Martin Jurna

Influence of absorption induced thermal initiation pathway on irradiance threshold for laser induced breakdown.

We investigated the influence of thermal initiation pathway on the irradiance threshold for laser induced breakdown in transparent, absorbing and scattering phantoms. We observed a transition from laser-induced optical breakdown to laser-induced thermal breakdown as the absorption coefficient of the medium is increased. We found that the irradiance threshold after correction for the path length dependent absorption and scattering losses in the medium is lower due to the thermal pathway for the generation of seed electrons compared to the laser-induced optical breakdown. Furthermore, irradiance threshold gradually decreases with the increase in the absorption properties of the medium. Creating breakdown with lower irradiance threshold that is specific at the target chromophore can provide intrinsic target selectivity and improve safety and efficacy of skin treatment methods that use laser induced breakdown.

Fractional laser photothermolysis using Bessel beams.

Fractional photothermolysis uses lasers to generate a pattern of microscopic columnar thermal lesions within the skin stimulating collagen remodeling. In this paper we investigate the use of Bessel beams as an alternative to conventional Gaussian beams in creating laser photothermal lesions of different aspect ratios in skin. We show for the first time the improved photothermal lesion depth-to-diameter aspect ratio using Bessel beams in ex vivo human skin as well as in numerical simulations using electric field Monte Carlo photon transport, finite difference methods and Arrhenius model. Bessel beams allow the creation of deep and narrow thermal lesions necessary for improved efficacy in fractional photothermolysis.

Real-time imaging of suction blistering in human skin using optical coherence tomography

Separation of skin epidermis from the dermis by suction blistering has been used with high success rate for autologous skin epidermal grafting in burns, chronic wounds and vitiligo transplantation treatment. Although commercial products that achieve epidermal grafting by suction blistering are presently available, there is still limited knowledge and understanding on the dynamic process of epidermal-dermal separation during suction blistering. In this report we integrated a suction system to an Optical Coherence Tomography (OCT) which allowed for the first time, real-time imaging of the suction blistering process in human skin. We describe in this report the evolution of a suction blister where the growth is modeled with a Boltzmann sigmoid function. We further investigated the relationship between onset and steady-state blister times, blister growth rate, applied suction pressure and applied local skin temperature. Our results show that while the blister time is inversely proportional to the applied suction pressure, the relationship between the blister time and the applied temperature is described by an exponential decay.