7.5 USING FINITE ELEMENT ANALYSIS TO MODEL ACOUSTIC RADIATION FORCE IMAGING (ARFI) OF CAROTID ARTERY PLAQUES

This dissertation describes techniques that use Optical Coherence Tomography techniques developed for the detection of shear wave propagation in different phantoms, and the use of such waves to enhance the transport of nanoparticles in tissue equivalent phantoms. In the first study, we explored the potential of measuring shear wave propagation using optical co-herence elastography (OCE) in an inhomogeneous phantom and carotid artery samples based on a swept source optical coherence tomography (OCT) system. Shear waves were generated using a piezoelectric transducer transmitting sine-wave bursts of 400 μs duration, applying acoustic radiation force (ARF) to inhomogeneous phantoms and carotid artery samples, syn-chronized with a swept-source OCT (SS-OCT) imaging system. The phantoms were com-posed of gelatin and titanium dioxide whereas the carotid artery samples were embedded in propagating shear waves in inhomogeneous tissue equivalent phantoms and carotid artery samples using the ARF of an ultrasound transducer, and measuring the shear wave speed and its associated properties in the different layers with OCT phase maps. In the second study, we present a technique to image the enhanced particle displacement generated using an acoustic radiation force (ARF) excitation source. A MEMS-VCSEL swept source Optical Coherence Tomography (SS-OCT) system with a center wavelength of 1310 nm, a bandwidth of 100nm, and an A-scan rate of 100 kHz was used to detect gold nanoparticle displacement. ARF was applied after the nanoparticles diffused into a collagen matrix (of different collagen concen-trations and for a tissue engineered MCF-7 breast cancer cell construct). Differential OCT speckle variance images with and without the ARF were used to estimate the particle dis-placement. The images were used to detect the microscopic enhancement of nanoparticle displacement generated by the ARF. Using this OCT imaging technique, the enhanced transport of particles though a collagen gel after using an ARF excitation was imaged and analysed.

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Dynamic Analysis of Soft Tissue Viscoelasticity Under Ultrasonic Radiation Force Using FEM

Volume 2: Biomedical and Biotechnology Engineering ◽

10.1115/imece2007-42013 ◽

2007 ◽

Author(s):

Megan L. Kogit ◽

Baoxiang Shan ◽

Assimina A. Pelegri

Keyword(s):

Finite Element ◽

Soft Tissue ◽

Dynamic Analysis ◽

Young’S Modulus ◽

Acoustic Radiation ◽

Young's Modulus ◽

Radiation Force ◽

Acoustic Radiation Force ◽

Damping Coefficient ◽

Response Data

We have developed a solid mechanics model of nearly incompressible, viscoelastic soft tissue for finite element analysis (FEA) in MATLAB 7.2. Newmark’s method was used to solve the finite element equations of motion for our model. The solution to our dynamic problem was validated with a transient dynamic analysis in ANSYS 10.0. We further demonstrated that our MATLAB FEA qualitatively agrees with those results observed with acoustic radiation force methods on soft tissues and tissue-mimicking materials. We showed that changes in Young’s modulus and the damping coefficient affect the displacement amplitude and phase shift of the response data in the same manner: An increase in Young’s modulus or damping coefficient decreases both the displacement amplitude and response lag. Future work on this project will involve frequency analysis on response data and studying the initial transient region to help uncouple the effects of Young’s modulus and damping coefficient on response characteristics. This will get us one step closer to being able to explicitly determine Young’s modulus and the damping coefficient from the temporal response data of acoustic radiation force methods, which is the ultimate goal of our project.

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