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Guo D.,Sichuan University | Guo D.,Neijiang Vocational and Technical College | Liu P.,Sichuan University | She Y.,Saset Healthcare | And 3 more authors.
Electronics Letters | Year: 2013

In practical ultrasonic images, post-processing that involves incoherent frame averaging such as persistence, spatial compounding and frequency compounding creates a layer of smoothed out electronic noise that is analogous to fog in photographic images. A novel approach to enhance ultrasound image contrast based on a modified dark channel model used to dehaze photographs is presented. Local minimum intensity is used to highlight image contrast, control influence of noise layer and improve detail resolution by different levels. The experimental results show that the proposed method has better performance over the existing methods in improving the quality of the ultrasonic image. © The Institution of Engineering and Technology 2013.


Shao D.,Sichuan University | Liu P.,Saset Healthcare | Liu D.C.,Sichuan University
ICIC Express Letters, Part B: Applications | Year: 2012

Ultrasound images show a granular pattern of noise known as speckle which diminishes its quality and results in difficulties in diagnosis. In order to reduce the speckle noise, this paper presents an adaptive iterative bilateral filtering adjusted by the detection of speckle statistics (AIBF). The criterion of speckle region is defined from a similarity value obtained from local characteristic matching between the ratios of the variance to the mean in the processing window and a reference ratio derived from a speckle area. The proposed algorithm can reduce the speckle noise and, at the same time, maintain the tissue structure. Ultrasound phantom testing and in vivo imaging show that the proposed method can improve the quality of an ultrasound image in terms of tissue SNR and CNR values. © 2012 ISSN 2185-2766.


Zhang Z.-H.,Sichuan University | Liu H.-L.,Sichuan University | He Y.-N.,Sichuan University | Liu D.-Q.,Sichuan University | Liu D.-Q.,Saset Healthcare
Journal of Central South University | Year: 2014

To improve the quality of ultrasonic elastography, by taking the advantage of code excitation and frequency compounding, a transmitting-side multi-frequency with coded excitation for elastography (TFCCE) was proposed. TFCCE adopts the chirp signal excitation scheme and strikes a balance in the selection of sub-signal bandwidth, the bandwidth overlap and the number of sub-strain image based on theoretical derivation, so as to further improve the quality of elastic image. Experiments have proved that, compared with the other optimizing methods, the elastographyic signal-to-niose ratio(R e-SN) and contrast-to-noise ratio(R e-CN) are improved significantly with different echo signal-to-noise ratios (R eSN) and attenuation coefficients. When R eSN is 50 dB, compared with short pulse, R e-SN and R e-CN obtained by TFCCE increase by 53% and 143%, respectively. Moreover, in a deeper investigation (85-95 mm), the image has lower strain noise and clear details. When the attenuation coefficient is in the range of 0-1 dB/(cm·MHz), R e-SN and R e-CN obtained by TFCCE can be kept in moderate ranges of 5


Liu P.,Sichuan University | Liu P.,Saset Healthcare | Liu D.,Sichuan University | Liu D.,Saset Healthcare
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2016

We propose a time-domain delay estimator that takes the slope of the best fit line crossing the origin in the instantaneous frequency-phase difference plane as the delay estimate. This formulation differs from existing phase-based estimators in two respects. First, we find the instantaneous frequency at all individual sample points, including large and abrupt spikes caused by destructive interference in the coherent scattering process. This differs from Loupas which finds a smoothed-out center frequency estimate within an observation window. We show that under high signal-to-noise ratio (SNR), the information from these spikes can be properly used. Second, we show that error ought to be considered as the deviation of the phase difference from the best fit line rather than deviation from the averaged phase difference. Without considering instantaneous frequency, phase-based estimators make the following two errors: samples with phase difference far away from the center frequency need not be errors as they naturally have large phase difference when their instantaneous frequency is large; samples with phase difference close to the center frequency may in fact be errors if their instantaneous frequency is large. We derive the Gauss-Markov least-squares best fit line and then propose an iterative variant that removes samples from the line-fitting process if its deviation from the best fit line is sufficiently large. The iterative version can reduce the effect of aliasing for larger delays and also further reduce the root-mean-square error (RMSE) of the estimate. Simulation studies using various bandwidth, SNR, and delay parameters indicate that iterative phase least squares (PLS) begins to outperform correlation phase Loupas at between SNR of 30 dB (for larger bandwidths and larger delays) and 60 dB (for smaller bandwidths and smaller delays). As SNR increases, iterative PLS can reach a 30- to 50-dB increase in performance over correlation phase Loupas with respect to RMSE in the most favorable conditions. © 2016 IEEE.


Liu P.,Saset Healthcare | Liu D.,Saset Healthcare | Liu D.,Sichuan University
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2011

Ultrasonic wave interference produces local fluctuations in both the envelope, known as speckle, and phase of echoes. Furthermore, such fluctuations are correlated in space, and subsequent motion estimation from the envelope and/or phase signal produces patterned, correlated errors. Compounding, or combining information from multiple decorrelated looks, reduces such effects. We propose using a filter bank to create multiple looks to produce a compounded motion estimate. In particular, filtering in the lateral direction is shown to preserve delay estimation accuracy in the filtered sub-bands while creating decorrelation between sub-bands at the expense of some lateral resolution. For Gaussian apodization, we explicitly compute the induced signal decorrelation produced by Gabor filters. Furthermore, it is shown that lateral filtering is approximately equivalent to steering, in which filtered sub-bands correspond to signals extracted from shifted sub-apertures. Field II simulation of a point spread function verifies this claim. We use phase zero and its variants as displacement estimators for our compounded result. A simplified deformation model is used to provide computer simulations of deforming an elastic phantom. Simulations demonstrate root mean square error (RMSE) reduction in both displacement and strain of the compounded result over conventional and its laterally blurred versions. Then we apply the methods to experimental data using a commercial elastic phantom, demonstrating an improvement in strain SNR. © 2011 IEEE.


Liu W.,Sichuan University | Cheng Y.,General Electric | Liu D.C.,Sichuan University | Liu D.C.,Saset Healthcare
Bio-Medical Materials and Engineering | Year: 2014

Veterinary ultrasound has been used in a large number of animal husbandry-related circumstances while many corresponding applications also call for the use of ultrasound in human patients. However, veterinary ultrasound images are affected by speckle, an interference pattern that can reduce the quality and contrast of ultrasound images. In this paper, a filter-based receive-side spatial compounding technique for veterinary ultrasound B-Mode imaging is used to create a compounded veterinary B-Mode image based on multiple looks. In particular, filtering in the lateral direction has been proved to be able to preserve the axial information in the sub-bands and to create decorrelation between sub-bands at the expense of some lateral resolution. A new method was proposed to obtain B-Mode IQ data by special veterinary ultrasonic probe. This approach is tested on 275 in-vivo swine. The effect is accomplished in real-time veterinary ultrasonic imaging with a measurable improvement of SNRe. Meanwhile, the speckle and electronic noise in the compounded image have been greatly reduced and smoothed in the visual result. © 2014 - IOS Press and the authors. All rights reserved.


Zhang K.,Sichuan University | Liu D.C.,Sichuan University | Liu P.,Saset Healthcare
2010 4th International Conference on Bioinformatics and Biomedical Engineering, iCBBE 2010 | Year: 2010

Ultrasound elastography has been well applied in medical detection as a tool to aid diagnosis. However, in conventional ultrasound elastograms, there are patterned artifacts from non-white estimation errors. In this paper, we investigate spatial angular compounding methods to reduce the errors. The method involves averaging ultrasound angular elastograms around the same region-of-interest but from different angle views. N decorrelated sub-elastograms are weighted averaged to produce the compounded elastrogram. For our experiments, we use 3 different angled elastograms calculated from alternating frames with different steering angles obtained from base-band data captured by the iMago c21. We present results from a commercial elastic phantom showing improvement in the elastogram's quality parameters such as SNR and CNR. © 2010 IEEE.


Liu P.,University of Sichuan | Liu D.,Saset Healthcare
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2013

Duplex and triplex transmit patterns that involve gaps in the spectrum Doppler samples allow pulse repetition frequency increases and/or frame rate increases that cannot be flexibly achieved by conventional uniformly sampled transmit schemes. We make two claims in this paper. First, previously reported nonparametric gapped sampled spectrum estimators are technically feasible for handling the duplex and triplex transmit patterns found in common medical ultrasound applications. Second, such estimators that coherently average within an axial/temporal 2-D window have superior SNR compared with their incoherent counterparts. Moreover, this fact extends to previously reported fully sampled incoherent estimators, which can be improved by using their coherent version. We verify the methods by steady-state flow phantom experiments and in vivo examples of the left clavicular artery and the ascending aorta. For the flow phantom experiments, we use the three quantitative metrics of SNR, root mean square error, and zero frequency peak full-width at half-maximum to evaluate robustness and resolution. Results indicate that through proper parameters, periodically gapped estimators can produce results similar to their fully sampled counterparts. Fourier synthesis of the spectral estimates produces the fully sampled time-domain audio signal, and we give stereo audio examples for the clavicular artery. © 1986-2012 IEEE.


PubMed | Saset Healthcare
Type: Journal Article | Journal: IEEE transactions on ultrasonics, ferroelectrics, and frequency control | Year: 2011

Ultrasonic wave interference produces local fluctuations in both the envelope, known as speckle, and phase of echoes. Furthermore, such fluctuations are correlated in space, and subsequent motion estimation from the envelope and/or phase signal produces patterned, correlated errors. Compounding, or combining information from multiple decorrelated looks, reduces such effects. We propose using a filter bank to create multiple looks to produce a compounded motion estimate. In particular, filtering in the lateral direction is shown to preserve delay estimation accuracy in the filtered sub-bands while creating decorrelation between sub-bands at the expense of some lateral resolution. For Gaussian apodization, we explicitly compute the induced signal decorrelation produced by Gabor filters. Furthermore, it is shown that lateral filtering is approximately equivalent to steering, in which filtered sub-bands correspond to signals extracted from shifted sub-apertures. Field II simulation of a point spread function verifies this claim. We use phase zero and its variants as displacement estimators for our compounded result. A simplified deformation model is used to provide computer simulations of deforming an elastic phantom. Simulations demonstrate root mean square error (RMSE) reduction in both displacement and strain of the compounded result over conventional and its laterally blurred versions. Then we apply the methods to experimental data using a commercial elastic phantom, demonstrating an improvement in strain SNR.

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