Perfusion measures for symptom severity and differential outcome of revascularization in limb ischemia: Preliminary results with arterial spin labeling reactive hyperemia.

Background: Previously, a theoretical model based on microvascular physiology was established to facilitate the interpretation of calf perfusion dynamics recorded by arterial spin labeling (ASL). Purpose: To investigate the clinical relevance of novel perfusion indices by comparing them to the symptoms, response to revascularization, and short-term functional outcome in patients with peripheral arterial disease (PAD). Study Type: Prospective cohort study. Population: Nineteen patients with PAD. Field Strength/Sequence: Pulsed ASL at 3T. Assessment: The mid-calf reactive hyperemia induced by 2 minutes of arterial occlusion was recorded in PAD patients. The perfusion responses were characterized by the peak, time-to-peak, and physiological model-derived indices including the baseline perfusion f(r), arterial resistance R-a, and compliance C-a, and sensitivity g(ATP) and response time (ATP) of downstream microvasculature to metabolic stress. These indices were compared to the disease severity and outcome within 6 months after revascularization assessed by self-reported symptoms and the ankle-brachial index. Disease severity was categorized as asymptomatic, claudication, or critical limb ischemia. The outcome was categorized as symptom resolved or limited improvement. Statistical Tests: Severity and outcome groups were compared using Mann-Whitney and Kruskal-Wallis tests with Holm-Sidak adjustments. Results: The peak perfusion decreased and model arterial resistance increased progressively with increasing severity of limb ischemia (P=0.0402 and 0.0413, respectively). Eleven patients had a successful endovascular procedure, including six patients who had symptoms resolved, four patients who had remaining leg pain, and one patient lost to follow-up. The subjects with limited improvement had significantly lower preintervention microvascular sensitivity g(ATP) than those with symptoms resolved (8.721.46 vs. 4.930.91, P=0.0466). Data Conclusion: ASL reactive hyperemia reflects multiple aspects of the pathophysiology. Measures of macrovascular arterial disease are related to the manifested symptom severity, whereas preintervention g(ATP) associated with microvascular dysfunction is related to prognosis following revascularization. Technical Efficacy: Stage 4