Dr. Sheng-Fu Lo Profile

Dr. Sheng-Fu Lo

at Johns Hopkins Hospital

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Publications (2)

Proceedings Article | 16 March 2020 Presentation + Paper

Method for metal artifact avoidance in C-arm cone-beam CT

P. Wu, N. Sheth, A. Sisniega, A. Uneri, R. Han, R. Vijayan, P. Vagdargi, B. Kreher, H. Kunze, G. Kleinszig, S. Vogt, S.-F. Lo, N. Theodore, J. Siewerdsen

Proceedings Volume 11312, 1131226 (2020) https://doi.org/10.1117/12.2549840

KEYWORDS: Metals, Calibration, Image segmentation, Signal attenuation, Chest, Spine, Imaging systems, Surgery, Modulation transfer functions, Visualization

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Purpose: Metal artifacts remain a challenge for CBCT systems in diagnostic imaging and image-guided surgery, obscuring visualization of metal instruments and surrounding anatomy. We present a method to predict C-arm CBCT orbits that will avoid metal artifacts by acquiring projection data that is least affected by polyenergetic bias. Methods: The metal artifact avoidance (MAA) method operates with a minimum of prior information, is compatible with simple mobile C-arms that are increasingly prevalent in routine use, and is consistent with either 3D filtered backprojection (FBP), more advanced (polyenergetic) model-based image reconstruction (MBIR), and/or metal artifact reduction (MAR) post-processing methods. MAA consists of the following steps: (i) coarse localization of metal objects in the field of view (FOV) via two or more low-dose scout views, coarse backprojection, and segmentation (e.g., with a U-Net); (ii) a simple model-based prediction of metal-induced x-ray spectral shift for all source-detector vertices (gantry rotation and tilt angles) accessible by the imaging system; and (iii) definition of a source-detector orbit that minimizes the view-to-view inconsistency in spectral shift. The method was evaluated in anthropomorphic phantom study emulating pedicle screw placement in spine surgery. Results: Phantom studies confirmed that the MAA method could accurately predict tilt angles that minimize metal artifacts. The proposed U-Net segmentation method was able to localize complex distributions of metal instrumentation (over 70% Dice coefficient) with 6 low-dose scout projections acquired during routine pre-scan collision check. CBCT images acquired at MAA-prescribed tilt angles demonstrated ~50% reduction in “blooming” artifacts (measured as FWHM of the screw shaft). Geometric calibration for tilted orbits at prescribed angular increments with interpolation for intermediate values demonstrated accuracy comparable to non-tilted circular trajectories in terms of the modulation transfer function. Conclusion: The preliminary results demonstrate the ability to predict C-arm orbits that provide projection data with minimal spectral bias from metal instrumentation. Such orbits exhibit strongly reduced metal artifacts, and the projection data are compatible with additional post-processing (metal artifact reduction, MAR) methods to further reduce artifacts and/or reduce noise. Ongoing studies aim to improve the robustness of metal object localization from scout views and investigate additional benefits of non-circular C-arm trajectories.

Proceedings Article | 8 March 2019 Presentation + Paper

Improved intraoperative imaging in spine surgery: clinical translation of known-component 3D image reconstruction on the O-arm system

X. Zhang, A. Uneri, J. Stayman, C. Zygourakis, S. Lo, N. Theodore, J. Siewerdsen

Proceedings Volume 10951, 1095103 (2019) https://doi.org/10.1117/12.2513777

KEYWORDS: Imaging systems, 3D image reconstruction, Spine, Data acquisition, Surgery, Image quality

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