Objective: To quantify the directivity of electrical and thermal conductivities in perfused liver caused by local blood vessel distribution and determine their influence on RF ablation zones.

Methods: Micro probes for local electrical and thermal conductivity measurement have been developed recently by using photolithography techniques. The micro electrical probe is a two-electrode probe which can obtain the electrical conductivity of tissues by measuring the impedance between two electrodes. The micro thermal probe is based on the principle of the traditional hot-wire transient method with miniaturization and geometric modification. An ex vivo pig liver model was developed in the tissue lab at Valleylab, Tyco Healthcare (Boulder, CO). After the liver was harvested and transported to the lab, the portal vein and hepatic artery were connected to a perfusion circuit with a perfusion pump. The flow rate was adjusted to simulate human values (1050ml/min in portal vein and 480ml/min in hepatic artery). The micro probes were inserted into different locations of the perfused liver for the measurement of tissue properties. Four measurements in different directions were taken at each insertion site by turning the probe around its long axis ninety degrees in order to investigate the directivity of tissue properties. We identified the relative location of micro probes to major blood vessels by using ultrasound imaging. Also, the RF ablation treatments were applied in the insertion locations and ablation outcomes were compared with the directivity measurement of electrical and thermal conductivity of tissues.

Results: The directivity changes for both of electrical and thermal conductivity were observed in perfused pig liver. These changes were more significant when probe placement was close to major blood vessels. We also observed that the RF ablation area and shape has an inverse relationship with the values of directional effective thermal conductivity.

Conclusions: The major blood vessels can significantly affect the directivity of local tissue properties. The RF ablation outcome area and shape may be predicted by the local measurement of directional effective thermal conductivity of tissues.