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Solution to extend the Field of View of Computed Tomography using Deep Learning approaches

Type: MA thesis

Status: finished

Date: September 1, 2020 - March 1, 2021

Supervisors: Yixing Huang, Andreas Maier, Tino Haderlein

Deep learning has been successfully applied in various applications of computed tomography (CT). Due to limited
detector size and low dose requirements, the problem of data truncation is essentially present in CT. The reconstructed images from such limited field-of-view (FoV) projections suffer from cupping artifacts inside the FoV and distortion or missing of anatomical structures that are outside the FoV [1]. One practical approach to solve the data truncation problem is to apply an extrapolation technique that increases the FoV, then apply an artifact removal technique. The water cylinder extrapolation based reconstruction [2] is a promising method that estimates the projections outside the scan field-of-view (SFoV) by using the knowledge from the projections inside the SFoV. Alternatively, the linear extrapolation technique is the simplest extrapolation technique that always increases the FoV without using any prior information, however, artifacts are still visible on the reconstructed image. Recently, Fourni´e et al. [3] have proposed a deep learning based method “Deep EFoV” to extend the FoV of CT images. First, the FoV is increased by linearly extrapolating the outer channels in the sinogram space. The reconstructed image from this extended FoV sinogram produces artifacts. Finally, the U-net model is used to remove the artifacts in the reconstructed image. The reconstructed image from a neural network model might affect the anatomical structures that are inside the SFoV. To compensate this effect, a standard algorithm “HDFoV” is used where projections inside the SFoV and projections from the neural network model that are outside the FoV are merged.

The aim of the master’s thesis will be to integrate “Deep EFoV” and “HDFoV” algorithms in the C#-based proprietary
reconstruction tool “ReconCT” developed by Siemens Healthineers. The result from the integrated algorithms needs
to be compared with the result from only the “Deep EFoV” algorithm. Another goal is to evaluate and improve the
proposed deep learning model in “Deep EFoV” for the CT FoV extension. The model needs to be improved w. r. t.
tweaking architecture, adapting parameters or even using a different architecture. The dataset and software provided
by Siemens Healthineers will be used in the thesis. The final software needs to be integrated into the “ReconCT” and
has to be presented to the supervisors.

The thesis will include the following points:

• Review of the state-of-the-art method and deep learning approaches to extend the FoV
• Comparison of the proposed method “Deep EFoV” with the integrated “Deep EFoV” and “HDFoV” method
• Improvement and simplification of the proposed deep learning model in “Deep EFoV”
• Integration of the proposed model in the reconstruction tool.

 

References
[1] Y. Huang, L. Gao, A. Preuhs, and A. Maier, “Field of View Extension in Computed Tomography Using Deep
Learning Prior,” in Bildverarbeitung f¨ur die Medizin: Algorithmen – Systeme – Anwendungen, pp. 186–191,
Springer, 2020.
[2] J. Hsieh, E. Chao, J. Thibault, B. Grekowicz, A. Horst, S. McOlash, and T. J. Myers, “A novel reconstruction
algorithm to extend the CT scan field-of-view,” Medical Physics, vol. 31, no. 9, pp. 2385–2391, 2004.
[3] ´ E. Fourni´e, M. Baer-Beck, and K. Stierstorfer, “CT field of view extension using combined channels extension
and deep learning methods,” in International Conference on Medical Imaging with Deep Learning – Extended
Abstract Track, (London, United Kingdom), 08–10 Jul 2019.