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Registration of Preoperative MRI to Intraoperative Radiographs for Automatic Vertebral Target Localization

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T De Silva

T De Silva1*, A Uneri1 , M Ketcha1 , S Reaungamornrat1 , J Goerres1 , S Vogt2 , G Kleinszig2 , J Wolinsky3 , JH Siewerdsen4 , (1) Johns Hopkins Univeristy, Baltimore, MD, (2) Siemens Healthcare , Erlangen, Germany, (3) The Johns Hopkins Hospital, Baltimore, MD


WE-AB-BRA-9 (Wednesday, August 3, 2016) 7:30 AM - 9:30 AM Room: Ballroom A

Purpose:Accurate localization of target vertebrae is essential to safe, effective spine surgery, but wrong-level surgery occurs with surprisingly high frequency. Recent research yielded the “LevelCheck” method for 3D-2D registration of preoperative CT to intraoperative radiographs, providing decision support for level localization. We report a new method (MR-LevelCheck) to perform 3D-2D registration based on preoperative MRI, presenting a solution for the increasingly common scenario in which MRI (not CT) is used for preoperative planning.

Methods:Direct extension of LevelCheck is confounded by large mismatch in image intensity between MRI and radiographs. The proposed method overcomes such challenges with a simple vertebrae segmentation. Using seed points at centroids, vertebrae are segmented using continuous max-flow method and dilated by 1.8 mm to include surrounding cortical bone (inconspicuous in T2w-MRI). MRI projections are computed (analogous to DRR) using segmentation and registered to intraoperative radiographs. The method was tested in a retrospective IRB-approved study involving 11 patients undergoing cervical, thoracic, or lumbar spine surgery following preoperative MRI. Registration accuracy was evaluated in terms of projection-distance-error (PDE) between the true and estimated location of vertebrae in each radiograph.

Results:The method successfully registered each preoperative MRI to intraoperative radiographs and maintained desirable properties of robustness against image content mismatch, and large capture range. Segmentation achieved Dice coefficient = 89.2 ± 2.3 and mean-absolute-distance (MAD) = 1.5 ± 0.3 mm. Registration demonstrated robust performance under realistic patient variations, with PDE = 4.0 ± 1.9 mm (median ± iqr) and converged with run-time = 23.3 ± 1.7 s.

Conclusion:The MR-LevelCheck algorithm provides an important extension to a previously validated decision support tool in spine surgery by extending its utility to preoperative MRI. With initial studies demonstrating PDE <5 mm and 0% failure rate, the method is now in translation to larger scale prospective clinical studies.

Funding Support, Disclosures, and Conflict of Interest: S. Vogt and G. Kleinszig are employees of Siemens Healthcare

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