Diagnostic performance of qualitative and quantitative shear wave elastography in differentiating malignant from benign breast masses, and association with the histological prognostic factors

Gray scale ultrasound has been widely accepted for use as an effective tool to detect mammographically occult cancers in dense breast tissue and small invasive node-negative breast cancers with high sensitivity, while providing moderate specificity and increasing the biopsy rate (1,2). Generally, the standardized interpretation of breast ultrasound uses the breast imaging reporting and data system (BI-RADS), which was developed by the American College of Radiology (3). In the BI-RADS lexicon, breast masses that are clinically palpable with benign features and masses that are partially well-defined are categorized as 4A (low suspicion for malignancy); a biopsy is recommended in the guidelines in spite of a low positive predictive value (PPV) of malignancy (6%) (4). Recently introduced, shear wave elastography (SWE) is a conjunctive imaging technique that has been employed to assess tissue stiffness by generating an acoustic radiation force from a focused ultrasound beam in order to induce mechanical vibration and create shear waves that are propagated transversely into the tissue. The speed of the shear wave in stiff tissue is faster than in soft tissue (5). The SWE images are displayed in a real-time color overlay box with different colors to indicate the speed of the shear wave (in meters per second, m/sec) or the degree of tissue stiffness (Young modulus; in kilopascal, kPa) in each pixel. The assessment of the stiffness masses can be performed using either a qualitative color map or a quantitative measurement