Optical and magnetic resonance changes in photothermally coagulating blood

Cutaneous vascular disorders such as port wine stains can now be treated using lasers with a high probability of success. However, the predictability of the outcome, both in terms of satisfactory lesion clearance and risk of side effects, remains a major challenge. The investigators have found evidence that laser coagulation of blood is much more complex process than previously anticipated, involving chemical changes in the hemoglobin molecule, shape changes in the red blood cells, and protein coagulation on at least two different time scales. The optical (scattering and absorption) and thermal properties of blood are therefore time- and temperature-dependent. Thus, modeling using "cold" optical properties of blood may fail to predict experimental results. We have performed several investigations into the laser coagulation of blood to further elucidate the coagulation mechanisms:-A pump-probe experiment has been used to investigate the optical property changes of coagulating blood in cuvettes at various wavelengths. Measurements have been made of the time-domain integrated reflectance and transmission of the samples.-Rapid optical coherence tomography imaging of the coagulation process in cuvettes of blood shows distinct waves of coagulation.-A decrease of the longitudinal spin relaxation time in magnetic resonance imaging is observed in photothermally coagulated blood as compared to native blood.