Advancing Sensorless Freehand 3D Ultrasound Reconstruction with a Novel Coupling Pad

Sensorless freehand 3D ultrasound (US) reconstruction poses a significant challenge, yet it holds considerable importance in improving the accessibility of 3D US applications in clinics. Current mainstream solutions, relying on inertial measurement units or deep learning, encounter issues like cumulative drift. To overcome these limitations, we present a novel sensorless 3D US solution with two key contributions. Firstly, we develop a novel coupling pad for 3D US, which can be seamlessly integrated into the conventional 2D US scanning process. This pad, featuring 3 N-shaped lines, provides 3D spatial information without relying on external tracking devices. Secondly, we introduce a coarse-to-fine optimization method for calculating poses of sequential 2D US images. The optimization begins with a rough estimation of poses and undergoes refinement using a distance-topology discrepancy reduction strategy. The proposed method is validated by both simulation and practical phantom studies, demonstrating its superior performance compared to state-of-the-art methods and good accuracy in 3D US reconstruction.