moorFLPI Theory

The full field laser technique is used to provide real time images of blood flow. The technique, known as laser speckle contrast imaging, exploits the fact that the random speckle pattern that is generated when tissue is illuminated by laser light, changes when blood cells move within the region of interest. When there is a high level of movement (fast flow) the changing pattern becomes more blurred and the contrast in that region reduces accordingly. Therefore low contrast is related to high flow, high contrast to low flow. The contrast image is processed to produce a colour-coded image that correlates with blood flow in the tissue

Laser speckle imaging is based on a technique pioneered by Fercher and Briers at the University of Essen in Germany in the early nineteen-eighties. Originally called Single-exposure Speckle Photography, it was a two-stage process involving photography under laser illumination followed by optical image processing (spatial filtering) to convert the contrast variations to intensity variations. The first digital version, called LASCA (LAser Speckle Contrast Analysis), was developed by Briers and co-workers at Kingston University in the early nineties; by passing the photographic stage allowed a real-time technique to be realised. Many refinements, including a video capability, have since been added by our own team at Moor Instrument

The strength of this technique is video frame rate blood flow images (25 per second). It enables the tracking of fast transient blood flow changes that could not be seen by conventional laser imaging techniques. It is possible to view pulsation in finger tips and spatial variations due to deep breath, occlusion, reactive hyperaemia and other stimul