A system is suggested comprising an optical sensing means and a processing unit. The optical sensing means may include an optical guide with a distal end, wherein the optical guide may be configured to be arranged in a device to be inserted into tissue in a region of interest. The processing unit may be configured to receive information of a region of interest including different tissue types as well as of a path through the tissues, to determine a sequence of tissue types along the path, to determine a tissue type at the distal end of the optical guide based on information received from the optical sensing means, to compare the determined tissue type with the tissue types on the path, to determine possible positions of the distal end of the optical guide on the path based on the comparison of tissue types, and to generate a signal indicative for the possible positions.