UBone3D: Physics-Rectified Conditional Flow Matching for Anatomical 3D Shape Completion from Ultrasound

Three-dimensional ultrasound (US) is a safe, radiation-freecomplementary modality to CT and X-rays for longitudinal monitoring,yet its segmentation-derived partial point clouds are extremely artifact-laden. Consequently, it is challenging to recover a clean and completeanatomical structure from such US point clouds. In this paper, we presentUBone3D, a novel framework based on physics-rectified conditional flowmatching (CFM) that performs point cloud completion directly from par-tial US observations. UBone3D models deterministic physics artifacts(e.g., surface thickening, streaking, dropouts) via a simulated physicsproxy, and introduces test-time physics rectification to steer the shapecompletion. At inference, the completion is jointly steered by two decou-pled forces: (1) anatomical plausibility enforced by a CT-trained gen-erative shape prior, BoneFM, and (2) physics consistency enforced byUSimNet in the ultrasound formation space. Extensive experimentson simulated and in-vivo data demonstrate significant improvements inreconstruction accuracy and anatomical fidelity over existing baselines.Project page: https://answerrtx.github.io/UBone3D-Proj/.