Coronary artery disease (CAd) is one of the leading causes of death globally. Currently, diagnosis and intervention in CAd are typically performed via minimally invasive cardiac catheterization procedures. Using curre...
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Coronary artery disease (CAd) is one of the leading causes of death globally. Currently, diagnosis and intervention in CAd are typically performed via minimally invasive cardiac catheterization procedures. Using current diagnostic technology, such as angiography and fractional flow reserve (FFR), interventional cardiologists must decide which patients require intervention and which can be deferred;10% of patients with stable CAd are incorrectly deferred using current diagnostic best practices. By developing a forward-viewing intravascular ultrasound (FV-IVUS) 2-d array capable of simultaneously evaluating morphology, hemodynamics, and plaque composition, physicians would be better able to stratify risk of major adverse cardiac events in patients with intermediate stenosis. For this application, a forward-viewing, 16-MHz 2-d array transducer was designed and fabricated. A 2-mm-diameter aperture consisting of 140 elements, with element dimensions of 98 x 98 x 70 mu m ( w x h x t ) and a nominal interelement spacing of 120 mu m, was designed for this application based on simulations. The acoustic stack for this array was developed with a designed center frequency of 16 MHz. A novel via-less interconnect was developed to enable electrical connections to fan-out from a 140-element 2-d array with 120- mu m interelement spacing. The fabricatedarray transducer had 96/140 functioning elements operating at a center frequency of 16 MHz with a -6-dB fractional bandwidth of 62% +/- 7 %. Single-element SNR was 23 +/- 3 dB, and the measured electrical crosstalk was -33 +/- 3 dB. In imaging experiments, the measured lateral resolution was 0.231 mm and the measured axial resolution was 0.244 mm at a depth of 5 mm. Finally, the transducer was used to perform 3-d B-mode imaging of a 3-mm-diameter spring and 3-d B-mode and power doppler imaging of a tissue-mimicking phantom.
We present experimental results from a prototype 5 MHz, 64 x 64 (4096 elements, 16 mm x 16 mm) 2-d array transducer with row-column addressing. The main benefits of our design are a reduced number of interconnects, a ...
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ISBN:
(纸本)9781424402014
We present experimental results from a prototype 5 MHz, 64 x 64 (4096 elements, 16 mm x 16 mm) 2-d array transducer with row-column addressing. The main benefits of our design are a reduced number of interconnects, a T/R switching scheme with a simple diode circuit, and an ability to perform transmit and receive beamforming. With transmit beamforming in elevational direction and receive beamforming in azimuth direction, it is possible to perform 3-d imaging of targets near the transducer. The series resonant impedance was measured at 120 Ohms near 5.5 MHz. The spectrum of the pulse has a center frequency of 5.6 MHz and a -6 dB fractional bandwidth of 43%. In azimuth direction with receive beamforming, we measured the -6 dB width to be 1.22 mm at a depth of 55 mm compared to a theoretical beamwidth of 0.91 mm. In elevational direction with transmit beamforming, -6 dB width was 0.92 mm at a depth of 27 mm compared to a theoretical beamwidth of 0.45 mm. Finally, we introduce results from 266 x 266 2-d array transducer. to 64
In previous work we presented experimental results using a prototype 64 x 64 2-d array with row-column methods. The main benefits of this row-column design are a reduced number of interconnects, a T/R switching scheme...
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ISBN:
(纸本)9781424413836
In previous work we presented experimental results using a prototype 64 x 64 2-d array with row-column methods. The main benefits of this row-column design are a reduced number of interconnects, a T/R switching scheme with a simple diode circuit, and an ability to perform transmit beamforming In azimuth direction and receive beamforming in elevational direction for a volumetric imaging of targets near the transducer. In this paper, we present experimental results acquired from a new 256 x 256 2-d array transducer. The center frequency was 6.4 MHz with a -6 dill bandwidth of 57%. The series resonant impedance was 120 Ohms near 5.8 MHz. The mean crosstalk of the adjacent element was -22dB in the frequency range of interest. For a wire target, in azimuth direction with transmit beamforming, we measured the -6 dB beamwidth to be 0.75 rum at a depth of 25.5 mm compared to a theoretical beamwidth of 0.68 mm. We successfully acquired 3-d images of a wire target and a cylindrical anechoic cyst of 10 mm in diameter made of graphite scatterers in gelatin.
In previous work, we presented initial experimental results using a 256 x 256 2-d array with row-column methods. The main benefits of this design are a reduced number of interconnects, a T/R switching scheme with a si...
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ISBN:
(纸本)9781424424283
In previous work, we presented initial experimental results using a 256 x 256 2-d array with row-column methods. The main benefits of this design are a reduced number of interconnects, a T/R switching scheme with a simple diode circuit, and an ability to perform transmit beamforming in azimuth and receive beamforming in elevation for volumetric imaging of targets near the transducer. In this paper, we present 3-d images of axial wires embedded in a clear gelatin phantom, of an 8 mm diameter cylindrical anechoic cyst phantom and of a 10 min diameter spherical anechoic cyst phantom acquired from a new 256 x 256 2-d array transducer. dAX processing was used to reduce clutter due to 1-way beamforming.
This paper proposes a neural network-based robust imaging method from compressive measurements exploiting a two-dimensional (2-d) array. The practical implementation of a 2-d array becomes much more complicated as the...
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ISBN:
(纸本)9781665459068
This paper proposes a neural network-based robust imaging method from compressive measurements exploiting a two-dimensional (2-d) array. The practical implementation of a 2-d array becomes much more complicated as the number of antennas increases due to the requirement to allocate a different radio frequency front-end circuit to each antenna. An effective solution to this problem is to compress the received signal prior to digitization at the array. In this paper, we use the maximization of the mutual information between compressed measurement and the signal locations to determine the optimal compressive measurement. A neural network-based strategy for localizing sources using these compressed measurements is then proposed. We treat neural network training as a 2-d multilabel classification problem anddesign an appropriate loss function to train the network. Compared to the conventional approach, the proposed neural network-based approach provides more robust performance as it does not rely on any prior knowledge of received signals and the antenna configuration.
Most works that address 2-d array ultrasonic transducers for underwater applications are about the geometry aspects of the array and beamforming techniques to make 3-d images. They look for techniques to reduce the nu...
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Most works that address 2-d array ultrasonic transducers for underwater applications are about the geometry aspects of the array and beamforming techniques to make 3-d images. They look for techniques to reduce the number of elements from wide apertures, maintaining the side lobes and the grating lobes at acceptable levels, but not many details about the materials and fabrication processes are described. To overcome these gaps, this paper presents in detail the development of a 2-d array ultrasonic transducer prototype that can individually emit and receive ultrasonic pulses to make 3-d images of immersed reflectors within a volume of interest (VOI). It consists of a 4 x 4 matrix ultrasonic transducer with a central frequency of 480 kHz. Each element is a 5 mm sided square cut into a 1-3 piezocomposite. The center-to-center distance of two contiguous elements (pitch) was chosen to be greater than half wavelength, to increase the amplitude of emission and reception of signals with larger elements. Artifacts generated by grating lobes were avoided by restricting the field of view in the azimuth and elevation directions within 40 degrees x 40 degrees and applying the sign coherence factor (SCF) filter. Two types of backing layer materials were tested, one with air and another made of epoxy resin, on the transducers called T1 and T2, respectively. The pulse echoes measured with T1 had2.6 dB higher amplitude than those measured with T2, and the bandwidths were 54% and 50% @ -6 dB, respectively, exciting the element with a single rectangular negative pulse. The 3-d images obtained with full matrix capture (FMC) data sets acquired of objects from 0.2 to 1.15 m motivate the development of a 2-d array transducer with more elements, to increase the angular resolution and the range.
Under mechanical compression, tissue movements are inherently three-dimensional. 2-d, strain imaging can suffer from decorrelation noise caused by out-of-plane tissue movement in elevation. With 3-d strain imaging, al...
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Under mechanical compression, tissue movements are inherently three-dimensional. 2-d, strain imaging can suffer from decorrelation noise caused by out-of-plane tissue movement in elevation. With 3-d strain imaging, all tissue movements can be estimated and compensated, hence minimizing out-of-plane decorrelation noise. Promising 3-d strain imaging results have been shown using 1-darrays with mechanical translation in elevation. However, the relatively large slice thickness and mechanical translation can degrade image quality. Using 2-d arrays, an improved elevational resolution can be achieved with electronic focusing. Furthermore, scanning with 2-d arrays is also done electronically, which eliminates the need for mechanical translation. In this paper, we demonstrate the feasibility of 3-d strain imaging using a 4 cm x 4 cm ultrasonic sparse rectilinear 2-d array operating at 5MHz. The signal processing combinations of 2-d or 3-d beamforming followed by 2-d or 3-d strain imaging are studied and compared to each other to evaluate the performance of our 3-d strain imaging system. 3-d beamforming followed by 3-d strain imaging showed best performance in all experiments.
2-d spatial compounding has long been investigated to reduce speckle in ultrasound images. To further reduce speckle, several 3-d spatial compounding studies using 1-d and 1.5 darrays with mechanical translation and ...
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2-d spatial compounding has long been investigated to reduce speckle in ultrasound images. To further reduce speckle, several 3-d spatial compounding studies using 1-d and 1.5 darrays with mechanical translation and position tracking have been reported. However, the fixed elevational focus and mechanical translation can degrade image quality in elevation. Using 2-d arrays, a better elevational resolution can be achieved with electronic focusing. Furthermore, 2-d arrays can generate greater number of independent images than 1-darrays and the need for mechanical scanning is eliminated. In this paper, we present our 3-d spatial compounding images of two gel-based contrast phantoms and one resolution phantom. These images were acquired using a prototype 4 cm x 4 cm ultrasonic row-column prototype 2-d array operating at 5 MHz. Compounding nine decorrelated volumes showed a speckle signal-to-noise ratio (SNR) improvement of 2.68. The average improvement of the lesion contrast-to-noise ratio (CNR) was 2.45. However, using a smaller aperture to generate these volumes worsened the lateral resolution as predicted by theory.
Two-dimensional arrays enable volumetric ultrasound imaging but have been limited to small aperture size and hence low resolution due to the high cost and complexity of fabrication, addressing, and processing associat...
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Two-dimensional arrays enable volumetric ultrasound imaging but have been limited to small aperture size and hence low resolution due to the high cost and complexity of fabrication, addressing, and processing associated with large fully addressedarrays. Here, we propose Costas arrays as a gridded sparse 2-d array architecture for volumetric ultrasound imaging. Costas arrays have exactly one element for every row and column, such that the vector displacement between any pair of elements is unique. These properties ensure aperiodicity, which helps eliminate grating lobes. Compared with previously reported works, we studied the distribution of active elements based on an order-256 Costas layout on a wider aperture (96. x 96. at 7.5 MHz center frequency) for high-resolution imaging. Our investigations with focused scanline imaging of point targets and cyst phantoms showed that Costas arrays exhibit lower peak sidelobe levels compared with random sparse arrays of the same size and offer comparable performance in terms of contrast compared with Fermat spiral arrays. In addition, Costas arrays are gridded, which could ease the manufacturing and has one element for each row/column, which enables simple interconnection strategies. Compared with state-of-the-art matrix probes, which are commonly 32 x 32, the proposed sparse arrays achieve higher lateral resolution and a wider field of view.
2-d array transducers have shown significant promise for medical ultrasound over conventional linear arrays, at the cost of increasing the number of channels, difficulty of fabrication andarray element impedance. The...
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2-d array transducers have shown significant promise for medical ultrasound over conventional linear arrays, at the cost of increasing the number of channels, difficulty of fabrication andarray element impedance. The increase in element impedance reduces the power coupled to a 2-d array element from a conventional 50 Ohm source in transmit mode. If the array is sparse, which is typical of 2-d arrays, then the net power coupled into the front acoustic load is reduced when compared to a fully sampled aperture. Furthermore, the received signal-to-noise ratio (SNR), when measured through a nonideal amplifier, is degraded because the high impedance 2-d array transducer element cannot efficiently drive the coaxial cable. The reduction in transmit sensitivity and received SNR can be circumvented with the application of multilayer piezoelectric elements. The improvement in transmit occurs because the transducer impedance is better matched to the impedance of the source. In receive, multilayer elements allow more of the open circuit received voltage to fall across the input of the high impedance preamplifier. In this case, the same number of layers are used in transmit and receive. Recently, it has been suggested that separate optimization of the transmit channel and receive channel (a hybridarray) would further improve the pulse-echo SNR. In this paper, we fabricated and tested a hybridarray operating at 1 MHz using a multilayer transmit element and single layer receive element. A 7 Ohm transmitter and high impedance preamplifier were placed adjacent to the transmit and receive elements within the transducer assembly. The hybrid pulse-echo SNR improved by 26.4 dB over the conventional array. The experimental result showed good agreement with the KLM model. Furthermore, KLM simulations showed that as the operating frequency of the array increases, the overall improvement over the conventional array increases. For example, a 1.5-darray operating at 2 MHz had an improvemen
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