A Review of methods for quantifying tissue thermal conductivity

Analytical and numerical modeling of heat transfer in soft tissues can help improve the safety and efficacy of thermal therapies and aid in characterizing the extent of tissue thermal effects such as thermal damage. Modeling of tissue temperatures requires several thermophysical properties as well as description of the thermal contribution of blood flow or perfusion, as appropriate. One of the essential properties is the thermal conductivity of the tissue for which no suitable standard measurement method exists. Thermal conductivity varies with the type of tissue and its composition in terms of water content, fat, and protein. Because these constituents vary from sample to sample and with time, measuring tissue thermal conductivity poses significant challenges and standardized methods have yet to emerge. This review critically examines common and emerging methods that have been used to determine thermal conductivity of soft tissue. Although some of the techniques (e.g., the guarded hotplate) are standardized for use with inorganic materials, extending their application to measuring tissues is not straightforward. Some of the methods are applicable only to ex vivo tissue samples, which may be advantageous as they avoid uncertainties associated with blood perfusion. Methods applicable to in vivo tissues require description of the contribution of the blood perfusion to estimate the thermal conductivity accurately. Methods to measure the thermal conductivity of bone and blood are outside the scope of this review.