Thermochromic tissue-mimicking phantom for optimisation of thermal tumour ablation

Abstract

Purpose The purpose of this study was to (1) develop a novel tissue-mimicking thermochromic (TMTC) phantom that permanently changes colour from white to magenta upon heating above ablative temperatures, and (2) assess its utility for specific applications in evaluating thermal therapy devices.

Materials and methods Polyacrylamide gel mixed with thermochromic ink was custom made to produce a TMTC phantom that changes its colour upon heating above biological ablative temperatures (> 60 °C). The thermal properties of the phantom were characterised, and compared to those of human tissue. In addition, utility of this phantom as a tool for the assessment of laser and microwave thermal ablation was examined.

Results The mass density, thermal conductivity, and thermal diffusivity of the TMTC phantom were measured as 1033 ± 1.0 kg/m³, 0.590 ± 0.015 W/m.K, and 0.145 ± 0.002 mm²/s, respectively, and found to be in agreement with reported values for human soft tissues. Heating the phantom with laser and microwave ablation devices produced clearly demarcated regions of permanent colour change geographically corresponding to regions with temperature elevations above 60 °C.

Conclusion The TMTC phantom provides direct visualisation of ablation dynamics, including ablation volume and geometry as well as peak absolute temperatures within the treated region post-ablation. This phantom can be specifically tailored for different thermal therapy modalities, such as radiofrequency, laser, microwave, or therapeutic ultrasound ablation. Such modality-specific phantoms may enable better quality assurance, device characterisation, and ablation parameter optimisation, or optimise the study of dynamic heating parameters integral to drug device combination therapies relying upon heat.

Keywords:

• HIFU
• laser
• microwave
• RF
• thermal phantom
• thermal therapy
• thermal ablation
• thermochromic
• tissue-mimicking

Acknowledgements

We thank Fil Banovac, Ankur Kapoor, and Roxanna Juarez for their contributions to this study.

Disclosure statement

A.H.N., A.S.M., S.X., N.A.-J., S.M. and B.J.W. have no conflict of interest to declare. A. P. is a paid employee of Philips. The authors alone are responsible for the content and writing of the paper.