Experimental Validation of Scaphoid Tracking Using a Flexible Dual-Array Ultrasound Probe: From Proof-of-Concept to...

Accurate intra-operative tracking of the scaphoid bone is essential for successful percutaneous scaphoid fixation, a minimally invasive procedure commonly guided by fluoroscopy. However, fluoroscopy provides only 2-D imaging and exposes both the patient and the surgeon to ionizing radiation. To address these limitations, we propose and validate a novel, flexible, dual-array ultrasound transducer for real-time scaphoid tracking. The dual-array probe acquires two parallel ultrasound images, enabling 3-D point cloud generation of a portion of the scaphoid surface. In addition to the probe itself, we introduce a template matching algorithm for real-time tracking, and its precision is evaluated against a reference measurement generated by simultaneous 4-D imaging using a GE Vivid E95 system and a CT-derived scaphoid model. By registering both datasets to a common coordinate system, we compute translation and rotation tracking errors. The system achieved a median frame-by-frame translation error of 0.48 mm, with median cumulative translation errors of 0.75, 0.45 and 0.90 mm along the azimuth, depth and elevation axes, respectively. The median rotation error was 3.90°, with the largest cumulative error observed around the azimuth axis (median: 8.50°). Errors around the depth and elevation axes were lower, with median values of approximately 2.50° and 3.20°, respectively. These results demonstrate that the proposed system provides clinically acceptable accuracy and temporal resolution (28 Hz) suitable for surgical guidance. This work represents a significant step toward the deployment of ultrasound navigation systems in orthopedic procedures, offering a radiation-free and real-time alternative to fluoroscopy.