Design of a clinical free-hand 3D ultrasound system

The user interface is critical to the clinical acceptance of free-hand 3D ultrasound imaging. In the system described here, the acquisition of scans from a conventional 2D probe is synchronised to probe movement. Motion-gated acquisition reduces the dependency of scan quality on the operator and can detect poor scanning technique. Automatic: annotation is facilitated by recording the orientation of the patient. A 'virtual probe' enables a clinician to reslice the acquired data as if the patient were being rescanned. A 'thick reslice' enables spatial compounding to be implemented in the visualisation process. The critical scale parameter, which is difficult to automatically determine, is intuitively interpreted as the slice thickness and interactively controlled by the clinician. Real-time volume rendering without prior segmentation of the data is possible using this technique. Shape-based interpolation assists manual segmentation of the data. The distance field from the segmentation process is used to mask the raw. data and the result is volume rendered. A 3D scalpel enables efficient refinement of the segmentation by directly editing the volume-rendered view. The 3D scalpel prunes a set of user-defined contours to which a surface is fitted and the enclosed volume computed. A compact set of contours is retained by the system which allows the actions of the user to be undone. Three clinicians have tested the system, acquiring over 100 3D fetal scans, in a hospital environment.