2011 Summer project Week Open Source Electromagnetic Trackers using OpenIGTLink

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  • Stylized image of three orthogonal coils used in 6-DOF electromagnetic tracker sensor

Key Investigators

  • Retired: Peter Traneus Anderson

Objectives

One goal of this open-source electromagnetic tracker project is to extend the tracker simulators in OpenIGTLink, by replacing the simulated position and orientation data with real data from real sensors using real hardware, all open-sourced.

Another goal of this project, is to provide an open forum for tracker designers to discuss the technology in all its aspects. Open-source tracker projects provide a common basis for discussion among tracker designers who are otherwise trapped behind proprietary walls.

The physics of electromagnetic trackers only just works. Tracker designers are continually struggling to get enough signal/noise from a small-enough sensor at a large-enough distance for a particular application. Magnetic-field distortion adds to the challenges.

Another goal of this project, is to enable researchers to simulate trackers for themselves, to better understand the limits imposed by the physics.

Another goal of this project, is to provide opportunities to gain experience on simple, unusual, and state-of-the-art analog hardware, digital hardware, digital-signal-processing algorithms, electromagnetic modeling, and position-calculation algorithms.

Approach, Plan

My approach is to start from the physics with simulation programs, and then implement hardware emphasizing performance and clarity of operation. Everything is intended as a starting point for others to improve upon.

My plan for the project week is to use the OpenIGTLink library to add OpenIGTLink output to [my existing 6DOF tracker simulator].

Progress

Open Source Electromagnetic Trackers

My published work to date is on [https://web.archive.org/web/20151002101400/http://home.comcast.net/~traneus/dry_emtrackertricoil.htm].

I am partway through building an initial 6DOF tracker electronics around an eight-channel ADC evaluation board and a USB device interface chip. I have ADC data transferring to the USB host workstation. I have transmitter driver circuitry partially constructed, and what is built works. I plan to build coil trios using clusters of six off-the-shelf RF chokes. I know how to do the signal processing, but have not yet written that code. I have the apparatus needed to manually characterize the coil trios. I know how to extract the characterization parameters from the data, but have not yet written that code.

I made contacts with people interested in pursuing this project in various ways.

To Do:

  • Visit Tina Kapur at AMIGO to discuss tracking options.
  • Work with Gregory Fischer at WPI on EM tracker using their analog interface board, and on interdisciplinary student tracker project.
  • Develop EM tracker design workshop and demo for Summer Project Week 2012.
  • Write tracker coil design fundamentals.
  • Support Sonia Pujol at BWH in developing tracker coils for her project.
  • Finish initial 6DOF tracker hardware and software.
  • Write, write, write documentation and tutorials.
  • Setup EM tracker pages on NA-MIC wiki.
  • Develop a general-case seed for the 5DOF tracker fitter. I don't know how to do this, and help is welcome.
  • Develop analytic fix for equatorial hole in field-and-gradient solution in paper: Takaai Nura, Satoshi Suzuki, and Shigeru Ando, "A Closed-Form Formula for Magnetic Dipole Localization by Measurement of its Magnetic Field and Spatial Gradients", IEEE Transactions on Magnetics, Volume 42, Number 10, October 2006, pp. 3291-3293.
  • Image (tracker position error = pixel intensity) versus position into NRRD format for viewing in Slicer.
  • Post detailed references to tracker papers and patents, including Frederick Raab's papers, Martinelli's patents, and Mark Schneider's patents.
  • Develop list of manufacturers of telecoils.
  • Get TrackerServer2.cxx to compile as a standalone .cpp program.
  • Develop goodness-of-fit criteria for assessing uncertainty of tracked position in real time.
  • Understand orientation-dependent position errors in 5DOF trackers.
  • Develop and document tracker design-for-application (thanks to James Millen) process.
  • Which license for documentation, both text and hardware design documentation?
  • Thoroughly isolated receiver electronics
  • Lots more!

Delivery Mechanism

I plan to post items on Open Source Electromagnetic Trackers.

References

  • Tracker patents
  • IEEE Transactions on Magnetics has had a thin stream of good tracker papers at least since 2000.
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