PA experiment setup of this cooling study. (A) Experimental dark-field fPAM system integrated with a thermoregulation setup. Commercially available ultrasound gel was applied on the rat sciatic nerve for acoustic and thermal coupling; the rat subjects were placed between the water container and a custom-made stereotaxic apparatus for imaging. (B) The laser was pulsed with frequency of 10 Hz and coupled to an optical fiber into the strong focusing dark-field PA path to illuminate the target cross-section at the nerve. PA waves were detected by a 50-MHz transducer and then through the A/D card to the computer for further data analysis. (C) Localized temperature modulation was achieved via immediate heat transfer between the sciatic nerve and the perfused thermoregulatory water tube. A fixed scanning cross-section was selected during all experiments. The nerve thermocouple couple probe was placed directly below the sciatic trifurcation. We also applied sutures as needed to reinforce the stability of the tube and thermocouple probe.