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Nevil Brownlee - IEEE Xplore Author Profile

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Row-column (RC) arrays typically suffer from a limited field of view (FOV), with the imaging area confined to a rectangular region equal to the footprint of the probe. This limitation can be solved by using a diverging lens in front of the probe. Previous studies have introduced a thin lens model for beamforming lensed RC arrays, but this model inaccurately assumes the lens to be infinitely thin, ...Show More
Velocity estimation in ultrasound imaging is a technique to measure the speed and direction of blood flow. The flow velocity in small blood vessels, i.e., arterioles, venules, and capillaries, can be estimated using super-resolution ultrasound imaging (SRUS). However, the vessel width in SRUS is relatively small compared with the full-width-half-maximum of the ultrasound beam in the elevation dire...Show More
Super-resolution ultrasound imaging using the erythrocytes (SURE) has recently been introduced. The method uses erythrocytes as targets instead of fragile microbubbles (MBs). The abundance of erythrocyte scatterers makes it possible to acquire SURE data in just a few seconds compared with several minutes in ultrasound localization microscopy (ULM) using MBs. A high number of scatterers can reduce ...Show More
A new approach for vascular super-resolution (SR) imaging using the erythrocytes as targets (SUper-Resolution ultrasound imaging of Erythrocytes (SURE) imaging) is described and investigated. SURE imaging does not require fragile contrast agent bubbles, making it possible to use the maximum allowable mechanical index (MI) for ultrasound scanning for an increased penetration depth. A synthetic aper...Show More
Spherical diverging acoustic lenses mounted on flat 2-D row–column-addressed (RCA) ultrasound transducers have shown the potential to extend the field of view (FOV) from a rectilinear to a curvilinear volume region and, thereby, enable 3-D imaging of large organs. Such lenses are usually designed for small aperture low-frequency transducers, which have limited resolution. Moreover, they are made o...Show More
Double-curved diverging lenses are used to extend the Field of View (FOV) of flat 2D Row-Column Addressed (RCA) transducers, for performing real-time volumetric imaging of large organs. Such lenses are usually made in a spherical shape geometry, which poorly fits the square footprint of RCA arrays. In particular, for large arrays, the radius of curvature of the lens is constrained to increase sign...Show More
A key component of super-resolution ultrasound imaging (SRI) is the detection and tracking of scatterers. These scatterers can be microbubbles (MBs) in SRI, or erythrocytes in SUper Resolution ultrasound imaging using Erythrocytes (SURE). To ensure the reliability of MBs tracking in SRI, the MBs must be sparse. However, the sparse distribution of the MBs necessitates several minutes of acquisition...Show More
The transducer resonance frequency is a key parameter for the field of ultrasound. The resonance frequency in vacuum is well understood, and an analytical expression for the center frequency in immersion was derived by Lamb in 1920 [1], however this expression has limited validity. Importantly, the model fails to cover plate aspect ratios needed by imaging requirements and met by recently fabricat...Show More
Row-column (RC) matrix probes can yield 3-D volumetric imaging using a number of receiving elements similar to traditional linear arrays for commercial scanners. Some doubts have, however, been raised on the B-mode image quality of RC probes. It is hypothesized that synthetic aperture (SA) RC imaging can yield a better volumetric resolution than commercial spatially translated linear arrays, and a...Show More
Coded excitation (CE) signals have the potential to greatly improve image quality and penetration depth by increasing the signal-to-noise ratio (SNR). However, CE can increase the operating temperature of a transducer beyond the safety limits defined by the International Electrotechnical Commission (IEC), and this has often limited the use of CE with Lead Zirconate Titanate (PZT) probes. Capacitiv...Show More
Double-curved diverging lenses mounted on flat 2D Row-Column Addressed (RCA) transducers have shown the potential to extend the Field of View (FOV) from a rectilinear to a curvilinear volume region and thereby enable real-time 3D imaging of large organs. Such lenses are usually made of off-the-shelf pieces of materials, which leaves no room for optimization. In this work, acoustic lenses have been...Show More
Super-resolution ultrasound imaging (SRI) has shown the potential for visualization of the vasculature with sub-wavelength resolution. Microbubble (MB) tracking in SRI can improve image quality and enable velocity estimation. However, it is usually neglected that the size of the vessel might be relatively small compared to the full width half maximum resolution in the elevation direction (FWHMy) a...Show More
Row–column (RC) arrays have the potential to yield full 3-D ultrasound imaging with a greatly reduced number of elements compared to fully populated arrays. They, however, have several challenges due to their special geometry. This review article summarizes the current literature for RC imaging and demonstrates that full anatomic and functional imaging can attain a high quality using synthetic ape...Show More
This paper presents a new type of insulating substrate, polysilicon-on-quartz (POOQ), that can be used for wafer bonded capacitive micromachined ultrasonic transducers (CMUTs). The substrate is based on a quartz handle wafer on which a device layer of polysilicon is deposited. The polysilicon is polished to an average surface roughness below 0.2 nm which allows for wafer bonding. Fusion bonding of...Show More
This paper presents fabrication, characterization and modelling of delay-line based capacitive micromachined ultrasonic transducers (CMUT). CMUTs have been fabricated using standard semiconductor processes, the electrical frequency response has been modelled by an equivalent circuit diagram and excellent agreement between theory and measurement is observed. Finally, the electrical crosstalk betwee...Show More
The search for improved resolution in super-resolution ultrasound (SRUS) imaging leads to larger ultrasound arrays and smaller elements. A current large row-column addressed (RCA) array spans $\approx 21\times 21\ \text{mm}^{2}$ with $190 +190$ elements separated by a kerf of $3\ \mu\mathrm{m}$. Increasing array dimensions and decreasing feature sizes not only makes fabrication more complex, but m...Show More
This paper presents a zeroth and first order perturbative analysis of prestressed electrostatic actuated Microelectromechanical systems (MEMS). Perturbation theory is used to calculate the deflection profile of various MEMS structures, from which the pull-in voltage is estimated using the weighed residual method, where both a Galerkin expression and a Dirac delta function have been used as weight ...Show More
This paper presents a novel fabrication design for capacitive micromachined ultrasonic transducers (CMUT) that utilizes a designed delay line in the silicon substrate for element separation. All elements in this design are electrically connected through the substrate, however, high resistivity (> 10.000 Ωcm) float zone silicon is used for the substrate to suppress cross-talk between elements. The ...Show More
This paper presents the design and fabrication of a novel 384 channel modular ultrasonic probe for row-column addressed capacitive micromachined ultrasound transducers. The nose-piece and front-electronics can be freely interchanged in situ, allowing different combinations of transducer arrays and front-end architectures to be characterized and compared, without fabricating an entire probe for eac...Show More
This paper demonstrates a novel fabrication process to implement a capacitive micromachined ultrasound transducer (CMUT) into a laparoscope. Due to the limited space in the laparoscope, a new method for electrically contacting the transducer elements is required. Using a state-of-the-art high aspect ratio dry etching process called Deposit, Remove, Etch, Multistep (DREM), it is possible to separat...Show More
Capacitive micromachined ultrasonic transducers (CMUTs) are inherently non-linear and often believed to be unsuitable for non-linear contrast-enhanced ultrasound (CEUS) imaging. The ability of CMUTs to perform contrast-enhanced ultrasound imaging has been investigated by experimentally evaluating the contrast-to-noise ratio (CTR) and its variation with emitted pressure. This has been evaluated usi...Show More
This paper presents a novel characterization method for the pull-in voltage of a Capacitive Micromachined Ultrasonic Transducer (CMUT) element. The presented method allows pull-in estimation of all CMUT cells contained in an element, which is in contrast to conventional methods that only allows for a pull-in average across an element. The methodology has been conducted on four different CMUT eleme...Show More
This work presents the fabrication process of anodically bonded 192+192 2D row-column addressed (RCA) capacitive micromachined ultrasonic transducer (CMUT) arrays. Four large 2.1 by 2.1 cm2 arrays with a resonance frequency of 7.5 MHz in water and λ/2 element pitch at 95 μm are shown successfully fabricated. The arrays exhibit a 100% bond yield by anodically bonding an SOI wafer to a borosilicate ...Show More
Delay-and-sum (DAS) beamforming is unable to identify individual scatterers when their density is so high that their point spread functions overlap. This paper proposes a convolutional neural network (CNN)-based method to detect and localize high-density scatterers, some of which are closer than the resolution limit of delay-andsum (DAS) beamforming. A CNN was designed to take radio frequency chan...Show More