Elastic stiffness characterization using three-dimensional full-field deformation obtained with optical coherence tomography and digital volume correlation

Optical coherence elastography – OCT at work in tissue biomechanics [Invited]

“…Then, correlation averaging kernels (volumes here) must contain sufficient speckles to enable sufficiently accurate displacement measurement, representing a trade-off between spatial resolution and strain sensitivity and degrading the resolution of the measurement compared to the underlying OCT resolution. Kernel size has varied widely in the speckle-tracking literature to date, from 7 to 16 pixels [1], to a few voxels [149], to many tens of voxels [166]. This resolution degradation is to be contrasted with phase-sensitive, compressive OCE, in which the lateral resolution of OCT is maintained, but only the axial strain component is measured, and with axial resolution that is close to that of speckle tracking [4].…”

“…Early indications are that in applications such as breast cancer, the capacity to resolve such micro-structures addresses, at least to some degree, the issue of differentiating benign from malignant tissues [161,162]. In moving to higher resolution, OCE faces an additional challenge in that, since the speckle decorrelation length scales with speckle size [47,166], this reduces the maximum displacement that can be measured between frames. This issue can always be addressed by collecting more frames per measurement, incrementing the displacement by less per frame, so as to maintain correlation, but this adds to the acquisition overhead.…”

“…(As an aside, "speckle" in image correlation is sometimes not the coherent speckle we observe in OCT, but often describes the effect of imaging artificial texture applied to a sample surface [167,169].) Digital volume correlation methods have recently been applied to OCT [149,166], enabling measurement of the full strain tensor. Speckle tracking methods require the speckle field in both images to remain correlated, thus, displacement between measurements must be limited to around half of the speckle size [47,166], commonly corresponding to strain in the 1-2 percent range.…”

“…Digital volume correlation methods have recently been applied to OCT [149,166], enabling measurement of the full strain tensor. Speckle tracking methods require the speckle field in both images to remain correlated, thus, displacement between measurements must be limited to around half of the speckle size [47,166], commonly corresponding to strain in the 1-2 percent range. Then, correlation averaging kernels (volumes here) must contain sufficient speckles to enable sufficiently accurate displacement measurement, representing a trade-off between spatial resolution and strain sensitivity and degrading the resolution of the measurement compared to the underlying OCT resolution.…”

“…In the meantime, other groups have been seeking to advance compression methods based on speckle tracking [46,149,166,167], largely borrowing from digital image correlation [21,22] methodologies, as described in Section 2. Such methods have also been developed for volumes, so-called digital volume correlation, which was first developed for X-ray computed tomography [168].…”