Temporal and Spatial Calibration of a freehand 3D ultrasound reconstructions system by using an N-wire phantom

Freehand three-dimensional (3D) ultrasound is a method for reconstructing a 3D volume from two-dimensional (2D) ultrasound (US) images. Indeed, the US scan is very common in the medical world; it is a noninvasive, fast and cheap exam. The objective is to enable the practitioner to have a 3D visualization inside the body, in real-time. The medical staff can rotate, move or scale it inside the 3D space. Another important possibility is a view inside the volume. In order to do so, we must move the US probe on the area of interest and the movement, the path is taken in by the Polaris Spectra System. The problem is that the system follows the probe and not the scan plane. The objective is to define the transformation between the US probe markers (rigid body) and the scan plan. For this, the system must be calibrate. During the calibration, the user must use a phantom with known dimensions. For this system, the method of improved N-wire phantom-based freehand ultrasound is used. We must make a temporal and a spatial calibration to obtain different matrixes which enable to know the different offset and transformation for having a good 3D reconstruction.