Tissue-mimicking thermochromic phantom for characterization of HIFU devices and applications

Abstract

Purpose: Tissue-mimicking phantoms (TMPs) are synthetic materials designed to replicate properties of biological tissues. There is a need to quantify temperature changes following ultrasound or magnetic resonance imaging-guided high intensity focused ultrasound (MR-HIFU). This work describes development, characterization, and evaluation of tissue-mimicking thermochromic phantom (TMTCP) for direct visualization and quantification of HIFU heating. The objectives were to 1) develop an MR-imageable, HIFU-compatible TMTCP that reports absolute temperatures, 2) characterize TMTCP physical properties, and 3) examine TMTCP color change after HIFU. Methods and Materials: A TMTCP was prepared containing thermochromic ink, silicon dioxide, and bovine serum albumin and its properties were quantified. A clinical MRI-guided and a preclinical US-guided HIFU system were used to perform sonications in TMTCP. MRI thermometry was performed during HIFU, followed by T2-weighted MRI post-HIFU. Locations of color and signal intensity change were compared to the sonication plan and to MRI temperature maps. Results: TMTCP properties were comparable to those in human soft tissues. Upon heating, the TMTCP exhibited an incremental but permanent color change for temperatures between 45 and 70°C. For HIFU sonications the TMTCP revealed spatially sharp regions of color change at the target locations, correlating with MRI thermometry and hypointense regions on T2-weighted MRI. TMTCP-based assessment of various HIFU applications was also demonstrated. Conclusion: We developed a novel MR-imageable and HIFU-compatible TMTCP to characterize HIFU heating without MRI or thermocouples. The HIFU-optimized TMTCP reports absolute temperatures and ablation zone geometry with high spatial resolution. Consequently, the TMTCP can be used to evaluate HIFU heating and may provide an in vitro tool for peak temperature assessment, and reduce preclinical in vivo requirements for clinical translation.

Effect of the Concentration of Pigment Slurry on the Film Performances of Waterborne Wood Coatings

“…A thermochromic system refers to a color change of printed patterns and text when the material is heated to a certain temperature [1]. When the temperature drops to the original temperature, the solution of thermochromic microcapsules returns to the original color [2]. Temperature-sensitive reversible systems of thermochromic microcapsules can be divided into organic reversible [3], inorganic reversible, [4] and liquid crystal reversible categories [5].…”

Beam characterization of a custom, handheld focused ultrasound system using thermochromic liquid crystal films

“…axial) plane. Efforts are currently underway to ascertain true temperature elevations from the signals generated on the films, using an empirical calibration process (Eranki et al, 2019). This, if accurate, would allow true energy deposition to be determined based on spatial distributions of the colour patterns on the films, which could yield accurate −3 (4) y = 0.013x 4 − 1.592x 3 + 71.133x 2 − 1, 408.568x + 10, 431.842 ; R 2 = 0.94 (All values are based on those presented in Table 2) a Differences for H -F were not statistically different (p > 0.05).…”

“…axial) plane. Efforts are currently underway to ascertain true temperature elevations from the signals generated on the films, using an empirical calibration process (Eranki et al, 2019). This, if accurate, would allow true energy deposition to be determined based on spatial distributions of the colour patterns on the films, which could yield accurate −3 Abbreviations: N, Numerical simulation; H, Hydrophone method; F, TLC film method; D H/F , distance between transducer to film or hydrophone.…”

“…Hydrogel phantoms play an important role in FUS transducer characterization and quality assurance and are used to verify transducer alignment, visualize focal region geometry/location and monitor temperature rise (Civale et al, 2015; Lafon et al, 2005; Martin & Fernandez, 1997; Patel et al, 2008; Wang et al, 2011). Heat‐sensitive albumin protein and thermochromic dyes alike have been incorporated into gel phantoms for characterizing focused ultrasound transducers as well as a variety of other thermal ablation devices (microwave, radiofrequency, cryoablation) (Dabbagh et al, 2014; Eranki et al, 2019; Menikou & Damianou, 2017; Qureshi et al, 2015). Albumin, for example can be dissolved in the gels, which then denatures when heated, becoming optically opaque and also visible by diagnostic ultrasound (Lafon et al, 2005; Wang et al, 2011).…”

“…Heat-sensitive albumin protein and thermochromic dyes alike have been incorporated into gel phantoms for characterizing focused ultrasound transducers as well as a variety of other thermal ablation devices (microwave, radiofrequency, cryoablation) (Dabbagh et al, 2014;Eranki et al, 2019;Menikou & Damianou, 2017;Qureshi et al, 2015). Albumin, for example can be dissolved in the gels, which then denatures when heated, becoming optically opaque and also visible by diagnostic ultrasound (Lafon et al, 2005;Wang et al, 2011).…”