp SPECT (infarct/myoc ratio of 15.3 ± 7.7) were inversely cold regions on ^99mTc-sestamibi SPECT (infarct/myoc ratio of 0.029 ± 0.021). Autoradiography of heart slices showed 9.8 times higher ¹³¹I-Hyp uptake in infarcted over normal myocardium. With γ counting, the mean ¹³¹I-Hyp uptake in infarcts was 10.69 ID%/g, 12.05 times of that in viable myocardium.

Conclusion: ¹³¹I-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.