Spatial Calibration for 3D Freehand Ultrasound via Independent General Motions

The concept of 3D freehand ultrasound has been of great interest to researchers for decades due to many advantages over conventional 2D ultrasound, such as image quality that is less dependent on a sonographer's skills and more intuitive and interactive 3D views of scanned objects. However, obstacles such as the need for spatial calibration remain, which hinder the effective application of this technique in clinical settings. Here we report the feasibility and accuracy of performing spatial calibration based upon a closed-form solution to matrix equations formed by two independent general motions. We achieved millimeter-level accuracy for translational and degree-level accuracy for rotational degrees of freedom. The calibration accuracy may be further improved by optimizing the matrix solution.