Elastic properties of soft tissue-mimicking phantoms assessed by combined use of laser ultrasonics and low coherence interferometry

Abstract

Advances in the field of laser ultrasonics have opened up new possibilities in medical applications. This paper evaluates this technique as a method that would allow for rapid characterization of the elastic properties of soft biological tissue. In doing so, we propose a novel approach that utilizes a low coherence interferometer to detect the laser-induced surface acoustic waves (SAW) from the tissue-mimicking phantoms. A Nd:YAG focused laser line-source is applied to one- and two-layer tissue-mimicking agar-agar phantoms, and the generated SAW signals are detected by a time domain low coherence interferometry system. SAW phase velocity dispersion curves are calculated, from which the elasticity of the specimens is evaluated. We show that the experimental results agree well with those of the theoretical expectations. This study is the first report that a laser-generated SAW phase velocity dispersion technique is applied to soft materials. This technique may open a way for laser ultrasonics to detect the mechanical properties of soft tissues, such as skin.

Quantitative elasticity measurement of urinary bladder wall using laser-induced surface acoustic waves

“…However, the propagation of SAWs in a heterogeneous medium (i.e., layered materials or structures) shows a unique dispersive behavior [38][39][40][41], meaning that the different frequency components travel at different phase velocities within the material. The phase velocity (C R ) depends on the elastic and geometric properties of the material or structure through all the layers it penetrates [32][33][34][35][36][37][38]. In a single, isotropic homogeneous layer, the surface wave phase velocity can be approximated as:…”

“…Wang et al was the first to describe the application of laserinduced SAWs to clinical dental disease diagnosis [30,31]. Our group pioneered the use of shaker-and laser-induced SAWs to evaluate the Young's modulus of heterogeneous soft tissue and phantoms [32][33][34][35][36][37]. In the laser-induced SAW method, the deformation experienced by the target sample is less than 1 µm (typically ~100 nm) [37], which ensures linear behavior of the soft tissue.…”

“…In the laser-induced SAW method, the deformation experienced by the target sample is less than 1 µm (typically ~100 nm) [37], which ensures linear behavior of the soft tissue. Our previous works proved that SAWs can be used to accurately evaluate the mechanical properties of layered viscoelastic soft tissues such as those in the skin, liver, and cornea [32][33][34][35][36][37]. On the other hand, optical coherence tomography (OCT) is a promising noninvasive, noncontact imaging technique capable of providing microstructural information on tissue with high resolution.…”

Noncontact depth-resolved micro-scale optical coherence elastography of the cornea

“…General OCE techniques employ a loading device to induce tissue deformation and utilize OCT-based displacement-detection technique to monitor the dynamic response of the tissue [34][35][36]. The feasibilities of using OCE for three-dimensional elastic imaging [37,38], in vivo detection [39][40][41] and Young's modulus measurement [42][43][44] have been demonstrated on tissue-mimicking phantoms and different types of biological tissues, such as skin and soft-tissue tumor.…”

Assessing mechanical properties of tissue phantoms with non-contact optical coherence elastography and Michelson interferometric vibrometry

“…All of these methods combine an imaging technique with external loading, such as mechanical compression [11], acoustic radiation force [12], pulsed laser [13], or focused air-pulse [14]. The imaging modalities measure the tissue response to the excitation, and these measurements can then characterize the biomechanical properties of tissue through the use of appropriate mechanical models.…”