Fast and efficient error correction of electromagnetic tracking and its application in prostate cancer treatment

"Fehlerkorrektur in elektromagnetischem Tracking und ihre Anwendung bei der Behandlung von Prostatakrebs"

Thesis by:	Claudia Thormann
Advisor:	Prof. Navab
Supervisor:	Jörg Traub
medical partner:	Prof. Kneschaurek (Radiation Therapy Department, Rechts der Isar)
Due date:	2007/03/15

Abstract

Electromagnetic tracking systems are very popular for medical applications because they are able to track flexible instruments inside the human body. Unfortunately electromagnetic tracking systems are very sensitive to distortion caused by ferromagnetive metal and electromagnetic fields in their range. When the sources of distortion cannot be removed from the setting because they are needed to perform a task, error correction algorithms can be used to compensate the distortions.

In this diploma thesis an improved method for error correction algorithm was implemented and tested. The errror correction method is based on a lookup-table containing correct positions of a magnetic sensor in an distorted setting and the corresponding distorted positions. The correct position of the sensor is acquired with the help of an optical tracking system and benefits from its high precision. The algorithm uses the lookup-table for online error correction of the position of the magnetic sensor in an distorted setting. An important requirement for this is the synchronization of the used magnetic and the optical tracking system.

The application was motivated by the medical domain of prostate cancer treatment. The current treatment is confronted with the problem of a prostate gland that moves slighly during radiotherapy. A magnetic sensor shall be used to track the position of the prostate gland and the cancer within. This diploma thesis provides an application that can be used for this purpose.

The results of my experiments are very promising. In every experimental setting the error correction method could improve the distortion of the tracking data. In the setting that was the most distorted by metal, the distortion could be reduced from 40.55 mm to 0.60 mm by the implemented method that is based on Hardy's multiquadric method.

Used Hardware

• optical tracking system: dtrack-system with 4 cameras, model ARTtrack2, by Advances Realtime Technologies (A.R.T.)
• magnetic tracking system: 3D Guidance/Microbird by Ascension Technologies

Documents

• DA-kickoff_revised_slides.pdf: revised slides of my Diploma thesis kick-off, 2006/07/14
• thesis-ClaudiaThormann.pdf: my diploma thesis (23 MB), handed in 2007/03/15
  One printed copy of my thesis is available in the library of the technical university Munich in Garching.
• DA-final_revised_slides.pdf: revised slides of my final presentation, 2007/06/20

Literature

• "Tracking: Beyond 15 minutes of thought: Siggraph 2001 course 11" by B.D. Allen, G. Bishop and G. Welch
• "A survey of electromagnetic position tracker calibration techniques" by Volodymyr V. Kindratenko
• "An improved calibration framework for electromagnetic tracking devices" by M. Ikits, J.D. Brederson, C.D. Hansen and J.M. Hollerbach
• "Calibration of electromagnetic tracking devices" by Volodymyr V. Kindratenko
• "Tracking Systems in Surgical Navigation" by Wolfgang Birkfellner, Chapter 5
• "The integration of optical and magnetic tracking for multi-user augmented reality" by T. Auer A. and Pinz

• "Error Correction for Electromagnetic Tracking", Master thesis by Suhkbansbir Kaur, handed in 2006/04/28
• "Aligning Optical and Electromagnetic Tracking Systems", Diploma thesis by Sintje Göritz, handed in 2005/05/15