PWS is a congenital, progressive vascular malformation of the skin that occurs in an estimated 7 children per 1,000 live births. Approximately 1,500,000 individuals in the United States and thirty-two million people worldwide have PWS. The pulsed dye laser produces reasonably good clinical results in a select population of PWS patients due to its ability to destroy selectively PWS blood vessels. However, the treatment success rate for the vast majority of patients is very low (< 10 percent) if the ultimate standard required is complete blanching of the lesion. The clinical objective in the treatment of PWS patients receiving laser therapy is to maximize thermal damage to the targeted blood vessels, while avoiding injury to the epidermis. For practical implementation of cooling for PWS laser therapy, a large, spatially selective temperature gradient at the skin surface is required. Our central hypothesis for the proposed research is that with cryogen spray cooling (CSC), the epidermis can be cooled selectively. When a cryogen spurt is applied to the skin surface for a short period of time (milliseconds), cooling remains localized in the epidermis, while leaving the temperature of deeper PWS blood vessels unchanged The selection of optimal parameters for CSC and laser light dosage for PWS treatment is governed by two constraints: (1) CSC must provide a spatially selective temperature reduction sufficient to protect the epidermis; and (2) epidermal temperature must not exceed 70 degrees C to avoid necrosis after laser therapy. Presently, all patients are treated with CSC spurt durations and laser light dosages based on clinical judgement of the physician without taking into consideration individual variations in the biophysical, structural, optical and thermal properties of PWS skin. Epidermal melanin concentration, epidermal thickness and PWS depth (150-1000 um) vary on an individual patient basis and even from site to site on the same patient. Infrared tomography (IRT) provides a practical methodology for PWS characterization on an individual patient basis prior to the institution of laser therapy. IRT provides a means to determine the temperature increase in epidermal melanin immediately after laser exposure, and PWS blood vessel depth. Based on this methodology, we have proposed a strategic sequence to determine the: (1) optimal parameters for CSC; and (2) maximum incident light dosage that may be delivered in conjunction with CSC without exceeding the threshold for epidermal damage.
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