3D simulation of diffraction in ultrasonic computed tomography (original) (raw)
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The contribution presents some results obtained on the way to checking (and partly complementing) the standard reconstruction procedures in USCT by wave-equation based simulations. Mathematical models emerging from the transparent physical background for both the surrounding fluid and the object tissue are presented, followed by the present results of developing a realistic original finite-element- method based simulation. With respect to the need of comparison with the calibration measurements, a preliminary optimization of initial guesses to boundary conditions at the transducer array is discussed, based on a point-source model. The computational requirements of the procedures are also mentioned together with concrete examples of achieved results.
2008
Transmission Ultrasound Computed Tomography (CT) is strongly affected by the acoustic refraction properties of the imaged tissue, and proper modeling and correction of these effects is crucial to achieving high-quality image reconstructions. A method that can account for these refractive effects solves the governing Eikonal equation within an iterative reconstruction framework, using a wave-front tracking approach. Excellent results can be obtained, but at considerable computational expense. Here, we report on the acceleration of three Eikonal solvers (Fast Marching Method (FMM), Fast Sweeping Method (FSM), Fast Iterative Method (FIM)) on three computational platforms (commodity graphics hardware (GPUs), multi-core and cluster CPUs), within this refractive Transmission Ultrasound CT framework. Our efforts provide insight into the capabilities of the various architectures for acoustic wave-front tracking, and they also yield a framework that meets the interactive demands of clinical practice, without a loss in reconstruction quality.
Ultrasonic Computed Tomography
Bone Quantitative Ultrasound, 2010
Ultrasonic Computed Tomography (UCT) is a full digital imaging technique, which consists in numerically solving the inverse scattering problem associated to the forward scattering problem describing the interaction of ultrasonic waves with inhomogeneous media. For weakly inhomogeneous media such as soft tissues, various approximations of the solution of the forward problem (straight ray approximation, Born approximation…), leading to easy-to-implement approximations of the inverse scattering problem (back-projection or backpropagation algorithms) can be used. In the case of highly heterogeneous media such as bone surrounded by soft tissues, such approximations are no more valid. We present here two non-linear inversion schemes based on high-order approximations. These methods are conceived like the prolongation of the methods implemented in the weakly inhomogeneous case for soft tissues. The results show the feasibility of this UCT approach to bones and its potential to perform measurements in vivo.
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Ultrasound computer tomography aims at safe and fast high resolution imaging. One can imagine Ultrasound computer tomography (USCT) as an imaging procedure where X-rays in a CT scanner are replaced by Ultrasound waves, but unlike imagination the X-ray imaging principle cannot be directly applied because ultrasound does not travel in a simple straight line alone. It undergoes diffraction due to relatively large wavelengths associated with typical ultrasound sources. USCT in diffraction mode tomography uses an alternate approach known as inverse scattering problem for reconstructing the parameters of interest. In this paper, the wave equation is theoretically and numerically solved considering wave as a function of compressibility and velocity. The received field found by solving wave equation was simulated. These experimental results indicate that derived method can yield images with higher image resolution in a strong scattering field.
2009 9th International Conference on Information Technology and Applications in Biomedicine, 2009
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Acta Acustica united with Acustica, 2016
A time-domain numerical code based on the constitutive relations of nonlinear acoustics for simulating ultrasound propagation is presented. To model frequency power law attenuation, such as observed in biological media, multiple relaxation processes are included and relaxation parameters are fitted to both exact frequency power law attenuation and empirically measured attenuation of a variety of tissues that does not fit an exact power law. A computational technique based on artificial relaxation is included to correct the non-negligible numerical dispersion of the numerical method and to improve stability when shock waves are present. This technique avoids the use of high order finite difference schemes, leading to fast calculations. The numerical code is especially suitable to study high intensity and focused axisymmetric acoustic beams in tissue-like medium, as it is based on the full constitutive relations that overcomes the limitations of the parabolic approximations, while some specific effects not contemplated by the Westervelt equation can be also studied. The accuracy of the method is discussed by comparing the proposed simulation solutions to one-dimensional analytical ones, to k-space numerical solutions and also to experimental data from a focused beam propagating in a frequency power law attenuation media.
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2011
Time domain simulation tools for ultrasonic wave propagation in a target material with a complex outer surface or various inclusions are developed by combining the finite integration technique (FIT) and the finite element method (FEM) with an image-based modeling. In our simulation, the geometry of the target is determined by a digital image such as X-ray picture, CAD data, etc. and the processed voxel data is directly fed into the numerical calculation with the FIT or FEM. The accuracy of the two methods is discussed by comparison with the boundary element method. A simulation of the ultrasonic testing for a concrete material is shown with the 3-D image-based FIT.
Ultrasonic Imaging, 2006
This study focuses on the application of an ultrasonic diffraction tomography to non-circular 2Dcylindrical objects immersed in an infinite fluid. The distorted Born iterative method used to solve the inverse scattering problem belongs to the class of algebraic reconstruction algorithms. This method was developed to increase the order of application of the Born approximation (in the case of weakly contrasted media) to higher orders. This yields quantitative information about the scatterer, such as the speed of sound and the attenuation. Quantitative ultrasonic imaging techniques of this kind are of great potential value in fields such as medicine, underwater acoustics and non-destructive testing.
Computer simulation of forward wave propagation in non-linear, heterogeneous, absorbing tissue
2002
A method for simulating forward wavefront propagation in heterogeneous tissue is discussed. The intended application of this method is for the study of aberration produced when performing ultrasound imaging through a layer of soft tissue. A one-way wave equation that permits smooth variation in all acoustically important variables is derived. This equation also describes tissue exhibiting nonlinear elasticity and arbitrary frequency-dependent relaxation. A numerical solution to this equation is found by means of operator splitting and propagation along the spatial depth coordinate. The numerical solution is accurate when compared to analytical solutions for special cases, and when compared to numerical solutions of the full wave equation by other methods. The presented implementation provides a fast numerical method for studying the impact of aberration in medical ultrasound imaging through soft tissue-both on the transmitted beam and the nonlinearly generated harmonic beam.