1. A device for non-invasive analysis in a region of interest of a body medium, the device comprising: (a) an illuminator configured to produce pulsed light of at least two different wavelengths; (b) an acoustic unit configured and operable to collect acoustic radiation and generate data indicative thereof, the acoustic unit being operable to collect acoustical radiation at a location on a body surface generated in the region of interest by a photoacoustic effect when the region of interest is irradiated with the illuminating pulsed light and generate measured data indicative of the received radiation; and (c) a processor configured to receive the measured data, and analyze the received data to determine at least one desired characteristic of the region of interest, said at least one desired parameter comprising a cross-sectional dimension of the region of interest, the processor being preprogrammed to carry out at least one of the following: i) determining time variations of at least one predetermined parameter of a time dependent acoustic signal in the collected acoustic radiation for each of said at least two wavelengths, and determining oxygen saturation level in the region of interest; ii) operating a plurality of acoustic elements of the acoustic unit to thereby define a focal volume for the acoustic radiation collection, said focal volume matching dimensions of the region of interest.