Wave Propagation In Biological Tissues Research Articles

Modified Lorentz Model-Based ADE-WLP-FDTD Method Simulation on THz Wave Propagation Properties of Tumor Tissue

An auxiliary differential equation (ADE) finite-difference time-domain (FDTD) method based on the weighted Laguerre polynomials (WLP) algorithm is developed to study wave propagation in biological tissue in the Terahertz (THz) frequency band. The relative permittivity of dispersive tissue can be expressed by the double Debye model or Cole–Cole model, which can be transformed into the modified Lorentz model by using the Padé approximation technique. The modified Lorentz model is numerically solved by means of the ADE-WLP-FDTD method. Numerical results validate the accuracy and efficiency of the proposed method. The effects caused by the slide and medium parameters on THz waves propagation properties of biological tissue are investigated. This letter enriches the high efficient ADE-WLP-FDTD method for terahertz imaging and tumor diagnosis to detect medium parameters of biological tissue.

ADE-TLM Algorithm for Modeling Wave Propagation in Biological Tissues with Debye Dispersion

In this paper we present a Transmission Line Matrix (TLM) algorithm for the simulation of electromagnetic wave interaction with a Debye dispersive medium. This new formulation is based on the use of the polarization currents in the medium. The auxiliary differential equation (ADE) method is considered to deal with dispersion after the classical discretization. The accuracy and efficiency of this approach were tested on 1D Debye medium by calculating the reflection coefficient on an air-dielectric interface. The potential of the developed algorithm to model the existence of tumors in a human breast is also demonstrated. The obtained results compared with the analytic model show a good agreement. The number of operations needed for each iteration has been reduced, hence the computational time in comparison with time convolution techniques, while maintaining a comparable numerical accuracy.

Numerical modeling of ultrasound propagation in heterogeneous media using a mixed domain method

A mixed domain method (MDM) is presented in this paper for modeling one-way linear/nonlinear wave propagation in biological tissue with arbitrary heterogeneities, in which sound speed, density, attenuation coefficients, and nonlinear coefficients are all spatial varying functions. The MDM is based on solving a Westervelt-like equation. We validated the algorithm by studying a number of one-dimensional and two-dimensional problems. Overall, this study demonstrates that the MDM is a computationally efficient and accurate method when used to model wave propagation in biological tissue with relatively weak heterogeneities. We also proposed methods to improve the algorithm for moderately heterogeneous media.

Numerical Modeling of Ultrasound Propagation in Weakly Heterogeneous Media Using a Mixed-Domain Method.

A mixed-domain method (MDM) is presented in this paper for modeling one-way linear/nonlinear wave propagation in biological tissue with arbitrary heterogeneities, in which sound speed, density, attenuation coefficients, and nonlinear coefficients are all spatial varying functions. The present method is based on solving an integral equation derived from a Westervelt-like equation. One-dimensional problems are first studied to verify the MDM and to reveal its limitations. It is shown that this method is accurate for cases with small variation of sound speed. A 2-D case is further studied with focused ultrasound beams to validate the application of the method in the medical field. Results from the MATLAB toolbox k-Wave are used as the benchmark. Normalized root-mean-square (rms) error estimated at the focus of the transducer is 0.0133 when the coarsest mesh (1/3 of the wavelength) is used in the MDM. Fundamental and second-harmonic fields throughout the considered computational domains are compared and good agreement is observed. Overall, this paper demonstrates that the MDM is a computationally efficient and accurate method when used to model wave propagation in biological tissue with relatively weak heterogeneities.

New Techniques and Designs of Focusing Piezoelectric Transducers for Ultrasonic Diagnostics and Therapy

New techniques of forming high intensity focused ultrasound (HIFU) fields using dynamic focusing and harmonic multifrequency excitation are developed for ultrasonic diagnostics and therapy. New designs of HIFU transducers based on high-performance composite materials are developed and studied. Finite-element and finite-difference simulations of HIFU transducers and processes of ultrasonic wave propagation in biological tissues are performed. The parameters of piezoceramic materials, piezoelements, and the acoustic fields of focusing ultrasonic transducers are measured. Experiments are performed on biological tissues ex vivo that confirm the efficiency, selectivity, and safety of the developed HIFU transducers and techniques of forming acoustic fields.

Noise signal propagation in soft biological tissues

Mathematical models are formulated that discribe linear and nonlinear wave propagation in biological tissues. The basis of the method is evolutionary integro-differential equations with a kernel that takes into account the specific properties of tissue. An equation is obtained for the correlation function of acoustic noise in a medium with memory. The procedure for calculating the correlation function by the given type of kernel and noise spectrum at the entrance to the medium is described. It is shown that in different tissue, there is a difference in the laws of decrease in full intensity of a wideband signal with distance. It is demonstrated that the nonlinear equation in the limiting cases of “short-” and “long-term” memory reduces to equations that have been well studied in statistical nonlinear acoustics.

An improved FDTD scheme with polarization piece‐linearity technique for biological tissue modeling

AbstractThe finite difference time domain (FDTD) has been popular to characterize wave propagation in biological tissue, which permittivity is generally described by Cole‐Cole dispersive model.The FDTD scheme by using fractional derivative to time‐domain polarization equation results in a fast and computational efficient algorithm. The accuracy obtained is, however, not generally as good as thoes of z‐transform and auxiliary differential equation methods. In this article, polarization piece‐linearity and nonlinear optimization techniques are proposed and utilized on the polarization fractional derivative appoach, which improved the accuracy while retains the high speed and efficiency advantage. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:888–891, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26698

THREE-DIMENSIONAL FDTD ANALYSIS OF THE DUAL-BAND IMPLANTABLE ANTENNA FOR CONTINUOUS GLUCOSE MONITORING

The flnite difierence time domain (FDTD) method is widely used as a computational tool to simulate the electromagnetic wave propagation in biological tissues. When expressed in terms of Debye parameters, dispersive biological tissues dielectric properties can be e-ciently incorporated into FDTD codes. In this paper, FDTD formulation with nonuniform grid is presented to simulate a dual medical implant communications service (MICS) (402{405MHz) and industrial, scientiflc, and medical (ISM) (2.4{2.48GHz) band implantable antenna for continuous glucose-monitoring applications. In addition, we present computationally simpler two-pole Debye models that retain the high accuracy of the Cole-Cole Model for dry skin in MICS and ISM bands. The re∞ection coe-cient simulation result with Debye dispersion is presented and compared with the published results. FDTD was also applied to analyze antenna's far- fleld.

Método ultrassônico de detecção de microvibração: Desenvolvimento da técnica

Many investigations have been devoted, during the last years, to implement an ultrasonic method able to generate shear waves and to detect the microvibrations caused by the wave propagation in biological tissues. Applications of such method include measuring rheological parameters for tissue characterization. Considering the potential to use shear wave propagation, this work presents an ultrasonic method able to detect microvibrations (UDmV), which is based on Kalman filtering to estimate the medium vibrations from a signal contaminated with noise. The UDmV was tested employing a speaker to generate microvibrations on a membrane and a pulse-echo ultrasonic system, operating at a center frequency of 4.96 MHz, to detect the membrane microvibrations. The UDmV demonstrated promising future potential, being able to detect the vibration frequency and amplitude with the same order of magnitude as presented in the literature (≈10 mm). Moreover, the method implemented in the present work confirmed previous results, from the literature, related with a reduction of the estimated vibration amplitude as the vibration frequency increases. The method developed in the present work can be employed to estimate the phase velocity and the attenuation coefficient of a shear wave propagating in a viscoelastic medium.

Aberration in nonlinear acoustic wave propagation

Theory and simulations are presented indicating that imaging at the second-harmonic frequency does not solve the problem of ultrasonic wave aberration. The nonlinearity of acoustic wave propagation in biological tissue is routinely exploited in medical imaging because the improved contrast resolution leads to better image quality in many applications. The major sources of acoustic noise in ultrasound images are aberration and multiple reflections between the transducer and tissue structures (reverberations), both of which are the result of spatial variations in the acoustic properties of the tissue. These variations mainly occur close to the body surface, i.e., the body wall. As a result, the nonlinearly generated, second harmonic is believed to alleviate both reverberation and aberration because it is assumed that the second harmonic is mainly generated after the body wall. However, in the case of aberration, the second harmonic is generated by an aberrated source. Thus the second harmonic experiences considerable aberration at all depths, originating from this source. The results in this paper show that the second harmonic experiences similar aberration as its generating source, the first harmonic.

A New FDTD Formulation for Wave Propagation in Biological Media With Cole–Cole Model

The finite-difference time-domain (FDTD) method has been widely used to simulate the electromagnetic wave propagation in biological tissues. The Cole-Cole model is a formulation which can describe many types of biological tissues accurately over a very wide frequency band. However, the implementation of the Cole-Cole model using the FDTD method is difficult because of the fractional order differentiators in the model. In this letter, a new FDTD formulation is presented for the modeling of electromagnetic wave propagation in dispersive biological tissues with the Cole-Cole model. The Z-transform is used to represent the frequency dependent dielectric properties. The fractional order differentiators in the Cole-Cole model is approximated by a polynomial. The coefficients of the polynomial are found using a least-squares fitting method

Realistic numerical modelling of human head tissue exposure to electromagnetic waves from cellular phones

The ever-rising diffusion of cellular phones has brought about an increased concern for the possible consequences of electromagnetic radiation on human health. Possible thermal effects have been investigated, via experimentation or simulation, by several research projects in the last decade. Concerning numerical modeling, the power absorption in a user's head is generally computed using discretized models built from clinical MRI data. The vast majority of such numerical studies have been conducted using Finite Differences Time Domain methods, although strong limitations of their accuracy are due to heterogeneity, poor definition of the detailed structures of head tissues (staircasing effects), etc. In order to propose numerical modeling using Finite Element or Discontinuous Galerkin Time Domain methods, reliable automated tools for the unstructured discretization of human heads are also needed. Results presented in this article aim at filling the gap between human head MRI images and the accurate numerical modeling of wave propagation in biological tissues and its thermal effects. To cite this article: G. Scarella et al., C. R. Physique 7 (2006).

Simulation of the thermal wave propagation in biological tissues by the dual reciprocity boundary element method

The dual reciprocity boundary element method (DRBEM) is extended to simulate the thermal wave propagation in biological tissues. A deep insight into the thermal wave behaviors, like reflection, decay, phase jumping, superposition and resolution etc. in a two-dimensional zone under certain boundary conditions is obtained. Certain conditions for applying the effects of thermal waves to address some complicated biothermal problems as well as to identify the thermal states of living tissues are thus detailed. Due to DRBEM's unique advantages, such as not being confined by the complex shape of biological bodies and thus not needing to discretize the inner domain, can save vast CPU time and easily deal with complex bioheat models. Therefore, DRBEM may possibly become an important method for predicting and controlling the temperature evolution in biological bodies under hyperthermia or hypothermia.

Numerical simulations of tissue heating created by high-intensity focused ultrasound

Modeling of high-intensity focused ultrasound (HIFU) propagation and heating effects in tissue has usually been studied under the assumption of linear acoustics. Nevertheless, nonlinear propagation can lead to important differences in heat deposition depending on the degree of nonlinearity achieved in a HIFU field. To be presented are calculations of the spatial patterns of acoustic intensity (I) and heat generation [H=−(∂/∂z+1/r∂/∂r)I for strongly nonlinear acoustic waves and H=2αI for weakly nonlinear acoustic waves, where α is acoustic absorption] associated with focused weakly and strongly nonlinear acoustic wave propagation in biological tissue. The propagation is modeled using a KZK equation method with special attention to correct modeling of shock generation and biologically relevant attenuation, as well as using initializing data based on existing designs of transducers for acoustic hemostasis. The heat generation term forces the ‘‘bio-heat’’ equation, which predicts the generation, movement, and dissipation of heat within biological tissue. The tissue model contains blood flow in an artery or vein and is perfused by a capillary bed. For this talk the differences in spatial patterns of acoustic intensity created by weakly and strongly nonlinear CW 1-Mhz acoustic wave propagation are shown. How those differences translate into differences in heat generation and therefore bioeffect within biological tissue are then demonstrated. [Work sponsored by DARPA.]

Evolution equations and ultrasonic wave propagation in biological tissues

The complexity of ultrasonic wave propagation in tissue arises from a combination of factors. First, there is the biochemical sophistication of the media concerned. Second, there is the variety of physical phenomena involved: the diffractive nature of the ultrasonic field, the presence of absorption, the presence of large scale inhomogeneities and small scale scatterers, and the possibility of finite amplitude propagation effects. The authors have been concerned to find a unified approach which will permit each of the effects to be taken into account in relation to the others. This approach is based on the application of two-dimensional evolution equations modelling ultrasonic propagation in non-cavitating soft tissues. The model incorporates all the propagation phenomena known from experimental studies, indicating a need for knowledge of nine material parameters for a complete description. It thus provides a basis for numerical investigation of the relative significance of the parameters under different conditions.