Interpretation and medical application of laser biospeckle

Abstract

Laser biospeckle is the dynamic laser speckle pattern produced by illuminating tissue with laser light. The dynamic nature of the speckle indicates the movement of particles in the tissue, particularly blood cells. Contrast analysis of laser biospeckle generates flow maps showing areas of higher or lower blood flow, for example vessels or background perfusion, and can detect changes in flow associated with inflammation, wounds or disease. This thesis presents methods of analysing laser speckle contrast, particularly a method using multiple camera exposures to generate the find the same spectral information from laser speckle fluctuations as laser Doppler, allowing quantitative measurements of flow. This work also presents a correction for spatial averaging in speckle, and confirms the validity of that correction using simulation and experiment. Spatial effects on laser speckle imaging techniques in tissues are tested experimentally. Multiple exposure speckle imaging was tested in vivo in a variety of situations, and clinically in measurements around diabetic foot ulcers. Measurements were made on three groups: patients with diabetic foot ulcers, patients with peripheral vascular disease, and normal control subjects. No difference in mean flow speed was found between the groups, but a significant difference in mean static contrast, indicating blood volume in tissue, was found.