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. 2018 Feb;14(1):10.1002/rcs.1871.
doi: 10.1002/rcs.1871. Epub 2017 Nov 28.

Real-time probe tracking using EM-optical sensor for MRI-guided cryoablation

Wenpeng Gao  1   2 , Baichuan Jiang  3   2 , Daniel F Kacher  2 , Barry Fetics  4 , Erez Nevo  4 , Thomas C Lee  2 , Jagadeesan Jayender  2
Affiliations

Real-time probe tracking using EM-optical sensor for MRI-guided cryoablation

Wenpeng Gao et al. Int J Med Robot. 2018 Feb.

Abstract

Background: A method of real-time, accurate probe tracking at the entrance of the MRI bore is developed, which, fused with pre-procedural MR images, will enable clinicians to perform cryoablation efficiently in a large workspace with image guidance.

Methods: Electromagnetic (EM) tracking coupled with optical tracking is used to track the probe. EM tracking is achieved with an MRI-safe EM sensor working under the scanner's magnetic field to compensate the line-of-sight issue of optical tracking. Unscented Kalman filter-based probe tracking is developed to smooth the EM sensor measurements when occlusion occurs and to improve the tracking accuracy by fusing the measurements of two sensors.

Results: Experiments with a spine phantom show that the mean targeting errors using the EM sensor alone and using the proposed method are 2.21 mm and 1.80 mm, respectively.

Conclusion: The proposed method achieves more accurate probe tracking than using an EM sensor alone at the MRI scanner entrance.

Keywords: MRI-guided cryoablation; electromagnetic tracking; optical tracking; probe tracking; unscented Kalman filter.

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Figures

Fig.1
Fig.1
Probe with EM-optical sensor.
Fig.2
Fig.2
Multiple coordinate systems.
Fig.3
Fig.3
Localization of fiducial markers: (a) phantom with seven attached markers, two of which were occluded by the phantom body; (b) manual localization of the markers in 3D Slicer.
Fig.4
Fig.4
Experiment setup in AMIGO MRI room.
Fig.5
Fig.5
Generation of the EM sensor’s error map: (a) sample points by optical tracking (red) and EM tracking (blue); (b) grid representation of the error map. Color bar shows the error in mm.
Fig.6
Fig.6
Validation using CT as the ground truth. (a) Axial MR image of the phantom; (b) Phantom with 17 probes; (c) Axial CT image corresponding to (a) after registration; (d) Ground truth of the tips’ position (red points) shown in volume rendering mode.
Fig.7
Fig.7
Targeting error using optical sensor only (Opt), EM sensor only (EM), EM sensor with UKF (EM-UKF), and EM-Optical sensor with UKF (EM-Opt-UKF).
Fig.8
Fig.8
Noise affects the measurement of the EM sensor in Case #16. Blue points represent the trajectory measured by the EM sensor alone and red points are the estimated trajectory using the proposed method.
See this image and copyright information in PMC

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