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An adaptive harmonic separation (HS) technique is proposed to overcome the limitations in conventional filtering techniques for ultrasound (US) tissue harmonic imaging (THI). Based on expectation-maximization source separation, the proposed HS technique adaptively models the depth-varying fundamental and harmonic components in the frequency domain and separates the two by applying their calculated posterior probabilities. Phantom experiments with a Tx center frequency of 2 MHz are conducted to evaluate the proposed HS-based US THI schemes. The phantom images show that the proposed single-pulse THI scheme utilizing the HS technique provides not only an average improvement of 19.2% in axial resolution compared to the conventional bandpass filtering scheme but also similar image quality to that of the conventional pulse-inversion (PI) scheme which requires two Tx/Rx sequences for each scan line. Furthermore, when combined with the PI technique, the HS technique provides a uniform axial resolution over the entire 170 mm imaging depth with an average improvement of 17.1% compared to the conventional PI scheme. These results show that the proposed adaptive HS technique is capable of improving both the frame rate and the image quality of US THI. [ABSTRACT FROM AUTHOR]

Objective: Two-dimensional (2D) photoacoustic (PA) imaging based on array transducers provide high spatial resolution in the lateral direction by adopting receive dynamic focusing. However, the quality of PA image is often deteriorated by poor elevational resolution which is achieved by an acoustic lens. To overcome this limitation, we present a three-dimensional (3D) image reconstruction method using a commercial one-dimensional (1D) array transducer. Methods: In the method, the elevational resolution is improved by applying synthetic aperture focusing (SAF) technique along the elevational direction. For this, a commercially available 1D array transducer with an acoustic lens is modeled and appropriate synthetic focusing delay that can minimize the effect of the acoustic lens is derived by mathematical analysis. Results: From the simulation and experiment results, it was demonstrated that the proposed method can enhance the image quality of PA imaging, i.e., elevational resolution and signal-to-noise ratio (SNR). Conclusion: 3D PA images with improved elevational resolution were achieved using a clinical 1D array transducer. Significance: The presented method may be useful for clinical application such as detecting microcalcification, imaging of tumor vasculature and guidance of biopsy in real time. [ABSTRACT FROM AUTHOR]

In three-dimensional (3D) medical ultrasound imaging with two-dimensional (2D) arrays, sparse 2D arrays have been studied to reduce the number of active channels. Among them, sparse 2D arrays with regular or uniform arrangements of elements have advantages of low side lobe energy and uniform field responses over the entire field of view. This paper presents two uniform sparse array models: sparse rectangular arrays (SRAs) on a rectangular grid and sparse spiral arrays (SSAs) on a sunflower grid. Both arrays can be easily implemented on the commercially available or the custom-made arrays. To suppress the overall grating lobe levels, the transmit (Tx) and receive (Rx) array pairs of both the array models are designed not to have grating lobes at the same locations in the Tx/Rx beam patterns, for which the theoretical design rules are also proposed. Computer simulation results indicate that the proposed array pairs for both the SRAs and the SSAs achieve peak grating lobe levels below –40 dB using about a quarter of the number of elements in the dense rectangular array while maintaining similar beam widths to that of the dense array pair. [ABSTRACT FROM AUTHOR]

Objective: The ultrasound baseband in-phase/quadrature beamformer (IQBF) has been widely employed in medical ultrasound imaging to reduce the amount of channel data or to decrease the data rate of the beamforming process. The aim of this study is to assess the effect of the time and phase delay compensation accuracies on the IQBF and thereby to suggest the criteria for selecting the delay resolutions of the IQBF. Methods: Mathematical models of the gain loss (GL) and sidelobe level (SL) in closed form are suggested, and the relationships between the parameters (time and phase delay resolutions of the IQBF and the signal bandwidth) and the errors (GL and SL) are investigated. The performance of the IQBF is compared with that of the traditional radio-frequency beamformer (RFBF). Simulation and phantom and in vivo experimental results are shown to corroborate the theoretical analysis. Results and Conclusion: Theoretical analysis and simulation and experimental results show that a phase delay resolution with a quantization step of 2π/64 is sufficient for phase compensation and that a time delay resolution with a sampling rate of 4f0 and 2f0 in the IQBF is sufficient for data with a –6 dB bandwidth of 50% and 25%, respectively, for similar performance as the RFBF with a sampling rate of 16f0, where f0 is the center frequency of the ultrasound signal. Significance: The suggested criteria have the potential to be used for designing an efficient IQBF satisfying the desired specifications and beamforming accuracy. [ABSTRACT FROM AUTHOR]

Low-complexity ultrasound systems are increasingly desired for both wearable, point-of-care ultrasound and high-end massive-channel ultrasound for 3-D matrix imaging. However, the imaging capabilities, including spatial resolution and contrast, could suffer as low complexity systems are pursued, which remains as an unresolved tradeoff. To mitigate this limitation, this study revisits the general structures of analog and digital beamformers and introduces a hybrid approach, referred to as analog-digital hybrid beamforming, to implement efficient ultrasound systems. The suggested hybrid beamforming takes two stages sequentially, where the first analog stage partially beamforms M-channel RF signals to N sum-out data (i.e., M-to-N beamforming), and the second digital stage beamforms N partial sums to single final beamformed data (i.e., N-to-1 beamforming). Our approach was systematically designed and implemented with only four major integrated circuits, which was capable of driving full 64-channel transmission and reception. The developed system was demonstrated with a customized 64-channel 1-D phased array using a commercial tissue mimicking phantom. From the phantom imaging results, signal-to-noise ratio, contrast-to-noise ratio, and full beam width at half maximum values were quantitatively evaluated. The demonstrated results indicate that the analog-digital hybrid beamforming can be applied to any type of array for sophisticated 3-D imaging and tiny wearable ultrasound applications. [ABSTRACT FROM AUTHOR]

Three-dimensional plane wave imaging (PWI) with a 2-D array has been studied for ultrafast volumetric imaging in medical ultrasound. Compared to 2-D PWI, 3-D PWI requires the transmission of an increased number of plane waves (PWs) to scan a volume of interest and achieve transmit dynamic focusing in both the lateral and elevational directions. To reduce the number of PW angles for a given 2-D angular range by mitigating the grating lobe level, we propose two aperiodic patterns of PW angles: concentric rings with a uniform radial interval and the well-known sunflower pattern. Both patterns are validated to provide uniform angle distributions without regular periodicity, and thereby reduce the grating lobe level compared to a periodic angle distribution with the same number of PW angles. Simulation studies show that the aperiodic patterns enhance the contrast of B-mode images by approximately 3–6 dB over all depths. This enhancement implies that the aperiodic angle sets can increase the volume rate by approximately 2–6 times compared to the periodic angle set at the same contrast and spatial resolution. [ABSTRACT FROM AUTHOR]

Synthetic transmit focusing (STF) methods using unfocused waves or plane waves (PWs) have recently been investigated extensively. However, STF using PWs with a convex array (PWSTF-CA) has not been rigorously studied for high-resolution sector imaging. In this paper, the authors suggest an analytical model for accurate characterization of the spatial beam patterns of PWSTF-CA using a large range of either uniformly or non-uniformly distributed PW angles. On the basis of the model, a frame-based PWSTF-CA approach with non-uniform PW angles is suggested to achieve superior image quality at a higher frame rate than conventional transmit focusing (CTF). The analytical model can also be used for optimal selection of a set of PW angles to scan the entire sectorial field of view and its subsets employed for STF at each imaging point. The authors also investigate how to select transmit subarrays for each of the PWs to obtain the best spatial resolution. A theoretical analysis and simulations are conducted for the verification of the analytical model and the optimal utilization strategy of PWSTF-CA. The results indicate that the PWSTF-CA improves not only the frame rate but also the contrast, signal-to-noise ratio, and resolution compared with the CTF, as in the case of PWSTF with linear arrays. [ABSTRACT FROM AUTHOR]

Spatial resolution of an ultrasound image is limited by diffraction of ultrasound as it propagates along the axial direction. This paper proposes a method for reducing the diffraction spreading effect of ultrasound by using a synthetic aperture focusing (SAF) method that uses plane waves instead of spherical waves. The new method performs data acquisition and beamforming in the same manner as conventional SAF methods. The main difference is that all array elements are used on each firing to generate a plane wave, the traveling angle of which varies with the position of a receive subaperture. On reception, each scan line is formed by synthesizing RF samples acquired by relevant receive subapertures with delays to force the plane waves to meet at each imaging point. Theoretical analysis and computer simulation with infinite transmit aperture show that the proposed method is capable of suppressing the diffraction of ultrasound and especially causing the lateral beam width to remain unchanged beyond a certain depth determined by the size of a receive subaperture and the maximum traveling angle of plane waves. It is demonstrated that the proposed method is realizable using a linear array transducer. It is also shown that the lateral radiation pattern produced by the proposed method has smaller beam width than that using conventional SAF methods in the region of interest because it suppresses the diffraction of ultrasound. [ABSTRACT FROM PUBLISHER]

Objective: Although plane wave imaging (PWI) with multiple plane waves (PWs) steered at different angles enables ultrafast three-dimensional (3-D) ultrasonic imaging, there is still a challenging tradeoff between image quality and frame rate. To address this challenge, we recently proposed the aperiodic PWI (APWI) with mathematical analysis and simulation study. In this paper, we demonstrate the feasibility of APWI and evaluate the performance with phantom and in vivo experiments. Methods: APWI with a concentric ring angle pattern (APWI-C) and APWI with a sunflower pattern (APWI-S) are evaluated. For experimental verification of the methods, the experimental results are compared with simulation results in terms of the spatial resolution and the mainlobe-to-sidelobe ratio. In addition, the performance of APWI is compared with that of conventional PWI by using a commercial phantom. To examine the potential for clinical use of APWI, a gallstone phantom study and an in vivo carotid artery experiment are also conducted. Results: In the phantom study, the APWI methods provide a contrast ratio approximately 2–3 dB higher than that of PWI. In a gallstone experiment, the proposed methods yield 3-D rendered stone images more similar to the real stones than PWI. In the in vivo carotid artery images, APWI reduces the clutter artifacts inside the artery. Conclusion: Phantom and in vivo studies show that the APWI enhances the contrast without compromising the spatial resolution and frame rate. Significance: This study experimentally demonstrates the feasibility and advantage of APWI for ultrafast 3-D ultrasonic imaging. [ABSTRACT FROM AUTHOR]

Abstract: Coded tissue harmonic imaging with pulse inversion (CTHI-PI) based on a linear chirp signal can improve the signal-to-noise ratio with minimizing the peak range sidelobe level (PRSL), which is the main advantage over CTHI with bandpass filtering (CTHI-BF). However, the CTHI-PI technique could suffer from motion artifacts due to decreasing frame rate caused by two firings of opposite phase signals for each scanline. In this paper, a new CTHI method based on a nonlinear chirp signal (CTHI-NC) is presented, which can improve the separation of fundamental and harmonic components without sacrificing frame rate. The nonlinear chirp signal is designed to minimize the PRSL value by optimizing its frequency sweep rate and time duration. The performance of the CTHI-NC method was evaluated by measuring the PRSL and mainlobe width after compression. From the in vitro experiments, the CTHI-NC provided the PRSL of −40.6dB and the mainlobe width of 2.1μs for the transmit quadratic nonlinear chirp signal with the center frequency of 2.1MHz, the fractional bandwidth at −6dB of 0.6 and the time duration of 15μs. These results indicate that the proposed method could be used for improving frame rates in CTHI while providing comparable image quality to CTHI-PI. [ABSTRACT FROM AUTHOR]

Abstract: The compression error of post-compression based coded excitation techniques increases with decreasing f-number, which causes the elevation of side-lobe levels. In this paper, a post-compression based coded excitation technique with reduced compression errors through dynamic aperture control is proposed. To improve the near-field resolution with no frame rate reduction, the proposed method performs simultaneous transmit multi-zone focusing using two mutually orthogonal complementary Golay codes. In the proposed method, the two mutually orthogonal sequences of length 16 are simultaneously transmitted toward two different focal depths, which are separately compressed into two short pulses on receive after dynamic focusing is performed. After carrying out the same transmit-receive operation for the same scan line with the complementary set of the orthogonal Golay codes, a single scan line with two transmit foci is obtained.The computer simulation results using a linear array with a center frequency of 7.5MHz and 60% 6dB bandwidth show that the range side-lobe level can be suppressed below −50dB, when f-number is maintained not smaller than 3. The performance of the proposed scheme for a smaller f-number of 2 was also verified through actual experiments using a 3.85MHz curved linear array with 60% 6dB bandwidth. Both the simulation and experimental results show that the proposed method provides improved lateral resolution compared to the conventional pre-compressed and post-compression based coded excitation imaging using Golay codes. [Copyright &y& Elsevier]

• A new frequency domain passive acoustic mapping method using Hilbert beamforming. • The data rate can be reduced to its frequency bandwidth utilized for PAM reconstruction. • Redundant FFT computation for unutilized frequency bins was eliminated. • Less hardware utilization for implementing FFT than conventional frequency domain PAM. Passive acoustic mapping (PAM) is the current state-of-the-art imaging tool for monitoring cavitation activity during focused ultrasound therapy such as blood-brain barrier opening. However, PAM incurs huge computational complexity. To address this issue, frequency-domain PAM (FD-PAM) was proposed. Nevertheless, FD-PAM still requires a large number of fast Fourier transforms (FFTs) to produce the frequency components utilized for cavitation monitoring with PAM. Hence, in this paper, we proposes a frequency domain PAM method using passive Hilbert beamforming (PHB-PAM), which can significantly reduce the number of input samples for FFT by down-sampling the analytic signal of the received RF samples at each channel at a rate equal to the bandwidth of the frequency components of interest. The experimental results show that the proposed PHB-PAM provides comparable image quality to that of FD-PAM (correlation coefficient > 0.98). Additionally, the study experimentally verifies that the pre-processing block for generating the decimated analytic signal and FFT in PHB-PAM can be realized using lesser logic resources than FFT in FD-PAM when implemented in an FPGA. Especially, with 128-fold decimation, PHB-PAM reduces the amount of LUTs and DSP slices to implement the pre-processing block by 72.16% and 53.4%, respectively, compared to those of FD-PAM, which allows the 64-channel implementation of the pre-processing block in a low-cost single FPGA. Finally, a hardware-efficient architecture for the pre-processing block of PHB-PAM is described, which can be implemented by replacing the two lowpass filters of an off-the-shelf analog front-end component for ultrasound imaging with a pair of band-pass filters. If PHB-PAM is realized using such a component, it can truly minimize the computational complexity of FD-PAM. [ABSTRACT FROM AUTHOR]

Sparse arrays have been studied mainly to reduce the large numbers of elements in 2-D arrays. However, they can also provide an effective means of miniaturizing ultrasound 1-D array systems for point-of-care applications. Although a variety of sparse array design strategies have been proposed, designing an optimum sparse array to simultaneously satisfy the system specification requirements and performance criteria remains a challenge. This article presents an analytical approach for the design of an optimum pair of periodic sparse arrays (PSAs), one for transmission and the other for reception. The approach is based on three newly derived theorems that describe the most important properties of the two PSAs forming the sparse array pair and their relationship pertaining to the overall beam pattern. The proposed approach can be used to design 1-D sparse array pairs with arbitrary sparseness factors while meeting given performance criteria. The computer simulation verified that the spatial resolution of a 64-element phased array can be obtained with a PSA pair consisting of transmit and receive sparse arrays, of which the number of elements is reduced to 32 and 22, respectively. [ABSTRACT FROM AUTHOR]

The spatiotemporal accuracy of passive acoustic mapping (PAM) for monitoring in situ cavitation bubbles has not been assessed directly via optical means. Here, the cavitation bubbles are monitored from two image sequences obtained simultaneously with PAM and high-speed photography (HSP). The temporal accuracy of PAM for detecting cavitation nucleation and the spatial resolution for cavitation localization are compared with those measured from HSP. The results show that PAM has a temporal accuracy of 20 μ s. Mean differences in the spatial locations of PAM and HSP are as small as 10.0 and 30.5 μm along the lateral and axial directions, respectively. [ABSTRACT FROM AUTHOR]

In medical ultrasound imaging, the focused echo signal is decimated with a finite impulse response filter by a rational factor M/L, the frequency response of which dynamically changes over time. Presented is, an efficient structure for dynamic decimation by a programmable rational factor that use a fixed number of polyphase multiplier‐accumulators (MACs) regardless of the values of M and L. The proposed structure uses the minimum number of MAC units operating at the input data rate to minimise both power consumption and hardware complexity. [ABSTRACT FROM AUTHOR]

Background: The aim of this study was to evaluate the diagnostic utility of PAI at detecting thyroid microcalcifications at 700 nm laser wavelengths. Methods: This study included 36 resected samples in 18 patients. To evaluate the PA manifestation of microcalcifications in PAI, gray level histogram and co-occurrence matrix (COM) texture parameters were extracted from the 3 fixed ROI US and PA images, respectively, per sample. We compared the textural parameters obtained from specimen PAIs between samples with punctate microcalcifications on specimen radiography and those without microcalcifications. Results: On specimen US, the mean value (2748.4±862.5) of samples with microcalcifications on specimen radiography was higher than that (1961.9±780.2) of those without microcalcifications (P = 0.007). However, there were no significant differences in textural parameters obtained from specimen PAIs between samples with punctate microcalcifications on specimen radiography and those without when applying both the mean value of the three slices of thyroid specimens and the value of the thyroid specimen slice which had the highest value of the mean values in specimen US. Conclusion: PAI did not show significant PA contrast on thyroid microcalcifications indicating that the experimental setup and protocols should be enhanced, e.g., method of complete blood rejection from ex vivo specimens, the multi-wavelength spectroscopic PA imaging method which can solely extract the PA signal from microcalcifications even with high spectral interferences, or PA imaging with narrower slice thickness using 2-dimensional array transducer, etc. [ABSTRACT FROM AUTHOR]

In medical ultrasound imaging, lateral resolution is limited when using a fixed transmit focusing. Various synthetic aperture (SA) techniques, in which two-way dynamic focusing is enabled by utilizing prebeamformed radio-frequency (RF) data have been proposed for improving the spatial resolution. However, SA methods were not extensively evaluated in terms of their clinical performance. In this paper, a phantom and an in vivo evaluation of the SA method with bidirectional pixel-based focusing (BiPBF) is presented in comparison with the conventional beamforming. The performance of the proposed SA-BiPBF was assessed with a blind study and the established breast imaging–reporting and data system (BI-RADS), in addition to measuring contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR). Prebeamformed RF data were acquired from a tissue mimicking phantom (Model 040, CIRS Inc., Norfolk, VA, USA) and from patients with breast lesions by using a commercial ultrasound scanning system with a linear array transducer equipped with a research package and parallel data acquisition system (SonixTouch, SonixDAQ, and L14-5/38, Ultrasonix Corp., Canada). In phantom and in vivo experiments, a default setting of a breast preset was applied (e.g., the center frequency of 10 MHz and acoustic output of MI = 0.66). In phantom experiment, the SA-BiPBF method showed higher CNR and SNR values compared to the conventional method (3.4 and 23.9 dB versus 3.1 and 15.8 dB, respectively). In addition, the lateral resolution and penetration depth were increased by 95.4% and 40.3%, respectively. Consistent with the phantom experiment, in the in vivo experiment with ten patients, the CNR value for the SA method was 3.3 \pm 0.5 compared to 2.8 \pm 0.8 for the conventional method. Similarly, the SNR values with the SA-BiPBF and conventional methods were 34.0 \pm 3.6 and 27.2 \pm 3.4 dB, respectively. From the experiments, it was shown in side-by-side comparisons that the image quality of the SA-BiPBF method was considerably improved in both phantom and in vivo breast images. However, the SA-BiPBF image showed different features compared to the conventional one in the in vivo experiments. These features are resulting from the increased image quality of the SA-BiPBF method but are not always perceived as improvements by the radiologists. [ABSTRACT FROM PUBLISHER]

In medical ultrasound imaging, multi-zone focusing on transmission is used to enhance the lateral resolution at the expense of frame rate. As an alternative, this paper proposes a simultaneous multi-zone focusing method using orthogonal quadratic chirp signals to improve lateral resolution without sacrificing frame rate. In the proposed method, two weighted quadratic chirp signals with different spectra are simultaneously transmitted with different transmit time delays for multi-zone focusing. Because the two weighted quadratic chirps can be designed to have a desired level of cross-correlation after compression, the degradation of axial resolution resulting from the division of a spectrum is minimized. Through simulation, the performances of the proposed method were evaluated and compared with those of two-cycle pulsed excitation as a gold standard and two sub-band weighted linear chirps. In the simulation, the proposed method improved –6-dB and –20-dB lateral beam widths by factors of 1.67 and 1.84, respectively, compared with the pulsed excitation. The degradation of axial resolution in the proposed method was maximally 43% less than that in the linear chirp case. The results demonstrate that the proposed method is useful in the improvement of overall ultrasound image quality because the axial resolution of conventional ultrasound images is generally a few times higher than the lateral resolution. [ABSTRACT FROM PUBLISHER]

Abstract: Effective receive beamforming in medical ultrasound imaging is important for enhancing spatial and contrast resolution. In current ultrasound receive beamforming, a constant sound speed (e.g., 1540m/s) is assumed. However, the variations of sound speed in soft tissues could introduce phase distortions, leading to degradation in spatial and contrast resolution. This degradation becomes even more severe in imaging fatty tissues (e.g., breast) and with obese patients. In this paper, a mean sound speed estimation method where phase variance of radio-frequency channel data in the region of interest is evaluated is presented for improving spatial and contrast resolution. The proposed estimation method was validated by the Field II simulation and the tissue mimicking phantom experiments. In the simulation, the sound speed of the medium was set to 1450m/s and the proposed method was capable of capturing this value correctly. From the phantom experiments, the −18-dB lateral resolution of the point target at 50mm obtained with the estimated mean sound speed was improved by a factor of 1.3, i.e., from 3.9mm to 2.9mm. The proposed estimation method also provides an improvement of 0.4 in the contrast-to-noise ratio, i.e., from 2.4 to 2.8. These results indicate that the proposed mean sound speed estimation method could enhance the spatial and contrast resolution in the medical ultrasound imaging systems. [Copyright &y& Elsevier]

Abstract: Coded excitation can improve the signal-to-noise ratio (SNR) in ultrasound tissue harmonic imaging (THI). However, it could suffer from the increased sidelobe artifact caused by incomplete pulse compression due to the spectral overlap between the fundamental and harmonic components of ultrasound signal after nonlinear propagation in tissues. In this paper, three coded tissue harmonic imaging (CTHI) techniques based on bandpass filtering, power modulation and pulse inversion (i.e., CTHI-BF, CTHI-PM, and CTHI-PI) were evaluated by measuring the peak range sidelobe level (PRSL) with varying frequency bandwidths. From simulation and in vitro studies, the CTHI-PI outperforms the CTHI-BF and CTHI-PM methods in terms of the PRSL, e.g., −43.5dB vs. −24.8dB and −23.0dB, respectively. [Copyright &y& Elsevier]

Point-of-care ultrasound (POCUS), realized by recent developments in portable ultrasound imaging systems for prompt diagnosis and treatment, has become a major tool in accidents or emergencies. Concomitantly, the number of untrained/unskilled staff not familiar with the operation of the ultrasound system for diagnosis is increasing. By providing an imaging guide to assist clinical decisions and support diagnosis, the risk brought by inexperienced users can be managed. Recently, deep learning has been employed to guide users in ultrasound scanning and diagnosis. However, in a cloud-based ultrasonic artificial intelligence system, the use of POCUS is limited due to information security, network integrity, and significant energy consumption. To address this, we propose (1) a structure that simultaneously provides ultrasound imaging and a mobile device-based ultrasound image guide using deep learning, and (2) a reverse scan conversion (RSC) method for building an ultrasound training dataset to increase the accuracy of the deep learning model. Experimental results show that the proposed structure can achieve ultrasound imaging and deep learning simultaneously at a maximum rate of 42.9 frames per second, and that the RSC method improves the image classification accuracy by more than 3%. [ABSTRACT FROM AUTHOR]

Although plane wave imaging (PWI) has been extensively employed for ultrafast ultrasound imaging, its potential for sectorial B-mode imaging with a convex array transducer has not yet been widely recognized. Recently, we reported an optimized PWI approach for sector scanning that exploits the dynamic transmit focusing capability. In this paper, we first report the clinical applicability of the optimized PWI for abdominal ultrasonography by in vivo image and video evaluations and compare it with conventional focusing (CF) and diverging wave imaging (DWI), which is another dynamic transmit focusing technique generally used for sectorial imaging. In vivo images and videos of the liver, kidney, and gallbladder were obtained from 30 healthy volunteers using PWI, DWI, and CF. Three radiologists assessed the phantom images, 156 in vivo images, and 66 in vivo videos. PWI showed significantly enhanced (p < 0.05) spatial resolution, contrast, and noise and artifact reduction, and a 4-fold higher acquisition rate compared to CF and provided similar performances compared to DWI. Because the computations required for PWI are considerably lower than that for DWI, PWI may represent a promising technique for sectorial imaging in abdominal ultrasonography that provides better image quality and eliminates the need for focal depth adjustment. [ABSTRACT FROM AUTHOR]

This paper presents photoacoustic imaging (PAI) for real-time detection of micro-scale calcifications (e.g., <1 mm) in the breast, which are an indicator of the cancer occurrence. Optimal wavelength of incident laser for the microcalcification imaging was ascertained through ex vivo experiments with seven breast specimens of volunteers. In the ex vivo experiments, the maximum amplitude of photoacoustic signals from the microcalcifications occurred when the laser wavelength ranged from 690 to 700 nm. This result demonstrated that PAI can serve as a real-time imaging and guidance tool for diagnosis and biopsy of the breast microcalcifications. [ABSTRACT FROM AUTHOR]

This paper reports the feasibility of Nakagami imaging in monitoring the regeneration process of zebrafish hearts in a noninvasive manner. In addition, spectral Doppler waveforms that are typically used to access the diastolic function were measured to validate the performance of Nakagami imaging. A 30-MHz high-frequency ultrasound array transducer was used to acquire backscattered echo signal for spectral Doppler and Nakagami imaging. The performances of both methods were validated with flow and tissue-mimicking phantom experiments. For in vivo experiments, both spectral Doppler and Nakagami imaging were simultaneously obtained from adult zebrafish with amputated hearts. Longitudinal measurements were performed for five zebrafish. From the experiments, the E/A ratio measured using spectral Doppler imaging increased at 3 days post-amputation (3 dpa) and then decreased to the value before amputation, which were consistent with previous studies. Similar results were obtained from the Nakagami imaging where the Nakagami parameter value increased at 3 dpa and decreased to its original value. These results suggested that the Nakagami and spectral Doppler imaging would be useful techniques in monitoring the regeneration of heart or tissues. [ABSTRACT FROM AUTHOR]

Software-based ultrasound imaging systems provide high flexibility that allows easy and fast adoption of newly developed algorithms. However, the extremely high data rate required for data transfer from sensors (e.g., transducers) to the ultrasound imaging systems is a major bottleneck in the software-based architecture, especially in the context of real-time imaging. To overcome this limitation, in this paper, we present a Binary cLuster (BL) code, which yields an improved compression ratio compared to the exponential Golomb code. Owing to the real-time encoding/decoding features without overheads, the universal code is a good solution to reduce the data transfer rate for software-based ultrasound imaging. The performance of the proposed method was evaluated using in vitro and in vivo data sets. It was demonstrated that the BL-beta code has a good stable lossless compression performance of 20%~30% while requiring no auxiliary memory or storage. [ABSTRACT FROM AUTHOR]

A commonly used phase rotation beamforming (PRBF) technique in medical ultrasound scanners requires four multipliers to realise phase rotation (PR) in addition to two lowpass filters for quadrature demodulation for each channel. A new scheme is presented to reduce the computational complexity of PRBF without sacrificing image quality that uses only 16 PRs located behind inter‐channel adders, regardless of the number of channels, each of which is dedicated for one of 16 quantised PR values using a step size of 2π/16. [ABSTRACT FROM AUTHOR]

Precise sentinel lymph node (SLN) identification is crucial not only for accurate diagnosis of micro-metastases at an early stage of cancer progression but also for reducing the number of SLN biopsies (SLNB) to minimize their severe side effects. Furthermore, it is desirable that an SLNB guidance should be as safe as possible in routine clinical use. Although there are currently various SLNB guidance methods for pre-operative or intra-operative assessment, none are ideal. We propose a real-time SLNB guidance method using contrast-enhanced tri-modal images (i.e., ultrasound, photoacoustic, and fluorescence) acquired by a recently developed hand-held tri-modal probe. The major advantage of tri-modal imaging is demonstrated here through an in vivo study of the technically-difficult case of nodal obstruction that frequently leads to false-negative results in patients. The results in a tumor model in rabbits and normal controls showed that tri-modal imaging is capable of clearly identifying obstructed SLNs and of indicating their metastatic involvement. Based on these findings, we propose an SLNB protocol to help surgeons take full advantage of the complementary information obtained from tri-modal imaging, including for pre-operative localization, intra-operative biopsy guidance and post-operative analysis. [ABSTRACT FROM AUTHOR]

Coded excitation can improve the SNR in medical ultrasound imaging. In coded excitation, pulse compression is applied to compress the elongated coded signals into a short pulse, which typically requires high computational complexity, i.e., a compression filter with a few hundred coefficients. In this paper, we propose an efficient pulse compression method of chirp-coded excitation, in which the pulse compression is conducted with complex baseband data after downsampling, to lower the computational complexity. In the proposed method, although compression is conducted with the complex data, the L-fold downsampling is applied for reducing both data rates and the number of compression filter coefficients; thus, total computational complexity is reduced to the order of 1/L2. The proposed method was evaluated with simulation and phantom experiments. From the simulation and experiment results, the proposed pulse compression method produced similar axial resolution compared with the conventional pulse compression method with negligible errors, i.e., ≫36 dB in signal-to-error ratio (SER). These results indicate that the proposed method can maintain the performance of pulse compression of chirpcoded excitation while substantially reducing computational complexity. [ABSTRACT FROM AUTHOR]

In ultrasound exams of obese patients and the breast, the spatial and contrast resolutions of ultrasound images are severely deteriorated when a constant sound speed corresponding to soft tissue is used in receive dynamic beamformation. This degradation is due to the defocusing of the ultrasound beam because of the disparity in sound speed between soft tissue and fatty layers. To minimize the degradation, this paper proposes a new method of estimating an optimal sound speed that can be used to achieve the best beamforming performance in a region of interest (ROI). The proposed method employs a new focusing quality factor (FQF) as an indicator of how well the focusing is conducted with a given sound speed. The FQF is closely associated with the degree of edge conspicuity, which can be obtained using the proposed modified nonlinear anisotropic diffusion (MNAD) technique. To calculate FQF, ultrasound images are formed with different sound speeds ranging from 1400 to 1600 m/s and, subsequently, the ROI is chosen. In the ROI, the degrees of edge conspicuity (i.e., FQF) are calculated. The sound speed can be considered an optimal one for the ROI if it is used to construct the image that provides the maximum FQF. The performances of the proposed method were evaluated through simulation and in vitro experiments with a tissue-mimicking phantom. The performance was also compared with that of the conventional image-based method employed in a commercial ultrasound imaging system. The experimental results demonstrated that the proposed method is capable of estimating an optimal sound speed with an error of 10 m/s regardless of whether strong targets are included in the ROI or not. On the other hand, the conventional image-based method generated an estimation error of 60 m/s maximally in the case in which there were no strong targets in ROI. This indicates that the proposed method is a useful tool to improve ultrasound image quality for clinical applications, especially for ultrasound exams of obese patients and the breast. [ABSTRACT FROM PUBLISHER]

In this paper, a new compounded direct pixel beamforming (CDPB) method is presented to remove blurring artifacts introduced by ultrasound scan conversion. In CDPB, receive focusing is directly performed on each display pixel in Cartesian coordinates using the raw RF data from adjacent transmit firings so that artifacts from the scan conversion can be removed. In addition, the energy variations resulting from the distance between the transmit scanline and display pixel are compensated by utilizing the gain factor obtained from the ultrasound beam pattern. The proposed CDPB method was evaluated using simulation and in vivo liver data acquired by a commercial ultrasound machine equipped with a research package. The experimental results showed that the proposed CDPB method improved the information entropy contrast (IEC) by 23.6% compared with the conventional scan conversion method and it reduced the blocking artifacts factor (BAF) by 16.4% over the direct pixel-based focusing method. These results indicate the proposed new direct pixel beamforming method could be used to enhance image quality in medical ultrasound imaging. [ABSTRACT FROM PUBLISHER]