Laser speckle contrast analysis (LASCA) for blood flow visualization: improved image processing

LASCA is a single-exposure, full-field technique for mapping flow velocities. The motion of the particles in a fluid flow causes fluctuations in the speckle patten produced when laser light is scattered by the particles. The frequency of these intensity fluctuations increases with increasing velocity. These intensity fluctuations blur the speckle pattern and hence reduce its contrast. With a suitable integration time for the exposure, velocity can be mapped as speckle contrast. The equipment required is very simple. A CCD camera and a framegrabber capture an image of the area of interest. The local speckle contrast is computed and used to produce a false-color map of velocities. LASCA can be used to map capillary blood flow. The results are similar to those obtained by the scanning laser Doppler technique, but are obtained without the need to scan. This reduces the time needed for capturing the image from several minutes to a fraction of a second, already a clinical advantage. Until recently, however, processing the captured image did take several minutes. Improvements in the software have now reduced the processing tome to one second, thus providing a truly real-time method for obtaining a map of capillary blood flow.