# Implementation of a Breast Phantom with Acoustic Properties for Ultrasonic Thermometry
## 1 Introduction
It comprised skin, fat, tumor and fibroglandular tissues, and was created with a mixture of agar and glass beads. Coconut and canola oil were used for skin and fat, respectively. Meanwhile, polyvinylpyrrolidone (PVP) was added to fibroglandular and tumor tissue phantoms. These phantoms can be used in the simulation of the following properties: relative permittivity and conductivity, the SOS, and attenuation. For microwave thermometry, phantoms oriented to mimic dielectric and thermal properties have been developed [34; 35; 36]. In [35], a phantom based on materials such as distilled water, gelatine, sunflower oil, sugar, sodium chloride (NaCl), xanthan, and propylene glycol (pure, 98%) was created. Relative permittivity and conductivity were characterized in a frequency range of 200 MHz to 20 GHz for different temperatures. A functional breast phantom was constructed in [34], attached to the real anatomy, and including a mechanism that allowed the researchers to simulate the blood flow and to control a thermal element, simulating a tumor. Density, thermal conductivity, specific heat capacity, electrical conductivity, and dielectric constant were modelled. Temperature measurements were acquired with the antenna applicator of the RTM-01-RES radiometer (RES Ltd., Moscow, Russia). [PERSON] et al. [36] developed a breast tissue phantom to mimic dielectric properties and its dependence on temperature for a frequency bandwidth from 50 MHz to 20 GHz. The phantom was created with distilled water, glycerine, agar, rapeseed oil, and dishwashing liquid. It comprised four tissue types: tumor, gland, skin, and fat. The complex permittivity was characterized in the temperature range from 25 \({}^{\circ}\)C to 46 \({}^{\circ}\)C. Another common category of phantoms comprises those that are developed to track focused ultrasound therapies by means of magnetic resonance imaging (MRI). Anexample is given in [37], where a specific tumoral tissue phantom was developed based on pure agar gel. It consists of a tumor tissue phantom surrounded by a normal tissue phantom. Silicone dioxide was used to differentiate the tumor. Ultrasonic, thermal, and MR relaxation properties were measured. MR thermometry was used to monitor ablation therapy. [PERSON] et al. [38] developed a homogenous breast phantom based on agar (2% \(w/v\)), wood powder (4% \(w/v\)), and degassed water. It was based on a previously reported phantom that simulated acoustic, magnetic, and thermal properties. In that study, the phantom curvature effect on temperature was analysed. Regarding phantoms developed for ultrasonic thermometry, [PERSON] et al. [39] used a 2D speckle tracking approach, achieving temperature estimation errors below \(\pm\)0.5 \({}^{\circ}\)C in a phantom constructed with a talc-in-agar mixture. [PERSON] et al. [40] employed thermal strain imaging with 2D speckle tracking on RF ultrasound data to estimate temperature-induced tissue deformation, extracting the thermal parameter \(1/k(z)\) from echo shifts. By correlating these measurements with CT-derived Hounsfield Units, they enhanced calibration accuracy in heterogeneous media. However, the developed phantom based on agarose mimics a generic tissue and consists of just one general body without layers that simulates a multi-composed organ like the breast. The phantom was characterized in the range of temperatures of 26.1 to 41.1 \({}^{\circ}\)C in average steps of 4.8 \({}^{\circ}\)C. To modify the content of mimetic fat tissue, different concentrations (0-50%) of glycerol trioleate were added. The results showed a negative correlation between temperature and the SOS for concentrations of trioleate greater than 30%. Although commercial phantoms are available, they are expensive and difficult to customize, making them impractical for certain purposes.