共查询到20条相似文献,搜索用时 339 毫秒
1.
Phukpattaranont P Ebbini ES 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(8):987-1001
We present a new algorithm for deriving a second-order Volterra filter (SVF) capable of separating linear and quadratic components from echo signals. Images based on the quadratic components are shown to provide contrast enhancement between tissue and ultrasound contrast agents (UCAs) without loss in spatial resolution. It is also shown that the quadratic images preserve the low scattering regions due to their high dynamic range when compared with standard B-mode or harmonic images. A robust algorithm for deriving the filter has been developed and tested on real-time imaging data from contrast and tissue-mimicking media. Illustrative examples from image targets containing contrast agent and tissue-mimicking media are presented and discussed. Quantitative assessment of the contrast enhancement is performed on both the RF data and the envelope-detected log-compressed image data. It is shown that the quadratic images offer levels of enhancement comparable or exceeding those from harmonic filters while maintaining the visibility of low scattering regions of the image. 相似文献
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Steel R Thompson RS Macaskill C 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2006,53(5):991-1000
In B-mode ultrasound images, the speckle distal to the edges of cavities of contrasting speed of sound (SOS) can be imprinted with a pattern characteristic of the cavity. This pattern, termed edge shadowing, is likely to involve alteration of both the speckle amplitude and its correlation length. Using the acoustic field calculated from the exact solution to the wave equation, we have simulated the ensemble-averaged speckle amplitude in B-mode images of cylindrical cavities both with and without walls, and compared the results to a simpler ray-based model. The simulations show that edge shadowing is caused predominantly by contrasts of the SOS, rather than of the density. The shadows on both walled and wall-less cylinders, for a focused incident beam, grow darker as the magnitude of the SOS contrast increases over a range up to +/- 10%. Extra shadows, caused by the inner wall boundary, appear on images of walled cylinders. The ray-based model agrees well with the wave model except in the shadow regions, within which the complexity of the phenomena seems to require the wave model. 相似文献
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Dantas RG Costa ET 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(3):530-538
B-mode ultrasound images are characterized by speckle artifact, which may make the interpretation of images difficult. One widely used method for ultrasound speckle reduction is the split spectrum processing (SSP), but the use of one-dimensional (1-D), narrow-band filters makes the resultant image experience a significant resolution loss. In order to overcome this critical drawback, we propose a novel method for speckle reduction in ultrasound medical imaging, which uses a bank of wideband 2-D directive filters, based on modified Gabor functions. Each filter is applied to the 2-D radio-frequency (RF) data, resulting in a B-mode image filtered in a given direction. The compounding of the filters outputs give rise to a final image in which speckle is reduced and the structure is enhanced. We have denoted this method as directive filtering (DF). Because the proposed filters have effectively the same bandwidth as the original image, it is possible to avoid the resolution loss caused by the use of narrow-band filters, as with SSP. The tests were carried out with both simulated and real clinical data. Using the signal-to-noise ratio (SNR) to quantify the amount of speckle of the ultrasound images, we have achieved an average SNR enhancement of 2.26 times with simulated data and 1.18 times with real clinical data. 相似文献
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Fringe-visibility issues of additive-subtractive phase-modulated (ASPM) electronic speckle pattern interferometry (ESPI) are explored. ASPM ESPI is a three-step method in which additive-speckle images are acquired rapidly in an analog fashion in every frame of a video sequence, a speckle phase modulation is intentionally introduced between frames, and a digital subtraction of consecutive pairs of additive-speckle images is performed. We show that this scheme has the good high-frequency noise immunity associated with additive-ESPI techniques as well as the good fringe visibility associated with subtractive-ESPI techniques. The method has better fringe visibility than can be obtained with purely additive ESPI and also does not suffer from the fringe distortions that can occur with subtractive ESPI in the presence of high-frequency noise. We show that even if full speckle decorrelation were to occur between the two additive speckle images that are to be subtracted, the visibility of ASPM ESPI fringes can be made to approach unity by suitable adjustment of the reference-to-object beam-intensity ratio. 相似文献
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Hokland J.H. Kelly P.A. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(4):660-669
Observed medical ultrasound images are degraded representations of the true tissue reflectance. The specular reflections at boundaries between regions of different tissue types are blurred, and the diffuse scattering within such regions also contains speckle. This reduces the diagnostic value of such images. In order to remove both blur and speckle, the authors develop a maximum a posteriori deconvolution algorithm for two-dimensional (2-D) ultrasound radio frequency (RF) images based on a new Markov random field image model incorporating spatial smoothness constraints and physical models for specular reflections and diffuse scattering. During stochastic relaxation, the algorithm alternates steps of restoration and segmentation, and includes estimation of reflectance parameters. The smoothness constraints regularize the overall procedure, and the algorithm uses the specular reflection model to locate region boundaries. The resulting restorations of some simulated and real RF images are significantly better than those produced by Wiener filtering 相似文献
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Ahn C Jung Y Kwon O Seo J 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2011,58(8):1577-1589
Segmentation of a target object in the form of a closed curve has many potential applications in medical imaging because it provides quantitative information related to the target objext's size and shape. However, ultrasound image segmentation for boundary delineation of the target object is a very difficult task because of its inherent drawbacks, including uncertainty of the segmentation boundary caused by speckle noise, relatively low SNR, and low contrast. Indeed, in automatic ultrasound image segmentation, conventional techniques with standard regularization often fail to reach the desired segmentation in the form of a simple closed curve because of the weakness of edge detector functions in finding the likely target boundary. In this paper, we propose a new regularization model which has the property of encouraging a closed curve by deliberately controlling the curve smoothness. The new model may be combined with various fitting terms to enhance segmentation results. The key features of the proposed model are demonstrated in detail. Numerical simulations and experiments show that the proposed model enhances the segmentation ability for extracting the target boundary as a closed contour. 相似文献
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Ghoshal G Oelze ML 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2010,57(12):2828-2832
Quantitative ultrasound (QUS) techniques have been widely used to estimate the size, shape and mechanical properties of tissue microstructure for specified regions of interest (ROIs). For conventional methods, an ROI size of 4 to 5 beamwidths laterally and 15 to 20 spatial pulse lengths axially has been suggested to estimate accuracy and precision better than 10% and 5%, respectively. A new method is developed to decrease the standard deviation of the quantitative ultrasound parameter estimate in terms of effective scatterer diameter (ESD) for small ROIs. The new method yielded estimates of the ESD within 10% of actual values at an ROI size of five spatial pulse lengths axially by two beamwidths laterally, and the estimates from all the ROIs had a standard deviation of 15% of the mean value. Such accuracy and precision cannot be achieved using conventional techniques with similar ROI sizes. 相似文献
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Hsu SJ Fahey BJ Dumont DM Wolf PD Trahey GE 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(5):996-1009
Intracardiac echocardiography (ICE) has been demonstrated to be an effective imaging modality for the guidance of several cardiac procedures, including radiofrequency ablation (RFA). However, assessing lesion size during the ablation with conventional ultrasound has been limited, as the associated changes within the B-mode images often are subtle. Acoustic radiation force impulse (ARFI) imaging is a promising modality to monitor RFAs as it is capable of visualizing variations in local stiffnesses within the myocardium. We demonstrate ARFI imaging with an intracardiac probe that creates higher quality images of the developing lesion. We evaluated the performance of an ICE probe with ARFI imaging in monitoring RFAs. The intracardiac probe was used to create high contrast, high resolution ARFI images of a tissue-mimicking phantom containing stiffer spherical inclusions. The probe also was used to examine an excised segment of an ovine right ventricle with a RFA-created surface lesion. Although the lesion was not visible in conventional B-mode images, the ARFI images were able to show the boundaries between the lesion and the surrounding tissue. ARFI imaging with an intracardiac probe then was used to monitor cardiac ablations in vivo. RFAs were performed within the right atrium of an ovine heart, and B-mode and ARFI imaging with the intracardiac probe was used to monitor the developing lesions. Although there was little indication of a developing lesion within the B-mode images, the corresponding ARFI images displayed regions around the ablation site that displaced less. 相似文献
11.
Strain compounding: a new approach for speckle reduction 总被引:1,自引:0,他引:1
Li PC Chen MJ 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(1):39-46
A new compounding technique for reducing speckle brightness variations is proposed. This method exploits the decorrelation between signals under different strain states. The different strain states can be created using externally applied forces such as the ones used in sonoelastography. Such forces produce three-dimensional tissue motion. By correcting only the in-plane (i.e., axial and lateral) motion, the images under different strain states have similar characteristics except for speckle appearance caused by the uncorrected out-of-plane (i.e., elevational) motion. Additional speckle decorrelation is also introduced through tissue motion correction caused by the change of effective in-plane sample volume geometry. Therefore, these images can be combined for speckle reduction with less degradation in in-plane spatial resolution than conventional approaches. In this paper, three-dimensional tissue motion under various strain conditions were simulated. It was found that significant speckle decorrelation existed at strains achievable in some clinical situations. Experiments were also conducted to test efficacy of this approach. Pulse-echo data from a gelatin-based phantom were acquired using a 5-MHz, single crystal transducer, and both conventional and compound B-mode images were formed. Results indicated that speckle brightness variations were reduced, and detectability of low contrast objects was enhanced. Performance limitations and fundamental differences between the proposed technique and existing techniques are discussed 相似文献
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Angel L Tebaldi M Bolognini N Trivi M 《Journal of the Optical Society of America. A, Optics, image science, and vision》2000,17(1):107-119
The use of different multiple-aperture pupils for recording each image in speckle photography is proposed. The introduction of suitable spatial frequency carriers, by internally modulating imaged speckles, allows one to selectively isolate or combine the spectral content of different images into spatially separated regions in the Fourier plane. Theoretical and experimental results extend the speckle photography technique to the depiction of several specklegrams of multiple uniform in-plane displacements. In this case, because different pupils are considered for recording, the cross-correlation functions for the amplitudes and intensities in the image plane are calculated on the basis of the statistical properties of the object. Also, the ensemble-average intensity in the Fourier plane is analytically derived, and fringe visibility is investigated. 相似文献
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Rogowska J Bryant CM Brezinski ME 《Journal of the Optical Society of America. A, Optics, image science, and vision》2003,20(2):357-367
We describe a new semiautomatic image processing method for detecting the cartilage boundaries in optical coherence tomography (OCT). In particular, we focus on rabbit cartilage since this is an important animal model for testing both chondroprotective agents and cartilage repair techniques. The novel boundary-detection system presented here consists of (1) an adaptive filtering technique for image enhancement and speckle reduction, (2) edge detection, and (3) edge linking by graph searching. The procedure requires several steps and can be automated. The quantitative measurements of cartilage thickness on OCT images correlated well with measurements from histology. 相似文献
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N. M. Ganzherli Yu. N. Denisyuk A. P. Serdobintseva D. F. Chernykh 《Technical Physics Letters》2006,32(6):542-544
It is experimentally demonstrated that a speckle screen based on a reference-free volume hologram is capable of concentrating light in the visibility zone. Holographic speckle screens for the projection of images were formed in a bulk photosensitive material based on glycerol-containing dichromated gelatin (DCG). With such screens formed using radiation with a wavelength (0.442 nm) in the spectral range of DCG photosensitivity, it is possible to obtain high-quality image projections using both coherent radiation with a different wavelength and white light. The projection properties of speckle screens were studied, and their ability to concentrate light in the visibility zone was confirmed. 相似文献
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Yoon C Seo H Lee Y Yoo Y Song TK Chang JH 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2012,59(5):905-914
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. 相似文献
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Dahl J Jakovljevic M Pinton GF Trahey GE 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2012,59(4):648-659
We introduce a harmonic version of the short-lag spatial coherence (SLSC) imaging technique, called harmonic spatial coherence imaging (HSCI). The method is based on the coherence of the second-harmonic backscatter. Because the same signals that are used to construct harmonic B-mode images are also used to construct HSCI images, the benefits obtained with harmonic imaging are also obtained with HSCI. Harmonic imaging has been the primary tool for suppressing clutter in diagnostic ultrasound imaging, however secondharmonic echoes are not necessarily immune to the effects of clutter. HSCI and SLSC imaging are less sensitive to clutter because clutter has low spatial coherence. HSCI shows favorable imaging characteristics such as improved contrast-to-noise ratio (CNR), improved speckle SNR, and better delineation of borders and other structures compared with fundamental and harmonic B-mode imaging. CNRs of up to 1.9 were obtained from in vivo imaging of human cardiac tissue with HSCI, compared with 0.6, 0.9, and 1.5 in fundamental B-mode, harmonic B-mode, and SLSC imaging, respectively. In vivo experiments in human liver tissue demonstrated SNRs of up to 3.4 for HSCI compared with 1.9 for harmonic B-mode. Nonlinear simulations of a heart chamber model were consistent with the in vivo experiments. 相似文献
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Ozcan A Bilenca A Desjardins AE Bouma BE Tearney GJ 《Journal of the Optical Society of America. A, Optics, image science, and vision》2007,24(7):1901-1910
Speckle noise is a ubiquitous artifact that limits the interpretation of optical coherence tomography images. Here we apply various speckle-reduction digital filters to optical coherence tomography images and compare their performance. Our results indicate that shift-invariant, nonorthogonal wavelet-transform-based filters together with enhanced Lee and adaptive Wiener filters can significantly reduce speckle and increase the signal-to-noise ratio, while preserving strong edges. The speckle reduction capabilities of these filters are also compared with speckle reduction from incoherent angular compounding. Our results suggest that by using these digital filters, the number of individual angles required to attain a certain level of speckle reduction can be decreased. 相似文献
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Galloway RL McDermott BA Thurstone FL 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1988,35(1):45-49
A pair of concurrent real-time B-mode image lines has been formed using a parallel processing system. In this system a wideband received echo is partitioned by a frequency diversity process and separate image lines are formed. Due to their differing constituent frequencies, these image lines have decorrelated speckle patterns. Upon averaging these filtered lines, the amount of speckle in the resultant displayed image is reduced. The reduction in image speckle and its accompanying improvement in perceived resolution is accomplished with no sacrifice of temporal resolution or real-time format. The effects of filter separation and filter quality factor (Q) are investigated through statistical analysis of images containing speckle-producing targets. A measurable improvement in image signal-to-noise ratio has been achieved. 相似文献