Scan-specific robust artificial-neural-networks for k-space interpolation (RAKI) reconstruction: Database-free deep learning for fast imaging

Mehmet Akcakaya, Steen Moeller, Sebastian Weingärtner, Kamil Ugurbil

Research output: Contribution to journalArticlepeer-review

81 Scopus citations

Abstract

Purpose: To develop an improved k-space reconstruction method using scan-specific deep learning that is trained on autocalibration signal (ACS) data. Theory: Robust artificial-neural-networks for k-space interpolation (RAKI) reconstruction trains convolutional neural networks on ACS data. This enables nonlinear estimation of missing k-space lines from acquired k-space data with improved noise resilience, as opposed to conventional linear k-space interpolation-based methods, such as GRAPPA, which are based on linear convolutional kernels. Methods: The training algorithm is implemented using a mean square error loss function over the target points in the ACS region, using a gradient descent algorithm. The neural network contains 3 layers of convolutional operators, with 2 of these including nonlinear activation functions. The noise performance and reconstruction quality of the RAKI method was compared with GRAPPA in phantom, as well as in neurological and cardiac in vivo data sets. Results: Phantom imaging shows that the proposed RAKI method outperforms GRAPPA at high (≥4) acceleration rates, both visually and quantitatively. Quantitative cardiac imaging shows improved noise resilience at high acceleration rates (rate 4:23% and rate 5:48%) over GRAPPA. The same trend of improved noise resilience is also observed in high-resolution brain imaging at high acceleration rates. Conclusion: The RAKI method offers a training database-free deep learning approach for MRI reconstruction, with the potential to improve many existing reconstruction approaches, and is compatible with conventional data acquisition protocols.

Original languageEnglish (US)
Pages (from-to)439-453
Number of pages15
JournalMagnetic resonance in medicine
Volume81
Issue number1
DOIs
StatePublished - Jan 2019

Bibliographical note

Funding Information:
FUNDING INFORMATION National Institutes of Health, Grant/Award Numbers: R00HL111410, P41EB015894, U01EB025144, R01NS085188, P30NS076408, and P50NS098573; National Science Foundation, Grant/Award Number: CAREER CCF-1651825.

Funding Information:
National Institutes of Health, Grant/Award Numbers: R00HL111410, P41EB015894, U01EB025144, R01NS085188, P30NS076408, and P50NS098573; National Science Foundation, Grant/Award Number: CAREER CCF‐1651825.

Publisher Copyright:
© 2018 International Society for Magnetic Resonance in Medicine

Keywords

  • accelerated imaging
  • convolutional neural networks
  • deep learning
  • image reconstruction
  • k-space interpolation
  • nonlinear estimation
  • parallel imaging

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