Biomechanical properties of soft tissue measurement using Optical Coherence Elastography

Optical Coherence Tomography (OCT) provides images at near histological resolution, which allows for the identification of micron sized morphological tissue structures. Optical coherence elastography (OCE) measures tissue displacement and utilizes the high resolution of OCT to generate high-resolution stiffness maps. In this work, we explored the potential of measuring shear wave propagation using OCE. A swept-source OCT system was used in this study. The laser had a center wavelength of 1310 nm and a bandwidth of ~110 nm. The lateral resolution was approximately 13 μm in the samples. Acoustic radiation force was applied to two different phantoms using a 20 MHz circular 8.5 mm diameter piezoelectric transducer element (PZT, f-number 2.35) transmitting sine-wave bursts of 400 μs. The first phantom consisted of a 355 μm glass sphere (dark) embedded in gelatin that was used to characterize the ultrasound pushing beam. The second consisted of gelatin mixed with titanium dioxide, which provided uniform acoustic and optical scattering. The OCT signal from this second set of phantoms was used for the measurement of the shear wave speed and viscosity. For both sets of experiments phase analysis was applied to B-mode and M-mode OCT images which were obtained while the ultrasound transducer was generating the “push” in the phantom. The experiments are the first step towards imaging shear wave propagation in tissue and characterization of tissue mechanical properties using OCE, with the eventual goal of developing OCE as a diagnostic tool for the assessment of pathological lesions with different mechanical tissue property.