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 divergin...
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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, leading to degraded resolution and contrast due to errors in the time of flight (TOF) calculations. This article presents a beamformer based on ray tracing for accurate TOF calculation. A Verasonics Vantage 256 scanner was equipped with a Vermon RC probe with 128+128 elements, lambda pitch, and a 6 MHz center frequency. A synthetic aperture ultrasound sequence with 96 virtual sources and 32 active elements for each emission with row elements was employed, and all column elements were used for acquiring data. This method was tested with a polystyrene (PS) lens with a spherical shape and polymethyl methacrylate (PMMA) in a bicylindrical shape. Based on pressure field measurements, these two lenses provide a 20 degrees and 33 degrees FOV, respectively. The thin lens model had a lateral resolution of around 17.4 lambda for the bicylindrical lens, whereas the new method achieves a resolution of around 3.8 lambda , representing a 4.6-fold improvement. The contrast is enhanced from 23.1 to 29.8 dB for the bicylindrical lens while preserving the FOV.
Objective: This 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 ...
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Objective: This 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 rowcolumnarray, transcutaneously on a rabbit model and in a human. Methods: To 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. Results: Using 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. Conclusion: It 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.
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 an...
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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 degrees) 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 degrees, 6.3 degrees, 8.1 degrees, 11.7 degrees, 0.6 degrees, and 10.4 degrees;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 d
row-column arrays (RCAs) have been shown to produce high-resolution, three-dimensional ultrasound volumes while reducing the number of electronic connections. Typically, standard reconstruction methods in the time dom...
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ISBN:
(纸本)9798350313345;9798350313338
row-column arrays (RCAs) have been shown to produce high-resolution, three-dimensional ultrasound volumes while reducing the number of electronic connections. Typically, standard reconstruction methods in the time domain such as delay-and-sum (DAS) beamforming have been applied. Here, we derive the Fourier diffraction theorem for reconstructing 3D volumes from backscattered data obtained using an RCA with broadband plane wave excitation under a range of angles. Based on this theory, we propose a novel spatial frequency domain method that offers additional theoretical insight for the optimization of RCA beamforming. In comparison to time domain methods, it also promises higher computational efficiency by using the fast Fourier transform and it enables alternative signal processing and filtering schemes in the frequency domain. We validate our reconstruction algorithm with simulation data. The results demonstrate improved image quality and resolution compared to DAS beamforming.
Super resolution ultrasound imaging (SR-US) is an evolving technology with promising applications in microvascular imaging deep into tissue. With high resolution, it offers enhanced visualization of fine anatomical st...
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ISBN:
(纸本)9798350371918;9798350371901
Super resolution ultrasound imaging (SR-US) is an evolving technology with promising applications in microvascular imaging deep into tissue. With high resolution, it offers enhanced visualization of fine anatomical structures and microvasculature. Existing SR-US has mostly realized with 2D matrix ultrasound array. Yet, known for its challenges including the long data acquisition, computationally expensive postprocessing times and complicated fabrication process due to a high channel-count ultrasound system. Recently, row-column (RC) arrays presented possible solutions to overcome the limitations with relatively easier structure, efficient data acquisition methods and large field-of-view (FOV). However, existing handheld RC arrays are rigid and bulky, which is strongly affected by skull interference and is difficult for continuous monitoring of brain micro-vessel systems. Thus, in this work, we demonstrated a 32 + 32 element flexible row-column array for imaging with a center frequency of 7.8 MHz and a total array aperture size of 8 by x8 mm(2). With a -6 dB bandwidth of 59 % and a bending curvature of 8 mm, the array showed its potential for wearable SR-US applications.
row-column (RC) arrays in volumetric imaging present a potential alternative to typical matrix arrays due to their fewer electrical connections. However, these probes have a limited field of view (FOV), which is recta...
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ISBN:
(纸本)9781510686021;9781510686038
row-column (RC) arrays in volumetric imaging present a potential alternative to typical matrix arrays due to their fewer electrical connections. However, these probes have a limited field of view (FOV), which is rectangular and equal to the probe's footprint. Using a diverging lens can expand the FOV, but the lens causes wave attenuation, which decreases the signal-to-noise ratio (SNR) and the penetration depth of the probe. This paper hypothesizes that incorporating a lens and coded excitation (CE) can maintain a larger field of view (FOV) in 3D ultrasound imaging while enhancing the signal-to-noise ratio (SNR) and penetration depth. A chirp signal with a center frequency of 6 MHz, a bandwidth of 4 MHz, and a duration of 5 mu s was used to evaluate the proposed method. The SNR measured from a cyst phantom increased by approximately 10 dB when using CE compared to single sinusoid excitation. This improvement is comparable to the 8 dB attenuation introduced by the lens. Consequently, the penetration depth improved by around 100 lambda while preserving the increased FOV provided by the lens.
Two-dimensional sparse arrays and row-column arrays are both alternatives to 2-D fully addressed arrays with lower channel counts. row-column arrays have recently demonstrated fast 3-D structural and flow imaging but ...
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Two-dimensional sparse arrays and row-column arrays are both alternatives to 2-D fully addressed arrays with lower channel counts. row-column arrays have recently demonstrated fast 3-D structural and flow imaging but commonly suffer from high grating lobes or require multiplexing to achieve better quality. Two-dimensional sparse arrays enable full-volume acquisitions for each 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 2-D 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 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 (128 lambda x 128 lambda at 7.5 MHz) in ultrafast plane-wave imaging of point targets and 3-D power Doppler imaging of synthetic flow phantoms. Our simulation results show that TOBE-Costas arrays exhibit superior resolution and lower sidelobe levels compared with plane-wave compounding with row-column arrays. Compared with density-tapered spiral arrays, they provide a larger field of view and finer resolution.
A new technique for 3D imaging with a row-column array configuration has been developed. The technique requires an electrostrictive piezoelectric for the active substrate. While the top set of electrodes are connected...
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ISBN:
(数字)9781665466578
ISBN:
(纸本)9781665466578
A new technique for 3D imaging with a row-column array configuration has been developed. The technique requires an electrostrictive piezoelectric for the active substrate. While the top set of electrodes are connected to RF transmit and receive channels for conventional diverging wave imaging, the orthogonal bottom set of electrodes are 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 to imaging with the top set of electrodes. This resulted in a high-quality 2-way focus in both azimuth and elevation. A 20 MHz electrostrictive composite substrate was fabricated and 64 top by 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 mu m axially, 272 mu m in the azimuth, and 328 mu m in the elevation dimension. This was in good agreement with the simulated resolutions of 80 mu m, 273 mu m, and 280 mu m respectively.
This paper presents an in-house developed 2-D capacitive micromachined ultrasonic transducer (CMUT) applied for 3-D blood flow estimation. The probe breaks with conventional transducers in two ways;first, the ultrason...
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ISBN:
(纸本)9781510600256
This paper presents an in-house developed 2-D capacitive micromachined ultrasonic transducer (CMUT) applied for 3-D blood flow estimation. The probe breaks with conventional transducers in two ways;first, the ultrasonic pressure field is generated from thousands of small vibrating micromachined cells, and second, elements are accessed by row and/or column indices. The 62+62 2-D row-column addressed prototype CMUT probe was used for vector flow estimation by transmitting focused ultrasound into a flow-rig with a fully developed parabolic flow. The beam-to-flow angle was 90 degrees. The received data was beamformed and processed offline. A transverse oscillation (TO) velocity estimator was used to estimate the 3-D vector flow along a line originating from the center of the transducer. The estimated velocities in the lateral and axial direction were close to zero as expected. In the transverse direction a characteristic parabolic velocity profile was estimated with a peak velocity of 0.48 m/s +/- 0.02 m/s in reference to the expected 0.54 m/s. The results presented are the first 3-D vector flow estimates obtained with a row-column CMUT probe, which demonstrates that the CMUT technology is feasible for 3-D flow estimation.
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