title: Hybrid electromagnetic and image-based tracking of endoscopes with guaranteed smooth output.
abstract: OBJECTIVE
  Flexible fiber-optic bronchoscopy is a widespread medical procedure for the diagnosis and treatment of lung diseases. Navigation systems are needed to track the flexible endoscope within the bronchial tree. Electromagnetic (EM) tracking is currently the only technology used clinically for this purpose. The registration between EM tracking and patient anatomy may become inaccurate due to breathing motion, so the addition of image-based tracking has been proposed as a hybrid EM-image-based system.
  
  
  METHODS
  When EM tracking is used as an initialization for image registration, small changes in the initialization may lead to different local minima and noise is amplified by hybrid tracking. The tracking output is modeled as continuous and uses splines for interpolation, thus smoothness is greatly improved. The bronchoscope pose relative to computed tomography data is interpolated using Catmull-Rom splines for position and spherical linear interpolation (SLERP) for orientation.
  
  
  RESULTS
  The hybrid method was evaluated using ground truth poses manually selected by experts, where mean inter-expert agreement was determined as 1.26 mm. Using four dynamic phantom data sets, the accuracy was 4.91 mm, which is equivalent to previous methods. Compared to state-of-art methods, inter-frame smoothness was improved from 2.77-3.72 to 1.24 mm.
  
  
  CONCLUSIONS
  Hybrid image and electromagnetic endoscope guidance provides a more realistic and physically plausible solution with significantly less jitter. This quantitative result is confirmed by visual comparison of real and virtual video, where the virtual video output is much more consistent and robust, with fewer occasions of tracking loss or unexpected movement compared with previous methods.
authors.affiliation: Computer-Aided Medical Procedures, TUM, Munich, Germany, reichl@tum.de.
authors.forename: Tobias
authors.initials: T
authors.lastname: Reichl
authors.forename: Xiongbiao
authors.initials: X
authors.lastname: Luo
authors.forename: Manuela
authors.initials: M
authors.lastname: Menzel
authors.forename: Hubert
authors.initials: H
authors.lastname: Hautmann
authors.forename: Kensaku
authors.initials: K
authors.lastname: Mori
authors.forename: Nassir
authors.initials: N
authors.lastname: Navab
mesh_terms: D000465:Algorithms; D020680:Bronchoscopes; D001999:Bronchoscopy / Q000379:methods*; D055590:Electromagnetic Phenomena; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D015203:Reproducibility of Results
references.citation: Comput Aided Surg. 2004;9(5):215-26
references.pmid: 16192063
references.citation: IEEE Trans Med Imaging. 1998 Oct;17(5):703-14
references.pmid: 9874294
references.citation: IEEE Trans Biomed Eng. 2004 Nov;51(11):2040-50
references.pmid: 15536906
references.citation: IEEE Trans Biomed Eng. 2010 Mar;57(3):736-45
references.pmid: 19846362
references.citation: IEEE Trans Med Imaging. 2005 Dec;24(12):1529-39
references.pmid: 16353370
references.citation: Int J Radiat Oncol Biol Phys. 2006 Jun 1;65(2):528-34
references.pmid: 16690435
references.citation: Med Image Comput Comput Assist Interv. 2009;12(Pt 1):459-66
references.pmid: 20426020
references.citation: IEEE Trans Med Imaging. 2006 Apr;25(4):385-405
references.pmid: 16608056
references.citation: Lung Cancer. 2004 Oct;46(1):43-8
references.pmid: 15364131
references.citation: Med Image Anal. 2012 Apr;16(3):642-61
references.pmid: 20452269
references.citation: Med Image Comput Comput Assist Interv. 2005;8(Pt 2):543-50
references.pmid: 16686002
references.citation: Chest. 2000 Dec;118(6):1783-7
references.pmid: 11115473
references.citation: Med Image Comput Comput Assist Interv. 2008;11(Pt 1):850-7
references.pmid: 18979825
references.citation: IEEE Trans Med Imaging. 1998 Oct;17(5):694-702
references.pmid: 9874293
references.citation: Pneumologie. 2004 May;58(5):344-56
references.pmid: 15162262
references.citation: CA Cancer J Clin. 2011 Mar-Apr;61(2):69-90
references.pmid: 21296855
references.citation: Chest. 2005 Jul;128(1):382-7
references.pmid: 16002960
references.citation: Med Image Anal. 2009 Aug;13(4):621-33
references.pmid: 19592291
references.citation: Chest. 2006 Apr;129(4):988-94
references.pmid: 16608948
references.citation: Lung Cancer. 2007 Sep;57(3):322-7
references.pmid: 17532538
references.citation: Int J Radiat Oncol Biol Phys. 2005 Mar 1;61(3):933-7
references.pmid: 15708277
references.citation: Int J Radiat Oncol Biol Phys. 1999 Oct 1;45(3):603-11
references.pmid: 10524412
references.citation: Int J Radiat Oncol Biol Phys. 2007 Mar 15;67(4):1088-98
references.pmid: 17187940
references.citation: Med Image Comput Comput Assist Interv. 2007;10(Pt 1):475-82
references.pmid: 18051093
references.citation: Med Image Comput Comput Assist Interv. 2011;14(Pt 1):17-24
references.pmid: 22003595