Actuator-Assisted Calibration of Freehand 3D Ultrasound System

Figure 3

Ultrasound images of a collinear point target phantom after the one-time alignment process of the point targets. The top left image was captured with the linear actuator fully extended. The arrow indicates the lowest point of the footprint of the ultrasound probe, which is ~10 mm above the point targets (i.e., between the two parallel lines). The probe was retracted at 10 mm increment to cover the entire image field of view at 6 depth levels. Due to the curvilinear nature of the ultrasound probe used in this study, all of the 7 point targets can be clearly visualized at each depth level except for the most superficial level; only 5 screw heads can be visualized.