Effect of Configuration Between Cryoprobe and Large Blood Vessels on the Tissue Freezing During Cryosurgery

For accurate predictions of the tissue temperature distribution during cryosurgery a thermal model should incorporate the individual impact of large blood vessels. In presence of large vessel, configuring cryoprobe becomes very important because misplacement of cryoprobes may result in either inadequate cooling temperatures in the target tissue due to the heating nature of large vessels or undesired damage to the downstream healthy tissues and organs as a result of arresting of key vessels. In this article, typical vascular models are applied to investigate the effects of large blood vessels and cryoprobe configurations on the transient temperature profiles of cooled tissues during cryosurgery. The thermal model describing heat transfer to or from large vessels is based on heat transfer coefficient derived from analytical solutions of forced convection in cylindrical ducts. A finite difference algorithm developed in our previous study is used to solve this complex problem with phase change heat transfer in biological tissues embedded with large blood vessels. Numerical computations are then performed to predict the transient temperature distributions of tissues under three different configurations of cryoprobe. The results indicate that different configurations of cryoprobe can produce significantly different temperature profiles and blood vessel heating in cooled tissues. Results of this study should be considered in the strategy for an optimal placement of cryoprobes when performing cryosurgical treatments in the vicinity of large blood vessels.

I. Introduction

CRYOSURGERY (also called cryotherapy) is the use of extreme cold produced by cryogenic agents to destroy abnormal tissue. It is used to treat some kinds of cancer and some precancerous or noncancerous conditions, and can be used both inside the body and on the skin. After several decades' development, some facets of modern cryosurgical technique are optimal for effective therapy, whether intended for cure of tumor or non-tumor disease. Good results are being achieved in widely diverse clinical problems. On the other hand, especially in the treatment of tumor in the vicinity of large blood vessels, cryosurgery is less than optimal. Fortunately, this problem has received more and more attentions [1]–[3] since Zhang et al. [4] made the first attempt to develop a theoretical model as well as design a simulating experiment for cryogenic heat transfer in biological tissues embedded with large blood vessels.