Phase-Domain Photoacoustic Mechanical Imaging for Quantitative Elastography and Viscography

The role and importance of mechanical properties of cells and tissues in pathophysiological processes have widely been acknowledged. However, current elastography techniques most based on transverse elastic waves, diminish the translation of wave speed into elastic modulus due to its limited wave propagation direction. Here, we propose phase-domain photoacoustic mechanical imaging (PD-PAMI), leveraging the initial time and phase response characteristics of an omnidirectional photoacoustic elastic wave to quantitatively extract elastic and viscous moduli. Theoretical simulations and experiment on tissue-mimicking phantoms with different levels of viscoelastic properties were conducted to validate the approach with a precision in elasticity and viscosity estimation of 4.6% and 6.6%, respectively. The trans-scale viscoelasticity mappings over three length scales—covering cell, tissue section, and in vivo organ, were provided to demonstrate the scalability of the technique with different implementations of PD-PAMI. Experiments on animal models of breast tumour and atherosclerosis reveal that PD-PAMI technique enables effective monitoring of the viscoelastic parameters for examinations of the diseases involved with the variations in collagen or lipid composition and in inflammation level. PD-PAMI technique opens new perspectives of conventional PA imaging and provides new technical way for biomechanical imaging, prefiguring potential clinical applications in mechanopathology-involved disease diagnosis.