Laser speckle contrast techniques have been increasingly applied to dermal perfusion measurements over the past few years. The interpretation of laser speckle contrast and its conversion to a physiologically-defined perfusion parameter related to that found from Doppler measurements is becoming clearer. Speckle contrast-based techniques provide both quantified perfusion images and a time-series record of perfusion.We use the image resolution available in speckle measurements to investigate spatial resolution which can be expected in tissue; in particular to reconcile speckle measurements with the large point-to-point variations reported from fibre Doppler probes. In vitro models show the extent of spatial blurring likely to be encountered in speckle measurements at different depths.Perfusion responses related to vascular challenges could have medical relevance. We find a small pulse-related signal in dermal speckle data. By identifying pulses in a temporal record using a matched filter, we find statistical average pulse shapes for several different subjects, allowing comparison of pulsatile flow profiles between them. The profiles measured by this technique are repeatable on the same subject, and vary between subjects. At some body sites, notably near arterioles, the response obviously relates to gross tissue motion, but at others the signature is of dermal origin. It is not yet clear whether it relates to actual capillary flow variation or distortion of the scattering tissue in response to changes in the driving pressure.

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Measurements of flow in retinal vessels is presented and compared with in vitro measurements on whole blood in capillaries ranging from 75 to 200µm diameter. The viewing angle of the capillaries and their range of size allows sizedependent effects to be investigated when estimating flow within actual vessels.Retinal measurements show a pulse effect. When this is removed by synchronisation, multi-exposure measurements show different spectral signature from single speed scatterers. Multi-exposure measurements of the retina demonstrate a varying contribution of stationary scatter across the field. Unlike scattering in dermal tissue, photons in retinal vessels must return by multiple scatter from moving Red Blood Cells, whose motion is directed. Speckle estimates of flow in retinal vessels are therefore possible.