Laser Speckle Contrast Analysis (LASCA) 1-6 is a method that visualizes tissue blood perfusion in the microcirculation instantaneously. It is an imaging technique that combines high resolution and speed.
When an object is illuminated by laser light, the backscattered light will form a random interference pattern consisting of dark and bright areas. This pattern is called a speckle pattern. If the illuminated object is static, the speckle pattern is stationary. When there is movement in the object, such as red blood cells in a tissue, the speckle pattern will change over time. In the PeriCam PSI System, a CCD camera will record these changes in the speckle pattern.
Depending on the degree of movement in the imaged area, the level of blurring will differ. The more movement there is in an image, the more blurred it will appear. The level of blurring is quantified by the speckle contrast. The contrast has been found to correlate with blood flow and this is how the LASCA technique can be implemented for blood perfusion measurements. The speckle contrast is defined as the ratio between the standard deviation of the intensity and the mean of the intensity. If there is a lot of movement, the blurring will increase and the standard deviation of the intensity will decrease, and consequently the speckle contrast will be lower. On the contrary, if there is no movement, the speckle contrast will be larger since the blurring will decrease and the standard deviation will increase. The mean intensity will remain unchanged.
The PeriCam PSI System records the blood perfusion using the arbitrary units, Perfusion Units (PU). In order to compare result accurately each instrument is factory calibrated. In addition, a Calibration Box is delivered with the PeriCam PSI System to allow for continuous control of calibration and adjustments.
Static speckle pattern.
Moving speckle pattern.
1. Laser Speckle Contrast Analysis (LASCA): A nonscanning, full-field technique for monitoring capillary blood flow. Briers J. D. and Webster S. Journal of Biomedical Optics 1(2), p. 174-179, 1996
2. Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging. Briers, J. D. Physiological measurement 22(4), p. R35-R66, 2001
3. Linear response range characterization and in vivo application of laser speckle imaging of blood flow dynamics. Nelson, J. S. et al. Journal of Biomedical Optics 11(4), p. 1, 2006
4. Dynamic imaging of cerebral blood flow using laser speckle. Boas, D. A. et al. Journal of cerebral blood flow and metabolism 21(3), p. 195-201, 2001
5. Development of a laser speckle imaging system for measuring relative blood flow velocity. Sowa, M. G. et al. International Society for Optical Engineering, Bellingham WA, WA 98227-0010, United States, p. 634304, 2006
6. Excellent reproducibility of laser speckle contrast imaging to assess skin microvascular reactivity. Roustit M. Microvasc Res. 2010