Ultrasound calibration framework for the image-guided surgery toolkit (IGSTK)

Registration is a key technology in image-guided navigation systems. By aligning pre-operative images with the intra-operative setting these systems provide visual feedback that improves the physician's understanding of the spatial relationships between anatomical structures and surgical tools. Most often the alignment is obtained using fiducials. Another option is to replace the use of fiducials with intra-operative imaging. Two dimensional ultrasound (US) is a widely available intra-operative non-ionizing imaging modality. To utilize this modality for registration one must first perform spatial calibration of the US. In this work we describe the implementation of three spatial calibration methods as part of the image-guided surgery toolkit (IGSTK). The implementation follows the IGSTK calibration framework, separating algorithmic aspects from user interaction aspects of the calibration. Our calibration framework includes three methods. The first is a phantom-less method using a tracked pointer tool in addition to the tracked US, the second method uses a cross-wire phantom, and the third method is based on the use of a plane phantom.