Registration of MRI to intraoperative radiographs for target localization in spinal interventions

Abstract

Purpose Decision support to assist in target vertebra localization could provide a useful aid to safe and effective spine surgery. Previous solutions have shown 3D-2D registration of preoperative CT to intraoperative radiographs to reliably annotate vertebral labels for assistance during level localization. We present an algorithm (referred to as MR-LevelCheck) to perform 3D-2D registration based on a preoperative MRI to accommodate the increasingly common clinical scenario in which MRI is used instead of CT for preoperative planning. Methods Straightforward adaptation of gradient/intensity-based methods appropriate to CT-to-radiograph registration is confounded by large mismatch and noncorrespondence in image intensity between MRI and radiographs. The proposed method overcomes such challenges with a simple vertebrae segmentation step using vertebra centroids as seed points (automatically defined within existing workflow). Forwards projections are computed using segmented MRI and registered to radiographs via gradient orientation (GO) similarity and the CMA-ES (Covariance-Matrix-Adaptation Evolutionary-Strategy) optimizer. The method was tested in an IRB-approved study involving 10 patients undergoing cervical, thoracic, or lumbar spine surgery following preoperative MRI. 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. Robust registration performance was achieved with projection distance error (PDE) (median ± iqr) = 4.3 ± 2.6 mm (median ± iqr) and 0% failure rate. Segmentation accuracy for the continuous max-flow method yielded Dice coefficient = 88.1 ± 5.2, Accuracy = 90.6 ± 5.7, RMSE = 1.8 ± 0.6 mm, and contour affinity ratio (CAR) = 0.82 ± 0.08. Registration performance was found to be robust for segmentation methods exhibiting RMSE < 3 mm and CAR > 0.50. Conclusion The MR-LevelCheck method provides a potentially valuable extension to a previously developed decision support tool for spine surgery target localization by extending its utility to preoperative MRI while maintaining characteristics of accuracy and robustness.

Magnetic resonance imaging–based synthetic computed tomography of the lumbar spine for surgical planning: a clinical proof-of-concept

“…An increase in MRI-only workflows has been seen in recent years. 7,8 However, this would mean losing the radiodensitometric information provided by the CT scan, which is problematic because spine surgeons often require CT images to evaluate osseous anatomy such as dysplastic or twisted pedicles, and because MRI-based neuronavigation is still poorly implemented. In spinal neurosurgery, CT imaging has particular importance in surgical navigation, for example, for the computerassisted insertion of pedicle screws.…”

“…For these reasons, MRI-only workflows have gained attention in recent years. 7,8 In this brief report, we evaluate a prototype of the "BoneMRI" method, for the first time applied to the lumbar spine, that allows generation of synthetic CT (sCT) images from generally available MRI based on deep learn-ABBREVIATIONS sCT = synthetic CT; T1W = T1-weighted; T2W = T2-weighted.…”

A Fast 3-Dimensional Magnetic Resonance Imaging Reconstruction for Surgical Planning of Uterine Myomectomy

“… 17 18 19 20 21 Recently, there have been attempts to use 3D visualization as an imaging adjunctive tool for successful surgery especially in orthopedic, plastic, and dental surgery mostly in computed tomography imaging. 17 18 19 20 21 However, it requires a significant amount of time and effort to acquire the ROIs necessary for 3D visualization in MRI. We investigated a faster method of positioning myomas with a 3D uterine template, where we are able to intuitively recognize the position and size of myomas in a single 3D image obtained from the conventional 2D MRI.…”

Pre- and intraoperative thoracic spine localization techniques: a systematic review

“…This technique has historically been used as an adjuvant to other techniques, but it could be used as a standalone technique if there is an osseous lesion in question that is too small to be readily appreciated by fluoroscopy but still visible on CT. Additionally, as technology improves along with a shift in implementing automated processes in the workflow of clinical practice, automated localization algorithms are being validated and show promise in facilitating correct surgical level intraoperatively. [35][36][37][38] The advantages of this technique include ease and safety. Intraoperative spinal navigation may obviate the need for a preoperative procedure such as pedicle marking or the associated risks of some other preoperative procedures.…”