3D strain estimation of soft biological tissues based on a constrained minimization strategy.
ABSTRACT The aim of this study is the estimation of the three dimensional strain occurring in soft biological tissues under compressive forces, through the processing of radiofrequency ultrasound volumes. This work is one of the first attempts to deal with the 3D problem of tissue motion under load. In this article, we propose a new adaptive and iterative numerical model, allowing full-resolved strain parameters estimation. This model is based on an objective function minimization with linear inequalities constraints. An original technique of adaptive displacement of the region of study is also considered. Preliminary tests are performed on a volume of ultrasound data obtained from a 3D numerical phantom. Axial, lateral, and elevational displacements and axial strain fields are estimated, and compared with the theory
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ABSTRACT: In traditional speckle tracking, lateral displacement (perpendicular to the beam direction) estimates are much less accurate than axial ones (along the beam direction). The accuracy of lateral tracking is very important whenever spatial derivatives of both axial and lateral displacements are required to give a full description of a two-dimensional (2-D) strain field. A number of methods have been proposed to improve lateral tracking by increasing the sampling rate in the lateral direction. We propose an alternate method using synthetic lateral phase (SLP). The algorithm, a direct analog of the phase zero-crossing approach used in axial displacement estimation, synthesizes the lateral phase first, then performs a zero-crossing detection on this synthetic phase to obtain lateral displacement estimates. The SLP is available by simply eliminating either the positive or negative half of the lateral spectrum of the original analytic signal. No new data need to be acquired for this procedure. This new algorithm was tested on both simulations and measurements from a cardiac phantom model. Results show that the method greatly improves the accuracy of lateral tracking, especially for low strain cases (< or =1%). The standard deviation of the estimation error of the lateral normal strain obtained with this approach has an approximate factor of 2-3 improvement for low strain cases. The conceptual and computational simplicity of this new method makes it a practical approach to improve lateral tracking for elasticity imaging.IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 06/2004; 51(5):540-50. · 1.82 Impact Factor
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ABSTRACT: To evaluate the dynamic range of tissue imaged by elastography, the mechanical behavior of breast and prostate tissue samples subject to compression loading has been investigated. A model for the loading was validated and used to guide the experimental design for data collection. The model allowed the use of small samples that could be considered homogeneous; this assumption was confirmed by histological analysis. The samples were tested at three strain rates to evaluate the viscoelastic nature of the material and determine the validity of modeling the tissue as an elastic material for the strain rates of interest. For loading frequencies above 1 Hz, the storage modulus accounted for over 93 percent of the complex modulus. The data show that breast fat tissue has a constant modulus over the strain range tested while the other tissues have a modulus that is dependent on the strain level. The fibrous tissue samples from the breast were found to be 1 to 2 orders of magnitude stiffer than fat tissue. Normal glandular breast tissue was found to have an elastic modulus similar to that of fat at low strain levels, but the modulus of the glandular tissue increased by an order of magnitude above fat at high strain levels. Carcinomas from the breast were stiffer than the other tissues at the higher strain level; intraductal in situ carcinomas were like fat at the low strain level and much stiffer than glandular tissue at the high strain level. Infiltrating ductal carcinomas were much stiffer than any of the other breast tissues. Normal prostate tissue has a modulus that is lower than the modulus of the prostate cancers tested. Tissue from prostate with benign prostatic hyperplasia (BPH) had modulus values significantly lower than normal tissue. There was a constant but not significant difference in the modulus of tissues taken from the anterior and posterior portions of the gland.Ultrasonic Imaging 11/1998; 20(4):260-74. · 1.58 Impact Factor