Comparing freehand and robotic techniques for standard scan plane localization in ultrasound imaging

<strong>Purpose</strong>. Locating appropriate scan planes in ultrasound (US) imaging is a critical first task that can be time-consuming and highly user-dependent. The choice between freehand and robotic techniques depends on the specific use case, the environment in which the ultrasound is being performed, and the priorities of the healthcare provider. This work aims to compare and evaluate these two techniques for the task of localizing standard scan planes in renal imaging. <strong>Methods</strong>. A prototype robotic US imaging system, integrated with a reinforcement learning (RL) agent, was developed and tasked with localizing the longitudinal scan plane of the kidney. Simulated perturbations were introduced to emulate potential errors in freehand acquisition, such as deviations in following directions and maintaining contact forces. The performance of the guidance system was evaluated on simulated images, a phantom model, and a cadaveric specimen in terms of the agent’s accuracy and efficiency in reaching the target. <strong>Results</strong>. The proposed method performed comparably in both freehand and robotic approaches. The freehand approach achieved similar levels of reachability (89±2%) as the robotic approach, despite inconsistencies in following the agent’s directions. The robotic approach had better overall efficiency (40° total travel) in reaching the target (i.e., taking shorter paths to reach the target plane). Acquired images had better consistency, as demonstrated by the higher-quality 3D volume reconstructions. The findings were successfully replicated in phantom and cadaver specimens. <strong>Conclusions</strong>. This work reports a comparison between freehand and robotic methods for the task of localizing standard scan planes. The integrated system enabled emulation of freehand and robotic operations, which were systematically compared in manipulation errors, force control deviations, and validated in phantom and cadaver studies. The comparable performance of the freehand approach suggests its suitability in applications, such as point-of-care imaging, where robotic US may not be feasible.