Anser EMT

An open electromagnetic tracking platform

H. A. Jaeger, A. M. Franz, K. O’ Donoghue, A. Seitel, F. Trauzettel, L. Maier-Hein and P. Cantillon-Murphy

h.jaeger@umail.ucc.ie

Original paper available here

In this talk...

  • Overview of EM tracking
    • Theory of operation
    • Clinical applications
  • Anser EMT
    • Motivation for an open platform
    • Design overview
    • Evaluation & results

Electromagnetic Tracking (EMT)

  1. Sensor placed in magnetic field, voltage induced on a sensor
  2. Signal sampled 🡪 processed 🡪 position & orientation

EMT Output

$$P = [x,y,z,\theta, \varphi, (\gamma)]$$

  • \([x,y,z]\), cartesian position of sensor
  • \([\theta,\varphi, (\gamma)]\), yaw, pitch and roll
  • No line of sight required

Applications of EMT

Neurosurgery, ENT Virtual bronchoscopy

Motivations

  • EMT is a key enabling technology
    • Safe, radiation free
    • No line-of-sight required
  • Technical challenges
    • Accuracy, precision & interference
    • Hardware cost
  • End-user needs
    • User survey

User survey

User Needs

Participate!

http://anser.io

and click on the survey link.

Anser EMT Goals

  • Create an open electromagnetic tracking platform
  • Address shortcomings of current solutions
  • Develop a user community
  • Provide a benchmark for future EMT designs

History of Anser

  • PhD project 2014, Kilian O’ Donoghue

    • “Electromagnetic Tracking and Steering for Catheter Navigation”, Thesis, University College Cork, Ireland

    • K.O’ Donoghue et. al. “Catheter position tracking system using planar magnetics and closed loop current control” IEEE Trans. Magn. 50(7):1–9, University College Cork, Ireland

Anser EMT - Prototype

For transport Deployed

Anser EMT - Prototype


Front panel

Anser Architecture

Reference Design

Transmitter Assembly

  • 8 Coils, 8 Frequencies
  • Lightweight, planar form factor

Plotkin et. al, IEEE Trans. Biomed. Eng. 2010, DOI: 10.1109/TBME.2009.2038495

Transmitter Coil

Dual sided Printed Circuit Board (PCB) emitter coil

Receiver

Solver

K.O’ Donoghue et. al. “Catheter position tracking system using planar magnetics and closed loop current control” IEEE Trans. Magn. 50(7):1–9

Solver

Need to translate solver from Matlab to Python
https://osf.io/47q8q

Anser Evaluation

  1. Standardised assessment [1]
    • Hummel Protocol
    • Performance comparison with commercial systems
  2. Siemens Artis Zeego evaluation
    • DynaCT - Image quaility & position


[1] Maier-Hein L, Franz AM, März K, Hummel J, Birkfellner W, Gergel I, Wegner I, and Meinzer HP (2012), Standardized assessment of new electromagnetic field generators in an interventional radiology setting. Med. Phys. 39(6):3424:3434

Assessment setup





Hummel board (left) [1] 5cm grid spacing, 5x5 grid (red) 32 point circle, 11.25 ° spacing Sensor mount (above, right)

Assessment setup


Physical setup

Assessment Method

  1. Position accuracy
    • $N_p=25$ points (averaged over 150 samples)
    • $N_d=20$ calculated distances
    • Compare each with reference (5cm)
  2. Precision
    • $N_p=25$ points
    • RMS jitter calculated over 150 samples at each point
  3. Orientation
    • 31 relative rotations
    • 11.25 ° angle increments

Assessment Method


Acquisition performed in MITK

Results

[27] Maier-Hein L, Franz AM et. al. (2012), Standardized assessment of new electromagnetic field generators in an interventional radiology setting. Med. Phys. 39(6):3424:3434 [28] Hummel J et. al. (2006) Evaluation of a new electromagnetic tracking system using a standardized assessment protocol. Phys. Med. Biol 51(2):205–210 [30] Much J (2008) Error classification and propagation for electromagnetic tracking. Master’s thesis, Tech. Univ. München, Munich, Germany

Artis Zeego Evaluation


Artis Zeego provides:
  • Interventional imaging
  • Fluoroscopy
  • 3D scan (DynaCT)
  • Carbon fibre bed (Great for EMT)



  1. Zeego effects on EMT?
    2.
  2. EMT effects on Zeego?
    3.

Zeego Operation


Original video available here

Experimental setup


IHU Strasbourg Artis Zeego Platform with carbon fibre table; Anser EMT (left) and NDI Aurora planar FG (right)

DynaCT procedure


  1. Targeting laser centred on tracking system field generator

  2. EMT acquisition started (2000 samples), DynaCT scan performed

  3. Position plotted over time

  4. Scan image quality compared with control

DynaCT

NDI Planar Transmitter Anser EMT


RMS Error = 0.12mm RMS Error = 0.27mm

DynaCT Image Quality

Experiment Notes


  • Zeego automatically adjusts the radiation dose depending on subject density

  • High density materials (bone, metal) will be subject to higher dosages

    • NDI Planar FG has larger spool coils & metal magnetic shielding

    • Anser EMT has low metal content coils and does not have shielding

  • Therefore radiation dosages differ between the two acquisitions

Conclusions

  • Anser EMT compares favourably to commercial systems

  • Precision and rotation measurements on-par with commercial systems

  • Accuracy needs improvement: error > 1mm
    • Improve enclosure tolerancing
    • Improve calibration procedure

  • Anser EMT not interfere significantly with Zeego imaging using a carbon fibre table

Anser v1.0

Currently in testing - Open design release Late 2017