Xingchi He

A Submillimetric 3-DOF Force Sensing Instrument With Integrated Fiber Bragg Grating for Retinal Microsurgery

Vitreoretinal surgery requires very fine motor control to perform precise manipulation of the delicate tissue in the interior of the eye. Besides physiological hand tremor, fatigue, poor kinesthetic feedback, and patient movement, the absence of force sensing is one of the main technical challenges. Previous two degrees of freedom (DOF) force sensing instruments have demonstrated robust force measuring performance. The main design challenge is to incorporate high sensitivity axial force sensing. This paper reports the development of a submillimetric 3-DOF force sensing pick instrument based on fiber Bragg grating (FBG) sensors. The configuration of the four FBG sensors is arranged to maximize the decoupling between axial and transverse force sensing. A superelastic nitinol flexure is designed to achieve high axial force sensitivity. An automated calibration system was developed for repeatability testing, calibration, and validation. Experimental results demonstrate a FBG sensor repeatability of 1.3 pm. The linear model for calculating the transverse forces provides an accurate global estimate. While the linear model for axial force is only locally accurate within a conical region with a 30° vertex angle, a second-order polynomial model can provide a useful global estimate for axial force. Combining the linear model for transverse forces and nonlinear model for axial force, the 3-DOF force sensing instrument can provide sub-millinewton resolution for axial force and a quarter millinewton for transverse forces. Validation with random samples show the force sensor can provide consistent and accurate measurement of 3-D forces.

Miniature fiber-optic force sensor based on low-coherence Fabry-Pérot interferometry for vitreoretinal microsurgery

During vitreoretinal surgery, the surgeon manipulates retinal tissue with tool-to-tissue interaction forces below the human sensory threshold. A force sensor (FS) integrated with conventional surgical tools may significantly improve the surgery outcome by providing tactile feedback to the surgeon. We designed and built a surgical tool integrated with a miniature FS with an outer diameter smaller than 1 mm for vitreoretinal surgery based on low-coherence Fabry–Pérot (FP) interferometry. The force sensing elements are located at the tool tip which is in direct contact with tissue during surgery and the FP cavity length is interrogated by a fiber-optic common-path phase-sensitive optical coherence tomography (OCT) system. We have calibrated the FSs response to axial and lateral forces and conducted experiments to verify that our FS can simultaneously measure both axial and lateral force components.

Force sensing micro-forceps with integrated fiber Bragg grating for vitreoretinal surgery

Vitreoretinal surgery is a technically demanding ophthalmologic discipline. One of the main technical challenges in vitreoretinal surgery is the lack of force sensing since the surgical maneuvers fall below the human sensory threshold. Previously, a 2-degree-of-freedom (DOF) force sensing instrument with a surgical pick was developed and tested. However, a more commonly used instrument for vitreoretinal surgery is the forceps, with which a surgeon can easily grasp and delaminate the scar tissue. We have designed, fabricated and calibrated a novel 20-gauge (Ga) microsurgical instrument with a 2-DOF force sensing forceps. Three fiber Bragg grating (FBG) sensors are integrated into the customized AlconTM forceps tip. The redundant sensor configuration provides good compensation for temperature-related drift. The calibration data show that the tool can provide a force resolution of 0.25 mN. In order to test the functionality and performance, the forceps was evaluated in inner shell membrane peeling experiments with chicken embryos as well as in in-vivo rabbit experiments. The instrument has demonstrated the capability of being applied in the clinical environment, with consistent force measurements. The force exerted in inner shell membrane peeling is from 6.07 to 34.65 mN. The development of the 2-DOF force sensing micro-forceps has shown that the fabrication process is feasible and reliable, and it can be used to develop a future 3-DOF force sensing tool.

Toward Clinically Applicable Steady-Hand Eye Robot for Vitreoretinal Surgery

This paper reports new developments and optimizations for clinical use of the Steady-Hand Eye Robot for vitreoretinal surgery. Vitreoretinal surgery requires precise micro-manipulation of delicate tissues. Surgical performance is limited by physiological hand tremor, fatigue, poor kinesthetic feedback, as well as patient movement. The previously developed Steady-Hand Eye Robot has been extensively used in in vivo experiments. Several safety and ergonomic limitations observed in the in vivo environment serve as motivation for a novel robot wrist design. The new robot wrist consists of a symmetric remote center of motion (RCM) tilt mechanism and a slim tool holder with a quick release mechanism for the surgical instruments. The RCM tilt mechanism provides a tilt motion range of ±45° and a stiffness of 21 N/mm. Two different release force thresholds for the quick release mechanism were designed. The soft configuration requires 2–3 N to retract the surgical instruments while the hard configuration requires 5–6 N.Copyright

A FORCE-SENSING MICROSURGICAL INSTRUMENT THAT DETECTS FORCES BELOW HUMAN TACTILE SENSATION

Purpose: To test the sensitivity and reproducibility of a 25-gauge force-sensing micropick during microsurgical maneuvers that are below tactile sensation. Methods: Forces were measured during membrane peeling in a “raw egg” and the chick chorioallantoic membrane models (N = 12) of epiretinal membranes. Forces were also measured during posterior hyaloid detachment and creation of retinal tears during vitrectomy in live rabbits (n = 6). Results: With the raw egg model, 0.5 ± 0.4 mN of force was detected during membrane peeling. In the chorioallantoic membrane model, delaminating the upper membrane produced 2.8 ± 0.2 mN of force. While intentionally rupturing the lower membrane to simulate a retinal tear, 7.3 ± 0.5 mN (range, 5.1–9.2 mN; P < 0.001) of force was generated while peeling the upper membrane. During vitrectomy, the minimum force that detached the posterior hyaloid was 6.7 ± 1.1 mN, which was similar to the force of 6.4 ± 1.4 mN that caused a retinal tear. The rate of force generation, as indicated by the first derivative of force generation, was 3.4 ± 1.2 mN/second during posterior hyaloid detachment, compared with 7.7 ± 2.4 mN/second during the creation of a retinal tear (P = 0.04). Conclusion: Force-sensing microsurgical instruments can detect forces below tactile sensation, and importantly, they can distinguish the forces generated during normal maneuvers from those that cause a surgical complication.

A novel dual force sensing instrument with cooperative robotic assistant for vitreoretinal surgery

Robotic assistants and smart surgical instruments have been developed to overcome many significant physiological limitations faced by vitreoretinal surgeons, one of which is lack of force perception below 7.5 mN. This paper reports the development of a new force sensor based on fiber Bragg grating (FBG) with the ability not just to sense forces at the tip of the surgical instrument located inside the eye, but also to provide information about the interaction force between the instrument shaft and the sclera. The sclera section provides vital feedback for cooperative robot control to minimize potentially dangerous forces on the eye. Preliminary results with 2×2 degrees-of-freedom (DOF) force sensor and force scaling robot control demonstrate significant reduction of forces on the sclera. The design and analysis of the sensor is presented along with a simulated robot assisted retinal membrane peeling on a phantom with sclera constraints and audio feedback.

A multi-function force sensing instrument for variable admittance robot control in retinal microsurgery

Robotic systems have the potential to assist vitre-oretinal surgeons in extremely difficult surgical tasks inside the human eye. In addition to reducing hand tremor and improving tool positioning, a robotic assistant can provide assistive motion guidance using virtual fixtures, and incorporate real-time feedback from intraocular force sensing ophthalmic instruments to present tissue manipulation forces, that are otherwise physically imperceptible to the surgeon. This paper presents the design of an FBG-based, multi-function instrument that is capable of measuring mN-level forces at the instrument tip located inside the eye, and also the sclera contact location on the instrument shaft and the corresponding contact force. The given information is used to augment cooperatively controlled robot behavior with variable admittance control. This effectively creates an adaptive remote center-of-motion (RCM) constraint to minimize eye motion, but also allows the translation of the RCM location if the instrument is not near the retina. In addition, it provides force scaling for sclera force feedback. The calibration and validation of the multifunction force sensing instrument are presented, along with demonstration and performance assessment of the variable admittance robot control on an eye phantom.

IRIS: Integrated Robotic Intraocular Snake

Retinal surgery is one of the most technically challenging surgical disciplines. Many robotic systems have been developed to enhance the surgical capabilities. However, very few of them provide the surgeon the dexterity within the patients eye to enable more flexible, more advanced surgical procedures. This paper presents a sub-millimeter intraocular dexterous robot, the Integrated Robotic Intraocular Snake (IRIS). The variable neutral-line mechanism is used to provide very high dexterity with a very small form factor. The IRIS distal dexterous unit is 0.9 mm in diameter and about 3 mm in length. It enables two rotational degrees of freedom at the distal end of the ophthalmic instruments. The analysis on contact mechanics provides a reference for the adjustment of the wire pretension. Redundant actuation is implemented by using one motor for each wire. A motion scaling transmission is developed to overcome the suboptimal resolution of the motors. A scale-up model of the IRIS is built for initial experimental evaluation. Preliminary results show that the scale-up IRIS can provide large range of motion. For given bending angle, the kinematic model can estimate the desired wire translation when the friction is not significant. The first prototype of the actual-scale IRIS is assembled and tested.

Development of a miniaturized 3-DOF force sensing instrument for robotically assisted retinal microsurgery and preliminary results

Lack of force sensing is one of the most formidable technical challenges in retinal microsurgery. Incorporating high sensitivity force sensing into the ophthalmic tools has the potential to provide the surgeon useful force feedback and to enable safe robotic assistance. This paper presents a new design of a three degrees of freedom force sensing instrument based on fiber Bragg grating sensors. A new flexure is developed to achieve high axial force sensing sensitivity and low crosstalk noise. The force sensing segment of the tool, located directly proximal to the tool tip, is ø0.9×8 mm. An extensive calibration shows that the force sensor can measure the transverse and axial force up to 21 mN with 0.5 mN and 3.3 mN accuracy, respectively. The new flexure design demonstrates the potential to improve axial force sensing. Analysis of the experiment results suggests improvements for the future iteration.

A dual-use imaging system for pre-clinical small animal radiation research

The current cone beam computed tomography (CBCT) system on the small animal radiation research platform (SARRP) is less effective in localizing soft-tissue targets. On the contrary, molecular optical imaging techniques, such as bioluminescence tomography (BLT) and fluorescence tomography (FT), can provide high contrast soft tissue images to complement CBCT and offer functional information. In this study, we present a dual-use optical imaging system that enables BLT/FT for both on-board and stand-alone applications. The system consists of a mobile cart and an imaging unit. Multi-projection optical images can be acquired in a range of -90°~90° angles. An optical fiber driven by an X-Y-Z Cartesian stage serves as an excitation light source specifically for FT. Our results show that the accuracy and reproducibility of the system meets the requirements set by the pre-clinical workflow (<;0.1 mm and 0.5 degree error). Preliminary experiments demonstrate the feasibility of bioluminescent imaging in a tissue-simulating phantom with a luminescent source embedded. In a considerable light-tight environment, we can achieve average background optical intensity significantly lower than the luminescent signal (<; 5%).