title: Electromagnetic tracking system with reduced distortion using quadratic excitation.
abstract: OBJECTIVE
  Electromagnetic tracking systems, frequently used in minimally invasive surgery, are affected by conductive distorters. The influence of conductive distorters on electromagnetic tracking system accuracy can be reduced through magnetic field modifications. This approach was developed and tested.
  
  
  METHODS
  The voltage induced directly by the emitting coil in the sensing coil without additional influence by the conductive distorter depends on the first derivative of the voltage on the emitting coil. The voltage which is induced indirectly by the emitting coil across the conductive distorter in the sensing coil, however, depends on the second derivative of the voltage on the emitting coil. The electromagnetic tracking system takes advantage of this difference by supplying the emitting coil with a quadratic excitation voltage. The method is adaptive relative to the amount of distortion cause by the conductive distorters. This approach is evaluated with an experimental setup of the electromagnetic tracking system.
  
  
  RESULTS
  In vitro testing showed that the maximal error decreased from 10.9 to 3.8 mm when the quadratic voltage was used to excite the emitting coil instead of the sinusoidal voltage. Furthermore, the root mean square error in the proximity of the aluminum disk used as a conductive distorter was reduced from 3.5 to 1.6 mm when the electromagnetic tracking system used the quadratic instead of sinusoidal excitation.
  
  
  CONCLUSIONS
  Electromagnetic tracking with quadratic excitation is immune to the effects of a conductive distorter, especially compared with sinusoidal excitation of the emitting coil. Quadratic excitation of electromagnetic tracking for computer-assisted surgery is promising for clinical applications.
authors.affiliation: Chair for Healthcare Telematics and Medical Engineering, Otto-von-Guericke University, Magdeburg, Germany, Tomasz.Bien@ovgu.de.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Bien
authors.forename: Mengfei
authors.initials: M
authors.lastname: Li
authors.forename: Zein
authors.initials: Z
authors.lastname: Salah
authors.forename: Georg
authors.initials: G
authors.lastname: Rose
mesh_terms: D003198:Computer Simulation; D055590:Electromagnetic Phenomena; D006801:Humans; D019047:Phantoms, Imaging; D025321:Surgery, Computer-Assisted / Q000379:methods*
references.citation: Phys Med Biol. 2006 May 21;51(10):N205-10
references.pmid: 16675856
references.citation: IEEE Trans Med Imaging. 1998 Oct;17(5):737-42
references.pmid: 9874297
references.citation: Ann Thorac Surg. 2008 Feb;85(2):S797-801
references.pmid: 18222220
references.citation: Acad Radiol. 2007 Mar;14(3):344-54
references.pmid: 17307668
references.citation: Phys Med Biol. 2000 Sep;45(9):N103-10
references.pmid: 11008969
references.citation: J Biomech. 2005 Oct;38(10):2113-7
references.pmid: 16084212
references.citation: J Biomech. 2003 Jan;36(1):141-4
references.pmid: 12485650
references.citation: J Biomech. 2002 Jun;35(6):733-7
references.pmid: 12020992
references.citation: Med Phys. 2013 Feb;40(2):021716
references.pmid: 23387739