OCT-based intra-cochlear imaging and 3D reconstruction: ex vivo validation of a robotic platform

PURPOSE

The small size of the cochlea, and its location deeply embedded in thick temporal bone, poses a challenge for intra-cochlear guidance and diagnostics. Current radiological imaging techniques are not able to visualize the cochlear microstructures in detail. Rotational optical coherence tomography (OCT) fibers show great potential for intra-cochlear guidance. The generated images could be used to map, and study, the tiny cochlear microstructures relevant for hearing.

METHODS

This work describes the design of a rotational OCT probe with an outer diameter of 0.9 mm. It further discusses a robotic system, which features a remote center of motion mechanism, dedicated to the probe's positioning, fine manipulation and stable insertion into the cochlear micro-spaces. Furthermore, the necessary calibration steps for 3D reconstruction are described, followed by a detailed quantitative analysis, comparing the 3D reconstructions using a synthetic, 2:1 scaled scala tympani model with a reconstruction from micro-CT, serving as the ground truth. Finally, the potential of the system is demonstrated by scanning a single ex vivo cadaveric human cochlea.

RESULTS

The study investigates five insertions in the same 2:1 scaled tympani model, along with their corresponding 3D reconstruction. The comparison with micro-CT results in an average root-mean-square error of 74.2 µm, a signed distance error of 38.1 µm and a standard deviation of 63.6 µm. The average F-score of the reconstructions, using a distance threshold of 100 and 74.2 µm, resulted in 83.0% and 71.8%, respectively. Insertion in the cadaveric human cochlea showed the challenges for straight insertion, i.e., navigating the hook region.

CONCLUSION

Overall, the system shows great potential for intra-cochlear guidance and diagnostics, due to the system's capability for precise and stable insertion into the basal turn in the scala tympani. The system, combined with the calibration procedure, results in detailed and precise 3D reconstructions.

Path tracking control of a steerable catheter in transcatheter cardiology interventions

PURPOSE

Intracardiac transcatheter interventions allow for reducing trauma and hospitalization stays as compared to standard surgery. In the treatment of mitral regurgitation, the most widely adopted transcatheter approach consists in deploying a clip on the mitral valve leaflets by means of a catheter that is run through veins from a peripheral access to the left atrium. However, precise manipulation of the catheter from outside the body while copying with the path constraints imposed by the vessels remains challenging.

METHODS

We proposed a path tracking control framework that provides adequate motion commands to the robotic steerable catheter for autonomous navigation through vascular lumens. The proposed work implements a catheter kinematic model featuring nonholonomic constraints. Relying on the real-time measurements from an electromagnetic sensor and a fiber Bragg grating sensor, a two-level feedback controller was designed to control the catheter.

RESULTS

The proposed method was tested in a patient-specific vessel phantom. A median position error between the center line of the vessel and the catheter tip trajectory was found to be below 2 mm, with a maximum error below 3 mm. Statistical testing confirmed that the performance of the proposed method exhibited no significant difference in both free space and the contact region.

CONCLUSION

The preliminary in vitro studies presented in this paper showed promising accuracy in navigating the catheter within the vessel. The proposed approach enables autonomous control of a steerable catheter for transcatheter cardiology interventions without the request of calibrating the intuitive parameters or acquiring a training dataset.

Comparative Analysis of Interactive Modalities for Intuitive Endovascular Interventions

Endovascular intervention is a minimally invasive method for treating cardiovascular diseases. Although fluoroscopy, known for real-time catheter visualization, is commonly used, it exposes patients and physicians to ionizing radiation and lacks depth perception due to its 2D nature. To address these limitations, a study was conducted using teleoperation and 3D visualization techniques. This in-vitro study involved the use of a robotic catheter system and aimed to evaluate user performance through both subjective and objective measures. The focus was on determining the most effective modes of interaction. Three interactive modes for guiding robotic catheters were compared in the study: 1) Mode GM, using a gamepad for control and a standard 2D monitor for visual feedback; 2) Mode GH, with a gamepad for control and HoloLens providing 3D visualization; and 3) Mode HH, where HoloLens serves as both control input and visualization device. Mode GH outperformed other modalities in subjective metrics, except for mental demand. It exhibited a median tracking error of 4.72 mm, a median targeting error of 1.01 mm, a median duration of 82.34 s, and a median natural logarithm of dimensionless squared jerk of 40.38 in the in-vitro study. Mode GH showed 8.5%, 4.7%, 6.5%, and 3.9% improvements over Mode GM and 1.5%, 33.6%, 34.9%, and 8.1% over Mode HH for tracking error, targeting error, duration, and dimensionless squared jerk, respectively. To sum up, the user study emphasizes the potential benefits of employing HoloLens for enhanced 3D visualization in catheterization. The user study also illustrates the advantages of using a gamepad for catheter teleoperation, including user-friendliness and passive haptic feedback, compared to HoloLens. To further gauge the potential of using a more traditional joystick as a control input device, an additional study utilizing the Haption VirtuoseTM robot was conducted. It reveals the potential for achieving smoother trajectories, with a 38.9% reduction in total path length compared to a gamepad, potentially due to its larger range of motion and single-handed control.

Development and validation of a flexible fetoscope for fetoscopic laser coagulation

PURPOSE

Fetoscopic laser coagulation for twin-to-twin transfusion syndrome is challenging for anterior placenta due to the rigidity of current tools. The capacity to keep entry port forces minimal is critical for this procedure, as is optimal coagulation distance and orientation. This work introduces technological tools to this end.

METHODS

A novel fetoscope is presented with a rigid shaft and a flexible steerable segment at the distal end. The steerable segment can bend up to 90[Formula: see text] even when loaded with a laser fiber. An artificial pneumatic muscle makes such acute bending possible while allowing for a low-weight and disposable device.

RESULTS

The flexible fetoscope was validated in a custom-made phantom model to measure visual range and coagulation efficacy. The flexible fetoscope shows promising results when compared to a clinical rigid curved fetoscope to reach anterior targets. The new fetoscope was then evaluated in vivo (pregnant ewe) where it successfully coagulated placental vasculature.

CONCLUSION

The flexible fetoscope improved the ability to achieve optimal coagulation angle and distance on anteriorly located targets. The fetoscope also showed the potential to lead fetoscopic laser coagulation and other fetal surgical procedures toward safer and more effective interventions.

Comparison of 2D and autostereoscopic 3D visualization during mixed reality simulation

PURPOSE

In general minimally invasive surgical procedures, surgeons are tied to 2D visualization, leading to the loss of depth perception. This can lead to large mental load for the surgeons and may be responsible for the long learning curve. To restore the sense of depth, this study investigated the use and benefits of an autostereoscopic (3D) display during a simulated laparoscopic task.

METHODS

A mixed reality simulator was developed for comparing the performance of participants while using 2D and autostereoscopic 3D visualization. An electromagnetic sensor was mounted on a physical instrument, and its pose was mapped to the virtual instrument. The virtual scene was developed using Simulation Open Framework Architecture (SOFA). Finite element modeling was used to calculate interaction forces, which were then mapped to visual soft tissue deformation.

RESULTS

Ten non-expert participants completed a virtual laparoscopic task, where the subjects were asked to contact eighteen target areas distributed on the surface of the vagina, both in 2D and 3D. Results showed an improvement with 3D vision in task completion time (-16%), total traveled distance (-25%) and errors made (-14%). There was no difference in the average contact forces between the vagina and the instrument. Only the difference in time and forces were shown to be statistically significant.

CONCLUSION

Overall, autostereoscopic 3D showed superiority over conventional 2D visualization. The traveled trajectory increased in 2D as the instrument was retracted more between the targets to avoid contact. The 2D and 3D deformation upon contact seems not to contribute differently to force perception. However, the participants only had visual feedback, but no haptic feedback. Therefore, it could be interesting to include haptic feedback in a future study.

Three-dimensional catheter tip force sensing using multi-core fiber Bragg gratings

Awareness of catheter tip interaction forces is a crucial aspect during cardiac ablation procedures. The most important contact forces are the ones that originate between the catheter tip and the beating cardiac tissue. Clinical studies have shown that effective ablation occurs when contact forces are in the proximity of 0.2 N. Lower contact forces lead to ineffective ablation, while higher contact forces may result in complications such as cardiac perforation. Accurate and high resolution force sensing is therefore indispensable in such critical situations. Accordingly, this work presents the development of a unique and novel catheter tip force sensor utilizing a multi-core fiber with inscribed fiber Bragg gratings. A customizable helical compression spring is designed to serve as the flexural component relaying external forces to the multi-core fiber. The limited number of components, simple construction, and compact nature of the sensor makes it an appealing solution towards clinical translation. An elaborated approach is proposed for the design and dimensioning of the necessary sensor components. The approach also presents a unique method to decouple longitudinal and lateral force measurements. A force sensor prototype and a dedicated calibration setup are developed to experimentally validate the theoretical performance. Results show that the proposed force sensor exhibits 7.4 mN longitudinal resolution, 0.8 mN lateral resolution, 0.72 mN mean longitudinal error, 0.96 mN mean lateral error, a high repeatability, and excellent decoupling between longitudinal and lateral forces.

Preclinical implementation of a steerable, Da Vinci Xi® compatible CO2 -laser fibre carrier for transoral robotic surgery (TORS): A cadaveric feasibility study

INTRODUCTION

Monopolar electrocautery is the most common dissection and coagulation tool during transoral robotic surgery (TORS) but causes significant collateral tissue damage as opposed to CO₂ laser. We aimed at combining both modalities in one robotic instrument arm.

METHODS

We developed a steerable CO₂ -laser fibre carrier serving as an add-on to the existing Endowrist® monopolar spatula of the Da Vinci Xi. Feasibility and safety were assessed in a preclinical setting.

RESULTS

One radical tonsillectomy with monopolar cautery and three with the instrument prototype were performed in two cadavers by two surgeons. No serious prototype-related intra-operative difficulties were observed. Safe and efficient switching between energy sources proved possible in all simulated intra-operative bleeding events. Prototype use allowed for the identification of the majority of key anatomical structures and was scored favourably on NASA-TLX questionnaires.

DISCUSSION

The reported prototype successfully combines the advantages of CO₂ -laser with the advantages of TORS.

FBG-Based Estimation of External Forces Along Flexible Instrument Bodies

A variety of medical treatment and diagnostic procedures rely on flexible instruments such as catheters and endoscopes to navigate through tortuous and soft anatomies like the vasculature. Knowledge of the interaction forces between these flexible instruments and patient anatomy is extremely valuable. This can aid interventionalists in having improved awareness and decision-making abilities, efficient navigation, and increased procedural safety. In many applications, force interactions are inherently distributed. While knowledge of their locations and magnitudes is highly important, retrieving this information from instruments with conventional dimensions is far from trivial. Robust and reliable methods have not yet been found for this purpose. In this work, we present two new approaches to estimate the location, magnitude, and number of external point and distributed forces applied to flexible and elastic instrument bodies. Both methods employ the knowledge of the instrument’s curvature profile. The former is based on piecewise polynomial-based curvature segmentation, whereas the latter on model-based parameter estimation. The proposed methods make use of Cosserat rod theory to model the instrument and provide force estimates at rates over 30 Hz. Experiments on a Nitinol rod embedded with a multi-core fiber, inscribed with fiber Bragg gratings, illustrate the feasibility of the proposed methods with mean force error reaching 7.3% of the maximum applied force, for the point load case. Furthermore, simulations of a rod subjected to two distributed loads with varying magnitudes and locations show a mean force estimation error of 1.6% of the maximum applied force.

Deep learning-based monocular placental pose estimation: towards collaborative robotics in fetoscopy

PURPOSE

Twin-to-twin transfusion syndrome (TTTS) is a placental defect occurring in monochorionic twin pregnancies. It is associated with high risks of fetal loss and perinatal death. Fetoscopic elective laser ablation (ELA) of placental anastomoses has been established as the most effective therapy for TTTS. Current tools and techniques face limitations in case of more complex ELA cases. Visualization of the entire placental surface and vascular equator; maintaining an adequate distance and a close to perpendicular angle between laser fiber and placental surface are central for the effectiveness of laser ablation and procedural success. Robot-assisted technology could address these challenges, offer enhanced dexterity and ultimately improve the safety and effectiveness of the therapeutic procedures.

METHODS

This work proposes a 'minimal' robotic TTTS approach whereby rather than deploying a massive and expensive robotic system, a compact instrument is 'robotised' and endowed with 'robotic' skills so that operators can quickly and efficiently use it. The work reports on automatic placental pose estimation in fetoscopic images. This estimator forms a key building block of a proposed shared-control approach for semi-autonomous fetoscopy. A convolutional neural network (CNN) is trained to predict the relative orientation of the placental surface from a single monocular fetoscope camera image. To overcome the absence of real-life ground-truth placenta pose data, similar to other works in literature (Handa et al. in: Proceedings of the IEEE conference on computer vision and pattern recognition, 2016; Gaidon et al. in: Proceedings of the IEEE conference on computer vision and pattern recognition, 2016; Vercauteren et al. in: Proceedings of the IEEE, 2019) the network is trained with data generated in a simulated environment and an in-silico phantom model. A limited set of coarsely manually labeled samples from real interventions are added to the training dataset to improve domain adaptation.

RESULTS

The trained network shows promising results on unseen samples from synthetic, phantom and in vivo patient data. The performance of the network for collaborative control purposes was evaluated in a virtual reality simulator in which the virtual flexible distal tip was autonomously controlled by the neural network.

CONCLUSION

Improved alignment was established compared to manual operation for this setting, demonstrating the feasibility to incorporate a CNN-based estimator in a real-time shared control scheme for fetoscopic applications.

Handheld Active Add-On Control Unit for a Cable-Driven Flexible Endoscope

The instruments currently used by surgeons for in utero treatment of the twin-to-twin transfusion syndrome (TTTS) are rigid or semi-rigid. Their poor dexterity makes this surgical intervention risky and the surgeon's work very complex. This paper proposes the design, assembly and quantitative evaluation of an add-on system intended to be placed on a commercialized cable-driven flexible endoscope. The add-on system is lightweight and easily exchangeable thanks to the McKibben muscle actuators embedded in its system. The combination of the flexible endoscope and the new add-on unit results in an easy controllable flexible instrument with great potential use in TTTS treatment, and especially for regions that are hard to reach with conventional instruments. The fetoscope has a precision of 7.4% over its entire bending range and allows to decrease the maximum planar force on the body wall of 6.15% compared to the original endoscope. The add-on control system also allows a more stable and precise actuation of the endoscope flexible tip.

From a Disposable Ureteroscope to an Active Lightweight Fetoscope-Characterization and Usability Evaluation

The twin-to-twin transfusion syndrome is a severe fetal anomaly appearing in up to 15% of identical twin pregnancies. This anomaly occurs when twins share blood vessels from a common placenta. The complication leads to an unbalanced blood transfusion between both fetuses. A current surgical treatment consists in coagulating the shared vessels using a fetoscope with an embedded laser. Such treatment is very delicate and constraining due to limited vision and size of the insertion area. The rigidity and lack of controllability of the current used instruments add an additional difficulty and limit the choice in insertion site. This letter proposes an improved flexible fetoscope, offering an enhanced laser controllability and higher versatility regarding the location of the insertion site. A better approach angle can therefore be realized. Also, tissue damage may be further reduced. This single-handed controllable active fetoscope is obtained after adaptation of a LithoVue (Boston Scientific, Natick, MA, USA), a commercially available passive flexible ureteroscope. The LithoVue is fitted with a unique lightweight add-on actuation module foreseen of an artificial muscle and a dedicated control system. Experiments in a mixed reality trainer suggested that the proposed fetoscope is compact, ergonomic, and intuitive in use, allowing an adequate control of the flexible end.

Combined OCT distance and FBG force sensing cannulation needle for retinal vein cannulation: in vivo animal validation

PURPOSE

Retinal vein cannulation is an experimental procedure during which a clot-dissolving drug is injected into an obstructed retinal vein. However, due to the fragility and minute size of retinal veins, such procedure is considered too risky to perform manually. With the aid of surgical robots, key limiting factors such as: unwanted eye rotations, hand tremor and instrument immobilization can be tackled. However, local instrument anatomy distance and force estimation remain unresolved issues. A reliable, real-time local interaction estimation between instrument tip and the retina could be a solution. This paper reports on the development of a combined force and distance sensing cannulation needle, and its experimental validation during in vivo animal trials.

METHODS

Two prototypes are reported, relying on force and distance measurements based on FBG and OCT A-scan fibres, respectively. Both instruments provide an 80 [Formula: see text] needle tip and have outer shaft diameters of 0.6 and 2.3 mm, respectively.

RESULTS

Both prototypes were characterized and experimentally validated ex vivo. Then, paired with a previously developed surgical robot, in vivo experimental validation was performed. The first prototype successfully demonstrated the feasibility of using a combined force and distance sensing instrument in an in vivo setting.

CONCLUSION

The results demonstrate the feasibility of deploying a combined sensing instrument in an in vivo setting. The performed study provides a foundation for further work on real-time local modelling of the surgical scene. This paper provides initial insights; however, additional processing remains necessary.

Laser generated guided waves and finite element modeling for the thickness gauging of thin layers

In this paper, nondestructive testing has been performed on a thin gold layer deposited on a 2 in. silicon wafer. Guided waves were generated and studied using a laser ultrasonic setup and a two-dimensional fast Fourier transform technique was employed to obtain the dispersion curves. A gold layer thickness of 1.33 microm has been determined with a +/-5% margin of error using the shape of the two first propagating modes, assuming for the substrate and the layer an uncertainty on the elastic parameters of +/-2.5%. A finite element model has been implemented to validate the data post-treatment and the experimental results. A good agreement between the numerical simulation, the analytical modeling and the experimentations has been observed. This method was considered suitable for thickness layer higher than 0.7 microm.

High frequency ultrasonic detection of C-crack defects in silicon nitride bearing balls

A non-destructive testing method for silicon nitride bearing balls based on ultrasonic resonance spectroscopy is proposed here. Through the theoretical study of their elastic vibrations, it is possible to characterize the balls using a vibration mode that is similar to surface wave propagation. The study of the influence of C-crack defects on the resonances of Rayleigh modes is presented here. These C-cracks are typically formed by impacts between balls during finishing or handling. They are frequently found on the surface of silicon nitride bearing balls and these C-cracks decrease the rolling contact fatigue life considerably. This kind of defect is difficult to detect because the C-shaped surface crack is very small and narrow (500 microm x 5 microm), and its depth does not exceed 50 microm. The proposed methodology can both excite spheroidal vibrations in the ceramic balls and detect such vibrations over a large frequency range. In particular, high frequency vibrations are considered because these are similar to the surface waves propagating in the cortical zone of the ceramic balls and consequently they can be used to detect C-crack defects.

Laser ultrasonics and neural networks for the characterization of thin isotropic plates

Nondestructive testing has been performed on a thin copper plate. Lamb waves were generated and studied with a noncontact method, using a laser ultrasonic setup. A two-dimensional Fourier transform technique has been employed to obtain the dispersion curves, revealing numerous symmetric and antisymmetric modes. The inverse problem, in other words, the determination of the thickness and the elastic constants of the tested plate, has been solved by means of a feed-forward neural network. These parameters were then evaluated simultaneously, the dispersion curves being entirely fitted. The experimental results show good agreement with the theoretical model. This inversion method was found to be prompt and easy to automate.

Inclusions detection using Lamb waves in flexible printed circuits

The materials used for the manufacture of flexible printed circuits are selected according to various characteristics: thermal and electrical behavior, moisture absorption, flexibility... Those are determined by the basic materials of the three components of the circuit, which are the conducting layer, the adhesive layer and the dielectric film. Such circuits have a typical thickness of about 200 microm and are therefore an interesting solution for a great number of electronic applications. However, these circuits can present various defects like inclusions, delaminations, cracks... In this work, we are interested in the detection of inclusions using guided waves propagation in such structures. These waves also called Lamb waves have the advantage of propagating over long distances while informing us about the totality of the inspected volume. According to the range of frequencies considered and the method used for their generation, it is possible to make profitable use of different propagation modes. To serve this purpose, laser-induced thermoelastic excitation of the first antisymmetric Lamb waves mode is studied. The results obtained are analysed using signal processing methods and then compared in order to clearly highlight the potentialities of these guided waves for the detection of inclusions in such samples.

Ultrasonic evaluation of residual stresses in flat glass tempering by an original double interferometric detection

In industrial thermal tempering of glass, the knowledge of the homogeneity of compressive residual stress field on the glass product is fundamental to guarantee the quality of the tempered glass product. In this paper, we use the acoustoelasticity phenomenon in order to estimate the residual stress distribution by using acoustic surface wave. We present an experimental setup based on a double interferometric detection in which an aspheric lens is associated with a beam splitter and a YAG laser whose power is 100 mW. This relative high power enables us to carry out measurements on surface flat glass although optical reflection coefficient is typically weak (< 10%). Using these two points of detection, the evolution of relative surface wave velocity is obtained with a good accuracy. At last, a comparison between the numerical modeling and experimental results shows the potentiality of an ultrasonic method to estimate stress distribution in flat glass tempering.

Non-destructive testing of ceramic balls using high frequency ultrasonic resonance spectroscopy

Although ceramic balls are used more and more for bearings in the aerospace and space industries, defects in this type of ceramic material could be dangerous, particularly if such defects are located close to the surface. In this paper, we propose a non-destructive testing method for silicon nitride balls, based on ultrasonic resonance spectroscopy. Through the theoretical study of their elastic vibrations, it is possible to characterize the balls using a vibration mode that is similar to surface wave propagation. The proposed methodology can both excite spheroidal vibrations in the ceramic balls and detect such vibrations over a large frequency range. Studying their resonance spectrums allows the balls' elastic parameters be characterized. Ours is an original method that can quickly estimate the velocity of surface waves using high frequency resonances, which permits surface and sub-surface areas to be tested specifically. Two applications are described in this paper. Both use velocity measurements to achieve their different goals, the first to differentiate between flawless balls from different manufacturing processes, and the second to detect small defects, such as cracks. Our method is rapid and permits the entire ceramic ball to be tested in an industrial context.

Determination of stresses in aluminum alloy using optical detection of Rayleigh waves

In this paper, a non-destructive method for the determination of residual stress profiles as a function of depth in laminated aluminium alloy sheets is presented. An ultrasonic method using Rayleigh waves propagating along the sides of the sheet is proposed. The determination of residual stresses is based on the measurement of the relative variation of the ultrasonic wave velocity versus the depth. An experimental device, using the acousto-optic interaction, has been developed to measure the velocity of the Rayleigh wave. Several residual stress profiles obtained by this technique are shown. The latter are compared to other stress profiles obtained by other methods: layer removal method and acoustic detection using wedge transducer.