Dynamic magnetic resonance measurements of calf muscle oxygenation and energy metabolism in peripheral artery disease.

Abstract

BackgroundClinical assessments of peripheral artery disease (PAD) severity are insensitive to pathophysiological changes in muscle tissue oxygenation and energy metabolism distal to the affected artery.PurposeTo quantify the blood oxygenation level‐dependent (BOLD) response and phosphocreatine (PCr) recovery kinetics on a clinical MR system during a single exercise‐recovery session in PAD patients.Study TypeCase–control study.SubjectsFifteen Fontaine stage II patients, and 18 healthy control subjectsField Strength/SequenceInterleaved dynamic multiecho gradient‐echo 1H T2* mapping and adiabatic pulse‐acquire 31P‐MR spectroscopy at 3T.AssessmentBlood pressure in the arms and ankles were measured to determine the ankle‐brachial index (ABI). Subjects performed a plantar flexion exercise‐recovery protocol. The gastrocnemius and soleus muscle BOLD responses were characterized using the T2* maps. High‐energy phosphate metabolite concentrations were quantified by fitting the series of 31P‐MR spectra. The PCr recovery time constant (τPCr) was derived as a measure of in vivo mitochondrial oxidative capacity.Statistical TestsComparisons between groups were performed using two‐sided Mann–Whitney U‐tests. Relations between variables were assessed by Pearson's r correlation coefficients.ResultsThe amplitude of the functional hyperemic BOLD response in the gastrocnemius muscle was higher in PAD patients compared with healthy subjects (–3.8 ± 1.4% vs. –1.4 ± 0.3%; P < 0.001), and correlated with the ABI (r = 0.79; P < 0.001). PCr recovery was slower in PAD patients (τPCr = 52.0 ± 13.5 vs. 30.3 ± 9.7 sec; P < 0.0001), and correlated with the ABI (r = –0.64; P < 0.001). Moreover, τPCr correlated with the hyperemic BOLD response in the gastrocnemius muscle (r = –0.66; P < 0.01).Data ConclusionMR readouts of calf muscle tissue oxygenation and high‐energy phosphate metabolism were acquired essentially simultaneously during a single exercise‐recovery session. A pronounced hypoxia‐triggered vasodilation in PAD is associated with a reduced mitochondrial oxidative capacity. Level of Evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2020;51:98–107.