Speckle patterning of soft tissues for strain field measurement using digital image correlation: preliminary quality assessment of patterns.

Methods for creating speckle patterns on mouse arteries for use in deformation and strain field measurements in a stereomicroscope digital image correlation (DIC) system are described. Both fluorescent microsphere binding and ethidium bromide (EB) nuclear staining were used to generate high contrast, random patterns on mouse carotid arteries. To quantify the quality of each pattern, several metrics are used including (a) histogram distribution for each intensity pattern and (b) pixel-level variance in intensity pattern noise. Results demonstrate that both approaches provide sufficient pattern contrast for use in image-based methods to measure deformations in soft tissue. While fluorescent nuclear staining generates higher pixel-level intensity noise, this method provides better overall pattern quality (greater spatial uniformity and broader histogram) for automated DIC analysis when used at the appropriate magnification. Using recently developed theoretical predictions, estimates for the standard deviation in image-correlation-based displacements due to the measured intensity pattern variance are presented for fluorescent microsphere binding and EB nuclear staining patterns. Results confirm that both patterning approaches provide relatively small standard deviation in displacement measurements and hence are appropriate for measurement of deformations in small artery specimens.