HyperMorph: Amortized Hyperparameter Learning for Image Registration

TL;DR

HyperMorph introduces a hypernetwork-based approach for image registration that efficiently learns the impact of hyperparameters, enabling rapid tuning, improved robustness, and reduced computational costs compared to traditional methods.

Contribution

It proposes a novel amortized hyperparameter learning framework using hypernetworks to optimize deformable image registration without extensive retraining.

Findings

Faster hyperparameter optimization compared to traditional search methods.

Enhanced robustness to initialization and dataset variability.

Ability to identify optimal hyperparameters for specific tasks or regions.

Abstract

We present HyperMorph, a learning-based strategy for deformable image registration that removes the need to tune important registration hyperparameters during training. Classical registration methods solve an optimization problem to find a set of spatial correspondences between two images, while learning-based methods leverage a training dataset to learn a function that generates these correspondences. The quality of the results for both types of techniques depends greatly on the choice of hyperparameters. Unfortunately, hyperparameter tuning is time-consuming and typically involves training many separate models with various hyperparameter values, potentially leading to suboptimal results. To address this inefficiency, we introduce amortized hyperparameter learning for image registration, a novel strategy to learn the effects of hyperparameters on deformation fields. The proposed framework learns a hypernetwork that takes in an input hyperparameter and modulates a registration network to produce the optimal deformation field for that hyperparameter value. In effect, this strategy trains a single, rich model that enables rapid, fine-grained discovery of hyperparameter values from a continuous interval at test-time. We demonstrate that this approach can be used to optimize multiple hyperparameters considerably faster than existing search strategies, leading to a reduced computational and human burden as well as increased flexibility. We also show several important benefits, including increased robustness to initialization and the ability to rapidly identify optimal hyperparameter values specific to a registration task, dataset, or even a single anatomical region, all without retraining the HyperMorph model. Our code is publicly available at http://voxelmorph.mit.edu.