The objective of this study is to demonstrate the initial clinical feasibility of using Harmonic Motion Imaging (HMI) for Focused Ultrasound Surgery (FUS) guidance and monitoring in patients with benign and stage 1 non-metastatic breast cancers. The investigators hypothesize that changes in HMI parameters will inform progression of FUS ablation.

Patients with small solid tumors without positive lymph nodes have the highest survival rate. However, especially for patients with benign tumors (most common in younger women) and older patients (>65 years old) who fit these criteria, an alternative treatment technique that is less invasive than the current surgical or invasive ablative intervention may be more beneficial. FUS is a noninvasive, non-ionizing treatment procedure that precisely focuses and delivers a large amount of ultrasound energy to the target area, causing localized temperature rise and cell necrosis at the target. The main advantage of focused ultrasound ablation (FUS) is that it avoids surgery. Without surgery, recovery from the procedure is much faster, patients may experience less pain, and cosmetological results may be improved.

The efficacy and safety of FUS rely heavily on treatment monitoring. Treatment imaging techniques currently used include MRI and ultrasound Bmode imaging. Magnetic resonance imaging (MRI) thermometry is used to detect the temperature rise across the FUS treatment area. However, MRI guidance can be expensive and time-consuming compared to ultrasound-based HIFU guidance methods. Conventional B-mode based 'hyperecho' tracking can be challenging for HIFU monitoring, as it is sensitive to cavitation, which occurs at high temperatures.

HMI is an ultrasound elasticity method that can provide measurements of the locally generated mechanical response and inherent mechanical properties of tissues . The result is a new image that contains unique localized information on the relative stiffness in and around the tumor. The investigators have shown in pre-clinical data that HMI has the ability to monitor mechanical changes in tissue that occur with ablation. The combination of FUS with HMI monitoring is termed HMI guided FUS, or HMIgFUS.

This study aims to evaluate the HMI technique for monitoring FUS ablation in a clinical setting. Eligible and consenting patients will be imaged using HMI, and then will undergo HMIgFUS at a central position inside the tumor. The tumor will be imaged using HMI again following ablation. Following our study, the patients will undergo their scheduled surgery. The purpose of this study is to evaluate HMIgFUS in a lower risk setting, as the tumor will be excised following our study, to better inform future studies, in which surgery may not be needed.

Inclusion Criteria:

• Women age ≥18
• Patients with fibroadenoma (benign tumor) or early-stage, non-metastatic breast cancer (stage I without the involvement of axillary lymph nodes)
• Scheduled to receive surgical resection of the tumor by the clinical care team (ideal target lesion upper boundary should be deeper than 1 cm below the skin, and the ideal size of the lesion should be 2-5 cm in diameter)

Exclusion Criteria:

• Pregnant or lactating women
• Patients with breast implants
• Patients with a history of laser or radiation therapy to the targeted breast
• Patients who have received or are scheduled to receive thermal ablation or treatment of the tumor (other than surgery) as part of clinical care

No individual participant data (IPD) will be shared with other researchers.