Robotic needle steering systems for minimally invasive medical procedures require complementary medical imaging systems to track the needles in real time. Ultrasound is a promising imaging modality because it offers relatively low-cost, real-time imaging of the needle. Previous methods applied vibration to the base of the needle using a voice coil actuator, in order to make the needle visible in power Doppler ultrasound. We propose a new method for needle tip vibration, using electromagnetic actuation of small permanent magnets placed inside the needle to improve needle tip visibility in power Doppler imaging. Robotic needle insertion experiments using artificial tissue and ex vivo porcine liver showed that the electromagnetic tip vibration method can generate a stronger Doppler response compared to the previous base vibration method, resulting in better imaging at greater needle depth in tissue. It also eliminates previous issues with vibration damping along the shaft of the needle.

Robotic systems can improve percutaneous interventions by steering flexible needles along nonlinear trajectories. These systems require medical image feedback for accurate closed-loop control. Three-dimensional (3D) ultrasound can provide real-time measurements of needle pose within tissue; however, the ultrasound produces relatively large amounts of measurement noise. A recursive estimation approach is described for accurately estimating the six-degree-of-freedom pose of a steerable needle tip, by applying an unscented Kalman filter (UKF) to 3D ultrasound segmentation results. The UKF is formulated based on a kinematic process model of needle steering, as well as experimental quantification of the statistical variability of steering and imaging needles in biological tissue. Validation testing shows that the UKF method makes accurate closed-loop robotic control of the needle tip possible in biological tissue. Compared to direct use of noisy ultrasound data for control feedback, the UKF reduced average positioning error by 9.58 mm (81%) when steering towards a simulated target. This new estimation scheme will contribute towards the future evaluation of needle steering robots in real-world clinical applications.

In this study we evaluated a new method for registering three-dimensional ultrasound (3DUS) data to external coordinate systems. First, 3DUS was registered to the stereo endoscope of a da Vinci Surgical System by placing a registration tool against an air-tissue boundary so that the 3DUS could image ultrasound fiducials while the stereo endoscope could image camera markers on the same tool. The common points were used to solve the registration between the 3DUS and camera coordinate systems. The target registration error (TRE) when imaging through a PVC tissue phantom ranged from 3.85 1.76 mm to 1.82 1.03 mm using one to four registration tool positions. TRE when imaging through an ex-vivo liver tissue sample ranged from 2.36 1.01 mm to 1.51 0.70 mm using one to four registration tool positions. Second, using a similar method, 3DUS was registered to the kinematic coordinate system of a da Vinci Surgical System by using the da Vinci surgical manipulators to identify common points on an air-tissue boundary. TRE when imaging through a PVC tissue phantom was 0.95 0.38 mm. This registration method is simpler and potentially more accurate than methods using commercial motion tracking systems. This method may be useful in the future in augmented reality systems for laparoscopic and robotic-assisted surgery.