Optical and thermal simulations of noninvasive laser coagulation of the human vas deferens

Successful noninvasive laser coagulation of the canine vas deferens, in vivo, has been previously reported. However, there is a significant difference between the optical properties of canine and human skin. In this study, Monte Carlo simulations of light transport through tissue and heat transfer simulations are performed to determine the feasibility of noninvasive laser vasectomy in humans. A laser wavelength of 1064 nm was chosen for deep optical penetration in tissue. Monte Carlo simulations determined the spatial distribution of absorbed photons inside the tissue layers (epidermis, dermis, and vas). The results were convolved with a 3-mm-diameter laser beam, and then used as the spatial heat source for the heat transfer model. A laser pulse duration of 500 ms and pulse rate of 1 Hz, and cryogen spray cooling were incident on the tissue for 60 s. Average laser power (5-9 W), cryogen pulse duration (60-100 ms), cryogen cooling rate (0.5-1.0 Hz), and increase in optical transmission due to optical clearing (0-50 %), were studied. After application of an optical clearing agent to increase skin transmission by 50%, an average laser power of 6 W, cryogen pulse duration of 60 ms, and cryogen cooling rate of 1 Hz resulted in vas temperatures of ∼ 60°C, sufficient for thermal coagulation, while 1 mm of the skin surface (epidermis and dermis) remained at a safe temperature of ∼ 45°C. Monte Carlo and heat transfer simulations indicate that it is possible to noninvasively thermally coagulate the human vas without adverse effects (e.g. scrotal skin burns), if an optical clearing agent is applied to the skin prior to the procedure.