Low-Complexity Motion-Compensated Beamforming Algorithm and Architecture for Synthetic Transmit Aperture in Ultrasound Imaging
TL;DR: A low-complexity global motion compensation algorithm is proposed that can improve the contrast ratio (CR) and contrast-to-noise ratio (CNR) in two-dimentional motion environment and reduce the computational complexity of the whole beamforming system.
Abstract: Synthetic transmit aperture (STA) has been widely investigated in ultrasound system recently with characteristics of high frame rate and low hardware cost. Since the high-resolution image (HRI) of STA is formed by summation of low-resolution images (LRIs), it is susceptible to inter-firing motions. In this paper, we propose a low-complexity global motion compensation algorithm. We use the common region of interest (ROIcom) between different transmissions of STA imaging to beamform backward and forward beam vectors. Then, the magnitude and direction of motion can be evaluated by cross-correlations between specific beam vectors in STA imaging. Compared with the uncompensated image in two-dimentional (2D) motion environment, the proposed motion compensation algorithm can improve the contrast ratio (CR) and contrast-to-noise ratio (CNR) by 13.73 and 2.04 dB, respectively. Also, the proposed algorithm improves the CR and CNR about 7.84 and 1.36 dB comparing with the reference work, respectively. In the Field II breath model, the proposed method also improves the CR and CNR about 6.65 and 1.04 dB than the reference method, respectively. Moreover, we propose a low-complexity delay generator in the architecture design to further reduce the computational complexity of the whole beamforming system. Finally, we verify the proposed low-complexity motion compensation beamforming engine by using the VLSI implementation with CMOS 90 nm technology. In the post-layout result, the core size is 2.39 mm2 at 125 MHz operating frequency and the frame rate of the beamforming system is 42.23 frames per second.
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TL;DR: Improvement of the B-mode and contrast-mode image quality with cardiac motion and blood flow-induced microbubble motion was achieved and a triplex cardiac imaging technique, consisting of B mode, contrast mode, and 2-D vector flow imaging with a high frame rate of 250 Hz was achieved.
Abstract: Combining diverging ultrasound waves and microbubbles could improve contrast-enhanced echocardiography (CEE), by providing enhanced temporal resolution for cardiac function assessment over a large imaging field of view. However, current image formation techniques using coherent summation of echoes from multiple steered diverging waves (DWs) are susceptible to tissue and microbubble motion artifacts, resulting in poor image quality. In this study, we used correlation-based 2-D motion estimation to perform motion compensation for CEE using DWs. The accuracy of this motion estimation method was evaluated with Field II simulations. The root-mean-square velocity errors were 5.9% ± 0.2% and 19.5% ± 0.4% in the axial and lateral directions, when normalized to the maximum value of 62.8 cm/s which is comparable to the highest speed of blood flow in the left ventricle (LV). The effects of this method on image contrast ratio (CR) and contrast-to-noise ratio (CNR) were tested in vitro using a tissue mimicking rotating disk with a diameter of 10 cm. Compared against the control without motion compensation, a mean increase of 12 dB in CR and 7 dB in CNR were demonstrated when using this motion compensation method. The motion correction algorithm was tested in vivo on a CEE data set acquired with the Ultrasound Array Research Platform II performing coherent DW imaging. Improvement of the B-mode and contrast-mode image quality with cardiac motion and blood flow-induced microbubble motion was achieved. The results of motion estimation were further processed to interpret blood flow in the LV. This allowed for a triplex cardiac imaging technique, consisting of B mode, contrast mode, and 2-D vector flow imaging with a high frame rate of 250 Hz.
10 citations
Additional excerpts
...As with synthetic transmit aperture imaging [26]–[29]...
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TL;DR: Simulation and experimental results show that signal eigenvalue factor (SEF) method can get higher resolution than CF and DAS and the contrast radio and contrast-to-noise radio can be enhanced, especially for massive cyst.
Abstract: Synthetic transmit aperture (STA) ultrasound imaging that obtain bi-directional focusing can create a high-resolution image. Delay-and-sum (DAS) approach is performed in both transmit and receive modes, which leads to low contrast and high sidelobe. Adaptive weighting technology is effective in improving image quality. This paper proposes a new adaptive weighting factor namely signal eigenvalue factor (SEF) for STA imaging. SEF performs eigenvalue decomposition on transmitting aperture, and then it uses the larger eigenvalues as the weighting factor to carry out the adaptive imaging. For comparison, conventional coherence factor (CF) method is also presented. Simulation and experimental results show that SEF method can get higher resolution than CF and DAS. In addition, the contrast radio and contrast-to-noise radio can be enhanced, especially for massive cyst.
8 citations
TL;DR: A delay calculation algorithm and corresponding hardware architecture for dynamically focusing the convex transducer array at large number of scan points are described and shows around 57–86% improvement in terms of hardware consumption with respect to those of other available architectures.
Abstract: In ultrasound systems synthetic transmit aperture and phased array imaging are widely used for obtaining the high quality images. These imaging systems require dynamic focusing of the multi-element transducer array at large number of scan points during transmission and reception. The array can be focused at any point by applying proper delay values to the signals, received or transmitted by each element of the array. Dynamic focusing requires on-line computation of the delay values, for large number of scan points, corresponding to all the elements of the array. This paper describes a delay calculation algorithm and corresponding hardware architecture for dynamically focusing the convex transducer array at large number of scan points. The hardware architecture for the 64-element convex transducer array, which scans 128 scan lines having 1024 scan points on each scan line, consumes 61k gates. It shows around 57–86% improvement in terms of hardware consumption with respect to those of other available architectures. To reduce the overall complexity and latency of the delay calculator, a 28- bit radicand square root calculator architecture which requires less initial memory than that of the linear approximation and less hardware resources than that of the quadratic approximation is also presented.
4 citations
TL;DR: The proposed beamformer provides real-time beamforming output which can be used to display high quality ultrasound images and consumes 1370k NAND-2 gate equivalent logic resources in UMC 90 nm CMOS standard cell library.
References
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TL;DR: It is concluded that the patient's skin should be abraded to reduce impedance, and measurements should be avoided in the first 10 min after electrode placement, to allow satisfactory images.
Abstract: A computer simulation is used to investigate the relationship between skin impedance and image artefacts in electrical impedance tomography. Sets of electrode impedance are generated with a pseudo-random distribution and used to introduce errors in boundary voltage measurements. To simplify the analysis, the non-idealities in the current injection circuit are replaced by a fixed common-mode error term. The boundary voltages are reconstructed into images and inspected. Where the simulated skin impedance remains constant between measurements, large impedances (> 2k omega) do not cause significant degradation of the image. Where the skin impedances 'drift' between measurements, a drift of 5% from a starting impedance of 100 omega is sufficient to cause significant image distortion. If the skin impedances vary randomly between measurements, they have to be less than 10 omega to allow satisfactory images. Skin impedances are typically 100-200 omega at 50 kHz on unprepared skin. These values are sufficient to cause image distortion if they drift over time. It is concluded that the patient's skin should be abraded to reduce impedance, and measurements should be avoided in the first 10 min after electrode placement.
1,976 citations
TL;DR: Multi-element synthetic aperture imaging methods suitable for applications with severe cost and size limitations are explored in this article, where each method uses different spatial frequencies and acquisition strategies for imaging, and therefore different sets of active transmit/receive element combinations.
Abstract: Multi-element synthetic aperture imaging methods suitable for applications with severe cost and size limitations are explored. Array apertures are synthesized using an active multi-element receive subaperture and a multi-element transmit subaperture defocused to emulate a single-element spatial response with high acoustic power. Echo signals are recorded independently by individual elements of the receive subaperture. Each method uses different spatial frequencies and acquisition strategies for imaging, and therefore different sets of active transmit/receive element combinations. Following acquisition, image points are reconstructed using the complete data set with full dynamic focus on both transmit and receive. Various factors affecting image quality have been evaluated and compared to conventional imagers through measurements with a 3.5 MHz, 128-element transducer array on different gel phantoms. Multielement synthetic aperture methods achieve higher electronic signal to noise ratio and better contrast resolution than conventional synthetic aperture techniques, approaching conventional phased array performance. >
595 citations
"Low-Complexity Motion-Compensated B..." refers background or methods in this paper
...Digital Object Identifier 10.1109/TSP.2013.2295551 nique (SAFT) [4], [35], [36], synthetic focusing [37], synthetic receive aperture [5], [37], and synthetic transmit aperture (STA) [6]–[8], [38]....
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...Since the frame rate of beamforming is dominated by the round trip delay between pulses transmission and echoes receiving, STA is used to increase the frame rate [1]–[4] by combining a series of low resolution images (LRIs) to form a high resolution image (HRI) with less number of firings....
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...2295551 nique (SAFT) [4], [35], [36], synthetic focusing [37], synthetic receive aperture [5], [37], and synthetic transmit aperture (STA) [6]–[8], [38]....
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TL;DR: In this article, a parallel processing scheme has been implemented which enables the data acquisition rate to increase by a factor of four through the simultaneous acquisition of four B-mode image lines from each individual broadened transmit pulse.
Abstract: The data acquisition rate in medical ultrasonic imaging devices is limited by the acoustic propagation velocity in the tissues. Typically in such machines the image lines are produced sequentially one line per transmitted pulse. A parallel processing scheme has been implemented which enables the data acquisition rate to increase by a factor of four through the simultaneous acquisition of four B‐mode image lines from each individual broadened transmit pulse. The higher data rate can be used to increase the image frame rate to produce independent images that can be averaged in the image frame to reduce noise, or to produce a conventional image at standard video frame rates while reducing patient exposure. Alternatively, the field of view can be increased over that of a normal scan without sacrificing frame rate. These advantages are achieved with little reduction in the measured resolution. The design and performance of this device are described. A sample in vivo image is included.
383 citations
TL;DR: By mechanically rocking the array, in a way similar to what is done with an annular array, a 3-D set of images can be collected in the time normally required for a single image.
Abstract: A method for real-time three-dimensional (3-D) ultrasound imaging using a mechanically scanned linear phased array is proposed. The high frame rate necessary for real-time volumetric imaging is achieved using a sparse synthetic aperture beamforming technique utilizing only a few transmit pulses for each image. Grating lobes in the two-way radiation pattern are avoided by adjusting the transmit element spacing and the receive aperture functions to account for the missing transmit elements. The signal loss associated with fewer transmit pulses is minimized by increasing the power delivered to each transmit element and by using multiple transmit elements for each transmit pulse. By mechanically rocking the array, in a way similar to what is done with an annular array, a 3-D set of images can be collected in the time normally required for a single image.
358 citations
"Low-Complexity Motion-Compensated B..." refers background or methods in this paper
...However, the SNR in STA system can be improved by increasing the amplitude of the signal [3]....
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...To compare the SNR in STA system with SNR in conventional system, we use the definition in [3] as follows,...
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...The ratio of transmitting power (P) for a conventional system to synthetic aperture system is defined in [3] as follows,...
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03 Nov 1996
TL;DR: In this paper, a review of the changes that have occurred and the current trends in beamformer design is presented, along with some of the factors causing these shifts along the the common types of designs and implementations.
Abstract: Real-time ultrasonic imaging systems have been available for more than thirty years. During this time much has occurred to the basic architecture and functions of these clinical systems and their beamformers, which are, in many ways, the most important components of these systems. This talk will review some of the changes that have occurred and will discuss current trends in beamformer design. Throughout most of the 30 years of real time imaging, analog beamformers have been the mainstay of all instruments. The common methods for the implementation of analog beamformers for annular, linear/curved arrays, and phased arrays will be reviewed and the distinguishing characteristics identified. At the present time the industry is undergoing a major shift toward digital beamformation with the introduction of several commercial systems. Given that the earliest digital systems were available roughly 15 years ago, it is fair to say that the introduction of digital beamformers has been relatively slow. Today this shift seems to be gaining momentum. Some of the factors causing these shifts will be reviewed along the the common types of designs and implementations. The ongoing search for improved imaging performance will continue to introduce new challenges for beamformer designers. Among already proposed imaging methods and techniques are elevation focusing (1.5D arrays), synthetic apertures, 2D and sparse arrays, phase aberration correction, and others. The most common complication introduced by these is a significant increase in channel count. Further, there will also be beamformer design issues related to signal processing. These include not only Doppler processing but also the processing of signals due to novel contrast agents. Finally, with advances in computer and microelectronics technologies, the way we view beamformation may have to undergo sizeable changes. These topics will be reviewed not only as technical challenges but also in light of the constraints introduced by today's marketplace.
352 citations