Texture correlation: a method for the measurement of detailed strain distributions within trabecular bone

A new technique, termed texture correlation, is described for the measurement of displacement and strain patterns within samples of trabecular bone. Texture correlation is a modification of digital image correlation, a method for analysis of deformation in objects marked with random surface speckle. Instead of surface speckle, the trabecular pattern itself is used as a basis for correlation. Digitized contact radiographs of samples in unloaded and loaded states are compared by computer to determine displacements of a grid of points. Displacements are filtered with Savitsky-Golay polynomial-convolution filters to reduce noise, and then strain is calculated with finite element techniques. The method is conceptually similar to the manual measurement of surface markers but has numerous advantages: no marking of the sample is required, displacements are measured automatically by computer, measurement of thousands of displacements is practical, and filtering allows calculation of strain over small regions of the sample. The validity of the technique is demonstrated by comparison of strain patterns measured by texture correlation at low resolution with the same patterns measured by a surface marker technique in six samples of trabecular bone from a human femoral head. The results of texture correlation at full resolution then are presented to demonstrate the capabilities of the method.