Tissue Properties

Lasers have revolutionized the treatment of cutaneous vascular disorders. Conditions such as port wine stains can now be treated with good to excellent results. However, there remains a large group of patients who do not respond fully to treatment and who may even experience negative side effects. Preliminary work performed in the Tissue Optics Lab and elsewhere has indicated that this variation in treatment is a result of a mismatch between the laser parameters and the anatomy of the cutaneous vasculature. Optical-thermal models of laser-tissue interaction have been developed in an attempt to determine the optimum laser parameters. We have found evidence that laser coagulation of blood is much more complex process than previously anticipated, involving chemical changes in hemoglobin, shape changes of the red blood cells and protein coagulation on two different time scales. The scattering and absorption properties of blood are thus time-dependent. Optical-thermal models cannot hope to be useful unless these mechanisms are understood. We are performing investigations involving:

- Using a pump-probe setup to investigate the optical property changes of coagulating blood at various wavelengths and with various laser settings.

- Using an imaging technique called optical coherence tomography to investigate the coagulation process in cuvettes of blood and in a hamster dorsal skin flap chamber.

- Using magnetic resonance imaging to explore the changes in susceptibility of hemoglobin as it changes from oxy- to met- form during rapid heating.

It is anticipated that this work will help determine strategies to improve the effectiveness of laser treatment of cutaneous vascular disorders.