Zhen Qiu

Characterization of piezocrystals for practical configurations with temperature- and pressure-dependent electrical impedance spectroscopy

Piezoelectric single crystal materials such as (x)Pb(Mg1/3Nb2/3)O3-(1-x)PbTiO3 (PMN-PT) have, by some measures, significantly better performance than established piezoelectric ceramics for ultrasound applications. However, they are also subject to phase transitions affecting their behavior at temperatures and pressures encountered in underwater sonar and actuator applications and in non-destructive testing at elevated temperatures. Materials with modified compositions to reduce these problems are now under development, but application-oriented characterization techniques need further attention. Characterization with temperature variation has been reported extensively, but the range of parameters measured is often limited and the effects of pressure variation have received almost no attention. Furthermore, variation in properties between samples is now rarely reported. The focus of this paper is an experimental system set up with commercially available equipment and software to carry out characterization of piezoelectric single crystals with variation in temperature, pressure, and electrical bias fields found in typical practical use. We illustrate its use with data from bulk thickness-mode PMN-29%PT samples, demonstrating variation among nominally identical samples and showing not only the commonly reported changes in permittivity with temperature for bulk material but also significant and complicated changes with pressure and bias field and additional ultrasonic modes which are attributed to material phase changes. The insight this provides may allow the transducer engineer to accelerate new material adoption in devices.

Intraoperative Ultrasound-Guided Resection of Gliomas: A Meta-Analysis and Review of the Literature

BACKGROUND Image-guided surgery has become standard practice during surgical resection, using preoperative magnetic resonance imaging. Intraoperative ultrasound (IoUS) has attracted interest because of its perceived safety, portability, and real-time imaging. This report is a meta-analysis of intraoperative ultrasound in gliomas. METHODS Critical literature review and meta-analyses, using the MEDLINE/PubMed service. The list of references in each article was double-checked for any missing references. We included all studies that reported the use of ultrasound to guide glioma-surgery. The meta-analyses were conducted according to statistical heterogeneity between the studies using Open MetaAnalyst Software. If there was no heterogeneity, fixed effects model was used for meta-analysis; otherwise, a random effect model was used. Statistical heterogeneity was explored by χ(2) and inconsistency (I(2)) statistics; an I(2) value of 50% or more represented substantial heterogeneity. RESULTS A wide search yielded 19,109 studies that might be relevant, of which 4819 were ultrasound in neurosurgery; 756 studies used ultrasound in cranial surgery, of which 24 studies used intraoperative ultrasound to guide surgical resection and 74 studies used it to guide biopsy. Fifteen studies fulfilled our stringent inclusion criteria, giving a total of 739 patients. The estimated average gross total resection rate was 77%. Furthermore, the relationship between extent of surgical resection and study population was not linear. Gross total resection was more likely under IoUS when the lesion was solitary and subcortical, with no history of surgery or radiotherapy. IoUS image quality, sensitivity, specificity, and positive and negative predictive values deteriorated as surgical resection proceeded. CONCLUSION IoUS-guided surgical resection of gliomas is a useful tool for guiding the resection and for improving the extent of resection. IoUS can be used in conjunction with other complementary technologies that can improve anatomic orientation during surgery. Real-time imaging, improved image quality, small probe sizes, repeatability, portability, and relatively low cost make IoUS a realistic, cost-effective tool that complements any existing tools in any neurosurgical operating environment.

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.

The development of therapeutic ultrasound with assistance of robotic manipulator

High Intensity Focused Ultrasound (HIFU) is finding increasing application and acceptance as a non-invasive approach to the treatment of targeted malignancy. Despite the wealth of research and interest in HIFU, there are still a number of issues that need to be overcome to extend its clinical applications. These relate to the accuracy of placing the HIFU beam, the ability to visualize the target volume, and the understanding of the beam interaction with tissue. In this paper, the output characteristics of a single element HIFU transducer have been investigated with the assistance of a six-axis modified industrial robot. It is shown in the experimental results that clearly defined thermal or mechanical damage can be produced by changing the parameters of the HIFU. The nature and patterns of damage produced by pre-programmed treatment are now being investigated in tissue.

The development of a robotic approach to therapeutic ultrasound

Despite the recent wealth of research into therapy with high intensity focused ultrasound (HIFU), its clinical application still has limitations. These relate to the accuracy of the HIFU beam, the ability to visualize the target volume, and the understanding of the beam interaction with tissue. In the work reported in this paper, the output characteristics of a single channel HIFU transducer have been investigated in detail with the aid of a six-axis robot. Results show that by altering the drive parameters of the transducer clearly defined thermal or mechanical damage can be produced. The nature and patterns of damage produced by preprogrammed treatment volumes are now being investigated in tissue.

Improving the operational bandwidth of a 1–3 piezoelectric composite transducer using Sierpinski Gasket fractal geometry

Wider operational bandwidth is an important requirement of an ultrasound transducer across many applications. It has been reported mathematically that by having elements with varying length scales in the piezoelectric transducer design, the device may possess a wider operational bandwidth or a higher sensitivity compared to a conventional device. In this paper, the potential for extending the operational bandwidth of a 1-3 piezoelectric composite transducer configured in a fractal geometry, known as the Sierpinski Gasket (SG), will be investigated using finite element analysis package PZFlex (Thornton Tomasetti). Two equivalent piezocomposite designs will be simulated: a conventional 1-3 piezocomposite structure and the novel SG fractal geometry arrangement. The transmit voltage response and open circuit voltage extracted from the simulations are used to illustrate the improved bandwidth predicted from the fractal composite design.

Dual Orientation 16-MHz Single-Element Ultrasound Needle Transducers for Image-Guided Neurosurgical Intervention

Image-guided surgery is today considered to be of significant importance in neurosurgical applications. However, one of its major shortcomings is its reliance on preoperative image data, which does not account for brain deformations and displacements that occur during surgery. In this work, we propose to tackle this issue through the incorporation of an ultrasound device within the type of biopsy needles commonly used as an interventional tool to provide immediate feedback to neurosurgeons during surgical procedures. To identify the most appropriate path to access a targeted tissue site, single-element transducers that look either forward or sideways have been designed and fabricated. Micromolded 1-3 piezocomposites were adopted as the active materials for feasibility tests and epoxy lenses have been applied to focus the ultrasound beam. Electrical impedance analysis, pulse-echo testing, and wire phantom scanning have been carried out, demonstrating the functionality of the needle transducers at ~16 MHz. The capabilities of these transducers for intraoperative image guidance were demonstrated by imaging within soft-embalmed cadaveric human brain and fresh porcine brain.

15 MHz single element ultrasound needle transducers for neurosurgical applications

Image-guided surgery is today considered to be of significant importance in neurosurgical applications. However, one of its major shortcomings is its reliance on preoperative image data, which does not account for the intraoperative brain deformations and displacements that occur during surgery. In this work, we propose to tackle this issue with the incorporation of an ultrasound device within a biopsy needle that is commonly used as an interventional tool so as to provide immediate feedback to neurosurgeons during surgical procedures. In order to identify the most appropriate path to access a targeted tissue site, needle single element transducers that look both forwards and sideways have been designed and fabricated. Monolithic PZT plates and micro-moulded 1-3 piezocomposites have been adopted as the active materials for feasibility tests. Impedance analysis and pulse-echo testing have been carried out, demonstrating the functionality of the transducers at frequencies of ~15 MHz. The imaging capabilities of these transducers have been studied by wire phantom scans. Variations in the transducer properties as a result of the use of different active materials are discussed.

Advanced electrical array interconnections for ultrasound probes integrated in surgical needles

Real-time ultrasound guidance during neurosurgery is a novel and sought-after technique that enables imaging data to be acquired with improved precision during surgical intervention. Surgical needles that are inserted in the tissue of interest can be guided using the real-time graphical information collected by an embedded ultrasound transducer. The miniaturisation capabilities of modern manufacturing technologies allow the fabrication of ultrasound probes that are small enough to be fitted in needles conventionally used in surgical practices (down to ~2 mm inner diameter). High lateral resolution may in fact be achieved by producing miniaturised ultrasound transducer arrays with a series of emitting/receiving elements, each electrically isolated from the others. To guarantee the functionality of such devices, a series of independent electrical interconnections must be implemented that enables the external driving electronics of the imaging system to be connected to the miniaturised ultrasound probe array. This paper presents a novel interconnection scheme designed to interface ultrasound probes integrated in surgical needles with the driving electronics. The presented solution utilises a flexible printed circuit board carrying the electrical tracks and a bonding technique with an anisotropic conductive paste.

Customized modular multichannel electronics for ultrasound-mediated targeted drug delivery with a geodesic piezocrystal phased array

Ultrasound-mediated targeted drug delivery (UmTDD) has the potential to enhance the chemotherapeutic treatment of cancer by allowing increased drug doses preferentially at the location of the tumor. Although gaining increasing interest over the past few years, research into UmTDD system configurations has been hindered by the lack of experimental driving systems and ultrasound devices. In the work reported here, a piezocrystal composite geodesic phased array with 96 elements was connected to commercial programmable multi-channel electronics based on NI-PXIe / FlexRIO-FPGA hardware. The system was modified to provide appropriate ultrasound intensities through power and heat dissipation strategies. Auto-focusing was applied by phase aberration correction. Preliminary results using cross-correlation are presented to demonstrate its applicability. The pressure intensity at the focus of the array was increased four times while the intensity of side lobes were below -12 dB.