共查询到20条相似文献,搜索用时 171 毫秒
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Phase aberration correction in medical ultrasound using speckle brightness as a quality factor 总被引:1,自引:0,他引:1
Medical ultrasonic images are degraded by tissues with inhomogeneous acoustic velocities. The resulting phase aberration raises the off-peak response of the imaging system's point spread function (PSF), decreasing dynamic range. In extreme cases, multiple images of a single target are displayed. Phase aberration may become a limiting factor to image quality as ultrasonic frequency and aperture size are increased in order to improve spatial resolution. A method is proposed to correct for unknown phase aberration, which uses speckle brightness as a quality factor. The phase delays of a phased array transducer are modified, element by element, to maximize mean speckle brightness in a region of interest. The technique proposed is analogous to the correction technique used by Muller and Buffington [J. Opt. Soc. Am. 64 (9), 1200-1209 (1974)] to adaptively focus incoherent optical telescopes. The method is demonstrated using a computer model with several different simulated aberration profiles. With this model, mean speckle brightness is calculated using the two-dimensional PSF. Experiments have also been conducted in which speckle brightness is shown to increase as the phase delays of an ultrasonic scanner are modified in order to compensate for a rippled aberrating layer made of silicone rubber. The characteristics of the proposed method, and the possibility of employing it clinically to correct for unknown inhomogeneities in acoustic velocity, are discussed. 相似文献
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Bloemhof EE 《Optics letters》2004,29(2):159-161
Ground-based optical searches for faint stellar or planetary companions about other stars may be limited by speckle noise, which is the rapid intensity fluctuations that are due to motions of remnant atmospheric speckles. Adaptive optics (AO) can reduce residual wave-front phase errors to low values, substantially reducing the unwanted power in the speckle halo. At high correction, however, the noise in the halo will be dominated by anomalously bright "pinned" speckles that have a number of unusual properties. They can have negative intensities and will appear in spatially antisymmetric patterns; they are spatially pinned to Airy rings and have zero mean in a sufficiently long integration. Some of these properties may be used to reduce the unanticipated effect of pinned speckles on companion searches, depending on details of the AO system. But, in short exposures, pinned speckles dominate speckle noise over much of the inner halo for Strehl ratios S as low as 0.6 and over much of the outer halo too as Strehl and deformable-mirror actuator densities increase. I show that these anomalously bright pinned speckles are not included in the traditional expression for speckle power in an image, (1 - S), on which sensitivity estimates of future high-performance AO systems have been based. 相似文献
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We consider quantum error correction of quantum noise that is created by a local interaction of qubits with a common bosonic bath. The possible exchange of bath bosons between qubits gives rise to spatial and temporal correlations in the noise. We find that these kinds of noise correlations have a strong negative impact on quantum error correction. 相似文献
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Minimizing the effect of noise is essential for quantum computers. The conventional method to protect qubits against noise is through quantum error correction. However, for current quantum hardware in the so-called noisy intermediate-scale quantum (NISQ) era, noise presents in these systems and is too high for error correction to be beneficial. Quantum error mitigation is a set of alternative methods for minimizing errors, including error extrapolation, probabilistic error cancellation, measurement error mitigation, subspace expansion, symmetry verification, virtual distillation, etc. The requirement for these methods is usually less demanding than error correction. Quantum error mitigation is a promising way of reducing errors on NISQ quantum computers. This paper gives a comprehensive introduction to quantum error mitigation. The state-of-art error mitigation methods are covered and formulated in a general form, which provides a basis for comparing, combining and optimizing different methods in future work. 相似文献
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HOU Tao WANG Yuanyuan GUO Yi 《声学学报:英文版》2011,(4):379-390
In view of inherent speckle noise in medical images,a speckle reduction method was proposed based on an expectation-maximization(EM) framework.First,the real component of the in-phase/quadrature(I/Q) ultrasound image is extracted.Then,it is used to blindly estimate the point spread function(PSF) of the imaging system.Finally,based on the EM framework,an iterative algorithm alternating between the Wiener Filter and the anisotropic diffusion(AD) is exploited to produce despeckled images.The comparison experiment is carried out on both simulated and in vivo ultrasound images.It is shown that,with respect to the I/Q image,the proposed method averagely improves the speckle-signal-to-noise ratio(S-SNR) and the edge preservation index(β) of images by the factor of 1.94 and 7.52.Meanwhile,it averagely reduces the normalized mean-squared error(NMSE) by the factor of 3.95.The simulation and in vivo results indicates that the proposed method has a better overall performance than exited ones. 相似文献
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Phase diversity speckle (PDS) is an image restoration technique which is based on the idea of phase diversity (PD). It uses multi-frame short-exposure image sequence to calculate their corresponding wave-front information. Each image pair consists of two images collected by two cameras at the same time with one in focus and the other with known defocus value. Multi-frame processing can significantly improve the target signal to noise ratio, and decrease noise influence. In this paper, based on the principle of pupil Fourier imaging, by adjusting the pupil size, we get different scales of the optical point spread function (PSF). Also, we analysis different camera noise distribution channels, location differences and other factors to optimize the objective evaluation function, and this can reduce the computational complexity and improve the processing speed of image restoration. In the indoor environment, we build optical platform, and use multi-frame phase diversity speckle to make experiment under different turbulence conditions. The experimental results show that the image restoration effect of the proposed method is close to the diffraction limit. 相似文献
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分析了微型激光投影引擎的两种主要光学噪音|干涉网格和激光散斑产生的基理|提出采用振动的随机位相板同时实现干涉网格和激光散斑抑制的方法并进行了理论分析|自行设计了微型激光投影引擎,利用微型电控马达带动随机位相板振动,用CCD相机在不同的F#及曝光时间下对投影图像进行了采集,并对图像的散斑对比度行了测试.结果表明,通过静止的随机位相板可以很好地抑制干涉网格噪音|通过使随机位相板以大于视觉暂留效应形成的融合频率进行振动,可以同时抑制干涉网格和激光散斑,使得散斑对比度小于5%,达到投影观察的要求. 相似文献
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噪声是影响激光相干场高分辨成像系统像质的重要因素,激光相干场成像系统既受背景光加性噪声影响,又受激光乘性散斑噪声影响.为解决激光相干场成像系统受激光乘性散斑噪声和背景光加性噪声叠加引起的成像像质退化效应问题,从噪声抑制角度提高激光相干场系统高分辨成像像质,研究建立了激光散斑乘性噪声和背景光加性噪声对大气下行链路激光回波场信号影响干扰模型,并基于该模型提出了一种基于同态滤波和稀疏基追踪级联复合去噪算法.首先基于同态滤波理论将激光乘性散斑噪声转化为加性噪声,再由高通滤波器滤除散斑噪声,最后采用基追踪稀疏理论方法抑制背景光等加性噪声对像质的影响.研究表明,较现有单一去噪方法,该级联复合去噪方法可一次性消除激光乘性散斑噪声和背景加性噪声两种不同性质的噪声,有效改善了激光相干场成像质量. 相似文献
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Chao Zuo Qian Chen Guohua Gu Xiubao Sui Jianle Ren 《Infrared Physics & Technology》2012,55(4):263-269
In this paper, an improved interframe registration based nonuniformity correction algorithm for focal plane arrays is proposed. The method simultaneously estimates detector parameters and carries out the nonuniformity correction by minimizing the mean square error between the two properly registered image frames. A new masked phase correlation algorithm is introduced to obtain reliable shift estimates in the presence of fixed pattern noise. The use of an outliers exclusion scheme, together with a variable step size strategy, could not only promote the correction precision considerably, but also eliminate ghosting artifacts effectively. The performance of the proposed algorithm is evaluated with clean infrared image sequences with simulated nonuniformity and real pattern noise. We also apply the method to a real-time imaging system to show how effective it is in reducing noise and the ghosting artifacts. 相似文献
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We propose an innovative method for localized wavefront correction based on area-mapped phase-shift (AMPS) interferometry. In this Letter, we present the theory and then experimentally compare it with a previously demonstrated method based on spot-optimized phase-stepping (SOPS) interferometry. We found that AMPS outperforms SOPS interferometry in terms of speed by threefold, although in noisy environments the improvements may be larger. AMPS yielded similar point-spread functions (PSF) as SOPS for moderate system-induced aberrations, but yielded a slightly less ideal PSF for larger aberrations. The method described in this Letter may prove crucial for applications where the phase-stepping solution does not have sufficient speed. 相似文献
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Conventional deblurring approaches such as the Richardson–Lucy (RL) algorithm will introduce strong noise and ringing artifacts, though the point spread function (PSF) is known. Since it is difficult to estimate an accurate PSF in real imaging system, the results of those algorithms will be worse. A spatial weight matrix (SWM) is adopted as local constraint, which is incorporated into image statistical prior to improve the RL approach. Experiments show that our approach can make a good balance between preserving image details and suppressing ringing artifacts and noise. 相似文献
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光散射是限制光传输以及降低和破坏光学成像性能的主要因素,透过复杂散射介质对运动目标的全光成像是光学领域极具挑战性的技术之一.本文提出一种利用散斑差值自相关透过散射介质对运动目标进行实时追踪的方法.采用赝热光照明,基于光学记忆效应理论,通过对运动目标采集的两帧散斑做差值,然后做自相关运算,计算目标移动的距离,实现对目标的实时追踪,并且利用相位恢复算法进行简单处理就可以重建隐藏目标.对该方法进行了实验验证,成功地对隐藏的运动目标实现了成像与追踪.这种透过散射介质对运动目标的全光成像及实时追踪技术,在生物医学等领域具有重要应用潜力. 相似文献
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Cellular motion produces highly dynamic speckle in wide-field depth-gated holographic optical coherence imaging. The speckle provides cell scale information such as cell membrane and organelle motion, even though the spatial resolution of the optics is above the cell scale. The statistical properties of dynamic speckle can be used for functional imaging of motile activity at depth within tissue. In this paper we develop a motility metric using time autocorrelation to create a three-dimensional motility map of tissue. The effect of noise and the shimmering showerglass effect in functional optical coherence imaging are evaluated quantitatively, and we demonstrate that meaningful motility information can be extracted from functional imaging using dynamic speckle. 相似文献
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在数字全息成像中,散斑噪声严重影响了再现像的信噪比和成像分辨率,因此为了提高数字全息成像质量,迫切需要抑制再现像的散斑噪声.分析并给出了矩形散射光斑的强度协方差,定量计算了特定实验条件下产生退相关散斑图样的最小角度差.结合透镜的性质设计并搭建了多角度无透镜傅里叶变换数字全息成像系统,利用光纤端面在透镜焦平面的二维机械移动代替传统反射镜的旋转,使照明光束在不改变照明位置和大小的同时,可任意改变光束方向.移动光纤端面使多角度照明满足最小角度差,获取了81幅数字全息图.利用单次快速傅里叶逆变换实现数值再现,对多幅再现像的强度像求平均,实验结果表明散斑对比度降低为单幅再现像的14.6%,使图像信噪比提高了6.9倍.该抑制散斑的多角度数字全息成像方法有效的抑制了散斑噪声,且成像光路结构简单,可操作性强. 相似文献
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Respiratory noise is a confounding factor in functional magnetic resonance imaging (MRI) data analysis. A novel method called Respiratory noise Correction using Phase information is proposed to retrospectively correct for the respiratory noise in functional MRI (fMRI) time series. It is demonstrated that the respiratory movement and the phase of functional MRI images are highly correlated in time. The signal fluctuation due to respiratory movements can be effectively estimated from the phase variation and removed from the functional MRI time series using a Wiener filtering technique. In our experiments, this new method is compared with RETROICOR, which requires recording respiration signal simultaneously in an fMRI experiment. The two techniques show comparable performance with respect to the respiratory noise correction for fMRI time series. However, this technique is more advantageous because there is no need for monitoring the subjects’ respiration or changing functional MRI protocols. This technique is also potentially useful for correcting respiratory noise from abnormal breathing or when the respiration is not periodic. 相似文献