A system for monitoring parameters of a sample includes an imaging unit including a lens assembly and a detector unit configured for collecting light arriving from a region of interest on an object while being defocused with respect to the region of interest and generating defocused image data pieces indicative of light collected from the region of interest. The lens assembly includes at least one lens and is configured for defining at least one intermediate optical plane being a conjugate image plane or an intermediate Fourier plane with respect to an image plane of the detector unit. The system includes at least one symmetry replicator located at the at least one intermediate optical plane, thereby providing imaging of secondary speckle pattern on the detector array having a selected symmetry condition.