# Implementation of a Breast Phantom with Acoustic Properties for Ultrasonic Thermometry
## 1 Introduction  
Breast cancer is the most significant female mammary disease due to its high mortality and morbidity rates among women, as well as the projected increase in cases of this pathology. Each year, 2.3 million new cases and 458,000 deaths occur globally due to breast cancer, attributed to late diagnosis. Breast lesions can be characterized by abnormal tissue changes, including thermal elevation in the growth zone and surrounding areas [1]. Many researchers have explored noninvasive methods for measuring temperature [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]. Although MRI is the most advanced clinical technology for this purpose, its high cost and complexity limit its use. In contrast, ultrasound is a non-ionizing, convenient, and cost-effective modality with relatively simple signal processing requirements [17, 18, 19, 20, 21, 22]. This makes it a promising method for temperature estimation, under the condition that temperature-sensitive ultrasonic parameters can be identified, accurately measured, and properly calibrated [23, 24]. Scientific efforts have focused on estimating temperature using changes in speed of sound (SOS), i.e., changes in time of flight (ToF), variations in the ultrasonic attenuation coefficient, or changes in backscattered energy due to thermal effects [25, 26]. However, quantifying the thermal dependence of ToF has been crucial, as echo shift computationforms the basis of many recent studies in temperature estimation. Attempts to implement this approach in clinical applications have faced significant challenges due to differences in temperature dependence across tissue types, e.g., SOS change due to temperature rise in fatty breast tissue presents a behavior that is opposite to that given in the rest of the tissues [27]. The acoustic properties of biological tissues exhibit significant variation between individuals and can fluctuate within the same body, resulting in substantial inconsistencies in the literature [28]. This highlights the need for more precise and adaptable experimental models for temperature measurement in inhomogeneous tissues, as encountered in vivo. Tissue-mimicking materials (TMMs) or phantoms are models designed to replicate the physical properties of human tissues. These materials offer numerous benefits, particularly in quality assurance for medical imaging, study validation, and pre-training, providing an ethical and valuable alternative to human tissue testing [29]. Although several studies have reviewed the fabrication of phantoms, available phantoms still present limitations, such as reliance on single-modality approaches and simple single-layer structures. The components of the TMMs are selected depending on the application, e.g., diagnostic or therapy, and on the scanning technology, e.g., ultrasound, microwave, etc. In [30], a prostate phantom based on polyacrylamide gel was developed to simulate optical features. Given that the application was oriented to thermal therapy using a laser, the material used was selected due to its high melting point. In this sense, for ablative temperatures greater than 60 \({}^{\circ}\)C, the authors of [31] present a thermochromic phantom based on polyacrylamide gel. The phantom changes color from white to magenta when the temperature increases from 60 to 65 \({}^{\circ}\)C. The results show a thermal pattern of ablation for microwave- and laser-based therapies. [PERSON] et al. [32] report a validation study of a tissue-mimicking phantom used in the detection of prostate cancer. This phantom was constructed with polyvinyl alcohol (PVA), and materials like glycerol, silicon carbide, and aluminum oxide were added to ensure variation in the molecular weight. They showed that, with high molecular weight, properties such as the SOS, acoustic attenuation, and Young's modulus were similar to those of the prostate tissue. A breast phantom that mimics properties for B-mode ultrasound and microwave imaging was described in [33].