Confinement of Freezing Front by Laser Irradiation During Cryosurgery

A new methodology to control the freezing front propagation during cryosurgical procedures is studied through the use of numerical techniques. Laser irradiation of a target tissue is explored as a new methodology for localizing heat generation and, thus, confining more accurately the desired cryoinjury region and to protect a thicker superficial layer of tissue. In addition to the irradiation of laser energy, the use of dyes is proposed as a means of localizing heat absorption and increasing the thickness of the protected region. A 2D finite volume numerical code based on the enthalpy method was developed to model the freezing process during cryoprobe cooling of a volume of tissue, while heating was applied to the external boundary protecting the superficial layer of tissue. Laser irradiation was modeled with Beer’s Law, and the energy absorption, which is proportional to the intensity, was taken as a source term in the energy equation. The thermophysical properties of the tissue are modeled as temperature dependent properties of water. Temperature contours resulting from a) constant temperature heating b) and regulated laser irradiation heating of tissue indicate that the latter methodology may be more effective in limiting cryoinjury to a predefined region. Additionally, if dyes are used, the protected area increases in thickness. The most dramatic differences between the two methodologies occur when the cryoprobe is placed near the surface, the effective attenuation coefficient of the material is low, and dyes are injected into the tissue to promote localized absorption of laser irradiated energy.