Towards detecting surgical clips in 3D ultrasound for target localization in radiation therapy: a study on tissue phantoms.

A study is performed to measure the visibility of small surgical clips in 3D ultrasound volumes of a phantom as the first step towards using such clips as fiducial markers in radiation therapy. Visibility is calculated as the contrast to noise ratio of the echo from the clip to the background. The appearance of a resonance tail is also calculated using a moment analysis. Contrast is found to be high and mostly independent of material and size of the clip. All clips are visible, but the length of the tail is found to be dependent on clip orientation to the ultrasound beam. The consistent visibility of the clips suggests they are suitable as fiducial markers in ultrasound and the dependency of the resonance tail on orientation provides an opportunity to distinguish clips from other specular reflectors.