Two-dimensional (2D) harmonic oscillation optical coherence elastography

Mechanical properties of tissues are an important indicator because they are associated with disease states. One of the common excitation sources in optical coherence elastography (OCE) to determine mechanical properties is acoustic radiation force (ARF). Using ARF as an excitation source requires a complicated focusing alignment, that potentially increases the difficulty for translational applications. Additionally, for tissue engineering applications, samples are usually cultured in a 35 mm Petri dish or 6-well cell culture plate. As the samples placed in a such limited space and with polystyrene material, using ARF as the excitation source could generate undesired reflected waves from rigid boundaries which affect the evaluation of mechanical properties, and acoustic energy for the ARF generation could be attenuated by the bottom of the plate. Here, we reported a new technique to evaluate the mechanical property of samples placed in 6-well cell culture plate without contacting the sample, named harmonic oscillation OCE. A homogeneous 5% gelatin phantom was fabricated and placed in a 6-well cell culture plate. The actuator was driven by a 300 Hz signal with a 15-cycle burst to vibrate the plate. The spectral domain optical coherence tomography (OCT) system was used to make measurements with 100 mu m lateral spacing and 3.5 mu m axial resolution within 10 mm x 10 mm field of view (FOV). An 8-angle directional filter and low pass filter were used to decompose two-dimensional (2D) wave propagations and undesired frequency components, respectively. The 2D wave velocities in each direction were separately evaluated by a 2D local wave velocity algorithm. The experimental results demonstrated that the averaged 2D wave velocity represents a good agreement with the dispersion analysis via the ARF excitation. The proposed harmonic oscillation OCE with an easy-to-setup approach can be used to evaluate 2D mechanical properties of samples placed in the 6-well cell culture plate without tedious focusing alignment or directly contacting samples, which provides largely potential applications for histopathological and tissue engineering communities.

Automated summary

Mechanical properties of tissues are important indicators for disease states. Acoustic radiation force (ARF) is commonly used as an excitation source in optical coherence elastography (OCE) to determine mechanical properties, but its use requires complicated focusing alignment. This study introduces a new technique, harmonic oscillation OCE, which allows for the evaluation of mechanical properties of samples placed in a cell culture plate without contacting the samples.