Ultra-wideband optical coherence elastography from acoustic to ultrasonic frequencies

Visualizing elastic waves by noninvasive imaging has been useful for analyzing the mechanical properties of materials and tissues. However, the maximum wave frequency of elastography has been limited to ~10 kHz due to the finite sensitivity to small vibration and finite imaging speed. Here, we present an optical coherence elastography technique that extends the frequency range to MHz by noise reduction, anti-aliasing demodulation, and advanced wave analysis. Our system can measure the stiffness of hard (GPa) materials including bones with mm-scale resolution and characterize soft, viscoelastic materials from 100 Hz to 1 MHz. The dispersion of Rayleigh surface waves over the wide frequency range allowed us to profile depth-dependent shear modulus (10 kPa to 100 MPa) in cartilages ex vivo and the human skin in vivo. This technique opened a new window for the characterization of materials in situ with 3-dimensional resolution.