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Errors in Device Localization in MRI Using Z-Frames
Jeremy Cepek1, 2, Blaine A. Chronik1, 3, and Aaron Fenster1, 2
1Robarts Research Institute, The University of Western Ontario, London, Canada
jcepek@robarts.ca
bchronik@uwo.ca
afenster@robarts.ca
2Biomedical Engineering, The University of Western Ontario, London, Canada
3Department of Physics and Astronomy, The University of Western Ontario, London, Canada
Abstract. The use of a passive MRI-visible tracking frame is a common method of localizing devices in MRI space for MRI-guided procedures. One of the most common tracking frame designs found in the literature is the z-frame, as it allows six degree-of-freedom pose estimation using only a single image slice. Despite the popularity of this design, it is susceptible to errors in pose estimation due to various image distortion mechanisms in MRI. In this paper, the absolute error in using a z-frame to localize a tool in MRI is quantified over various positions of the z-frame relative to the MRI isocenter, and for various levels of static magnetic field inhomogeneity. It was found that the error increases rapidly with distance from the isocenter in both the horizontal and vertical directions, but the error is much less sensitive to position when multiple contiguous slices are used with slice-select gradient nonlinearity correction enabled, as opposed to the more common approach of only using a single image slice. In addition, the error is found to increase rapidly with an increasing level of static field inhomogeneity, even with the z-frame placed within 10 cm of the isocenter.
Keywords: MRI-guided, stereotactic, z-frame, passive tracking
LNCS 8149, p. 348 ff.
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© Springer-Verlag Berlin Heidelberg 2013