Development of a coagulation area presenting system in liver radio frequency ablation (Modeling for temperature-dependence of viscoelasticity in liver tissue)

Recently radio frequency ablation (RFA) has been increasingly important in treating liver cancers. RFA is ordinarily conducted using elastographic imaging to monitor the ablation procedure and the temperature of the electrode needle is displayed on the radiofrequency generator. However, the coagulation boundary of liver tissue in RFA is unclear and unconfident. This can lead to both excessive and insufficient RFA thereby diminishing the advantages of the procedure. In the present study, we developed a method for determining the coagulation boundary of liver tissue in liver RFA. To investigate this boundary we used the mechanical characteristics of biochemical components as an indicator of coagulation to produce a relational model for viscoelasticity and temperature. This paper presents the data acquisition procedures for the viscoelasticity characteristics and the results of relationship model of viscoelasticity's temperature dependence. We employed a rheometer to measure the viscoelastic characteristics of porcine liver tissue. To determine relationship model between temperature and viscoelasticity, we used a least-square method and the minimum root mean square error was calculated to optimize the model functional relations. The functional relation between temperature and viscoelasticity was divided into linear and non-linear in different temperature regions. The boundary between linear and non-linear functional relation was 58.0°C.