Peripheral arterial disease: the role of extracellular volume measurements in lower limb muscles with MRI.

Peripheral arterial disease (PAD) is characterised by arterial occlusion and fibrosis in the lower extremities. Extracellular volume matrix fraction (ECV) is a biomarker of skeletal muscle fibrosis, but has not been applied to the lower extremities with PAD. This study investigated the clinical feasibility of using ECV for calf muscle fibrosis quantification by comparing normal controls (NC) and PAD patients. From October 2016 to December 2017, we recruited patients with PAD, and patients with head and neck cancer receiving fibular flap as NC group. All participants underwent magnetic resonance imaging (MRI) to determine the ECV of the calves and the differences between the NC and PAD groups. ECV was calculated from T1 values at steady-state equilibrium, defined as the point in time after contrast agent injection when the variance of T1 relaxation time in blood and muscle becomes less than 5%. A total of 46 patients (18 in the NC group and 28 in the PAD group) were recruited. Steady-state equilibrium was reached at 11-12 min after contrast agent injection. The NC group had significantly lower mean ECV than the PAD group (12.71% vs. 31.92%, respectively, p < 0.001). In the PAD group, the mean ECV was slightly lower in patients with collateral vessels than in those without (26.58% vs. 34.88%, respectively, p = 0.047). Evaluation of skeletal fibrosis in PAD using ECV is feasible. ECV can help identify PAD patients with collateral vessel formation and lay the foundation for future research in PAD management. • Steady-state equilibrium for ECV measurement of the lower limbs can be reached at around 11-12 min. • Quantification of lower limb muscle fibrosis by measuring ECV is clinically feasible and can be used to differentiate between patients with PAD and histologically proven normal controls. • ECV can differentiate PAD patients with or without visible collateral vessels, further expanding its role in identifying the presence of collateral supply in clinical decision-making.