IVVM images of normal (nontumour-bearing) murine mammary fat pad and lymph node. (a) Mammary fat pad, viewed with IVVM, showing three-dimensional structure of vessels and tissue. Direction of lymphatic flow is indicated by the arrow located within the lymphatic vessel (→). Flow within the adjacent blood vessels (➢) was in the same direction. Another vessel (indicated with open arrowhead), was out of the plane of focus and could be resolved by focusing up and down through the tissue. 200×. (b) The inguinal lymph node (LN) found within mammary fat pad #4 where a large internal mammary vessel (*) branches. 40×.