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Abstract: Mechanical properties of plantar soft tissues are important characteristics of the foot and are prone to being affected by foot pathologies such as diabetes. Therefore, it is of great importance to measure the mechanical properties of plantar soft tissues in vivo. However, such measurement in previous studies is mostly conducted in foot without loading and there is a paucity of instrument available which can assess the foot mechanical properties under a weight-loading status. In this study, a foot scanner incorporating a tissue ultrasound palpation (indentation) system (TUPS) which could assess the mechanical properties of plantar soft tissues under different body-weight loading was developed. The movement of the foot could also be monitored in real time during the indentation test to improve the test reliability. Preliminary tests were conducted on ten normal subjects at the heel region under various loading of the bodyweight. The results showed that the thickness decreased by 12.0% (from 13.83±2.52mm to 12.10±1.95mm) while the stiffness increased by 83.4% (from 40.0±20.7kPa to 69.0±26.0kPa) when the loading increased from 0% to 80% of the bodyweight (both p <0.001, repeated measure one-way ANOVA). Therefore, our system has been demonstrated to be useful in studying the loading dependence of mechanical properties of plantar soft tissues. Potential applications of the system in clinical studies for characterization and monitoring of foot pathologies such as ageing and diabetes are discussed at the end of this note. [Copyright &y& Elsevier]

Abstract: We previously reported an ultrasound method for measuring the depth-dependent equilibrium mechanical properties of articular cartilage using quasi-static compression. The objective of this paper was to introduce our recent development for nondestructively measuring the transient depth-dependent strains of full-thickness articular cartilage specimens prepared from bovine patellae. A 50MHz focused ultrasound transducer was used to collect ultrasound echoes from articular cartilage specimens () and sponge phantoms with open pores () during tests of compression and subsequent stress–relaxation. The transient displacements of the tissues at different depths along the compression direction were calculated from the ultrasound echoes using a cross-correlation tracking technique. An LVDT sensor and a load cell were used to measure the overall deformation of the tissue and the applied force, respectively. Results showed that the tissues inside the cartilage layer continued to move during the stress–relaxation phase after the compression was completed. In the equilibrium state, the displacements of the cartilage tissues at the depths of 1/4, 1/2, and 3/4 of the full-thickness reduced by 51%±22%, 54%±17%, and 50±17%, respectively, in comparison with its peak value. However, no similar phenomenon was observed in the sponge phantoms. Our preliminary results demonstrated that this ultrasound method may provide a potential tool for the nondestructive measurement of the transient depth-dependent processes involved in biological and bioengineered soft tissues as well as soft biomaterials under dynamic loading. [Copyright &y& Elsevier]

This study is aimed towards developing a novel noncontact ultrasonic indentation system for measuring or imaging quantitative mechanical properties of soft tissues, which are increasingly important for tissue assessment and characterization. The key idea of this method is to use a water beam as an indenter to stimulate the soft tissue. The water beam also serves as a medium for an ultrasound beam propagating through. The application of water beam benefits the system to use focused high-frequency ultrasound without any additional attenuation. The indentation deformation was estimated from the ultrasound echoes using cross-correlation algorithm and the indentation force was calculated from the measured pressure and an overall force. Experiments were performed on tissue-mimicking phantoms whose Young''s moduli and Poisson''s ratio were measured using uniaxial compression and the indentation pressure/deformation curves were obtained. This system shows good ability in measuring the phantoms with different stiffness. It is expected that this novel water beam indentation method can be used to construct an ultrasound elastomicroscopy for imaging tissue''s elasticity in a high resolution. [Copyright &y& Elsevier]