Whole organ deformation analysis by digital optical metrology

This chapter presents the main optical metrology methods used to obtain direct deformation measurements of cut or whole biomineralized samples. It discusses the generic principles of the most important commercially available numeric and physical correlation-based deformation measurement systems, with a strong emphasis on the practical aspects of performing meaningful and reproducible measurements on loaded mineralized biological tissues. The fundamental assumption underlying digital image correlation is that local subsets of intensities in the image of the unloaded sample are transformed to the target subset in the image of the deformed sample by a homogeneous linear transformation. Image correlation has advantages compared with speckle pattern interferometry when large deformations are to be measured, and thus the method is particularly well suited to study extensive or nonlinear deformation, which is typically relevant for less mineralized tissues. Phasestepping consists of recording multiple images of the sample under the same conditions, while imposing known phase-shifts to the reference laser-beam.