A model of distributed phase aberration for deblurring phase estimated from scattering

Department of Electrical and Computer Engineering, University of Rochester, Rochester, NY, USA.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control (Impact Factor: 1.51). 01/2010; 57(1):214-28. DOI: 10.1109/TUFFC.2010.1400
Source: PubMed


Correction of aberration in ultrasound imaging uses the response of a point reflector or its equivalent to characterize the aberration. Because a point reflector is usually unavailable, its equivalent is obtained using statistical methods, such as processing reflections from multiple focal regions in a random medium. However, the validity of methods that use reflections from multiple points is limited to isoplanatic patches for which the aberration is essentially the same. In this study, aberration is modeled by an offset phase screen to relax the isoplanatic restriction. Methods are developed to determine the depth and phase of the screen and to use the model for compensation of aberration as the beam is steered. Use of the model to enhance the performance of the noted statistical estimation procedure is also described. Experimental results obtained with tissue-mimicking phantoms that implement different models and produce different amounts of aberration are presented to show the efficacy of these methods. The improvement in b-scan resolution realized with the model is illustrated. The results show that the isoplanatic patch assumption for estimation of aberration can be relaxed and that propagation-path characteristics and aberration estimation are closely related.

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    • "optimization of a coherence metric has also demonstrated success, especially for the case of an offset phase screen [62], [63]. Propagation path effects in aberration estimation and correction in the absence of a point target using statistical methods have been investigated by Waag and astheimer [64], astheimer et al. [65], and Tillet et al. [66]. The time-reversal mirror technique [67] has demonstrated success at focusing through aberrating layers [68]– [72] by addressing the aberration problem as a complex filtering operation, allowing variation of both amplitude and phase with frequency and more fully addressing the various degradation phenomena described previously. "
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    ABSTRACT: Having previously presented the ultrasound brain helmet, a system for simultaneous 3-D ultrasound imaging via both temporal bone acoustic windows, the scanning geometry of this system is utilized to allow each matrix array to serve as a correction source for the opposing array. Aberration is estimated using cross-correlation of RF channel signals, followed by least mean squares solution of the resulting overdetermined system. Delay maps are updated and real-time 3-D scanning resumes. A first attempt is made at using multiple arrival time maps to correct multiple unique aberrators within a single transcranial imaging volume, i.e., several isoplanatic patches. This adaptive imaging technique, which uses steered unfocused waves transmitted by the opposing, or beacon, array, updates the transmit and receive delays of 5 isoplanatic patches within a 64° x 64° volume. In phantom experiments, color flow voxels above a common threshold have also increased by an average of 92%, whereas color flow variance decreased by an average of 10%. This approach has been applied to both temporal acoustic windows of two human subjects, yielding increases in echo brightness in 5 isoplanatic patches with a mean value of 24.3 ± 9.1%, suggesting that such a technique may be beneficial in the future for performing noninvasive 3-D color flow imaging of cerebrovascular disease, including stroke.
    Full-text · Article · Mar 2013 · IEEE transactions on ultrasonics, ferroelectrics, and frequency control
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    • "The aberration was estimated using received signals from arrays of synthetic elements with a variety of different pitches in the elevation and array directions. A least-mean-square-error method [6] of time-shift estimation was used to estimate the aberration in echoes from a point reflector and a statistical method based on a filter-bank model [12] was used to estimate the aberration for imaging a scatterer-free (cyst-mimicking) region surrounded by random tissue-mimicking scatterers. The quality of receiver sensitivity patterns with compensations derived from synthetic arrays with different pitches were quantified in elevation and array directions by effective widths and radii as well as peripheral energy ratios. "
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    ABSTRACT: Focusing and imaging qualities of an ultrasound imaging system that uses aberration correction were experimentally investigated as functions of the number of parallel channels. Front-end electronics that consolidate signals from multiple physical elements can be used to lower hardware and computational costs by reducing the number of parallel channels. However, the signals from sparse arrays of synthetic elements yield poorer aberration estimates. In this study, aberration estimates derived from synthetic arrays of varying element sizes are evaluated by comparing compensated receive focuses, compensated transmit focuses, and compensated b-scan images of a point target and a cyst phantom. An array of 80 x 80 physical elements with a pitch of 0.6 x 0.6 mm was used for all of the experiments and the aberration was produced by a phantom selected to mimic propagation through abdominal wall. The results show that aberration correction derived from synthetic arrays with pitches that have a diagonal length smaller than 70% of the correlation length of the aberration yield focuses and images of approximately the same quality. This connection between correlation length of the aberration and synthetic element size provides a guideline for determining the number of parallel channels that are required when designing imaging systems that employ aberration correction.
    Full-text · Article · Oct 2012 · IEEE transactions on ultrasonics, ferroelectrics, and frequency control
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    ABSTRACT: Efficient inverse scattering algorithms for nonradial lossy objects are presented using singular-value decomposition to form reduced-rank representations of the scattering operator. These algorithms extend eigenfunction methods that are not applicable to nonradial lossy scattering objects because the scattering operators for these objects do not have orthonormal eigenfunction decompositions. A method of local reconstruction by segregation of scattering contributions from different local regions is also presented. Scattering from each region is isolated by forming a reduced-rank representation of the scattering operator that has domain and range spaces comprised of far-field patterns with retransmitted fields that focus on the local region. Methods for the estimation of the boundary, average sound speed, and average attenuation slope of the scattering object are also given. These methods yielded approximations of scattering objects that were sufficiently accurate to allow residual variations to be reconstructed in a single iteration. Calculated scattering from a lossy elliptical object with a random background, internal features, and white noise is used to evaluate the proposed methods. Local reconstruction yielded images with spatial resolution that is finer than a half wavelength of the center frequency and reproduces sound speed and attenuation slope with relative root-mean-square errors of 1.09% and 11.45%, respectively.
    Full-text · Article · Mar 2012 · IEEE transactions on ultrasonics, ferroelectrics, and frequency control
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