Steven Freear

University of Leeds · Institute of Integrated Information Systems (I3S)

In ultrasound B-mode imaging, the axial resolution (AR) is commonly determined by the duration or bandwidth of an excitation signal. A shorter-duration pulse will produce better resolution compared to a longer one but with compromised penetration depth. Instead of relying on the pulse duration or bandwidth to improve the AR, an alternative method t...

Traditionally, single element transducers are used for localizing objects in 1D through A-mode scans, where only the echo envelope is used. Due to the transducer surface symmetry, A-mode scans performed for azimuthally or elevationally translated scatterers will produce the same 1D information, radial distance. The current study extends the previou...

No PDF available ABSTRACT The use of plasmonic gold nanoparticles (AuNP) that have been actively targeted to a specific tumour region is a highly active area of research for both drug delivery and hypothermia applications. One application is providing in situ cavitation nuclei for enhancing high intensity focused ultrasound (HIFU) ablation. When th...

This paper demonstrates hybrid sub-aperture beamforming (SAB) with time-division multiplexing (TDM) for massive interconnect reduction in ultrasound imaging systems. A single-chip front-end system prototype has been fabricated in 180-nm HV BCD technology that combines 5×1 SAB with 8×1 TDM to efficiently reduce the number of receive signal interconn...

The concept of employing air volumes trapped inside polymer shells to make a lens for ultrasound focusing in water is investigated. The proposed lenses use evenly-spaced concentric rings, each having an air-filled polymer shell construction, defining concentric water-filled channels. Numerical simulations and experiments have shown that a plane wav...

Staphylococcus aureus (S. aureus) is an important human pathogen and a common cause of bloodstream infection. The ability of S. aureus to form biofilms, particularly on medical devices, makes treatment difficult, as does its tendency to spread within the body and cause secondary foci of infection. Prolonged courses of intravenous antimicrobial trea...

Microbubbles are used as contrast agents in clinical ultrasound for Left Ventricular Opacification (LVO) and perfusion imaging. They are also the subject of promising research in therapeutics as a drug delivery mechanism or for sonoporation and co-administration. For maximum efficacy in these applications, it is important to understand the acoustic...

As an alternative to delay-and-sum beamforming, a novel beamforming technique called filtered-delay multiply and sum (FDMAS) was introduced recently to improve ultrasound B-mode image quality. Although a considerable amount of work has been performed to evaluate FDMAS performance, no study has yet focused on the beamforming step size, Δx, in the la...

The combination of ultrasound and microbubbles allows treatment of indications that would be impossible or too risk adverse with conventional surgery. During treatment, subharmonic and ultraharmonic components that can only be generated from microbubbles are of great interest for intraoperative monitoring. However, the microbubble emissions are sev...

In this study, an acoustic backscatter system was used with single broadband transducers utilising narrowband excitation at multiple frequencies of 2.00, 2.25 and 2.50 MHz, to determine the scattering properties of three sizes of glass particles (40, 78 and 212 µm) in liquid suspensions. A calibration procedure was developed to initially measure th...

Metamaterials exhibiting Fabry-Perot resonances are shown to achieve ultrasonic imaging of a sub-wavelength aperture in water immersion across a broad bandwidth. Holey-structured metamaterials of different thickness were additively manufactured using a tungsten substrate and selective laser melting, tungsten being chosen so as to create a significa...

Stiffness of soft tissues as a biomarker complements existing methods to detect breast and liver pathologies. An accurate and real-time estimation of tissue elasticity with a capability to image deeper regions may benefit various clinical applications such as breast, liver, thyroid, and prostate. Among existing methods, Supersonic Shear Imaging (SS...

High-Intensity Focused Ultrasound (HIFU) therapy provides a non-invasive technique with which to destroy cancerous tissue without using ionizing radiation. To drive large single-element HIFU transducers, ultrasound transmitters capable of delivering high powers at relevant frequencies are required. The acoustic power delivered to a transducers foca...

In recent years, the Ultrasound Group at the University of Leeds has developed an open platform (OP) known as Ultrasound Array Research Platform II (UARPII). The OP serves as a main component for researchers to test and implement new algorithms which is not feasible with the commercially available clinical scanners. In this paper, three types of ex...

The short-lag spatial coherence (SLSC) beamformer measures the accumulated similarity of echoes, received by individual transducer elements as a function of spatial separation. It proved beneficial in suppressing incoherent clutter to improve detectability of hypoechoic and anechoic targets. However, with focused beams spatial coherence of backscat...

Conventionally an A-mode scan, a single measurement with a single element transducer, is only used to detect the depth of a reflector or scatterer. In this case, a single measurement reveals only one-dimensional information; the axial distance. However, if the number of scatterers in the ultrasonic field is sparse, it is possible to detect the loca...

Metamaterials exhibit properties beyond those exhibited by conventional materials in conventional scenarios. These have been investigated both theoretically and experimentally at length. In many cases the underpinning physical understanding of metamaterials has greatly preceded our ability to manufacture constituent structures. However, the develop...

https://www.thno.org/toc/acceptms

Cardiac function and vascular function are closely related to the flow of blood within. The flow velocities in these larger cavities easily reach 1 m/s, and generally complex spatiotemporal flow patterns are involved, especially in a non-physiologic state. Visualization of such flow patterns using ultrasound can be greatly enhanced by administratio...

Lung cancer is a particularly difficult form of cancer to diagnose and treat, due largely to the inaccessibility of tumours and the limited available treatment options. The development of plasmonic gold nanoparticles has led to their potential use in a large range of disciplines, and they have shown promise for applications in this area. The abilit...

Acoustic metamaterials constructed from conventional base materials can exhibit exotic phenomena not commonly found in nature, achieved by combining geometrical and resonance effects. However, the use of polymer-based metamaterials that could operate in water is difficult, due to the low acoustic impedance mismatch between water and polymers. Here...

This paper proposes a new approach to determine the depth and location of buried pipelines using the remote magnetic field measured by aboveground magnetometer surveys. Calculation is presented and verified by the experimental results on 152-mm (6-in.). steel vessels. Performance of the technique is also evaluated through field trials against indus...

Fabry-Pérot ultrasonic metamaterials have been additively manufactured using laser powder bed fusion to contain subwavelength holes with a high aspect-ratio of width to depth. Such metamaterials require the acoustic impedance mismatch between the structure and the immersion medium to be large. It is shown for the first time that metallic structures...

Acoustic metamaterials constructed from conventional base materials can exhibit exotic phenomena such as negative refractive index, extraordinary transmission-absorption and sub-wavelength imaging. These are typically achieved by combining geometrical and resonance effects. Holey-structured acoustic metamaterials have already shown potential for su...

The performance of a pilot-scale horizontal sedimentation tank was characterised utilising computational fluid dynamics (CFD) and a bespoke ultrasonic backscatter array, for both spherical glass and flocculated calcite separation. The CFD simulation was developed in OpenFOAM, using algebraic slip and hindered settling models, in order to solve the...

The phase error caused by non-ideal physical transducer characteristics can affect the ultrasonic wave front during beamforming. If not compensated, the phase error can degrade the focusing capability and reduce the B-mode image spatial resolution. In this paper, the effect of the phase error on ultrafast coherent plane wave imaging (CPWI) was inve...

Multi-level switched mode transmitters provide a simplified method of exciting ultrasound transducers compared to linear amplifiers. Excitation waveforms are created which switch between typically 3 or 5 high voltage supplies with high drive current. Previously, Harmonic Reduction Pulse Width Modulation (HRPWM) has shown how control of amplitude an...

High-Intensity Focussed Ultrasound (HIFU) techniques make use of ultrasound transducers capable of delivering high powers to be delivered at high frequencies. Real-time monitoring of power delivered can avoid damage to the transducer and injury to patients due to overexposure. This paper demonstrates the real-time current and voltage monitoring cap...

By using diverging ultrasound waves, a B-mode image can be reconstructed from a single transmission with parallel beamforming. For echocardiography, this approach can provide a frame rate up to 5 kHz, which is two orders of magnitude faster than the most clinical scanners. However, image degradation arising from the lack of transmit focusing when u...

This study aimed to estimate angled tissue motion for shear wave compounding applications. Shear wave elastography produces the quantitative elasticity biomarker for assessing the health status of tissues. In sheer wave compounding, steered shear waves are generated with different angles, and individual angle elasticity maps are averaged to improve...

Phononic crystals are acoustic metamaterials designed to manipulate sound when its wavelength is in the order of magnitude of the crystal lattice constant. Metallic phononic crystals for use in water were assembled using commercially available stainless steel rods with an average superficial roughness R a =0.5±0.5 μm, while Laser Powder Bed Fabrica...

Compounding techniques have been used in ultra-fast ultrasound imaging to improve image quality by reducing clutter noise, smoothing speckle variance and enhancing its spatial resolution at the cost of reducing frame rate. However, the reduction of clutter noise and side lobes inside the anechoic regions is minimal when combining conventional spati...

As a part of the diagnosis pathway for breast cancer, a needle biopsy of the sentinel lymph node (SLN) is taken for analysis. Photoacoustic imaging is a better approach for guiding a needle than ultrasound imaging. However, the photoacoustic image will be affected by clutter, phase aberration and artefact from the needle. In this study, a dynamic f...

Within the Ultrasound Array Research Platform (UARP) open research system project, imaging and high-intensity focussed ultrasound (HIFU) implementations are used independently for diagnostic and therapeutic research respectively. In this paper, the hardware of each system remains unmodified, but the timing and control subsystems present on both imp...

During HIFU therapy it is important that the electrical power delivered to the transducer is monitored to avoid under or over exposure, ensure patient safety and to protect the transducer itself. Due to ease of measurement, the transducer’s potential difference may be as an indicator of power delivery. However, even when a transducer’s complex impe...

A combined supply-inverted bipolar pulser and a Tx/Rx switch is proposed to drive capacitive micromachined ultrasonic transducers (CMUTs). The supply-inverted bipolar pulser adopts a bootstrap circuit combined with stacked transistors, which guarantees high voltage (HV) operation above the process limit without lowering device reliability. This cir...

To aid in the transportation, dewatering and storage of radioactive UK legacy waste sludges at Sellafield Ltd., the application of an Acoustic Backscatter System (ABS) was investigated in this study, as a method for monitoring suspended solids concentration and consolidation of cohesive and aggregated sludges (that form the basis of many wastes at...

The production and stability of microbubbles (MBs) is enhanced by increasing the viscosity of both the formation and storage solution, respectively. Glycerol is a good candidate for biomedical applications of MBs, since it is biocompatible, although the exact molecular mechanisms of its action is not fully understood. Here, we investigate the influ...

A 2-step method to encapsulate an oil core with an impermeable shell has been developed. A thin metallic shell is deposited on the surface of emulsion droplets stabilised by metal nanoparticles. This thin shell is shown to prevent diffusion of the oil from within the core of the metal-shell microcapsules when placed in a continuous phase that fully...

High intensity focused ultrasound (HIFU) is a non-invasive and non-ionising approach used primarily for the thermal ablation of cancerous tumours. Even though it has been in clinical use for over 30 years, it has yet to achieve widespread use. Two key limitations for this approach are long treatment times and a difficulty in getting real-time feedb...

Gold nanorods (AuNRs) can be synthesised with different sizes but similar aspect ratios and therefore similar surface plasmon resonances (SPRs). Their strong optical absorbance governed by their SPRs facilitates their ability to be used as molecular-targeted contrast agents for photoacoustic (PA) imaging. The size of AuNRs has an effect on the PA c...

An ultrasonic transducer technology to generate wideband impulses using a one-dimensional chain of spheres was previously presented. The Hertzian contact between the spheres causes the nonlinearity of the system to increase, which transforms high amplitude narrowband sinusoidal input into a train of wideband impulses. Generation of short duration u...

Mechanisms for non-invasive target drug delivery using microbubbles and ultrasound have attracted growing interest. Microbubbles can be loaded with a therapeutic payload and tracked via ultrasound imaging to selectively release their payload at ultrasound-targeted locations. In this study, an ultrasonic trapping method is proposed for simultaneousl...

Combining diverging ultrasound waves and microbubbles could improve contrast-enhanced echocardiography (CEE), by providing enhanced temporal resolution for cardiac function assessment over a large imaging field of view. However, current image formation techniques using coherent summation of echoes from multiple steered diverging waves (DWs), are su...

This paper presents a single chip reduced-wire active catheter application-specific integrated circuit (ASIC), equipped with programmable transmit (Tx) beamforming and receive (Rx) time-division multiplexing (TDM). The proposed front-end ASIC is designed for driving a 64-channel one-dimensional transducer array in intracardiac echocardiography (ICE...

Switched excitation has the potential to improve on the cost, efficiency and size of the linear amplifier circuitry currently used in HIFU systems. Existing switching schemes are impaired by high harmonic distortion or lack array apodisation capability, so require adjustable supplies and/or large power filters to be useful. A multi-level PWM topolo...

CMUT-on-CMOS integration is particularly suitable for catheter based ultrasound imaging applications, where electronics integration enables multiplexing capabilities to reduce the number of electrical connections leading to smaller catheter cable profiles. Here, a single-chip CMUT-on-CMOS system for intracardiac echocardiography (ICE) is presented....

The use of diverging ultrasound waves provides enhanced temporal resolution for cardiac function assessment. However, current image formation techniques using coherent summation, are susceptible to motion artifacts. In this study, we used correlation based 2D motion estimation to perform motion compensation for coherent diverging wave imaging. The...

Plasmonic gold nanoparticles show potential for use in a range of cancer diagnostics and therapeutics, such as photoacoustic imaging (PAI) and plasmonic photothermal therapy (PPTT). Generally in PPTT, continuous wave (CW) lasers are used to destroy cancerous tissue. However, in order to add a diagnostic component through PAI, a pulsed wave (PW) las...

High Intensity Focused Ultrasound (HIFU) is reliant on carefully designed excitation systems capable of high power, and low distortion. The use of array transducers additionally requires amplitude control for apodization and attenuation compensation plus phase control for inter element timing for beamstearing, focusing and correction. Power amplifi...

The semi-automated balloon snake active contour (BSAC) based segmentations play a vital role in determining the intima-media thickness (IMT) for accessing the risk related to cardio vascular diseases (CVD). However, the speckle and clutter noise in the ultrasound B-mode images are known to interfere with the contour formation during segmentation. B...

A key component of targeted drug delivery using liposome-loaded microbubbles and ultrasound is the ability to track these drug vehicles in real time to guide payload release locally. As a uniquely identifiable emission from microbubbles, the subharmonic signal is of interest for this purpose. Acoustic characterization of liposome-loaded microbubble...

A typical ultrasound imaging system analogue front end (AFE) consists of a series of stages, including transmit/receive switch, amplifiers and analog-digital converter (ADC). Each stage will have an impact on the signal in the form of noise, but also in the form of distortion from a frequency-dependent gain profile. This gain response will be appli...

Open platform (OP) ultrasound systems are aimed primarily at the research community. They have been at the forefront of the development of synthetic aperture, plane wave, shear wave elastography, and vector flow imaging. Such platforms are driven by a need for broad flexibility of parameters that are normally preset or fixed within clinical scanner...

Open platform (OP) ultrasound systems are aimed primarily at the research community. They have been at the forefront of the development of synthetic aperture, plane wave, shear wave elastography and vector flow imaging. Such platforms are driven by a need for broad flexibility of parameters that are normally pre-set or fixed within clinical scanner...

The capability of accumulating microbubbles using ultrasound, could be beneficial for enhancing targeted drug delivery. When microbubbles are used to deliver a therapeutic payload, there is a need to track them, for a localized release of the payload. In this study, a method for localizing microbubble accumulation with fast image guidance is presen...

There is disclosed apparatus and methods for determining the position of an elongate structure. A plurality of magnetic field sensors arranged at fixed spacing, each sensor being arranged to sense a magnetic field of a remote structure induced by the Earth's magnetic field in at least two orthogonal directions. In use, the magnetic field sensors ar...

Lipid and polymer stabilized microbubbles are used in medicine as contrast agents for ultrasound imaging and are being developed for the delivery of water soluble drugs to diseased areas of the body. However, many new therapeutics exhibit poor water solubility or stability, which has led to the requirement for the development of effective hydrophob...

Intracardiac echocardiography (ICE) provides real-time ultrasound imaging of the heart anatomy from inside, guiding interventions like valve repair, closure of atrial septal defects (ASD) and catheter-based ablation to treat atrial fibrillation. With its better image quality and ease of use, ICE is becoming the preferred imaging modality over trans...

High intensity focused ultrasound (HIFU) or focused ultrasound surgery is a non-invasive technique for the treatment of cancerous tissue, which is limited by difficulties in getting real-time feedback on treatment progress and long treatment durations. The formation and activity of acoustic cavitation, specifically inertial cavitation, during HIFU...

The applications and uses of embedded systems is increasingly pervasive. Mission and safety critical systems relying on embedded systems pose specific challenges. Embedded systems is a multi-disciplinary domain, involving both hardware and software. Systems need to be designed in a holistic manner so that they are able to provide the desired reliab...

Wave propagation in granular chains is subject to dispersive effects as well as nonlinear effects arising from the Hertzian contact law. This enables the formation of wideband pulses, which is a desirable feature in the context of diagnostic and therapeutic ultrasound applications. However, coupling of the ultrasonic energy from a chain of spheres...

High intensity focused ultrasound (HIFU) or focused ultrasound surgery (FUS) is a non-invasive technique for the treatment of cancerous tissue, which is limited by difficulties in getting real-time feedback on treatment progress and long treatment durations. The formation and activity of acoustic cavitation, specifically inertial cavitation, during...