Detection and quantification of acute reperfused myocardial infarction in rabbits using DISA-SPECT/CT and 3.0T cardiac MRI.

Background: Necrosis avid tracer (123)I-hypericin ((123)I-HYP) enables hot-spot imaging on acute myocardial infarction (MI). We explored dual-isotope simultaneous acquisition single photon emission computed tomography/computed tomography (DISA-SPECT/CT) by using (123)I-HYP and standard (99m)Tc-sestamibi ((99m)Tc-MIBI), in comparison with cardiac magnetic resonance imaging (cMRI), autoradiography (AutoRx) and histomorphometry.

Methods: Acute MI was induced by 90-min coronary artery occlusion and 24-h reperfusion in 9 rabbits. They were scanned with cMRI at 3.0T, followed by intravenous injections of (123)I-HYP, and 8h later, of (99m)Tc-MIBI. Then, they were imaged with DISA-SPECT/CT for detection and localization of MI. The excised heart was sectioned for AutoRx, triphenyltetrazolium chloride (TTC) histochemistry, and haematoxylin-eosin (HE) staining. DISA-SPECT/CT and cMRI were co-registered, and MI was compared between different modalities and techniques for correlation with ex vivo findings. Tracer/contrast uptakes were quantified on polar maps. One way-ANOVA and Bonferroni's tests were used for comparison of multiple techniques. Linear regression and Bland-Altman analysis were used to compare measurements of MI.

Results: MI volumes were not significantly different as by (99m)Tc-MIBI-SPECT, (123)I-HYP-SPECT, cMRI and TTC (38.94 ± 13.97%, 37.76 ± 13.16%, 35.19 ± 12.53% and 33.26 ± 10.65%; p > 0.05). The MI areas were 41.13 ± 18.70%, 40.19 ± 18.45%, 38.23 ± 16.86%, 36.83 ± 16.70%, 36.16 ± 16.15% and 35.03 ± 14.75% on (99m)Tc-MIBI-SPECT, (123)I-HYP-SPECT, cMRI, AutoRx, TTC and HE. There was no significant differences between each of two techniques (p = 0.9). Tracer/contrast uptakes were well correlated ((123)I-HYP vs (99m)Tc-MIBI r(2) = 0.66; (123)I-HYP vs cMRI r(2) = 0.63; (99m)Tc-MIBI vs cMRI r(2) = 0.64). Infarct/normal myocardium activity ratio was 40/1 and 23/1 by AutoRx and γ-counting.

Conclusion: (123)I-HYP has shown pronounced necrosis-avidity, which proves complementary for imaging MI with potential clinical applicability for myocardial viability determination.