Time filter

Source Type

Cayman Islands

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. Source

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 Source

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. Source

Liu H.,Sichuan University | Zhang Z.,Changsha College | Liu W.,Sichuan University | Liu D.C.,Sichuan University | Liu D.C.,Saset Healthcare
Journal of Medical Imaging and Health Informatics | Year: 2014

Veterinary ultrasound is primarily used for diagnosing animal disease and pregnancy as well as assessing the quality of animal husbandry, such as the intramuscular fat content of beef and pork (Intramuscular Fat, IMF). However, speckle noise proves to be problematic for veterinary ultrasound images, which in turn affects the image analysis and medical diagnostics. Furthermore, the veterinary ultrasound equipment is relatively simple: the number of probe array elements is few, and the available bandwidth is small. Thus, the veterinary ultrasound imaging process is more easily affected by speckle noise, including a poor image resolution and low SNR. In particular, it has been proven that filtering in the lateral direction can preserve the axial information in the sub-bands and create decorrelation between the sub-bands at the expense of some of the lateral resolution. In this paper, the incorporation of various filter numbers is studied using the Gabor filter-bank with three, five, seven and nine filters. This approach is then tested on 275 live pigs. The experimental results have indicated that the more the image is filtered, the higher the image's SNR. Furthermore, the speckle in the compounded image was greatly reduced and was smoother in the final visual result. © 2014 American Scientific Publishers All rights reserved. Source

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. Source

Discover hidden collaborations