Ultrasound (US) scanning has become increasingly popular in the medical industry as it provides radiation-free, compact and real time imaging solutions for diagnosis and intraoperative navigation during interventions such as pedicle screw placement (PSP).  Robotic ultrasound scanning systems have shown to increase the imaging quality by maintaining constant contact between the US probe and the skin surface. To image bones, US waves travel through the skin and reflect or deflect on the bone depending on the inclination of the surface. Reflection and hence intensity of the image is maximal when the incident US wave is perpendicular to the bone surface. Therefore, optimising the orientation of the US probe with respect to the underlying anatomy could be especially beneficial in visualising complex bony structures such as the lumbar spine in which features such as the spinous process are rarely visualised when scanning at an angle perpendicular to the skin. Therefore, this abstract presents a robotic path planning approach that optimises the orientation of the US probe to maximise the ultrasound image quality and hence the resulting 3D reconstructions of complex bony structures such as the lumbar spine.

Purpose: Robot-assisted ultrasound (US) systems could be used to provide a non-radiative three-dimensional (3D) reconstruction that can form the basis for guiding spine surgical procedures. Despite promising studies on this technology, there are few studies that offer insight into the robustness and generality of the approach by e.g. verifying performance in various testing scenarios. Therefore, this study provides an assessment of the robot-assisted US system, with technical details from experiments starting at the bench-top up to the pre-clinical study. Methods: A semi-automatic control strategy is proposed to ensure continuous and smooth scanning. Next, a method based on U-Net was developed to automatically process the anatomic features and derive a high quality 3D US reconstruction. Experiments on phantoms and human cadavers validate the proposed approach. Results: Average deviations of scanning force were found of 2.84 ± 0.45 N on synthetic phantoms and of 5.64 ± 1.10 N on human cadavers. The reconstruction yielded a mean 3D representation error of 1.28 ± 0.87 mm for the synthetic phantoms and of 1.74 ± 0.89 mm for the human cadavers. Conclusion: These results show the proposed system has high safety performance and could keep the probe force stable within the range of 1 N to obtain a good reconstruction. The experiments indicate that the proposed robotassisted US approach works in quite different experimental settings. The results encourage to also explore the potential of this technology in in-vivo studies.

This study presents the first automated robotic system for PSP without the need for an external tracking system. The proposed system utilizes a U-Net-based framework to segment 2d US images and reconstruct 3D anatomy features, enabling visualization of the spinal structure. Then, the desired screw trajectories are automatically registered to the 3D reconstruction. By employing this robot-assisted system, the reliance on guide-tube-based approaches is eliminated, reducing the physical demands of the procedure and allowing the surgeon to focus more on planning and evaluation rather than execution. Experimental evaluation on two lamb vertebrae yielded four screw trajectories. The mean 3D error is 2.78 mm at the entry points and 4.82 mm at the stop points. Compared to commercial robotic systems, the use of non-radiation imaging decreases the second harm to the patient and surgeons. Meanwhile, it gets rid of the bone pin, which can lead to an incision in the patient’s body.