Leveraging Unsupervised Image Registration for Discovery of Landmark Shape Descriptor

TL;DR

This paper introduces a self-supervised deep learning method for automatic landmark discovery in images, enabling shape analysis without segmentation or manual preprocessing, applicable to 2D and 3D data.

Contribution

It proposes a novel unsupervised landmark detection approach using image registration as the main task, with regularization and variants to incorporate prior shape knowledge.

Findings

Successfully applied to multiple 2D and 3D datasets.

Produced meaningful shape descriptors without segmentation.

Enhanced robustness with regularization and prior shape integration.

Abstract

In current biological and medical research, statistical shape modeling (SSM) provides an essential framework for the characterization of anatomy/morphology. Such analysis is often driven by the identification of a relatively small number of geometrically consistent features found across the samples of a population. These features can subsequently provide information about the population shape variation. Dense correspondence models can provide ease of computation and yield an interpretable low-dimensional shape descriptor when followed by dimensionality reduction. However, automatic methods for obtaining such correspondences usually require image segmentation followed by significant preprocessing, which is taxing in terms of both computation as well as human resources. In many cases, the segmentation and subsequent processing require manual guidance and anatomy specific domain expertise. This paper proposes a self-supervised deep learning approach for discovering landmarks from images that can directly be used as a shape descriptor for subsequent analysis. We use landmark-driven image registration as the primary task to force the neural network to discover landmarks that register the images well. We also propose a regularization term that allows for robust optimization of the neural network and ensures that the landmarks uniformly span the image domain. The proposed method circumvents segmentation and preprocessing and directly produces a usable shape descriptor using just 2D or 3D images. In addition, we also propose two variants on the training loss function that allows for prior shape information to be integrated into the model. We apply this framework on several 2D and 3D datasets to obtain their shape descriptors, and analyze their utility for various applications.