1. A non-invasive method for determining blood flow distribution in a region of interest, the method comprising: illuminating a region of interest of a subject with a coherent light source; sequentially acquiring at least two speckle images of the region of interest, wherein sequentially acquiring the at least two speckle images comprises acquiring the at least two speckle images in synchronization with motion of the heart of the subject; and electronically processing the at least two acquired speckle images based on the temporal variation of the pixel intensities in the at least two acquired speckle images to generate a laser speckle contrast imaging (LSCI) image, determine distribution of blood flow speed in principal vessels and quantify perfusion distribution in tissue in the region of interest from the LSCI image, wherein the LSCI image enables detection of different blood flow speeds.