Abstract 19482: Integrated Non-Invasive Imaging Approach for Assessment of Tissue Perfusion, Oxygenation, and Collateralization in a Porcine Model of Peripheral Artery Disease

Abstract

Objectives: Currently, there is no standard quantitative imaging approach to evaluate peripheral artery disease (PAD).In this study, we use hybrid SPECT/CT and MR imaging to relate post-occlusion collateral formation to serial in vivo changes in lower extremity perfusion and tissue oxygenation before and during vasodilation.

Methods: Serial hybrid 64-slice CT/SPECT imaging and BOLD MRI were performed in pigs (n=8) at baseline, immediately post unilateral femoral artery occlusion, and 1 and 4 weeks post occlusion. Contrast X-ray CT angiography was performed to define the occlusion site and to visualize collateral vessels. Non-contrast CT images were used to identify individual muscle groups in the ischemic (I) and non-ischemic (NI) hind limb for quantification of changes in relative regional muscle perfusion with ²⁰¹Tl SPECT. At 4 weeks post occlusion, muscle ²⁰¹Tl activity was measured postmortem by gamma well counting. MR images were acquired on a 3T magnet and T2* maps were generated for multiple transverse images. BOLD images used to quantify tissue oxygenation were acquired for 5 minutes at rest and for 10 minutes during vasodilation by IV administration of nitroglycerin (5 mg/kg/min NTG).

Results: SPECT/CT imaging showed a significant decrease in regional ²⁰¹Tl activity (I/NI) (Fig. 1A) in ischemic calf muscle groups (Fig. 1B), which normalized over time. Relative ²⁰¹Tl activity at 4 weeks (0.91±.0.06) matched gamma well counting (0.99±0.08, p=ns). These changes were not observed in other muscle groups. The T2* signal intensity in the ischemic leg decreased acutely post occlusion in response to NTG, probably reflecting diminished vascular reserve, although this response normalized at 4 weeks in association with collateral vessel formation.

Conclusions: Physiological changes in tissue perfusion and oxygenation following peripheral ischemia were tracked non-invasively using multimodality imaging, and can be attributed to collateral formation.