DIGS: Dynamic CBCT Reconstruction using Deformation-Informed 4D Gaussian Splatting and a Low-Rank Free-Form Deformation Model

TL;DR

This paper introduces DIGS, a novel deformation-informed 4D Gaussian Splatting method for dynamic CBCT reconstruction, achieving high-quality images with significantly improved speed by modeling motion with a low-rank free-form deformation framework.

Contribution

We propose a deformation-informed 4D Gaussian Splatting approach with a free-form deformation model, enabling efficient, motion-aware CBCT reconstruction without phase sorting.

Findings

Achieved 6x faster reconstruction compared to HexPlane.

Produced superior image quality on six CBCT datasets.

Effectively modeled continuous respiratory motion in CBCT.

Abstract

3D Cone-Beam CT (CBCT) is widely used in radiotherapy but suffers from motion artifacts due to breathing. A common clinical approach mitigates this by sorting projections into respiratory phases and reconstructing images per phase, but this does not account for breathing variability. Dynamic CBCT instead reconstructs images at each projection, capturing continuous motion without phase sorting. Recent advancements in 4D Gaussian Splatting (4DGS) offer powerful tools for modeling dynamic scenes, yet their application to dynamic CBCT remains underexplored. Existing 4DGS methods, such as HexPlane, use implicit motion representations, which are computationally expensive. While explicit low-rank motion models have been proposed, they lack spatial regularization, leading to inconsistencies in Gaussian motion. To address these limitations, we introduce a free-form deformation (FFD)-based spatial basis function and a deformation-informed framework that enforces consistency by coupling the temporal evolution of Gaussian's mean position, scale, and rotation under a unified deformation field. We evaluate our approach on six CBCT datasets, demonstrating superior image quality with a 6x speedup over HexPlane. These results highlight the potential of deformation-informed 4DGS for efficient, motion-compensated CBCT reconstruction. The code is available at https://github.com/Yuliang-Huang/DIGS.