Aixplorer ShearWave Elastography for ultrasound imaging and assessing suspicious breast lesions

Introduction

Breast cancer is the most common cancer in the UK, representing around one‑third of all new cancers diagnosed in women (Office for National Statistics 2012). Around 55,000 people are diagnosed with breast cancer in the UK each year, about 350 of whom are men (Breast Cancer Care 2014). Around 12,000 people in the UK die from breast cancer every year, with crude mortality rates of 36 breast cancer deaths for every 100,000 females in the UK and less than 1 for every 100,000 males (Cancer Research UK 2014).

The NHS Breast Screening Programme in England screened 1.97 million women aged 45 years and over in 2012–13 (Health & Social Care Information Centre 2014). Mammographic abnormalities detected in screening are routinely subjected to further assessment through clinical examination, mammographically guided biopsy (fine‑needle aspiration or core biopsy), ultrasound imaging (with or without biopsy) or MRI.

The American College of Radiology Breast Imaging Reporting and Data System (BI‑RADS) includes a system of nomenclature designed to standardise mammography reporting, reduce confusion in breast imaging interpretations, and aid outcome monitoring. BI‑RADS classification can also be derived from greyscale ultrasound and MRI. BI‑RADS assessment categories range from 0 to 6, with a critical decision threshold for biopsy protocols between BI RADS 3 (probably benign) and BI‑RADS 4a (4 being a suspicious abnormality and 4a being a low suspicion for malignancy).

Ultrasound elastography is an adjunct to conventional greyscale (also termed 'brightness' or 'B‑mode') ultrasound imaging, and is used to qualitatively or quantitatively determine the elasticity of tissue. Force is applied across the tissue, and the resulting strain causes changes in tissue dimensions. Stiffness is defined as the ability of the tissue to resist this dimensional change, and elasticity is inversely related to stiffness. Stiffer objects in softer tissue tend to move as a whole, whereas soft tissue compresses more unevenly. Tumour tissue in the breast tends to exhibit increased stiffness (lower elasticity) compared with surrounding normal glandular and fatty soft tissue.

The claimed benefits of ultrasound elastography are improved diagnostic confidence and increased specificity (fewer false positives) compared with conventional B mode greyscale ultrasound alone. The addition of ultrasound elastography data may influence clinical decision‑making on lesion classification, potentially reducing the number of people who are recommended for breast tissue biopsy.