Steven Freear

University of Leeds

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i-10 index

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Document Type

Co-Authors

David M. J. Cowell

University of Leeds

115

Sevan Harput

London South Bank University

James R. McLaughlan

University of Leeds

Thomas M. Carpenter

University of Leeds

Paschalis C. Sofotasios

Khalifa University of Science and Technology

Luzhen Nie

University of Leeds

D.A. Hutchins

University of Warwick

Peter J. Thomas

University of Warwick

Peter R. Smith

Toshiba (United Kingdom)

Dan Stevens

University of Waterloo

Cooperative Institutions

University of Leeds

178

Institute of Electrical and Electronics Engineers

Drexel University

Ultrasonic Technologies (United States)

Georgia Institute of Technology

OEwaves (United States)

Siemens (United States)

University of Waterloo

St James's University Hospital

École Polytechnique Fédérale de Lausanne

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Enhancement of contrast and resolution of B-mode plane wave imaging (PWI) with non-linear filtered delay multiply and sum (FDMAS) beamforming

2017 IEEE International Ultrasonics Symposium (IUS) (2016)

Asraf Mohamed Moubark Zainab Alomari Sevan Harput David M. J. Cowell Steven Freear

FDMAS has been successfully used in microwave imaging for breast cancer detection. FDMAS gained its popularity due to its capability to produce results faster than any other adaptive beamforming technique such as minimum variance (MV) which requires higher computational complexity. The average computational time for single point spread function (PSF) at 40 mm depth for FDMAS is 87 times faster than MV. The new beamforming technique has been tested on PSF and cyst phantoms experimentally with the ultrasound array research platform version 2 (UARP II) using a 3-8 MHz 128 element clinical transducer. FDMAS is able to improve both imaging contrast and spatial resolution as compared to DAS. The wire phantom main lobes lateral resolution improved in FDMAS by 40.4% with square pulse excitation signal when compared to DAS. Meanwhile the contrast ratio (CR) obtained for an anechoic cyst located at 15 mm depth for PWI with DAS and FDMAS are -6.2 dB and -14.9 dB respectively. The ability to reduce noise from off axis with auto-correlation operation in FDMAS pave the way to display the B-mode image with high dynamic range. However, the contrast to noise ratio (CNR) measured at same cyst location for FDMAS give less reading compared to DAS. Nevertheless, this drawback can be compensated by applying compound plane wave imaging (CPWI) technique on FDMAS. In overall the new FDMAS beamforming technique outperforms DAS in laboratory experiments by narrowing its main lobes and increases the image contrast without sacrificing its frame rates.

Mode (computer interface)

10.1109/ultsym.2016.7728678

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Citations (18)

Lowering the centre frequency of thick film PZT devices using acoustically matched backing layers

IEEE International Ultrasonics Symposium (2009)

Stephen A. Ellwood Steven Freear Andrew J. Bell Tim P. Comyn

Our current research effort is directed towards fabricating PZT thick-films on a supporting substrate for use within industrial process monitoring equipment. The use of thick films in this application confers a number of important benefits. These include more straightforward device fabrication and the ability to fabricate transducers in more complex non-rectangular geometries. However, an important drawback of our current techniques is the low thickness (25-40¿m) of the deposited PZT film. The centre frequency of such a layer when used as a transducer is expected to be greater than 10MHz. Such high frequencies often make such transducers impractical for conventional B-scan imaging since overall beam penetration depth is severely curtailed. Ideally, to make such devices more practical a technique is required that allows the device centre frequency to be reduced without changing the thickness of the active PZT layer. In this paper we describe one such technique that uses multiple impedance matched ¿/2 backing layers to achieve the frequency reduction required.

10.1109/ultsym.2009.5441883

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Analytic Solutions to a Useful Marcum $Q{-}$Function Based Integral.

arXiv (Cornell University) (2015)

Paschalis C. Sofotasios Mikko Valkama Theodoros A. Tsiftsis Yury A. Brychkov Steven Freear

This work presents analytic solutions for a useful integral in wireless communications, which involves the Marcum $Q{-}$function in combination with an exponential function and arbitrary power terms. The derived expressions have a rather simple algebraic representation which renders them convenient both analytically and computationally. Furthermore, they can be useful in wireless communications and particularly in the context of cognitive radio communications and radar systems, where this integral is often encountered. To this end, we derive novel expressions for the probability of detection in energy detection based spectrum sensing over $\eta{-}\mu$ fading channels. These expressions are given in closed-form and are subsequently employed in analyzing the effects of generalised multipath fading conditions in cognitive radio systems. As expected, it is shown that the detector is highly dependent upon the severity of fading conditions as even slight variation of the fading parameters affect the corresponding performance significantly.

Exponential integral

Representation

Source

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Citations (2)

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control Publication Information

IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control (2022)

Mark Schafer -President Dragan Damjanovic -President-Elect Dan Stevens Steven Freear Alfred C. H. Yu

The Ultrasonics, Ferroelectrics, and Frequency Control Society is an organization, within the framework of the IEEE, of members with principal professional interest in ultrasonics, ferroelectrics, and frequency control.The field of interest of UFFC-S shall include theory, technology, materials, and applications relating to: (1) The generation, transmission, and detection of ultrasonic waves and related phenomena; (2) Medical ultrasound and associated technologies; (3) Ferroelectric, piezoelectric, and piezomagnetic materials; (4) Frequency generation and control, timing, and time coordination and distribution.Areas of interest range from fundamental studies to the design and/or applications of devices and systems within the general scope defined above.

10.1109/tuffc.2022.3196538

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Measurement and Modelling of Legacy Sludge Separation and Transport Processes

T.M. Hunter G Randall David Burt M Fairweather David M. J. Cowell

Separation (statistics)

Source

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Citations (1)

Extraction of an overlapped second harmonic chirp component using the fractional fourier transform

IEEE International Ultrasonics Symposium (2011)

Muhammad Arif Sevan Harput Peter R. Smith David M. J. Cowell Steven Freear

In ultrasound harmonic imaging with chirp coded excitation, the axial resolution can be improved by increasing the excitation signal bandwidth. However, increasing the bandwidth will cause overlapping between the received nonlinear second harmonic chirp component (SHCC) and the fundamental component. For the spectrally overlapping harmonics, signal decoding using the second harmonic matched filter (SHMF) typically produces higher range sidelobes level (RSLL), which reduces the image contrast. A multi-pulse detection scheme such as pulse inversion can be used to extract the overlapped SHCC; however it is susceptible to motion artifacts and reduced system frame-rate. In this study, the fractional Fourier transform (FrFT) is proposed with chirp coded excitation for the extraction of the overlapped SHCC. The experimental results indicate at least a 13 dB improvement in the RSLL of the FrFT filtered compressed SHCC when compared with the unfiltered compressed SHCC.

Chirp

Pulse compression

Harmonic

Matched filter

10.1109/ultsym.2011.0097

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Citations (3)

Optimizing the lateral beamforming step for filtered-delay multiply and sum beamforming to improve active contour segmentation using ultrafast ultrasound imaging

Biomedical Signal Processing and Control (2021)

Asraf Mohamed Moubark Zainab Alomari Mohd Hairi Mohd Zaman Mohd Asyraf Zulkifley Sawal Hamid Md Ali

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 lateral direction. Accordingly, the performance of FDMAS was evaluated in this study by fine-tuning Δx to find its optimal value and improve boundary definition when balloon snake active contour (BSAC) segmentation was applied to a B-mode image in ultrafast imaging. To demonstrate the effect of altering Δx in the lateral direction on FDMAS, measurements were performed on point targets, a tissue-mimicking phantom and in vivo carotid artery, by using the ultrasound array research platform II equipped with one 128-element linear array transducer, which was excited by 2-cycle sinusoidal signals. With 9-angle compounding, results showed that the lateral resolution (LR) of the point target was improved by 67.9% and 81.2%, when measured at −6 dB and −20 dB respectively, when Δx was reduced from λ to λ/5. Meanwhile the image contrast ratio (CR) measured on the CIRS phantom was improved by 10.38 dB at the same Δx reduction and the same number of compounding angles. The enhanced FDMAS results with lower side lobes and less clutter noise in the anechoic regions provides a means to improve boundary definition on a B-mode image when BSAC segmentation is applied.

Adaptive beamformer

10.1016/j.bspc.2021.103267

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Citations (4)

New improved unsharp masking methods compatible with ultrasound B-mode imaging

2017 IEEE International Ultrasonics Symposium (IUS) (2017)

Asraf Mohamed Moubark Sevan Harput David M. J. Cowell Steven Freear

In medical ultrasound B-Mode imaging, increasing the image contrast, spatial and temporal resolution will improve medical diagnostic and decision making process. One of the methods used to achieve those improvement in medical imaging is unsharp masking (UM) technique. Previously UM has been successfully implemented as noise filtering and edge enhancement techniques. However the outcomes of the method is limited and influenced by the image formats conversion, lower dynamic range and high frequency noises. Furthermore the technique only enhances the image more in darker compare to lighter regions. To overcome these issues, a new improved UM methods compatible with ultrasound B-Mode imaging applied on compound plane wave imaging (CPWI) and beamformed with delay and sum (DAS) and filtered delay and sum (FDMAS).

Unsharp masking

Medical ultrasound

10.1109/ultsym.2017.8091902

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Citations (2)

Acoustic microbubble trapping in blood mimicking fluid

2017 IEEE International Ultrasonics Symposium (IUS) (2017)

Luzhen Nie Sevan Harput James R. McLaughlan David M. J. Cowell Thomas Carpenter

With identical exposures, enhanced cavitation resulting from increased microbubble (MB) concentrations has been demonstrated in the literature. Through the generation of a low-pressure trap, our previous work described a means to locally accumulate MBs within large vessel lumen (fig. a). But the existence of blood in-vivo could impede the MB translation and retention, which calls for preliminary investigations for acoustic MB trap in blood mimicking fluid (BMF). This study validates the feasibility of the MB trapping in the presence of BMF, which could be beneficial for therapeutic regimes involving acoustic cavitation like sonothrombolysis.

Trap (plumbing)

Lumen (anatomy)

10.1109/ultsym.2017.8092254

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Localization of a Scatterer in 3D with a Single Measurement and Single Element Transducer

2017 IEEE International Ultrasonics Symposium (IUS) (2020)

Luzhen Nie Joshua Moo Matthieu Toulemonde Meng‐Xing Tang Steven Freear

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 location of the scatter in multiple spatial dimensions. In this study, we developed a method to find the location of a scatterer in 3-D with a single-element transducer and single measurement. The feasibility of the proposed method was verified in 2-D with experimental measurements.

Reflector (photography)

Single camera

Distance measurement

10.1109/ius46767.2020.9251618

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Citations (1)