Speckle contrast method and system that discriminates photons based on their path length in tissue, the method comprising the steps of:directing light from a pulsed light into a sample by optical elements；synchronizing the time between the pulse injection to sample and the detection unit；collecting the photons that have travelled through the sample by optics, and conveying the photons of a single or a limited number of speckles from the sample to one or more detection elements；time-tagging photons thanks to the synchronization of the detector element and/or the time-tagging electronics with the laser pulse emission；estimating each photon time-of-flight by the difference between its time tag and the laser pulse emission；categorizing the detected photons based on the value of the time-of-flight in a certain number of time gates；measuring the speckle contrast
