In vivo noninvasive PA images of subcutaneous microvasculature, melanoma, and cortical vasculature in mice using dark-field PAM. (A) Top: a composite image of a melanoma acquired at 764 nm and surrounding microvasculature acquired at 584 nm using a 50 MHz ultrasonic detection frequency. Bottom: a B-scan image along the cut in the corresponding top figure. M, melanoma. (B) Top: a cortical vasculature image obtained at 570 nm using a 20 MHz ultrasonic detection frequency. Bottom: a B-scan image along the cut in the corresponding top figure. SS, sagittal sinus; MCA, middle cerebral artery; CS, coronal suture. (Reprinted with permission from ref 9. Copyright 2006 Nature, and from ref 27. Copyright 2009 American Institute of Physics.)