Molecular photoacoustic imaging. (A) Correlation coefficient images, obtained by comparing multiwavelength photoacoustic images with optical spectra of targeted gold nanoparticles, nontargeted gold nanoparticles, and a dye, overlaid on ultrasound images of the subcutaneous gelatin implants in mouse tissue ex vivo. Only correlation coefficient values >0.75 were displayed in the images. Images measure 44 mm laterally and 9.1 mm axially. (B) Photographs of the tumors in mice and the corresponding photoacoustic subtraction images (green) shown as horizontal slices through the tumors. (C) (Left) Photoacoustic image of the zebrafish brain with fluorescent protein expression shown in color. (Right) Corresponding histology of a dissected fish. See text for details. (Adapted from De la Zerda et al. 2008, with permission from Macmillan © 2008, adapted from Mallidi et al. 2009, with permission from American Chemical Society © 2009, and adapted from Razansky et al. 2009, with permission from Macmillan © 2009.)