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Cardiovascular: Basic ScienceNew Approaches Using SPECT, PET and Hybrid Imaging |
1 Radiology and Radiological Sciences; ; 2 Cardiology, Johns Hopkins School of Medicine, Baltimore, Maryland; ; 3 Technical University of Munich, Munich, Germany
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Objectives: CT can detect infarct at high resolution by delayed myocardial contrast enhancement. In cardiac PET-CT, this may allow for replacement of rest perfusion studies and improved localization of viability and PET-derived molecular signals. This study sought to determine the feasibility of CT delayed enhancement in cardiac PET-CT, and to compare it to PET-defined rest perfusion.
Methods: We studied 7 pigs 4-6 weeks post-myocardial infarction(LAD occlusion/reperfusion). Using 64-slice PET-CT, perfusion was measured by rest N-13 ammonia PET. 120ml of contrast was given and retrospectively gated helical CT was performed after 1.5, 5, 10, and 15min delay. Two days later, contrast CT using a low radiation dose approach(calcium scoring) and same delays was performed. Polarmaps of PET perfusion and CT myocardial enhancement were created for analysis.
Results: HU in the infarct exceeded arterial blood at 5-10min after contrast, and ratios for infarct/remote myocardium and infarct/blood plateaued around 1.9 and 1.2 between 10-15min. There was excellent agreement between high- and low-dose acquisition(r=.87; p<.001). At 10min, infarct size was 33±5%LV using low dose CT(HU threshold >3.5sd from remote). PET perfusion defect was comparable at 35±6%LV(threshold 60% of max). Using a 16-segment model, there was excellent inverse relationship between ammonia retention and contrast enhancement(r=-.87; p<.001).
Conclusions: Infarct size can be measured in cardiac PET-CT using delayed CT contrast enhancement and a low-dose CT similar to calcium scoring. This will increase the versatility and integrative potential of clinical cardiac PET-CT.
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