Elastography of breast tumors: Pitfalls

Abstract

Ultrasonic elastography is a new technique that can be applied in combination with B-mode sonography for the assessment of breast lesions. There are various methods to obtain elastography of the breast. Several interpretation methods and their relationships based on a BI-RADS classification system have been proposed. The most commonly used interpretation methods include EI/ B (Ratio of the lesion size on elastography to the B-mode size), width ratio, strain ratio, lesion fat ratio (LFR, ratio of target mass stiffness to that of subcutaneous fat). These are semi quantitative value derived from strain elastography (SE). The Tsukuba score, a kind of strain pattern, using a fine-point scale has been used for differentiating between benign and malignant masses with satisfactory accuracy. Vs-shear wave velocity or shear wave speed (SWS) in units of m/s and stiffness or elasticity in units of kPa are quantitative values in shear wave elastography (SWE) systems. Most of recent studies confirmed higher specificity for elastography and higher sensitivity for conventional sonography. Procedures during elastography should be carefully done to avoid some pitfalls of image producing and interpretation. First of all, obtaining an optimal B-mode image and a good elastography image (EI) is essential. A nonperpendicular angle of the probe to the chest wall/ skin, unstable vibration, improper or uneven compression, and patient motion will cause suboptimal EI. A proper interpretation is based on a good EI, and multiple interpretation methods can be applied to a lesion to obtain a proper diagnosis. Difficulty may be encountered when measuring a fibrous tumor arising in dense breast tissue on the elastogram, and false positive result may be created. Some of the problems can be avoided by comparing the stiffness of the lesion to the surrounding tissue and LFR may help eliminate this problem. A cystic lesion may show tri-laminar appearance (blue, green, and red), but if not all three colors are present; comparison with B-mode image is helpful. Elastography systems and the applications themselves continue to evolve with the more recent SWE / SWS techniques; new tools and new evidence will likely emerge. The direction of development, imaging methods will change with new technologies and diagnostic algorithms.