Physical properties of hydrated tissue determined by surface interferometry of laser-induced thermoelastic deformation

Knee meniscus is a hydrated tissue; it is a fibrocartilage of the knee join t composed primarily of water. We present results of interferometric surfac e monitoring by which we measure physical properties of human knee meniscal cartilage. The physical response of biological tissue to a short laser pul se is primarily thermomechanical. When the pulse is shorter than characteri stic times (thermal diffusion time and acoustic relaxation time) stresses b uild and propagate as acoustic waves in the tissue. The tissue responds to the laser-induced stress by thermoelastic expansion. Solving the thermoelas tic wave equation numerically predicts the correct laser-induced expansion. By comparing theory with experimental data, we can obtain the longitudinal speed of sound, the effective optical penetration depth and the Gruneisen coefficient. This study yields information about the laser-tissue interacti on and determines properties of the meniscus samples that could be used as diagnostic parameters.