C-arm angle measurement with accelerometer for brachytherapy: an accuracy study

  • Thomas WolffEmail author
  • Andras Lasso
  • Markus Eblenkamp
  • Erich Wintermantel
  • Gabor Fichtinger
Original Article



 X-ray fluoroscopy guidance is frequently used in medical interventions. Image-guided interventional procedures that employ localization for registration require accurate information about the C-arm’s rotation angle that provides the data externally in real time. Optical, electromagnetic, and image-based pose tracking systems have limited convenience and accuracy. An alternative method to recover C-arm orientation was developed using an accelerometer as tilt sensor.


    The fluoroscopic C-arm’s orientation was estimated using a tri-axial acceleration sensor mounted on the X-ray detector as a tilt sensor. When the C-arm is stationary, the measured acceleration direction corresponds to the gravitational force direction. The accelerometer was calibrated with respect to the C-arm’s rotation along its two axes, using a high-accuracy optical tracker as a reference. The scaling and offset error of the sensor was compensated using polynomial fitting. The system was evaluated on a GE OEC 9800 C-arm. Results obtained by accelerometer, built-in sensor, and image-based tracking were compared, using optical tracking as ground truth data.


The accelerometer-based orientation measurement error for primary angle rotation was \(-0.1\pm 0.0^{\circ }\) and for secondary angle rotation it was \(0.1\pm 0.0^{\circ }\). The built-in sensor orientation measurement error for primary angle rotation was \(-0.1\pm 0.2^{\circ }\), and for secondary angle rotation it was \(0.1\pm 0.2^{\circ }\). The image-based orientation measurement error for primary angle rotation was \(-0.1\pm 1.3^{\circ }\), and for secondary angle rotation it was \(-1.3\pm 0.3^{\circ }\).


The accelerometer provided better results than the built-in sensor and image-based tracking. The accelerometer sensor is small, inexpensive, covers the full rotation range of the C-arm, does not require line of sight, and can be easily installed to any mobile X-ray machine. Therefore, accelerometer tilt sensing is a very promising applicant for orientation angle tracking of C-arm fluoroscopes.


Accelerometer C-arm Tilt sensor Angle measurement Accuracy study Brachytherapy 



This work was supported through the Applied Cancer Research Unit program of Cancer Care Ontario with funds provided by the Ontario Ministry of Health and Long-Term Care. Gabor Fichtinger was funded as a Cancer Ontario Research Chair. The authors thank Yashar Madjidi for the fabrication of the C-arm calibration phantom.

Conflict of Interest

Thomas Wolff, Andras Lasso, Markus Eblenkamp, Erich Wintermantel and Gabor Fichtinger declare that they have no conflict of interest.


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Copyright information

© CARS 2013

Authors and Affiliations

  • Thomas Wolff
    • 1
    Email author
  • Andras Lasso
    • 2
  • Markus Eblenkamp
    • 1
  • Erich Wintermantel
    • 1
  • Gabor Fichtinger
    • 2
  1. 1.Technische Universität MünchenMunichGermany
  2. 2.Queen’s UniversityKingstonCanada

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