Laser speckle contrast analysis (LASCA), also known as laser speckle contrast imaging (LSCI), is a method that instantly visualizes microcirculatory tissue blood perfusion. It is an imaging technique that combines high resolution and high speed.
When an object is illuminated by laser light, the backscattered light will form an 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 with a fixed exposure time will record these changes in the speckle pattern as motion blurring.
Static speckle pattern
Moving 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 local speckle contrast, i.e. the contrast between a small neighborhood of pixels over the entire image. The contrast has been found to correlate with blood flow and this is how the LASCA technique can be implemented for blood perfusion measurements. 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, blurring will increase, 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 blurring will decrease and the standard deviation will increase. The mean intensity will remain unchanged.
PeriCam PSI System records the blood perfusion using the arbitrary units, perfusion units (PU). Each instrument is factory calibrated in order to compare results accurately. In addition, PeriCam PSI System comes with a calibration box to allow for continuous control of calibration and adjustments.