Monitoring of healing process of burns based on multiwavelength photoacoustic measurement

We attempted to monitor the healing process of burn injuries by multiwavelength photoacoustic (PA) measurement. Deep dermal burn with 20% total body surface area was made in the dorsal skins of rats. The wavelengths of 532 nm, 556 nm, 576 nm and 600 nm were used: 532 nm is isosbestic point for oxyhemoglobin (HbO2) and deoxyhemoglobin (HHb); 576 nm is HbO2 absorption dominant; and 556 nm and 600 nm are HHb absorption dominant. At 532 nm, 556 nm and 576 nm, the depths of PA signal peak were shifted to the shallower region of the wound with the elapse of time, which was found to reflect angiogenesis due to wound healing by histological analysis. The amplitudes of PA signals increased at all the wavelengths until 24 h postburn time. At 48 h postburn time, the signal amplitude continued to increase at 532 nm and 576 nm, while it decreased at 556 nm and 600 nm. This is attributable to the change from a shock phase to the phase of hyperdynamic state, which is accompanied by increases in cardiac output and oxygen consumption. These results suggest that multiwavelength photoacoustic measurement is useful for monitoring healing process of burn injuries.