Optimisation and evaluation of an electromagnetic tracking device for high-accuracy three-dimensional ultrasound imaging of the carotid arteries

Electromagnetic tracking devices provide a flexible, low cost solution for three-dimensional ultrasound (3-D US) imaging. They are, however, susceptib le to interference. A commercial device (Ascension pcBIRD) was evaluated to assess the accuracy in locating the scan probe as part of a digital, freeh and 3-D US imaging system aimed at vascular applications. The device was op timised by selecting a measurement rate and filter setting that minimised t he mean deviation in repeated position and orientation measurements. Experi mental evaluation of accuracy indicated that, overall, absolute errors were small: the RMS absolute error was 0.2 mm (range: -0.7 to 0.5 mm) for posit ional measurements over translations up to 90 rum, and 0.2 degrees (range: -0.8 to 0.9 degrees) for rotational measurements up to 30 degrees. In the c ase of position measurements, the absolute errors were influenced by the lo cation of the scanner relative to the scan volume. We conclude that the dev ice tested provides an accuracy sufficient for use within a freehand 3-D US system for carotid artery imaging.