Caitlin Schneider

Remote ultrasound palpation for robotic interventions using absolute elastography

Although robotic surgery has addressed many of the challenges presented by minimally invasive surgery, haptic feedback and the lack of knowledge of tissue stiffness is an unsolved problem. This paper presents a system for finding the absolute elastic properties of tissue using a freehand ultrasound scanning technique, which utilizes the da Vinci Surgical robot and a custom 2D ultrasound transducer for intraoperative use. An external exciter creates shear waves in the tissue, and a local frequency estimation method computes the shear modulus. Results are reported for both phantom and in vivo models. This system can be extended to any 6 degree-of-freedom tracking method and any 2D transducer to provide real-time absolute elastic properties of tissue.

Motion of the Kidney Between Preoperative and Intraoperative Positioning

For many laparoscopic surgical procedures, the preoperative images are taken with the patient in a different position than that in which the surgery is performed. The organ shift between positions can affect surgical image guidance, as the organ shifts can complicate image registration. In particular, for partial nephrectomy, the standard clinical approach requires supine preoperative computed tomography, while the surgery is performed in the flank position. We studied ten subjects in both supine and flank positions. Rigid registration was used to determine the relative motion of the kidneys, using the spine as a pose-independent landmark. Our results showed that the kidney can move as much as 46.5 mm as a result of a supine-to-flank change in patient position, and rotate as much as 25°. From the results, significant kidney motion occurs due to the change of patient position from supine to flank. These changes warrant further study to understand and model the patient specific motion.

Intraoperative Registered Transrectal Ultrasound Guidance for Robot-Assisted Laparoscopic Radical Prostatectomy

PURPOSE To provide unencumbered real-time ultrasound image guidance during robot-assisted laparoscopic radical prostatectomy, we developed a robotic transrectal ultrasound system that tracks the da Vinci® Surgical System instruments. We describe our initial clinical experience with this system. MATERIALS AND METHODS After an evaluation in a canine model, 20 patients were enrolled in the study. During each procedure the transrectal ultrasound transducer was manually positioned using a brachytherapy stabilizer to provide good imaging of the prostate. Then the transrectal ultrasound was registered to the da Vinci robot by a previously validated procedure. Finally, automatic rotation of the transrectal ultrasound was enabled such that the transrectal ultrasound imaging plane safely tracked the tip of the da Vinci instrument controlled by the surgeon, while real-time transrectal ultrasound images were relayed to the surgeon at the da Vinci console. Tracking was activated during all critical stages of the surgery. RESULTS The transrectal ultrasound robot was easy to set up and use, adding 7 minutes (range 5 to 14) to the procedure. It did not require an assistant or additional control devices. Qualitative feedback was acquired from the surgeons, who found transrectal ultrasound useful in identifying the urethra while passing the dorsal venous complex suture, defining the prostate-bladder interface during bladder neck dissection, identifying the seminal vesicles and their location with respect to the rectal wall, and identifying the distal prostate boundary at the apex. CONCLUSIONS Real-time, registered robotic transrectal ultrasound guidance with automatic instrument tracking during robot-assisted laparoscopic radical prostatectomy is feasible and potentially useful. The results justify further studies to establish whether the approach can improve procedure outcomes.

Tracked “Pick-Up” Ultrasound for Robot-Assisted Minimally Invasive Surgery

Goal: We present a novel “pick-up” ultrasound transducer for intraabdominal robot-assisted minimally invasive surgery. Such a “pick-up” ultrasound transducer is inserted through an abdominal incision at the beginning of the procedure and remains in the abdominal cavity throughout, eliminating the need for a dedicated port or a patient bedside surgical assistant. The transducer has a handle that can be grasped in a repeatable manner using a da Vinci Prograsp tool, allowing the transducer to be accurately manipulated by the surgeon using the da Vinci Robot. This is one way to enable 3-D tracking of the transducer, and, thus, mapping of the vasculature. The 3-D vascular images can be used to register preoperative CT to intraoperative camera images. Methods: To demonstrate the feasibility of the approach, we use an ultrasound vessel phantom to register a CT surface model to extracted ultrasound vessel models. The 3-D vascular phantom images are generated by segmenting B-mode images and tracking the pick-up ultrasound transducer with the da Vinci kinematics, internal electromagnetic sensor, or visible fiducials suitable for camera tracking. Results: Reconstruction results using da Vinci kinematics for tracking give a target registration error of 5.4 ± 1.7 mm.

Augmented Reality Imaging for Robot-Assisted Partial Nephrectomy Surgery

Laparoscopic partial nephrectomy (LPN) is a standard of care for small kidney cancer tumours. A successful LPN is the complete excision of the kidney tumour while preserving as much of the non-cancerous kidney as possible. This is a challenging procedure because the surgeon has a limited field of view and reduced or no haptic feedback while performing delicate excisions as fast as possible. This work introduces and evaluates a novel surgical navigation marker called the Dynamic Augmented Reality Tracker (DART). The DART is used in a novel intra-operative augmented reality ultrasound navigation system (ARUNS) for robot-assisted minimally invasive surgery to overcome some of these challenges. The DART is inserted into a kidney and the DART and pick-up laparoscopic ultrasound transducer are tracked during an intra-operative freehand ultrasound scan of the tumour. After ultrasound, the system continues to track the DART and display the segmented 3D tumour and location of surgical instruments relative to the tumour throughout the surgery. The ultrasound point reconstruction root mean squared error (RMSE) was 0.9 mm, the RMSE of tracking the da Vinci surgical instruments was 1.5 mm and the total system RMSE, which includes ultrasound imaging and da Vinci kinematic instrument tracking, was 5.1 mm. The system was evaluated by an expert surgeon who used the DART and ARUNS to excise a tumour from a kidney phantom. This work serves as a preliminary evaluation in anticipation of further refinement and validation in vivo.

Bimanual telerobotic surgery with asymmetric force feedback: A daVinci ® surgical system implementation

This paper describes the applicability of an asymmetric force feedback control framework for bimanual robot-assisted surgery using the da Vinci surgical system (Intuitive Surgical Inc.). The core idea of this method, previously presented in [1], is that when completing two-handed tasks involving an action and a reaction force, the forces applied on the environment by the action hand are not transferred back to the same hand, but rather to the reaction hand. Such a method provides an intuitive way of feeling the force, while avoiding the instability issues, since the control loop in not closed from the slave to the master of the same hand. In the introductory paper [1], the technique was implemented using game controllers with simple tasks. In this paper, the technique was implemented on the da Vinci surgical system (Classic version) using the da Vinci Research Kit (dVRK) controllers that enable complete access to all control levels of the da Vinci robot manipulators via custom mechatronics and open-source software. The implementation involved a full re-write of a teleoperation controller based on kinematic correspondence with gravity compensation, as well as torque control functions for force rendering on the da Vinci master manipulators. A series of suture knot tying and haptic exploration experiments were conducted in which a small group of users, both surgeons (N=3) and novices (N=6) evaluated the system. The results show that the proposed technique has some promise when implemented in a realistic 14 degrees of freedom system, but further work is necessary to make the system fully usable.

Bimanual teleoperation with heart motion compensation on the da Vinci® Research Kit: Implementation and preliminary experiments

This paper describes the implementation of a heart motion compensation system on the da Vinci surgical system (Intuitive Surgical Inc.) with the da Vinci Research Kit, for the purpose of simulating minimally invasive coronary artery bypass surgery on the beating heart. A Novint Falcon device is used to simulate the motion of the coronary bypass site. The 3D position of the heart simulator is measured optically in real time using an NDI Optotrak Certus tracker. The NDI measurements are used to command the da Vinci patient side manipulators to track, from a fixed distance, the simulated heart surface. Visual stabilization is achieved by having a stereo endoscopic camera carried by another patient-side manipulator that is also tracking the heart surface. The system performance is evaluated and discussed. In a preliminary evaluation study, surgeons were asked to perform a bimanual teleoperation suturing task on the simulated heart, with the gold standard being a suturing task on a stationary surface. When motion compensation was enabled, the median completion time dropped from 1.24 to 1.07 of the gold standard, the number of errors was reduced, and subjective measures show higher preference for the use of motion compensation in the da Vinci controllers.

Blood pressure dependent elasticity measurements of porcine kidney ex-vivo

Kidney transplantation is standard of care for end-stage renal failure. Monitoring graft health after transplantation to ensure graft longevity is important and usually carried out through the use of biopsy. Ultrasound elastography has the potential to allow regular non-invasive monitoring of graft health via the level of fibrosis. Results of kidney elastography research to date have been variable. It is hypothesized that the changes in blood pressure are a confounding factor in elasticity measurements and may explain the varied results. Using a controlled set-up on porcine kidneys ex-vivo, the effects of changes in pressure with flow from a peristaltic pump were examined (n=5). Each kidney was measured from 0 mmHg to 130 mmHg. It was found that the measured elasticity of the kidney was dependent on the input pressure of the pump. Increasing the input pressure resulted in an increase in the measured elasticity, from an average 21 ± 3 kPa at 0 mmHg to approximately 34 ± 9 kPa at 130 mmHg. These results suggest that the phase of the cardiac cycle be considered in kidney elastography using electrocardiogram (ECG) monitoring.

Ultrasound-based image guidance for robot-assisted laparoscopic radical prostatectomy: initial in-vivo results

This paper describes the initial clinical evaluation of a real-time ultrasound-based guidance system for robot-assisted laparoscopic radical prostatectomy (RALRP). The surgical procedure was performed on a live anaesthetized canine with a da Vinci SI robot. Intraoperative imaging was performed using a robotic transrectal ultrasound (TRUS) manipulator and a bi-plane TRUS transducer. Two registration methods were implemented and tested: (i)using specialized fiducials placed at the air-tissue boundary, 3D TRUS data were registered to the da Vinci stereo endoscope with an average TRE of 2.37 ± 1.06 mm, (ii)using localizations of the da Vinci manipulator tips in 3D TRUS images, 3D TRUS data were registered to the kinematic frame of the da Vinci manipulators with average TRE of 1.88 ± 0.88 mm using manual tool tip localization, and average TRE of 2.68 ± 0.98 mm using an automatic tool tip localization algorithm. Registration time was consistently less than 2 minutes when performed by two experienced surgeons after limited learning. The location of the TRUS probe was remotely controlled through part of the procedure by a da Vinci tool, with the corresponding ultrasound images being displayed on the surgeon console using TilePro. Automatic tool tracking was achieved with angular accuracy of 1.65 ± 1.24 deg. This work demonstrates, for the first time, the in-vivo use of a robotically controlled TRUS probe calibrated to the da Vinci robot, and will allow the da Vinci tools to be tracked for safety and to be used as pointers for regions of interest to be imaged by ultrasound.

Monitoring cryoablation lesions with quantitative ultrasound elastography: A feasibility study

Percutaneous cryoablation (CA) is a minimally invasive approach where pathological areas are ablated by freezing them with a needle-shaped instrument inserted through the skin of the patient. CA requires image guidance to correctly reach the target lesion since the operator cannot directly see the area of intervention. Ultrasound (US) guidance is commonly used in percutaneous needle based procedures but the image quality is lower compared to other modalities and is user-dependent. On the other hand, US provides inexpensive, portable and real-time images and is harmless for the patient and operator. Unfortunately, in the case of CA the strong reflections and shadows in the US images caused by the ice-ball make the monitoring of the full coverage of the pathological area very difficult. One of the more promising developments in the US imaging is elastography, that could be used to improve the monitoring of the ablation area. US elastography has been already successfully applied to monitor other type of percutaneous ablation based on heat sources. The quality of US data during CA treatment makes very difficult to use elastography. In this work we show results of an ex-vivo animal experiment that proves the feasibility of using US elastography to monitor the frozen zone after the complete thawing of the tissue.