Optical Tracking for Freehand Swept Synthetic Aperture Imaging

Achieving higher resolution for deeper tissue structures remains a significant challenge in ultrasound (US) imaging due to the inherent limitations of diffraction. Swept synthetic aperture (SSA) techniques, which utilize the motion of a single transducer to effectively increase the imaging aperture, offer a promising solution. Building on SSA, we propose that freehand SSA provides a flexible approach with real-time adaptability to varying patient anatomies. This article introduces the optically tracked SSA (OT-SSA) platform, an approach that integrates external tracking to ensure accurate transducer positioning during freehand sweeps. Key sources of image degradation, such as spatial calibration error, tracking precision, and out-of-plane motion were directly analyzed and addressed within the system. In in vivo quadriceps imaging, OT-SSA reduced average lateral speckle autocorrelation size from 2.33 to 0.49 mm compared to a stationary aperture, demonstrating substantial resolution gains. The results establish OT-SSA as a robust and adaptable approach for high-resolution imaging.