Learning Deformable Point Set Registration with Regularized Dynamic Graph CNNs for Large Lung Motion in COPD Patients

TL;DR

This paper introduces a novel end-to-end framework using dynamic graph CNNs to learn regularized geometric features for robust deformable registration of lung keypoints in CT scans, addressing large deformations without relying on intensity data.

Contribution

It presents a new method combining learned geometric features with the CPD algorithm via differentiable layers for improved point set registration in medical imaging.

Findings

Significantly improved registration accuracy on lung CT keypoints.

Enhanced robustness to large deformations without intensity information.

Effective use of geometric features for point set registration.

Abstract

Deformable registration continues to be one of the key challenges in medical image analysis. While iconic registration methods have started to benefit from the recent advances in medical deep learning, the same does not yet apply for the registration of point sets, e.g. registration based on surfaces, keypoints or landmarks. This is mainly due to the restriction of the convolution operator in modern CNNs to densely gridded input. However, with the newly developed methods from the field of geometric deep learning suitable tools are now emerging, which enable powerful analysis of medical data on irregular domains. In this work, we present a new method that enables the learning of regularized feature descriptors with dynamic graph CNNs. By incorporating the learned geometric features as prior probabilities into the well-established coherent point drift (CPD) algorithm, formulated as differentiable network layer, we establish an end-to-end framework for robust registration of two point sets. Our approach is evaluated on the challenging task of aligning keypoints extracted from lung CT scans in inhale and exhale states with large deformations and without any additional intensity information. Our results indicate that the inherent geometric structure of the extracted keypoints is sufficient to establish descriptive point features, which yield a significantly improved performance and robustness of our registration framework.