AbstractUltrasound guidance of needle-based regional anaesthesia and tissue biopsy is widely used in clinical practice. Ultrasound imaging has improved the efficacy and reduced some side effects during regional nerve block. However, the presentation and interpretation of real-time ultrasound guided needle interventions remains inaccurate and unreliable. Poor visibility occurs especially when using a thin needle, inserting to a deep location and at a steep angle. Inaccurate needle placement increases the risk of adverse results, such as inadequate anaesthesia, internal bleeding and nerve damage during regional anaesthesia and mis-sampling and misdiagnosis during cancer biopsy. Therefore, the aim of the work here is to design and develop a needle actuation transducer using high performance piezoelectric single crystal, capable of activating a standard, unmodified surgical needle, so that the visibility of needle can be enhanced under colour Doppler ultrasound imaging.
Characterization of single crystals was first carried out to obtain the full elasto-electric matrix under ambient conditions and to determine the change in material behaviour when subject to a range of temperature and pressure. Using the data obtained and from the literature, finite element analysis was carried out to design the needle actuation transducer. Both piezoceramic and piezocrystal were used for transducer fabrication in order to investigate whether the benefits in material properties can be translated into improvements in transducer performance. Small and large signal characterization was performed on the fabricated transducers for performance comparison. Preliminary imaging tests were then carried out to investigate factors affecting the needle visibility, including the insertion angle, depth and drive voltage. Further, the needle tip accuracy of the ultrasound actuated needle under colour Doppler guidance was determined by comparing colour Doppler measurement with photographic measurement and B-Mode ultrasound.
The material characterization results show that pressure in excess of 20MPa has a detrimental effect on the performance of single crystals. Relatively little or no advantage was observed from Mn-doping with respect to immunity to the pressure. The design of the d31-mode needle actuation transducer eliminates prestress in the mass-spring configuration and its feasibility was verified by fabrication followed by characterization. Enhanced transducer performance was observed using single crystals, showing the benefits of piezocrystal over traditional piezoceramic in such actuator applications. Preliminary tests show that the needle tip accuracy in gelatine phantom was -0.59 ± 0.38mm at 30° insertion angle, -0.58 ± 0.44mm at 45° and -0.32 ± 0.32mm at 60°. Bland Altman bias (95% limits of agreement) between B mode and colour Doppler imaging was -0.16mm (-1.94mm to 1.61mm). The results demonstrate the accuracy possible with this technology and potential for application to cancer biopsy and ultrasound guided regional anaesthesia. Further studies are warranted investigating the accuracy and reliability of this device in animal and cadaver tissue.
|Date of Award||2017|
|Sponsors||China Scholarship Council & Engineering and Physical Sciences Research Council|
|Supervisor||Zhihong Huang (Supervisor) & Sandy Cochran (Supervisor)|