Deep Brain Ultrasound Ablation Thermal Dose Modeling with in Vivo Experimental Validation

TL;DR

A new finite element method (FEM) simulation with enhanced damage evaluation capabilities was conducted, showing a good agreement in accuracy between simulation and experiment, and showed that the highest temperature and ablated volume differed between experimental and simulation results.

Abstract

Intracorporeal needle-based therapeutic ultrasound (NBTU) is a minimally invasive option for intervening in malignant brain tumors, commonly used in thermal ablation procedures. This technique is suitable for both primary and metastatic cancers, utilizing a high-frequency alternating electric field (up to 10 MHz) to excite a piezoelectric transducer. The resulting rapid deformation of the transducer produces an acoustic wave that propagates through tissue, leading to localized high-temperature heating at the target tumor site and inducing rapid cell death. To optimize the design of NBTU transducers for thermal dose delivery during treatment, numerical modeling of the acoustic pressure field generated by the deforming piezoelectric transducer is frequently employed. The bioheat transfer process generated by the input pressure field is used to track the thermal propagation of the applicator over time. Magnetic resonance thermal imaging (MRTI) can be used to experimentally validate these models. Validation results using MRTI demonstrated the feasibility of this model, showing a consistent thermal propagation pattern. However, a thermal damage isodose map is more advantageous for evaluating therapeutic efficacy. To achieve a more accurate simulation based on the actual brain tissue environment, a new finite element method (FEM) simulation with enhanced damage evaluation capabilities was conducted. The results showed that the highest temperature and ablated volume differed between experimental and simulation results by 2.1884°C (3.71%) and 0.0631 cm$^3$ (5.74%), respectively. The lowest Pearson correlation coefficient (PCC) for peak temperature was 0.7117, and the lowest Dice coefficient for the ablated area was 0.7021, indicating a good agreement in accuracy between simulation and experiment.

Figures (9)

• Figure 1: Schematic of the PZT-4 transducer used by the applicator is also shown with units in mm. Image reproduced from gandomi2020modeling.
• Figure 2: Acoustic pressure field mapping pattern of 3 types of probes.
• Figure 3: Demonstration of the CEM43 of 70 thermal dose map for 3 types of probes, from left to right namely 4W under 120s, 4w under 180s, and 6w under 690s. The solid black line represents the 70 CEM43 isodose lines.
• Figure 4: Data from a 90$^\circ$ probe with 6w acoustic power under 690s duration time of ablation. (a) MRTI temperature change versus time with five 5mm-spaced slices. The whole process consisted of a short time range of low-power ablation for pre-testing and a high-power ablation range. (b) Selected slices (slice 2 and 3) versus the simulation result in temperature change over time. The Pearson correlation coefficient between slice 2 data and simulation peak temperature is 0.9527.
• Figure 5: Multiple MRTI results versus the simulation data using 180$^\circ$ probe. (a)-(b) Swine 4 experimental and simulation results. (c)-(d) Swine 6 data.