An analytical model of laser-induced dynamic thermoelastic deformation of the viscoelastic half-space (Conference Presentation)

Abstract

Laser-induced thermoelastic deformation can be an effective way to induce disturbances in soft biological tissues in elastography and photoacoustcs. A laser pulse results in rapid temperature increase, thermoelastic expansion and generation of compressional and shear waves in the tissue. After the expansion and wave attenuation, a quasi-steady state is reached. For several medical applications of elastography, laser-induced thermoelastic deformation has been proposed as a way to produce strain in the tissue to assess tissue mechanical properties. In combination with measuring tissue response using optical coherence tomography, such an approach could be an effective method for noncontact measurement of tissue mechanical properties. In our previous works we have derived a three-dimensional analytical solution for the quasi-steady state, when the tissue reaches equilibrium after the acoustic and shear waves have decayed. In this work, we consider dynamic tissue response at the moment of time immediately after the laser pulse. In the frequency domain, an analytical expression has been derived for the thermoelastic displacements and stresses caused by absorption of an axially symmetric laser beam. The solution was obtained for the Gaussian radial temperature profile on the upper surface of a viscoelastic half-space. The influence of the shear elastic properties on the elastic wave propagation and displacement profiles was evaluated. The proposed analytical solution could be used to model mechanical and photoacoustic tissue response to laser excitation, as well as to investigate the mechanism of photomechanical laser ablation. This study was supported by NIH grant R01EY022362.