Ultrasound Imaging and Therapeutics Research Laboratory

Laser-Induce Shear Wave Elasticity Imaging

Summary

Laser-induced shear wave imaging is to utilize a pulsed laser beam to generate shear waves based on thermoelastic effects. This method can be used to measure stiffness of biological tissues noninvasively. For example, to evaluate corneal ectasia, laser irradiation was used to induce displacement at corneal surface and optical coherence tomography (OCT) was employed to detect the laser-induced displacement.1,2,3

In this project, we proposed a new approach of laser-induced shear wave elasticity imaging based on optical perturbation of tissue to create shear waves and high frame rate ultrasound imaging to measure the propagation of laser-induced shear waves. In this approach, ultrafast ultrasound imaging is used to track the shear wave induced by laser irradiation. To validate the laser-induced SWEI method, we measured the shear wave velocity in the tissue mimicking phantoms and compared the results with acoustic radiation force (ARF) based SWEI. The result of this project shows that the combination of optical excitation and ultrafast ultrasound imaging of shear waves can be utilized to visualize both elastic and anatomical information of tissue with a potential in providing higher spatial resolution.

laser induced shear wave
Figure 1. Displacement maps at four different time points obtained using ultrafast ultrasound imaging for both (a) laser-induced SWEI and (b) ARF-based SWEI.

laser induced shear wave
Figure 2. (a) Co-registered ultrasound (grayscale map) and photoacoustic (color map) image of synthetic gel phantom. (b) Laser-induced shear wave displacement maps in the phantom at three different time points. (c) Scatter plot of mean value of shear wave displacement amplitude, measured 0.78 ms after the laser pulse, as a function of optical fluence. Error bars show standard deviation (n=6). (d) ARF-induced shear wave displacement maps in synthetic gel phantom at three different time points.

References

  1. C. Li, G. Guan, Z. Huang, M. Johnstone, and R. Wang, “Noncontact all-optical measurement of corneal elasticity,” Opt. Lett. 37(10), 1625-1627 (2012).^
  2. W. J. Dupps, “Biomechanical modeling of corneal ectasia,” J. Refract. Surg. 21(2), 186-190 (2005).^
  3. C. H. Liu, D. Nevozhay, H. Zhang, S. Das, A. Schill, M. Singh, S. Aglyamov, K. V. Sokolov, and K. V. Larin, “Longitudinal elastic wave imaging using nanobomb optical coherence elastography,” Opt. Lett. 44(12), 3162-3165 (2019).^