M. Feuerstein, T. Reichl, J. Vogel, J. Traub, N. Navab New Approaches to Online Estimation of Electromagnetic Tracking Errors for Laparoscopic Ultrasonography Computer Aided Surgery, vol. 13, no. 5, pp. 311-323, September 2008 (bib)
	In abdominal surgery, a laparoscopic ultrasound transducer is commonly used to detect lesions such as metastases. The determination and visualization of position and orientation of its flexible tip in relation to the patient or other surgical instruments can be of great support for surgeons using the transducer intraoperatively. This difficult subject has recently been paid attention to by the scientific community. Electromagnetic tracking systems can be applied to track the flexible tip. However, current limitations of electromagnetic tracking are its accuracy and its sensibility, i.e. the magnetic field can be distorted by ferromagnetic material. This paper presents two novel methods for electromagnetic tracking error estimation. Based on optical tracking of the laparoscope as well as magneto-optic and visual tracking of the transducer, these methods automatically detect in 85 % of all cases, whether tracking is erroneous or not, and reduce tracking errors by up to 2.5 mm.
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