# Implementation of a Breast Phantom with Acoustic Properties for Ultrasonic Thermometry
## 5 Discussion  
The aim of this research was to develop a breast phantom composed of multiple layers that simulate acoustic properties and to validate it for thermoacoustic measurements. Concisely, the contribution of this work was to develop a fully characterized breast phantom that simulates the SOS of fat, mammary gland, and breast tumor in the temperature range of 32 \({}^{\circ}\)C to 36 \({}^{\circ}\)C, which is the range for thermometric diagnosis. In this sense, the authors did not find previous reports about multilayer phantoms that mimic the human breast for diagnoses based on ultrasonic thermometry; most of them are present focused ultrasound therapies, where temperature ranges are greater (40-90 \({}^{\circ}\)C). This is because the objective of thermal therapies is to kill cancer cells or directly to burn the affected tissue. The materials and procedures used to fabricate the proposed phantom do not require sophisticated protection, nor do they represent high-risk maneuverability; so, the presented method is a viable and economic option for elaboration in a generic laboratory. Our phantom comprises three layers, simulating the acoustic behavior of (i) a mammary gland, (ii) breast fat, and (iii) the tumoral tissue both individually and as a whole system. This means that the phantom can be used to recreate the thermal behavior of acoustic velocity in each layer and the cumulative effects of ultrasonic signals due to the multilayer composition. The phantom has been considered and validated. Most of the phantoms found in other works consist of a based mixture containing masses with different compositions. Finally, we obtain the mathematical models based on linear regressions that characterize the thermal behavior of each layer contained in our breast phantom. These enable internal temperature measurements to be conducted using our phantom based on ultrasonic inspection for calibration; additionally, it is possible to test new algorithms, developed for thermometric purposes. However, not all acoustic and thermal parameters that could influence exposure, such as attenuation, reflection coefficients, or specific heat capacity, were considered. Our primary focus was on analyzing the SOS at different temperatures and validating its behavior in individual cases, ensuring that it remained consistent when layered for each tissue type. This behavior was validated using the cross-correlation method, with a proposal for eliminating accumulated delays. The obtained results are discussed in this section. According to the values reported by [PERSON] [62], the density of mammary gland tissue is 1050 kg/m\({}^{3}\), while the average density obtained for his gland phantom is 1037 kg/m\({}^{3}\). Comparing these values with the density of the gland phantom developed in this study, a percentage error of 17.81% is obtained with respect to the value measured in vivo, and a percentage error of 16.78% is obtained when compared to [PERSON]'s gland phantom. Similarly, the tumor phantom shows a percentage error of 17.50% compared to the value measured in vivo and 15.98% compared to the value reported by [PERSON]. On the other hand, [PERSON] [64] reports an agar density in the range of 1004 kg/m\({}^{3}\) to 1037 kg/m\({}^{3}\), resulting in a minimum error of 14.4% for the gland phantom and 13.72% for the tumor phantom. These considerable errors may be due to factors such as the sample's temperature at the time of measurement and potential inaccuracies during the measurement process. Although density was not specifically intended to be simulated, it is a relevant parameter, as improving it is crucial for developing more accurate phantoms. In Figure 8a,b, we can observe the structure of phantom proposed here; in contrast to the model proposed by [PERSON] [64], this phantom is spatially heterogeneous, allowing for the observation and analysis of reflections from the different layered structures within the breast phantom, both in the case of healthy tissue and tumor tissue.