Xiaochun Liao

Elastic properties of Thiel-embalmed human ankle tendon and ligament

Thiel embalming is recommended as an alternative to formalin‐based embalming because it preserves tissue elasticity, color, and flexibility in the long term, with low infection and toxicity risk. The degree to which Thiel embalming preserves elasticity has so far been assessed mainly by subjective scoring, with little quantitative verification. The aim of this study is to quantify the effect of Thiel embalming on the elastic properties of human ankle tendons and ligament. Biomechanical tensile tests were carried out on six Thiel‐embalmed samples each of the peroneus longus, peroneus brevis, and calcaneal tendons, and the calcaneofibular ligament, with strain rates of 0.25%s−1, 2%s−1, and 8%s−1. The stress−strain relationship was calculated from the force‐extension response with cross‐sectional area and gauge length. Youngs modulus was determined from the stress−strain curve. The results showed that the tendon and ligament elasticity were lower after Thiel embalming than the literature values for fresh nonembalmed tendons and ligament. The biomechanical tensile test showed that the measured elasticity of Thiel‐embalmed tendons and ligaments increased with the strain rate. The Thiel embalming method is useful for preserving human ankle tendons and ligaments for anatomy and surgery teaching and research, but users need to be aware of its softening effects. The method retains the mechanical strain rate effect on tendons and ligament. Clin. Anat. 28:917–924, 2015.

Functional piezocrystal characterisation under varying conditions

Piezocrystals, especially the relaxor-based ferroelectric crystals, have been subject to intense investigation and development within the past three decades, motivated by the performance advantages offered by their ultrahigh piezoelectric coefficients and higher electromechanical coupling coefficients than piezoceramics. Structural anisotropy of piezocrystals also provides opportunities for devices to operate in novel vibration modes, such as the d36 face shear mode, with domain engineering and special crystal cuts. These piezocrystal characteristics contribute to their potential usage in a wide range of low- and high-power ultrasound applications. In such applications, conventional piezoelectric materials are presently subject to varying mechanical stress/pressure, temperature and electric field conditions. However, as observed previously, piezocrystal properties are significantly affected by a single such condition or a combination of conditions. Laboratory characterisation of the piezocrystal properties under these conditions is therefore essential to fully understand these materials and to allow electroacoustic transducer design in realistic scenarios. This will help to establish the extent to which these high performance piezocrystals can replace conventional piezoceramics in demanding applications. However, such characterisation requires specific experimental arrangements, examples of which are reported here, along with relevant results. The measurements include high frequency-resolution impedance spectroscopy with the piezocrystal material under mechanical stress 0–60 MPa, temperature 20–200 °C, high electric AC drive and DC bias. A laser Doppler vibrometer and infrared thermal camera are also integrated into the measurement system for vibration mode shape scanning and thermal conditioning with high AC drive. Three generations of piezocrystal have been tested: (I) binary, PMN-PT; (II) ternary, PIN-PMN-PT; and (III) doped ternary, Mn:PIN-PMN-PT. Utilising resonant mode analysis, variations in elastic, dielectric and piezoelectric constants and coupling coefficients have been analysed, and tests with thermal conditioning have been carried out to assess the stability of the piezocrystals under high power conditions.

Reduced penetration force through ultrasound activation of a standard needle: An experimental and computational study

Needle insertion in soft tissue has attracted considerable attention in recent years because of its applications in minimally invasive percutaneous procedures such as cancer biopsy and regional anaesthesia. Tissue deformation and needle deflection contingent on needle penetration force are common reasons behind needle placement errors, leading to missampling in biopsy, incomplete anaesthesia, and possible post-operative morbidity. In this paper, we report the design of an ultrasonic device, based on a piezoelectric transducer with a sandwich structure, to reduce the standard needles penetration force and deflection. Experimental trials were carried out on brain-mimicking phantom and ex vivo porcine tissue. The results show that a standard needle with ultrasound actuation can achieve force reduction by 34.5% and deflection reduction by 38.3%. In addition, numerical simulation of static and dynamic forces was conducted. A comparison between experimental and computational results demonstrates very close agreement. All the experimental and computational results suggest success in the proposed ultrasonic devices ability to perform accurate biopsy and regional anaesthesia.

Functional characterization of piezocrystals monitored under high power driving conditions

Relaxor-based ferroelectric single crystals such as PMN-PT are known to exhibit high piezoelectric properties compared with conventional piezoelectric ceramic materials, such as PZT-8. With advances in piezoelectric material development, including compositional engineering, single crystals with higher rhombohedral-to-tetragonal phase transition temperature (TRT), higher coercive field (EC) and higher mechanical quality factor (QM) have emerged, the principal example being Mn:PIN-PMN-PT. The improvements have opened up a wider application range, including more demanding high power applications where the performance of conventional materials may deteriorate at elevated temperatures resulting from intrinsic loss mechanisms. Characterization of these piezocrystals under practical and active conditions is therefore important, improving understanding of material behavior and facilitating transducer design in finite element analysis for demanding applications. In this paper, we report an active piezoelectric material characterization system that allows high resolution impedance spectroscopy under conditions similar to those experienced by piezoelectric materials in high power ultrasonic applications. The temperature consequent on the drive voltage is adaptively stabilized using a control algorithm. System function has been verified by testing with a Mn:PIN-PMN-PT thicknessextensional plate and functional characterization has been conducted on Generation I, II and III piezocrystals, with detailed analyses and comparisons of performance stability and material property variation with temperature.

Automatic frequency tracking system for needle actuating device

Resonant frequency shift can occur during operation in the application of ultrasonic actuating device. It affects the resonance amplitude and therefore the performance of the device. To solve this problem, an automatic frequency tracking system based on embedded technology was developed. It has the ability to automatically track the resonant frequency shift in response to the load and adjust the excitation frequency accordingly to optimize the performance of the ultrasonic actuating device. The tracking algorithm realized by stm32 ARM processor ensures flexibility to suit different transducers and load conditions. The data acquisition module and serial port can achieve real time operation parameters monitoring and storage on PC. The effectiveness of this frequency tracking system is tested in a trial study of needle visualization during anesthesia procedure using needle actuating device. Results show that the visibility of the needle is greatly improved throughout needle insertion.

Performance optimization of ultrasonic needle actuating device for insertion operation into tissue mimics

Needle insertion with ultrasound actuation has been proven as an effective way to reduce the penetration force and needle deflection within soft tissue, facilitating operational manoeuverability and targeting accuracy in cancer biopsy and regional anaesthesia. In such percutaneous procedures, loading conditions from adjacent soft tissue alter the needle transducers impedance and cause deterioration of its vibration performance. In this paper, we report the needle transducers structure and working principle; we investigate the loading effects from tissue mimics on the transducers resonant impedance and vibration performance; and we show how to enhance the needle transducers vibration performance through optimization of geometrical dimensions and the electrical driving method. Structural optimization was carried out with different transversal dimensions of the needle. Electrical driving optimization was done by tracking the working resonant frequency and stabilizing the driving signal during operation. Experimental trials confirmed a force reduction of 70.2% with the structural optimization and 73.7% with the electrical driving optimization for the insertion operation into gelatin phantom, compared with a static needle.

Enhanced US-guided needle intervention through ultrasound actuation of a standard needle

In ultrasound (US)-guided percutaneous needle procedures, including regional anaesthesia, there are universal problems of poor visibility and deflection of needle tip, especially in dense tissues and at steep insertion angles. These can have serious consequences, including nerve damage, internal bleeding and false-negative biopsy. We have developed an innovative piezoceramic (PZT) based ultrasound needle-actuating device. Operating at low ultrasonic frequencies, 20 - 50 kHz, the device significantly enhances tip visibility under Doppler ultrasound imaging and reduces tip deflection of standard medical needles. The requirements of a device with low spatial volume and high performance have led us to investigate the potential of the Generation III relaxor-PT piezocrystals (Mn:PIN-PMN-PT). In this paper, we report a comparative study of PZT and Mn:PIN-PMN-PT based needle-actuating devices, particularly highlighting the performance benefits achieved with piezocrystal. The paper details the development and characterization of these devices and the pre-clinical trials carried out on soft-embalmed cadavers to assess their viability in clinical practice.

Loss characterisation of piezocrystals under elevated environmental conditions

Relaxor-based piezoelectric single crystals have experienced three generations of development, from binary (e.g. PMN-PT) through ternary (e.g. PIN-PMN-PT) to doped ternary (e.g. Mn:PIN-PMN-PT). With improved composition and other relevant factors, these materials exhibit an extraordinary degree of piezoelectricity and ultrahigh electromechanical coupling coefficients, making them suitable for applications requiring high sensitivity and high bandwidth. With further increases in rhombohedral-to-tetragonal phase transition temperature (TRT), coercive field (EC) and mechanical quality factor (Qm), these piezocrystals can now be expected to work at elevated temperature, T, and pressure, P, and with high electric field drive. However, in operation, material properties can vary and performance can degrade significantly because of these elevated conditions, and the situation can be exacerbated by losses in the materials, necessitating proper characterisation of loss factors. In this paper, we report an investigation of three different loss characterisation methods then propose one combined method, demonstrating its use on TE-mode plates of PIN-PMN-PT and Mn:PIN-PMN-PT. Characterisation was performed using impedance spectroscopy for 20°C ≤ T ≤ 100°C and 0 MPa ≤ P ≤ 60 MPa. Results relating to dielectric, elastic and piezoelectric losses are reported, with detailed analysis and comparisons.