A method for diagnosing a human condition from a characteristic of a plaque or tissue in a subject is presented. The method includes directing broadband light by means of a sensing light path at an area of interest in the subject, at a target depth defined by the sensing light path and a reference light path. The continues with receiving the broadband light reflected from the area of interest in the subject by means of the sensing light path. The method further includes directing the broadband light by means of the reference light path at a reflecting device, and receiving the broadband light reflected from the reflecting device by means of the reference light path.