Mirko Mirkov

Analytical modeling of laser pulse heating of embedded biological targets: An application to cutaneous vascular lesions

Detailed understanding of the thermal processes in biological targets undergoing laser irradiation continues to be a challenging problem. For example, the contemporary pulsed dye laser (PDL) delivers a complex pulse format which presents specific challenges for theoretical understanding and further development. Numerical methods allow for adequate description of the thermal processes, but are lacking for clarifying the effects of the laser parameters. The purpose of this work is to derive a simplified analytical model that can guide the development of future laser designs. A mathematical model of heating and cooling processes in tissue is developed. Exact analytical solutions of the model are found when applied to specific temporal and spatial profiles of heat sources. Solutions are reduced to simple algebraic expressions. An algorithm is presented for approximating realistic cases of laser heating of skin structures by heat sources of the type found to have exact solutions. The simple algebraic expressio...

Common Vascular Lesions

Wavelength is an important factor, for both hemoglobin absorption and depth of effective treatment. Longer wavelengths are better for deeper vascular lesions. Spot size is important, for both degree of coverage and depth of effective treatment. Bigger spots go deeper. Remember that melanin and hemoglobin absorption peaks are very similar. Attention to the degree of pigmentation and tan are important. While oxy-hemoglobin is the primary target, met-hemoglobin and clot area are also important, especially when considering multiple pass and multiple wavelength strategies. Attempt to match the appropriate pulse duration with the size of the intended target. Shorter pulse durations are better for smaller vessels, while longer pulse durations are better for larger vessels. Be cautious with high dose 1064 when treating vascular lesions. Runaway thermal damage is always a risk.

Delivery of light to the skin through ablated conduits

Non‐invasive laser skin treatment modalities are generally designed to protect the epidermis by cooling and limiting the laser energy deposition in accordance with skin type. We explore a treatment modality that uses a 2,940 nm Er:YAG laser with high tissue absorption to ablate an array of channels through the epidermis and upper dermis, and then deliver laser energy from a 1,320 nm Nd:YAG laser with lower tissue absorption through the ablated channels. Treatment through ablated conduits offers a unique capability to deliver laser radiation to a deeper level in the dermis or beyond the dermis and the delivered energy to be deposited in a nearly uniform distribution. The ablated channels represent a relatively small surface and volume fraction of the epidermis and upper dermis, and heal very fast. A pilot study was performed to explore the benefits of treatments through ablated conduits for skin tightening, cellulite, and acne scarring.

Häufige vaskuläre Hautveränderungen

Die Wellenlange ist eine wichtige Einflussgrose fur die Hamoglobinabsorption und die effektive Behandlungstiefe. Langere Wellenlangen sind besser fur tiefere vaskulare Hautveranderungen geeignet. Der Strahldurchmesser ist sowohl fur die Reichweite als auch fur die effektive Behandlungstiefe entscheidend. Grosere Strahldurchmesser reichen tiefer. Die Absorptionsmaxima von Melanin und Hamoglobin sind sehr ahnlich. Der Pigmentierungs- und Braunungsgrad des Patienten muss unbedingt beachtet werden. Obwohl die primare Zielstruktur Oxyhamoglobin ist, sind Methamoglobin und Blutgerinnsel ebenfalls wichtige Zielstrukturen, besonders wenn mehrere Durchgange und verschiedene Wellenlangen zum Einsatz kommen. Die Impulsdauer sollte der Grose der Zielstruktur entsprechen. Langere Impulsdauern sind am besten fur grosere, kurzere Pulsdauern besser fur kleinere Blutgefase geeignet. Bei der Behandlung von vaskularen Hautveranderungen muss vorsichtig mit hohen Dosierungen (1.064 nm) umgegangen werden, da das Risiko unkontrollierter thermischer Schadigungen besteht.