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/m(3), 0.590 ± 0.015 W/m.K, and 0.145 ± 0.002 mm(2)/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.

Evaluation of a tissue‐mimicking thermochromic phantom for radiofrequency ablation

“…We have previously developed a polyacrylamide-based TMTC phantom that possesses comparable thermal conductivity, thermal diffusivity, and mass density to human liver tissue. 19 In this study, the phantom material was formulated for RFA by adjusting the electrolyte concentration, colorcalibrated with temperature, and used for direct visualization and assessment of RFA thermal lesions. The thermochromic ink incorporated into the phantom matrix produced a color change from white to magenta that could be visualized when heated in the range of ∼40-64 • C, with no further appreciable color change above this range.…”

“…The TMTCP material was prepared as described by Negussie et al 19 using polyacrylamide gel (PAG) and thermochromic ink that permanently and gradually changes color from white to magenta when heated to temperatures between 25 and 75 • C. The phantom formulation, summarized in Table I, was prepared for RFA by adjusting salinity to match that of biological tissues, since this parameter has enhanced influence in RFA. Phantom ingredient ratios were selected based on existing literature, 4,6,19 as well as on preliminary experiments in which the ink concentration was adjusted to produce good color intensity and gradient. Briefly, an aqueous solution of 40% (w/v) acrylamide/bis-acrylamide (National Diagnostic, Atlanta) with feed ratio of 19:1 (acrylamide to bis-acrylamide) was mixed with degassed, deionized water.…”

“…The latter property, known as thermochromism, may be achieved by inclusion of liquid crystals, leuco dyes, or permanent colorchanging inks in a phantom formulation. [15][16][17][18][19] Recently, thermochromic phantom materials have been used to identify heating patterns during thermal therapies. 20,21 For example, Dabbagh et al described reusable heat sensitive tissue-mimicking phantoms that change color from transparent blue to colorless upon heating.…”

“…We have previously reported the development of a TMTCP material using a permanent color-changing ink. 19 In this study, our objective was to evaluate the ability of the TMTCP to provide quantitative and absolute measurements of temperature elevation for delineation of mild hyperthermic and thermally ablated volumes produced by radiofrequency ablation (RFA). Visual and computational methods are demonstrated for obtaining absolute temperatures achieved during heating based on visible and permanent color changes in the phantom.…”

Assessing fluorescence detection and effective photothermal therapy of near‐infrared polymer nanoparticles using alginate tissue phantoms

“…Tissue-mimicking phantoms have become an essential tool for testing nanoparticles and other materials for biomedical procedures and therapies [29][30][31][32][33][34][35][36][37][38]. Dabbagh et al, reviewed several different types of tissue phantoms and their specific advantages and limitations [39].…”