色素性病変に対する最適パルスレーザ療法の理論解析

抄録

Optimization of therapeutic conditions of a pulsed laser for pigmented lesions is discussed herein from the standpoint of the fundamental interactions of laser light with pigmented cells. Among the important mechanisms leading to cell damage is thermal in nature. This laser therapy is a process for damaging pigmented lesions in tissue by absorption of pulsed laser light. First, the wavelength must be selected in considering preferential absorption in target cells, which relate closely to the penetration depth of laser light and effectiveness for removing pigmented cells. The second thing we consider is thermal confinement. The pulse duration must be shorter than the time for thermal relaxation of the pigmented cells, and the energy delivered must be sufficient to cause irreversible thermal damage. The thermal damage is associated with the denaturation of proteins and the inactivation of enzymes. Accordingly, we consider that the models must include not only the solution of the heat conduction equation but also the Arrhenius equation for the inactivation process. Energy absorption and heat transfer processes occuring during the interaction of laser light pulses with pigmented lesions in tissues is investigated theoretically. As a result, the relation between the target size and the thermal relaxation time is formulated. Ideal therapy is defined as minimal heating of the epidermis and dermis, but with irreversible damage to the pigmented cells. By applying the Arrhenius equation for the inactivation process, we obtain the variation of the temperature rise as a function of the time required to give the same survival ratio. The possibility for selective interaction between short laser light pulses and pigmented cells is shown, resulting in the formation of thermo-denaturation of microregions near the pigmented granules.