The goal of the cooperative project of the Competence Centre for Minimally Invasive Medicine & Technology Tübingen-Tuttlingen (MITT) and the University Hospital of Tübingen was to facilitate the treatment of chronic wounds and improve their healing process using an innovative laser method. The partners developed a method that enables the recognition of necrotic tissue on wound surfaces and the contact-free ablation of the tissue using a pulsed Er:YAG laser. The method was clinically tested on chronic wounds.
An imaging diagnosis system, based on a speckle procedure that allows the differentiation of necrotic from vital tissue, was used. The method is based on the fact that the speckle pattern is static on necrotic tissue, but changes temporarily (instationary) in wound areas with surface perfusion due to a constantly changing scattering matrix. Therefore, this leads to a much lower contrast between the speckles in the perfused area. Speckle contrast is an indicator of perfusion.
The method was used to treat four anaesthetised patients in an initial clinical study that documented the wound healing process. The wounds were debrided, and the speckle contrast image was assessed, following which an ablation pattern was calculated that was scanned point for point with an Er:Yag laser. Firstly, the necrotic tissue in areas with the highest speckle contrast was ablated. The scan areas were stepwise expanded through repeated measurements and the calculation of a new scan pattern. This enabled the entire wound to be refreshed and ablated as far as the capillary bed, hence right into the areas supplied with blood. The treatment duration varied from around 15 minutes to one hour, depending on the size and thickness of the necroses. Overall, it was possible to achieve the cleaning of the wound in all patients, with results similar to surgical debridement. The subsequent wound healing progress was also similar to that following surgical debridement. The only difference was that in all cases laser treatment took much longer than surgical debridement. However, it is envisaged that this disadvantage might be compensated by the possibility of treating wound necrosis without anaesthesia. This will need to be confirmed in a future study.