Ultrasonic Viscoelasticity Imaging of Nonpalpable Breast Tumors. Preliminary Results

Rationale and Objectives: Improvements in the diagnosis of early breast cancers depend on a physician's ability to obtain the information necessary to distinguish nonpalpable malignant and benign tumors.Viscoelastic features that describe mechanical properties of tissues may help to distinguish these types of lesions. Materials and Methods: Twenty-one patients with nonpalpable, pathology-confirmed Breast Imaging Reporting and Data System (BIRADS) 4 or 5 breast lesions (10 benign, 11 malignant) detected by mammography were studied. Viscoelastic parameters were extracted from a time sequence of ultrasonic strain images, and differences in the parameters between malignant and benign tumors were compared. Parametric data were color coded and superimposed on sonograms. Results: The strain retardance time parameter, T₁, provided the best discrimination between malignant and benign tumors (P < .01). T₁ measures the time required for tissues to fully deform (strain) once compressed; therefore, it describes the time-varying viscous response of tissue to a small deforming force. Compared to the surrounding background tissues, malignant lesions have smaller average T₁ values, whereas benign lesions have higher T₁ values. This tissue-specific contrast correlates with known changes in the extracellular matrix of breast stroma. Conclusion: Characterization of nonpalpable breast lesions is improved by the addition of viscoelastic strain imaging parameters. The differentiation of malignant and benign BI-RADS 4 or 5 tumors is especially evident with the use of the retardation time estimates, T₁.