Grey-scale gating for freehand 3D ultrasound

Freehand three-dimensional (3D) ultrasound is a flexible imaging technique which allows a 3D data set to be constructed of sequential B-scans from a conventional ultrasound scanner. Since the data is acquired over several seconds, physiological motion generates spatial artifacts in visualisations of the data. Consequently, an electrocardiogram (ECG) signal is often used to gate the acquisition of B-scans to a single point in the cardiac cycle. We present a technique which can remove temporal artifacts by using properties of the grey-scale B-scan data, obviating the need for an external gating signal. B-scans are acquired throughout the cardiac cycle, and any phase can be selected for subsequent visualisation. This enables limited real-time 4D display of the data.