Generalizing Supervised Deep Learning MRI Reconstruction to Multiple and
  Unseen Contrasts using Meta-Learning Hypernetworks
Sriprabha Ramanarayanan Arun Palla Keerthi Ram Mohanasankar Sivaprakasam
Meta-learning has recently been an emerging data-efficient learning technique
for various medical imaging operations and has helped advance contemporary deep
learning models. Furthermore, meta-learning enhances the knowledge
generalization of the imaging tasks by learning both shared and discriminative
weights for various configurations of imaging tasks. However, existing
meta-learning models attempt to learn a single set of weight initializations of
a neural network that might be restrictive for multimodal data. This work aims
to develop a multimodal meta-learning model for image reconstruction, which
augments meta-learning with evolutionary capabilities to encompass diverse
acquisition settings of multimodal data. Our proposed model called KM-MAML
(Kernel Modulation-based Multimodal Meta-Learning), has hypernetworks that
evolve to generate mode-specific weights. These weights provide the
mode-specific inductive bias for multiple modes by re-calibrating each kernel
of the base network for image reconstruction via a low-rank kernel modulation
operation. We incorporate gradient-based meta-learning (GBML) in the contextual
space to update the weights of the hypernetworks for different modes. The
hypernetworks and the reconstruction network in the GBML setting provide
discriminative mode-specific features and low-level image features,
respectively. Experiments on multi-contrast MRI reconstruction show that our
model, (i) exhibits superior reconstruction performance over joint training,
other meta-learning methods, and context-specific MRI reconstruction methods,
and (ii) better adaptation capabilities with improvement margins of 0.5 dB in
PSNR and 0.01 in SSIM. Besides, a representation analysis with U-Net shows that
kernel modulation infuses 80% of mode-specific representation changes in the
high-resolution layers. Our source code is available at
https://github.com/sriprabhar/KM-MAML/.