## 2 Materials and Methods  
The whole study was carried out in accordance with the Declaration of Helsinki. Informed patients' consent was obtained for this prospective study. Permission for patients' medical records review was obtained from the hospital. Between November 2021 and September 2022, 85 patients aged between 12 and 85 years (mean age 52 \(\pm\) 12 SD) were enrolled, for a total of 92 focal breast lesions that were evaluated by a radiologist with extensive experience in breast imaging (at least 10 years) who provided the BI-RADS category for each lesion, in accordance with the latest ACR BI-RADS 2013 edition lexicon. All patients underwent a biopsy. The inclusion criteria of the study were: all ultrasound-detectable breast masses were candidates for biopsy and classified with a BI-RADS score between 3 and 5 (probably benign nodules but of first finding and/or growth at follow-up, nodules of uncertain category, or lesions with suspected malignancy). The exclusion criteria were: benign breast nodules that did not undergo biopsy or follow-up, patient's refusal to perform core-needle biopsy, biopsy performed before ultrasound examination in less than 1 month, clearly benign nodules (BI-RADS 2), or mixed lesions with the solid component poorly assessable due to the elastographic artifacts linked to the prevalent cystic component. All breast nodules included in the study were subsequently evaluated by a second investigator by means of a B-mode ultrasound, color Doppler, and analysis performed by the semi-automatic \"SmartBreast\" software (Mindray, Resona R9, 3-14 MHz transducer). The investigator was blinded to mammographic and previous ultrasound results. The analyses by \"SmartBreast\", in particular, involved the following parameters provided by the BI-RADS lexicon for each lesion: dimensions (mm), shape (oval, rounded, irregular), orientation (parallel, not parallel), margins (circumscribed or not circumscribed: indistinct, angular, microbolulated, spiculated), echo-pattern (anechoic, isoechoic, hypoechoic, hyperechoic, heterogeneous, complex cystic, and solid mass), posterior features (no features, enhancement, shadowing, combined pattern), microcalcifications, and vascularization at color Doppler (absent, peripheral, internal). All these ultrasound features were automatically detected and analyzed by the software, which, at the end, provided a summary table with the determination of a BI-RADS category and the consequent probability of benignity or suspicion of malignancy (Figure 1). In the same ultrasound session, the investigator also performed elastography using the three main techniques: SE (qualitative and semi-quantitative method with SR), 2D SWE (Kpa and m/s), and pSWE (Kpa). At least five measurements were performed for every elastographic technique in each breast nodule. Every elastographic evaluation included a quality bar that indicated the correct execution of the exam. The ROI was placed in the lesion, including as much tumoral area as possible. In both 2D SWE and pSWE analyses, the ROI was placed at least 3 mm below the skin surface; more superficial evaluations make the elastography examination unreliable. SE was performed, taking care not to apply any pre-compression. The ultrasound probe was kept perpendicular to the skin surface using a real-time quality indicator to control the optimal sequence of compression-release. Elastography and B-mode images were visible simultaneously on the display (double view) in order to evaluate the qualitative parameters of the color scale. When the compression-release cycles had been completed and the optimal dynamics had been obtained through a real-time quality indicator, the maximum decompression point was selected in post-processing, and a region of interest (ROI) was manually positioned into the lesion, trying to include most of the lesion without the surrounding tissue. A second ROI, approximately equal in size to the first one, was placed on the normal fat tissue near the lesion at the same depth, avoiding possible motion artifacts.