Micro-elastography of tissue with OCT

The goal of OCT elastography is to quantify microscopic strain induced inside a tissue by stress applied externally. Images of internal strain or displacement may provide valuable information about pathological processes such as edema and fibrosis which are known to alter the mechanical properties of tissue. In this study we developed experimental methods for measuring internal deformation in highly scattering tissue with OCT and applied them to tissue phantoms and living tissue. Piezoelectric actuators were configured to compress the samples in steps of 5-10 mu m as images were captured synchronously using either a frame or a line-by-line acquisition mode. The displacements of structures inside the samples were quantified using speckle-tracking algorithms based on cross correlation or optical flow of selected features. Displacements as small as a few micrometers were measurable in heterogeneous gelatin phantoms containing scattering particles and living skin. The results suggest that the composition of tissues layers whose elasticities differ greatly (e.g., fat and muscle) can be deduced visually from image sequences without the need for complicated image processing. However, better models are needed to transform the displacement images into quantitative maps of subtle regional variations of the elastic modulus.