Underlying factors that affect ultrasound conspicuity of breast biopsy markers: an exploratory study.

Background: During management of node-positive breast cancer, neoadjuvant systemic therapy (NST) is often used to de-escalate surgical intervention. To identify pathology-proven positive nodes regardless of visual changes after NST, breast biopsy clips or markers are inserted under ultrasound guidance as part of standard care, though most markers are used off-label in the axilla. However, clipped nodes may be difficult to visually confirm with ultrasound after a pathological complete response. This can affect the ease of executing subsequent procedures, such as surgical resection, because identifying the marked or clipped nodes in these cases is problematic. The mechanisms that affect these changes in clip conspicuity are poorly understood, making it challenging to improve ultrasound conspicuity of clips in the clinical setting. The aim of this study is to determine which of these mechanisms are inherent to ultrasound as an imaging modality and if they can be accounted for by adjustments to ultrasound scanner settings. Methods: The effect of viewing angle on brightness is assessed in multiple imaging targets, including five commercially-available clips, suspended in gelatin phantoms. Off-gassing from insertion of a dry clip into tissue is assessed as another possible explanation for the observed changes in conspicuity. Results: Brightness was found to vary significantly with viewing angle for some clips. An Conclusions: Viewing angle is not affected by any other settings on an ultrasound system besides probe position, suggesting that conspicuity may not be recoverable if repositioning cannot clarify clip location. Even when viewing angle is not a concern in tissue, the presence of other bright scatterers in the field of view can obscure the location of the clip.