CNN-Based Projected Gradient Descent for Consistent CT Image Reconstruction

IEEE Trans Med Imaging. 2018 Jun;37(6):1440-1453. doi: 10.1109/TMI.2018.2832656.

Abstract

We present a new image reconstruction method that replaces the projector in a projected gradient descent (PGD) with a convolutional neural network (CNN). Recently, CNNs trained as image-to-image regressors have been successfully used to solve inverse problems in imaging. However, unlike existing iterative image reconstruction algorithms, these CNN-based approaches usually lack a feedback mechanism to enforce that the reconstructed image is consistent with the measurements. We propose a relaxed version of PGD wherein gradient descent enforces measurement consistency, while a CNN recursively projects the solution closer to the space of desired reconstruction images. We show that this algorithm is guaranteed to converge and, under certain conditions, converges to a local minimum of a non-convex inverse problem. Finally, we propose a simple scheme to train the CNN to act like a projector. Our experiments on sparse-view computed-tomography reconstruction show an improvement over total variation-based regularization, dictionary learning, and a state-of-the-art deep learning-based direct reconstruction technique.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Deep Learning*
  • Humans
  • Image Processing, Computer-Assisted / methods*
  • Signal-To-Noise Ratio
  • Tomography, X-Ray Computed / methods*