Row-column Array Research Articles

Simultaneous Coherent and Displacement Compounding for 2-D Noninvasive Carotid Strain Imaging: A Proof of Principle Study.

Arteriosclerosis results from lipid buildup in artery walls, leading to plaque formation, and is a leading cause of death. Plaque rupture can cause blood clots that might lead to a stroke. Distinguishing plaque types is a challenge, but ultrasound (US) elastography can help by assessing plaque composition based on strain values. Since the artery has a circular structure, an accurate axial and lateral displacement strategy is needed to derive the radial and circumferential strains. A high-precision lateral displacement is challenging due to the lack of phase information in the lateral direction of the beamformed RF data. Previously, our group has developed a compounding technique in which the lateral displacement is estimated using triangulation of the axial displacement estimated from transmitting and beamforming US beams at ±20°. However, transmitting with a single plane wave will reduce signal-to-noise and contrast-to-noise ratio as well as lateral resolution. In this article, we combine our displacement compounding with coherent compounding. Instead of transmitting a single plane wave, multiple plane waves are transmitted at certain angles centered on the angle of the beamforming grids, and then, the backscattered wavefronts are beamformed and coherently compounded on the center of the transmit beams (-20°, +20°, and 0°). The numerical investigation using the GE9LD probe ( f0 = 5.32 MHz, pitch = 230 μ m, and width = 43.9 mm) led us to 19 plane waves spanning angles within -10° to 10° (with respect to center of the transmit beams), resulting in a total of 57 plane wave transmit (for three beamforming grids at 0° and ±20°). FIELD II simulations of a cylindrically shaped phantom (mimicking the carotid artery) at a signal-to-noise ratio (SNR) ≥ 20 dB show that the proposed method decreases the root-mean-square error (RMSE) of the lateral displacement and strain estimations by 40% and 45% compared to the previous method, respectively. The results of our experiments with a carotid artery phantom [made out of 10% polyvinyl alcohol (PVA)] show that the proposed method provides strain images with higher quality and more in agreement with the theory, with 26% lower standard deviation, especially at the peak systolic phase. The proposed method paves the path toward improved quality in vivo 2-D strain imaging using our displacement compounding technique and translating it to 3-D with a row-column array.

TOBE-Costas arrays for fast high-resolution 3D power Doppler imaging.

2D sparse arrays and row-column arrays are both alternatives to 2D fully-addressed arrays with lower channel counts. Row-column arrays have recently demonstrated fast 3D structural and flow imaging but commonly suffer from high grating lobes or require multiplexing to achieve better quality. 2D sparse arrays enable full-volume acquisitions for each to transmit event, but plane-wave transmissions with them usually lack quality in terms of uniformity of wavefronts. Here, we propose a novel architecture that combines both types of these arrays in one aperture, enabling imaging using row-column or sparse arrays alone or a hybrid imaging scheme where the row-column array is used in transmission and a 2D sparse array in reception. This hybrid imaging scheme can potentially solve the shortcomings of each of these approaches. The sparse array layout chosen is a Costas array, characterized by having only one element per row and column, facilitating its integration with row-column (TOBE) arrays. We simulate images acquired with TOBE-Costas arrays using the hybrid imaging scheme and compare them to row-column and sparse spiral arrays of equivalent aperture size (128λ×128λ at 7.5 MHz) in ultrafast plane-wave imaging of point targets and 3D power Doppler imaging of synthetic flow phantoms. Our simulation results show that TOBE-Costas arrays exhibit superior resolution and lower side lobe levels compared to plane-wave compounding with row-column arrays. Compared to density-tapered spiral arrays, they provide a larger field of view and finer resolution.

Ultrafast 3-D Transcutaneous Super Resolution Ultrasound Using Row-Column Array Specific Coherence-Based Beamforming and Rolling Acoustic Sub-aperture Processing: In Vitro, in Rabbit and in Human Study

ObjectiveThis study aimed to realise 3-D super-resolution ultrasound imaging transcutaneously with a row-column array which has far fewer independent electronic channels and a wider field of view than typical fully addressed 2-D matrix arrays. The in vivo image quality of the row-column array is generally poor, particularly when imaging non-invasively. This study aimed to develop a suite of image formation and post-processing methods to improve image quality and demonstrate the feasibility of ultrasound localisation microscopy using a row-column array, transcutaneously on a rabbit model and in a human. MethodsTo achieve this, a processing pipeline was developed which included a new type of rolling window image reconstruction, which integrated a row-column array specific coherence-based beamforming technique with acoustic sub-aperture processing. This and other processing steps reduced the ‘secondary’ lobe artefacts, and noise and increased the effective frame rate, thereby enabling ultrasound localisation images to be produced. ResultsUsing an in vitro cross tube, it was found that the procedure reduced the percentage of ‘false’ locations from ∼26% to ∼15% compared to orthogonal plane wave compounding. Additionally, it was found that the noise could be reduced by ∼7 dB and the effective frame rate was increased to over 4000 fps. In vivo, ultrasound localisation microscopy was used to produce images non-invasively of a rabbit kidney and a human thyroid. ConclusionIt has been demonstrated that the proposed methods using a row-column array can produce large field of view super-resolution microvascular images in vivo and in a human non-invasively.

A single crystal row–column-array for 3D ultrasound imaging

In vivo 3D ultrasound imaging with 2D-array transducers is of great importance for both clinical application and biomedical research, but it is complicated in fabrication and also very expensive in hardware due to thousands of electronic channels. In this work, we demonstrate a new fabrication process of 7-MHz 128 + 128 elements row-column-array (RCA) transducer with relaxor ferroelectric PMN-0.28PT single crystal. With piezoelectric single crystal and improved acoustic matching, the optimized performance of −6 dB bandwidth of ∼82 % and insertion loss of −44.6 dB is achieved. The axial and lateral imaging resolutions at different depth of the RCA transducer are quantified by the point spread function (PSF), and the results are respectively 0.20 mm and 0.41 mm at the depth of 7.7 mm, and 0.22 mm and 0.47 mm at the depth of 16.7 mm. The transducer is validated experimentally on a hyperechoic phantom, and 3D view and slices of B-mode images are obtained. The experimental results indicate that our developed RCA transducer can obtain high-quality 3D ultrasound images, demonstrating great potential on ultrafast 3D and functional imaging.

Distortion map and correction for ultrasound localization microscopy imaging with a row–column array

The row–column array is an emerging technology which can enable large fields of view without the need for a large number of electronic channels. In ultrasound localization microscopy, sparse microbubbles are localized and tracked to produce high-resolution images of the microvasculature. During the localization of the microbubbles, it is typically assumed that the center of the target observed can be used as a substitute for the true microbubble location. However, the true microbubble will be located at the onset of the received signal. This distortion between the true location and the observed location will result in a shift of the microbubble away from the true location, thus altering the accuracy of the images produced. In most forms of ultrasound imaging, this shift mostly manifests as a vertical shift so can often be safely ignored. However, we have observed that in row–column array imaging this distortion will be spatially variable and will result in distortions in the axial, elevational, and lateral directions, which can be on the order of a few wavelengths. Consequently, this distortion, if ignored, will result in inaccuracies in the resulting ultrasound localization microscopy images. Here, we present a technique to map and correct for these distortions.

Three-dimensional coherence beamforming using row-column arrays and matrix arrays

Much advancement in 3D ultrasound imaging has been achieved in recent years, allowing for its implementation in many research capacities. Translation of 3D imaging to a clinical setting has been hindered by small fields of view, expensive equipment and poor image quality. For ultrafast imaging, these challenges are accentuated by the need for a small number of transmission events. The row-column array is an emerging technology which can produce large field-of-view 3D ultrasound images, however, they can produce major artefacts when operated at high frame rates. Here we present some techniques which have been developed to improve the image quality and reduce the artifact level of row-column arrays by exploiting the incoherence of the transmission schemes. Presented will be the Row-Column specific Frame Multiply and Sum beamforming along with a technique for implementing Acoustic Sub-Aperture Processing which improves signal-to-noise ratio whilst also increasing the effective frame rate. Additional coherence-based algorithms, which have previously been developed for 2D imaging, are implemented and presented here for 3D imaging using a matrix array probe. All of the above algorithms have been optimised for super-resolution but should improve all types of 3D ultrasound imaging.

Volumetric beamforming in real-time using commodity hardware

Ultrasound imaging is widely used in medicine for its safety and affordability. However, it demands large transducer arrays because the image resolution is proportional to the number of elements, N, typically around 128 for 2D imaging. Three-dimensional imaging requires N2 audio channels (≈350 GB/s of data) if the equivalent 2D matrix array is used, which is practically impossible to process. To solve this issue, row-column arrays (RCAs) aggregate rows and columns of elements, reducing data rate and processing demands by a factor of N. A novel dual-stage beamforming algorithm further lowers the beamforming operations by N/2, with negligible impact on the image quality. For N = 128, the processing is 8192 times faster than with a matrix array, and it is hypothesized the 3D RCA beamforming can be done in real-time using a commodity graphics card. The beamforming rate of an NVIDIA RTX 4090 GPU was measured for in-vivo data from a rat kidney, achieving 1394 full volumes per second, which is over 150 times faster than previous implementations. Combining RCAs with the new beamforming algorithm and GPU processing thus enables volumetric beamforming to be done affordably at the bedside in real-time using a standard scanner and PC.

Transmit beam design for tissue harmonic volume imaging of muscular tissues with a row-column array

Row-Column-addressed Arrays (RCAs), which have recently become commercially available, transmit along the rows and receive along columns of a 2D array in order to produce 3D volume images with low channel count. Imaging of the inherently three-dimensional, layered, and fibrous structure of muscular tissues in 3D using an RCA can improve evaluations of muscle function and disease compared to conventional 2D cross-sectional imaging, but volume images obtained using an RCA suffer from low lateral spatial resolution, low contrast, and grating lobe artifacts. Tissue harmonic imaging (THI) employs nonlinear acoustic effects to image at twice the transmit frequency, and can yield increased spatial resolution, increased contrast, and decreased artifacts from grating lobes. Here we investigate transmission considerations for THI in muscular tissues using a commercially available RCA (Vermon RC6gV). The parameter space is explored efficiently with frequency domain simulations of the 3D Westervelt equation. Pulse inversion imaging is applied experimentally using both steered plane wave and focused transmits to evaluate THI with an RCA in tissue phantoms and in muscular tissue. Pulse inversion volume images are compared to conventional images in terms of signal-to-noise, contrast, and ability to identify layers and fibrous structures in muscle in 3D. [Work supported by NIH HEAL Initiative R61AT012282.]

Enhancing Row-column array (RCA)-based 3D ultrasound vascular imaging with spatial-temporal similarity weighting.

Ultrasound vascular imaging (UVI) is a valuable tool for monitoring the physiological states and evaluating the pathological diseases. Advancing from conventional two-dimensional (2D) to three-dimensional (3D) UVI would enhance the vasculature visualization, thereby improving its reliability. Row-column array (RCA) has emerged as a promising approach for cost-effective ultrafast 3D imaging with a low channel count. However, ultrafast RCA imaging is often hampered by high-level sidelobe artifacts and low signal-to-noise ratio (SNR), which makes RCA-based UVI challenging. In this study, we propose a spatial-temporal similarity weighting (St-SW) method to overcome these challenges by exploiting the incoherence of sidelobe artifacts and noise between datasets acquired using orthogonal transmissions. Simulation, in vitro blood flow phantom, and in vivo experiments were conducted to compare the proposed method with existing orthogonal plane wave imaging (OPW), row-column-specific frame-multiply-and-sum beamforming (RC-FMAS), and XDoppler techniques. Qualitative and quantitative results demonstrate the superior performance of the proposed method. In simulations, the proposed method reduced the sidelobe level by 31.3 dB, 20.8 dB, and 14.0 dB, compared to OPW, XDoppler, and RC-FMAS, respectively. In the blood flow phantom experiment, the proposed method significantly improved the contrast-to-noise ratio (CNR) of the tube by 26.8 dB, 25.5 dB, and 19.7 dB, compared to OPW, XDoppler, and RC-FMAS methods, respectively. In the human submandibular gland experiment, it not only reconstructed a more complete vasculature but also improved the CNR by more than 15 dB, compared to OPW, XDoppler, and RC-FMAS methods. In summary, the proposed method effectively suppresses the side-lobe artifacts and noise in images collected using an RCA under low SNR conditions, leading to improved visualization of 3D vasculatures.

Diverging Polymer Acoustic Lens Design for High-Resolution Row-Column Array Ultrasound Transducers.

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 of off-the-shelf pieces of materials, which leaves no room for optimization. We hypothesize that acoustic lenses can be designed to fit high-resolution transducers, and they can be fabricated in a fast, cost-effective, and flexible manner using a combination of 3-D printing and casting or computer numerical control (CNC) machining techniques. These lenses should increase the FOV of the array while preserving the image quality. In this work, such lenses are made in concave, convex, and compound spherical shapes and from thermoplastics and thermosetting polymers. Polymethylpentene (TPX), polystyrene (PS), polypropylene (PP), polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), and room-temperature-vulcanizing (RTV) silicone diverging lenses have been fabricated and mounted on a 128 + 128 6-MHz RCA transducer. The performances of the lenses have been assessed and compared in terms of FOV, signal-to-noise ratio (SNR), bandwidth, and potential artifacts. The largest FOV (24.0.) is obtained with a 42.64-mm radius PMMA-RTV compound lens, which maintains a decent fractional bandwidth (53%) and SNR at 6 MHz (.9.1-dB amplitude drop compared with the unlensed transducer). The simple PMMA TPX, PS, PP, PDMS, and RTV lenses provide an FOV of 12.2°, 6.3°, 8.1°, 11.7°, 0.6°, and 10.4°; a fractional bandwidth of 97%, 46%, 103%, 46%, 97%, 53%, and 49%; and an amplitude drop of -5.2, -4.4, -2.8, -15.4, -6.0, and -1.8 dB, respectively. This work demonstrates that thermoplastics are suitable materials for fabricating low-attenuation convex diverging lenses for large-aperture, high-frequency 2-D transducers. This is highly desired to achieve high-resolution volumetric imaging of large organs.

High sensitivity mapping of brain-wide functional networks in awake mice using simultaneous multi-slice fUS imaging

Abstract Functional ultrasound (fUS) has received growing attention in preclinical research in the past decade, providing a new tool to measure functional connectivity (FC) and brain task-evoked responses with single-trial detection capability in both anesthetized and awake conditions. Most fUS studies rely on 2D linear arrays to acquire one slice of the brain. Volumetric fUS using 2D matrix or row-column arrays has recently been demonstrated in rats and mice but requires invasive craniotomy to expose the brain due to a lack of sensitivity. In a previous study, we proposed the use of motorized linear arrays, allowing imaging through the skull in mice for multiple slices with high sensitivity. However, the tradeoff between the field of view and temporal resolution introduced by motorized scanning prevents acquiring brain-wide resting-state FC data with a sufficient volume rate for resting-state FC analysis. Here, we propose a new hybrid solution optimized and dedicated to brain-wide transcranial FC studies in mice, based on a newly developed multi-array transducer allowing simultaneous multi-slicing of the entire mouse cerebrum. We first demonstrate that our approach provides a better imaging quality compared to other existing methods. Then, we show the ability to image the whole mouse brain non-invasively through the intact skin and skull during visual stimulation under light anesthesia to validate this new approach. Significant activation was detected along the whole visual pathway, at both single and group levels, with more than 10% of augmentation of the cerebral blood volume (CBV) signal during the visual stimulation compared to baseline. Finally, we assessed resting-state FC in awake head-fixed animals. Several robust and long-ranged FC patterns were identified in both cortical and sub-cortical brain areas, corresponding to functional networks already described in previous fMRI studies. Together, these results show that the multi-array probe is a valuable approach to measure brain-wide hemodynamic activity in mice with an intact skull. Most importantly, its ability to identify robust resting-state networks is paving the way towards a better understanding of the mouse brain functional organization and its breakdown in genetic models of neuropsychiatric diseases.

Suppression of crosstalk in row–column actuator array using regulation of ferroelectric polarization

This article presents a method for suppressing electrical crosstalk in a ferroelectric row-column (RC) actuator array. In high-density two-dimensional (2D) arrays, the RC addressing scheme has advantages over the conventional method of fully addressing the array, primarily due to its requirement for fewer interconnections to drive the elements. However, electrical crosstalk is an undesirable side effect that restricts the practical use of RC arrays for sensing and actuation. To mitigate this crosstalk between elements and allow activation of the target element, an addressing method using orthogonal biasing is investigated for the RC array. Due to the voltage-dependent polarization state of the ferroelectric film, each element exhibits bias-sensitive activity. Applying a coercive voltage bias to the electrically coupled elements via row electrodes to minimize the net polarization and piezoelectric activity reduces electrical crosstalk, leaving only acoustic crosstalk in the array. The method using coercive voltage bias reduces crosstalk between the elements by 6.25 dB compared to the conventional method. Furthermore, applying a negative bias of 7 V to the target element enhances its activity and increases its dynamic displacement by 33%, thus alleviating the crosstalk by 7.25 dB. The on-off switching characteristics of the biasing method are examined to investigate the feasibility of adopting such biasing in area scanning techniques for potential applications, such as ultrasonic imaging. By adjusting the magnitude of the DC bias, on-off switching operation is demonstrated at 5 kHz while achieving a 3 dB on-off ratio.

High-Voltage Bias-Switching Electronics for Volumetric Imaging using Electrostrictive Row-Column Arrays.

Top Orthogonal to Bottom Electrode (TOBE) arrays, also known as row-column arrays, hold great promise for fast high-quality volumetric imaging. Bias-voltage-sensitive TOBE arrays based on electrostrictive relaxors or micromachined ultrasound transducers can enable readout from every element of the array using only row and column addressing. However, these transducers require fast bias-switching electronics which are not part of a conventional ultrasound system and are non-trivial. Here we report on the first modular bias-switching electronics enabling transmit, receive, and biasing on every row and every column of TOBE arrays, supporting up to 1024 channels. We demonstrate the performance of these arrays by connection to a transducer testing interface board and demonstrate 3D structural imaging of tissue and 3D power Doppler imaging of phantoms with realtime B-scan imaging and reconstruction rates. Our developed electronics enable interfacing of bias-switchable TOBE arrays to channel-domain ultrasound platforms with software-defined reconstruction for next-generation 3D imaging at unprecedented scales and imaging rates.

Shear wave elastography based on noise correlation and time reversal: From 1d to 3d shear elasticity imaging

Shear wave elastography (SWE) relies on the generation and tracking of coherent shear waves to image soft tissue’s shear elasticity. However, coherent shear wave tracking is not always possible due to scattered or interfering waves that arise from inhomogeneities, muscular activity, heart beating, or external sources. To overcome this limitation, we developed an alternative approach using a complex elastic wave-field. Based on the analogy between time reversal and seismic noise correlation, this complex field is “transformed” into a coherent converging-diverging time-reversal field using spatial-temporal cross-correlations [1]. Using the computed time reversal field, there are different ways to image the shear elasticity: tracking the coherent shear wave as it focuses, measuring the focus size (Rayleigh criteria) or evaluating the vibration amplitude at the focus [2]. One advantage of this approach is its compatibility with low imaging rates, which led to innovative applications in SWE. Thus, the goal of this talk is to review the major developments in wave-physics for 1D and 2D elasticity imaging using noise correlation of shear waves and to present its latest applications involving passive elastography and 3D elasticity imaging using row-column arrays. [1] Catheline, Phys. Rev. Lett. (2008); Brum, JASA (2008); Benech, IEEE-TUFFC (2009). [2] Brum, Front. Phys. (2021).

Transverse oscillation tensor velocity imaging using a row–column addressed array: Experimental validation

Tensor velocity imaging (TVI) performance with a row–column probe was assessed for constant flow in a straight vessel phantom and pulsatile flow in a carotid artery phantom. TVI, i.e., estimating the 3-D velocity vector as a function of time and spatial position, was performed using the transverse oscillation cross-correlation estimator, and the flow was acquired with a Vermon 128+128 row–column array probe connected to a Verasonics 256 research scanner. The emission sequence used 16 emissions per image, and a TVI volume rate of 234 Hz was obtained for a pulse repetition frequency (fprf) of 15 kHz. The TVI was validated by comparing estimates of the flow rate through several cross-sections with the flow rate set by the pump. For the constant 8 mL/s flow in the straight vessel phantom with relative estimator bias (RB) and standards deviation (RSD) was found in the range of −2.18% to 0.55% and 4.58% to 2.48% in measurements performed with an fprf of 15, 10, 8, and 5 kHz. The pulsatile flow in the carotid artery phantom the was set to an average flow rate of 2.44 mL/s, and the flow was acquired with an fprf of 15, 10, and 8 kHz. The pulsatile flow was estimated from two measurement sites: one at a straight section of the artery and one at the bifurcation. In the straight section, the estimator predicted the average flow rate with an RB value ranging from −7.99% to 0.10% and an RSD value ranging from 10.76% to 6.97%. At the bifurcation, RB and RSD values were between −7.47% to 2.02% and 14.46% to 8.89%. This demonstrates that an RCA with 128 receive elements can accurately capture the flow rate through any cross-section at a high sampling rate.

A High-Performance 3-D Imaging Technique Using Simultaneous Azimuth and Elevation Compounding.

A new technique for 3-D imaging with a row-column array (RCA) configuration has been developed. The technique requires an electrostrictive piezoelectric for the active substrate. While the top set of electrodes is connected to RF transmit and receive channels for conventional diverging wave imaging (DWI), the orthogonal bottom set of electrodes is connected to independently controlled variable dc bias channels. By implementing modulated bias patterns compounded across multiple pulses, fine delay control across the bottom elements can be achieved simultaneously with imaging with the top set of electrodes. This resulted in a high-quality two-way focus in both azimuth and elevation. A 20-MHz electrostrictive composite substrate was fabricated, and 64 top ×64 bottom electrodes were patterned and connected to custom beamforming and biasing electronics. The point spread functions were generated in all dimensions, and the -6 dB resolution was measured to be 93 [Formula: see text] axially, [Formula: see text] in the azimuth, and 328 [Formula: see text] in the elevation dimension. This was in good agreement with the simulated resolutions of 80, 273, and 280 [Formula: see text], respectively.

Anatomic and Functional Imaging Using Row-Column Arrays.

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 aperture (SA) sequences and modified delay-and-sum beamforming. Resolution can approach the diffraction limit with an isotropic resolution of half a wavelength with low sidelobe levels, and the field of view can be expanded by using convex or lensed RC probes. GPU beamforming allows for three orthogonal planes to be beamformed at 30 Hz, providing near real-time imaging ideal for positioning the probe and improving the operator's workflow. Functional imaging is also attainable using transverse oscillation and dedicated SA sequence for tensor velocity imaging for revealing the full 3-D velocity vector as a function of spatial position and time for both blood velocity and tissue motion estimation. Using RC arrays with commercial contrast agents can reveal super-resolution imaging (SRI) with isotropic resolution below [Formula: see text]. RC arrays can, thus, yield full 3-D imaging at high resolution, contrast, and volumetric rates for both anatomic and functional imaging with the same number of receive channels as current commercial 1-D arrays.

Ultrafast Orthogonal Row-Column Electronic Scanning (uFORCES) With Bias-Switchable Top-Orthogonal-to-Bottom Electrode 2-D Arrays.

Top-orthogonal-to-bottom electrode (TOBE) arrays, also known as row-column arrays, have shown great promise as an alternative to fully wired 2-D arrays, owing to a considerable reduction in channels. Novel imaging schemes with bias-switchable TOBE arrays were previously shown to offer promise compared with previous nonbias-switchable row-column imaging schemes and compared with previously developed explososcan methods, however, they required significant coherent compounding. Here, we introduce ultrafast orthogonal row-column electronic scanning (uFORCES), an ultrafast coded synthetic aperture imaging method. Unlike its FORCES predecessor, uFORCES can achieve coherent compounding with only a few transmit events and may, thus, be more robust to tissue motion. We demonstrate through simulations that uFORCES can potentially offer improved resolution compared with the matrix probes having beamformers constrained by the paraxial approximation. Also, unlike current matrix probe technology incorporating microbeamforming, uFORCES with bias-switchable TOBE arrays can achieve ultrafast imaging at thousands of frames per second using only row and column addressing. We also demonstrate the experimental implementation of uFORCES using a fabricated 128 ×128 electrostrictive TOBE array on a crossed 25- [Formula: see text] gold wire phantom and a tissue-mimicking phantom. The potential for improved resolution and ultrafast imaging with uFORCES could enable new essential imaging capabilities for clinical and preclinical ultrasound.

Accurate prediction of transmission through a lensed row-column addressed array.

Using a diverging lens on a row-column array (RCA) can increase the size of its volumetric image and thus significantly improve its clinical value. Here, a ray tracing method is presented to predict the position of the transmitted wave so that it can be used to make beamformed images. The usable transmitted field-of-view (FOV) is evaluated for a lensed 128 + 128 element RCA by comparing the theoretic prediction of the emitted wavefront position with three-dimensional (3D) finite element simulation of the emitted field. The FOV of the array is found to be 122° ± 2° in the direction orthogonal to the emitting elements and 28.5°-51.2°, depending on depth and element position, for the direction lying along the element. Moreover, the proposed ray tracing method is compared with a simpler thin lens model, and it is shown that the improved accuracy of the proposed method can increase the usable transmitted FOV up to 25.1°.

Ultrafast 3-D Ultrasound Imaging Using Row-Column Array-Specific Frame-Multiply-and-Sum Beamforming.

Row-column arrays have been shown to be able to generate 3-D ultrafast ultrasound images with an order of magnitude less independent electronic channels than traditional 2-D matrix arrays. Unfortunately, row-column array images suffer from major imaging artifacts due to high sidelobes, particularly when operating at high frame rates. This article proposes a row-column-specific beamforming technique, for orthogonal plane-wave transmissions, row-column-specific frame multiply and sum (RC-FMAS), that exploits the incoherent nature of certain row-column array artifacts. A series of volumetric images is produced using row or column transmissions of 3-D plane waves. The voxelwise geometric mean of the beamformed volumetric images from each row and column pair is taken prior to compounding, which drastically reduces the incoherent imaging artifacts in the resulting image compared to traditional coherent compounding. The effectiveness of this technique was demonstrated in silico and in vitro, and the results show a significant reduction in sidelobe level with over 16-dB improvement in sidelobe to main-lobe energy ratio. Significantly improved contrast was demonstrated with contrast ratio increased by ~10 dB and generalized contrast-to-noise ratio increased by 158% when using the proposed new method compared to the existing delay and sum during in vitro studies. The new technique allowed for higher quality 3-D imaging while maintaining high frame rate potential.