Photoacoustic monitoring of neovascularities in grafted skin

Background and Objectives: In skin grafting, evaluation of graft adhesion to the recipient site in the early postgrafting period is important. However, conventional diagnoses such as visual observation and thermography required about 1 week to obtain results and these methods cannot give quantitative information on the adhesion of a skin graft. We proposed a new method for monitoring adhesion of grafted skin that is based on measurement of photoacoustic signals. To investigate the validity of the method, we performed experiments using rat autografts models. Study Design/Materials and Methods: Grafted skin in a rat was irradiated with 200 mu J, 532-nm nanosecond laser pulses, and photoacoustic signals were detected with a piezoelectric transducer placed on the skin at various postgrafting time. Temporal profiles of the signals were converted to depth profiles using an assumed sound velocity of 1,500 m/second. Histological analysis was performed to observe neovascularities formed in the grafts. Results: At 6 hours postgrafting, a photoacoustic signal peak appeared in the depth region corresponding to the graft. The results of histological analysis also showed formation of neovascularities in the graft after 6 hours postgrafting, indicating that photoacoustic signal peaks observed in the graft originated from the neovascularities, which are an indication of graft adhesion. For up to 24 hours postgrafting, no significant difference was observed between the results of visual observation and laser Doppler imaging of the same grafted skins. Conclusion: We have demonstrated that photoacoustic signals originating from neovascularities in grafts can be sensitively detected in the early postgrafting period, suggesting the validity of photoacoustic measurement for adhesion monitoring of skin grafts.