Time-integrated speckle for the full-field visualisation of motion, with particular reference to capillary blood flow
This thesis describes the development of an instrument which uses the statistical properties of laser speckle to visualise skin blood flow. This technique has the advantages of being safe, non-invasive, non-contact and a full-field measuring device. The instrument is fully computational, and produces a qualitative false colour map of the skin blood flow. Related background material to the research is given in chapters one to four of this thesis. The subjects covered include the properties of laser speckle, relevant physiology, the optical properties of tissue, and alternative methods of measuring blood flow. Some work was done by the author on an existing photographic speckle technique, and this is also described in chapter four. Chapter five describes the computational method used in detail. The technique is based on the fact that stationary scatterers give rise to a fully-developed speckle pattern, with a high speckle contrast. Moving scatterers (such as the red blood cells moving through the microvascular circulation, beneath the skin surface), cause the resulting speckle pattern to appear blurred, and have a low speckle contrast. The contrast of the subjective speckle pattern can thus be used to give a qualitative measure of the skin blood flow. The experimental results are given in chapter six. These show that the technique has been successfully used to distinguish qualitatively between different levels of temporal and spatial skin blood flow. Various external stimuli, including heat, and the use of a blood pressure cuff to occlude flow, were used. The instrument was generally used to examine the skin blood flow in the hand, but can also be used to look at other areas of the human body. This technique could be further developed to visualise skin blood flow in the retina.