Monitoring of melanoma growth on a nude mouse ear. (a) PAM image of blood vesels in the ear acquired before injection of melanoma cells. (b) PAM image where in vivo red blood cells (RBCs) can be identified (the close-up image indicates the biconcave
structure of RBCs). (c) PAM image of blood vessels and melanoma taken four days after injecting melanoma cells. The melanoma image is extracted by taking the difference of the two PAM images [(a) and (c)] and is plotted in gray: MT, melanoma tumor. (d) Optical microscopy image (0.057 NA) of the same area in (a) and (c).