Mathematical Modeling of Vaporization during Laser-Induced Thermotherapy in Liver Tissue

TL;DR

The paper tackles the mismatch between laser-induced thermotherapy (LITT) simulations and observed temperature plateaus in liver tissue by introducing two vaporization frameworks that capture water phase change around $T=100^{\circ}\mathrm{C}$ with latent heat $\lambda$. It compares an effective specific heat (ESH) approach and an enthalpy-based method, each paired with a simple condensation mechanism to enforce energy conservation, against ex-vivo porcine liver data. Results show that both vaporization models markedly improve agreement with measurements over the baseline model that omits vaporization, though the simple condensation mechanism can cause non-physical heat redistribution in the mid-treatment period. The work underscores the importance of modeling vapor transport for accurate LITT planning and monitoring and points to future refinements, such as vapor diffusion or porous-media transport and perfusion-informed parameter identification for in vivo applications.

Abstract

Laser-induced thermotherapy (LITT) is a minimally invasive method causing tumor destruction due to heat ablation and coagulative effects. Computer simulations can play an important role to assist physicians with the planning and monitoring of the treatment. Our recent study with ex-vivo porcine livers has shown that the vaporization of the water in the tissue must be taken into account when modeling LITT. We extend the model used for simulating LITT to account for vaporization using two different approaches. Results obtained with these new models are then compared with the measurements from the original study.

Figures (7)

• Figure 1: Sketch of the geometry including the water-cooled applicator with radiating laser fiber.
• Figure 2: Function $W(T)$ and derivative $\frac{dW}{dT}(T)$ of tissue water density from Yang.
• Figure 3: Comparison of the models for the case P34F47.
• Figure 4: Difference between simulated and measured temperature for the case P34F47.
• Figure 5: Comparison of the models with temperature measurements.