This spatial division multiplexing in power-limited optical communication systems. The method is suitable for displaying video information such as an advertisement, information selected by the user, or a program guide. The invention finds a preferred application in the field of diagnosis. The handpiece is manipulated by the user to guide the needle during placement. When permanently assigned multicast addressing is used, several channel parameters are assigned to a multicast session, and any terminals desiring to tune in to the multicast session simply invoke those parameters from a storage location at which they have been previously stored.