Ultrasonic characterization of localized passive elastic properties of human pennate muscle with a single-probe setup

•SWE and B-mode imaging were used to construct modulus-strain curves.•Parameters were estimated from normalized modulus-strain curve using a Gauss-Newton method.•Parameters exhibit different ranges for 5 groups of subjects with various age or conditions. Quantitative evaluation of passive elastic properties of an individual skeletal muscle in vivo is among the major challenges of biomechanics, and its clinical application is severely limited. By combining shear-wave elastography (SWE) and B-mode imaging techniques, this study develops a novel non-invasive method to measure the local elastic modulus-fascicle strain curve of human pennation muscle during passive stretching using a single probe. Physiologically meaningful parameters are estimated and compared in subjects with different ages or pathological conditions. The in vivo experimental group comprised 12 healthy subjects (four children, four adults, and four seniors) and eight patients (four suffering from pseudohypertrophy, four from atrophy). Their gastrocnemius muscles were passively stretched using an ankle joint motion instrument. Local elastic moduli of the muscle were measured using SWE imaging frames and a built-in ‘F-ROI’ tool. The corresponding fascicle strains were simultaneously obtained using B-mode imaging frames and a gradient Radon transform. Three parameters (η, μ, G0) were estimated from a normalized elastic modulus-strain curve using the Gauss–Newton method. The measured elastic modulus-strain curves all agreed with models of the estimated parameters (0.910