  Generative adversarial models with convolutional neural network (CNN)
backbones have recently been established as state-of-the-art in numerous
medical image synthesis tasks. However, CNNs are designed to perform local
processing with compact filters, and this inductive bias compromises learning
of contextual features. Here, we propose a novel generative adversarial
approach for medical image synthesis, ResViT, that leverages the contextual
sensitivity of vision transformers along with the precision of convolution
operators and realism of adversarial learning.} ResViT's generator employs a
central bottleneck comprising novel aggregated residual transformer (ART)
blocks that synergistically combine residual convolutional and transformer
modules. Residual connections in ART blocks promote diversity in captured
representations, while a channel compression module distills task-relevant
information. A weight sharing strategy is introduced among ART blocks to
mitigate computational burden. A unified implementation is introduced to avoid
the need to rebuild separate synthesis models for varying source-target
modality configurations. Comprehensive demonstrations are performed for
synthesizing missing sequences in multi-contrast MRI, and CT images from MRI.
Our results indicate superiority of ResViT against competing CNN- and
transformer-based methods in terms of qualitative observations and quantitative
metrics.
