LSFG stands for Laser Speckle Flowgraphy, which is the name of a blood flow imaging device that utilizes laser scattering.
When a biological surface is illuminated with a laser, the scattered light interferes with each other to create a random speckle pattern as shown in the figure.
This pattern is generally called Laser Speckle, and because it is used to obtain blood flow maps, the device was named LSFG.