# Implementation of a Breast Phantom with Acoustic Properties for Ultrasonic Thermometry
## 3 Methodology  
### Protocol for the Elaboration of the Thermometry Phantom  
The phantom consists of a heterogeneous structure layer: gland and fat layers for the healthy model; in the tumoral model, the additional layer of tumor was included. These are illustrated in Figure 1.  
To simulate the thermal and acoustic properties of these cases, agar (suitable for plant cell culture, powder, A7921-Sigma-Aldrich, St. Louis, MO, USA) was used as a gelling agent. Its properties facilitate the formation of a solid mixture and enable the simulation of the acoustic velocity characteristic of female breast tissue. According to [PERSON] et al. [60], the thermal conductivity of agar-based phantoms is measured at 0.59 \(\pm\) 0.02 W/m\({}^{\circ}\)C, closely approximating the thermal properties of human tissue, which ranges between 0.45 and 0.56 W/m\({}^{\circ}\)C. Agar was chosen as the base material for phantom fabrication due to its common use by other authors and its physical properties, which closely resemble those of biological tissues, particularly its thermal conductivity coefficient, which is comparable to that of soft tissue [74; 75]. This characteristic is essential in studies involving thermal and acoustic analyses. Agar also offers practical advantages: it is non-corrosive, safe to handle in low-risk laboratory environments, and does not require specialized equipment. Basic precautions, such as gloves and avoiding inhalation of dry powder, are sufficient. These factors make it suitable for use in laboratories with moderate infrastructure. In technical terms, agar exhibits excellent thermal stability. It maintains structural consistency across the temperature ranges used in the experiments, with a melting point of approximately 78 \({}^{\circ}\)C, ensuring that it does not degrade or deform during controlled heating. Figure 1: Phantom case study diagrams. Porcine gelatin was also considered; however, it began to melt at temperatures as low as 30 \({}^{\circ}\)C, compromising its structural integrity [75]. Although agar is somewhat more fragile under mechanical impact, its thermal performance and ease of handling make it the most appropriate choice for the objectives of this study. Edible vegetable oil (Kirkland Signature) was used to simulate specific heat capacity and thermal conductivity, while sodium chloride was employed to mimic dielectric conductivity. It is important to clarify that, although the use of salt introduces changes in dielectric properties rather than ultrasonic ones, it has been employed by researchers such as [PERSON] [63], [PERSON] et al. [62], and [PERSON] et al. [67] in the development of phantoms that incorporate both thermal and ultrasonic properties. Therefore, the addition of salt was intended to minimize alterations to the materials utilized by other authors, ensuring consistency in the experimental conditions. Distilled water served as the solvent for the mixture and, in conjunction with the oil, helped to simulate specific heat capacity. Additionally, commercial dishwashing liquid detergent was added to achieve a homogeneous mixture. The concentrations used for the gland and tumor phantoms are detailed in Table 1.  
Lard was used to simulate adipose tissue, which, according to [PERSON] et al. [76], exhibits an average ultrasonic velocity ranging from 1436 \(\pm\) 9 m/s to 1470 \(\pm\) 37 m/s, characterized at 38 \({}^{\circ}\)C using a scanning acoustic microscope at a frequency of 10 MHz. Additionally, the thermal conductivity of lard was measured at 0.1258 W/m\({}^{\circ}\)C, based on the average of five independent measurements [77]. To prepare the fat for acquisition, a magnetic stirrer hotplate (Thermo Scientific, SP131325, Waltham, MA, USA), along with a beaker to heat the sample, was used.