Robotic Path Re-Planning for US Reconstruction of the Spine

Robotic ultrasound (US) scanning of the spine is becoming an increasingly viable radiation-free alternative to CT scans and fluoroscopy. However, due to the complex shape of the vertebra, three-dimensional (3D) US reconstructions generated from two-dimensional (2D) US scans often lack important anatomic information, such as the spinous process. This paper investigates scanning strategies that reorient the probe during US scanning to improve surface coverage of 3D US reconstructions. A two-scan procedure with a path re-planning algorithm is presented. The proposed algorithm uses information from a first exploratory scan to generate an improved imaging trajectory whereby the US probe is near-perpendicular to the targeted bone surface. The results show a 30.4%, 42.3%, and 75.0% improvement in surface coverage on a synthetic phantom, cadaver, and human volunteers, respectively, achieving up to 56% surface coverage on human volunteers. These results emphasise the value of exploiting information about the underlying anatomy to optimise the scanning trajectory. The increased surface coverage of the 3D US reconstructions will provide higher quality radiation-free visualisation, extending the role of US as a complementary imaging modality for safe and effective diagnosis and spine interventions.