Probe Localization for Freehand 3D Ultrasound by Tracking Skin Features

Ultrasound probe localization with respect to the patient's body is essential for freehand three-dimensional ultrasound and image-guided intervention. However, current methods for probe localization generally involve bulky and expensive equipment. In this paper, a highly cost-effective and miniature-mobile system is described for 6-DoF probe localization that is robust to rigid patient motion. In this system, skin features in the scan region are recorded at each ultrasound scan acquisition by a lightweight camera rigidly mounted to the probe. A skin map is built based on the skin features and optimal probe poses are estimated in a Bayesian probabilistic framework that incorporates a prior motion model, camera frames, and ultrasound scans. Through freehand scanning on three different body parts, it is shown that on average, for every probe travel distance of 10 mm, the translational and rotational errors are 0.91 ± 0.49 mm and 0.55 degrees ± 0.17 degrees, respectively. The 3D reconstructions were also validated by comparison with real ultrasound scans.