Accurate fiducial location for freehand 3D ultrasound calibration

The most intuitive way to perform freehand 3D ultrasound calibration is to locate fiducials in the scan plane directly with a pointer. The main problem of using this approach is the difficulty of aligning the tip of the pointer with the scan plane. The thick beam width makes the tip of the pointer visible in the B-scan even if the tip is not exactly in the elevational centre of the scan plane. Furthermore, reliable automatic segmentation of isolated points in ultrasonic imaging systems is difficult. As a result, it is usual to rely on manual segmentation, making calibration a lengthy process. In this paper, we present a novel phantom that solves the alignment problem and simplifies the segmentation process, while maintaining the other advantages of using a pointer.