Lüder Alexander Kahrs

• Dr.-Ing.
• Professor (Assistant) at University of Toronto

We introduce MuJoCo Playground, a fully open-source framework for robot learning built with MJX, with the express goal of streamlining simulation, training, and sim-to-real transfer onto robots. With a simple "pip install playground", researchers can train policies in minutes on a single GPU. Playground supports diverse robotic platforms, including...

Traditional methods for autonomous cutting in surgical robotics have relied on trajectory-based planning algorithms. These methods fail to compensate for dynamic changes in soft materials such as deformation and topological change. To apply recent advances such as reinforcement learning (RL), a simulation is needed that models the cutting of soft m...

To automate surgical (sub-)tasks in robotic surgery, the knowledge of the exact pose of the instrument is mandatory. The application of Optical Coherence Tomography (OCT) to the problem of pose measurement appears promising due to its advantages of 3D imaging and micron-scale resolution. To investigate this, 175 image sequences of the EndoWrist Rou...

Surface reconstructions from laryngoscopic videos have the potential to assist clinicians in diagnosing, quantifying, and monitoring airway diseases using minimally invasive techniques. However, tissue movements and deformations make these reconstructions challenging using conventional pipelines. To facilitate such reconstructions, we developed vid...

Cutting is a challenging area in the field of autonomous robotics but is especially interesting for applications such as surgery. One large challenge is the lack of simulations for cutting with surgical robots that can transfer to the real robot. In this work, we create a surgical robotic simulation of rope cutting with realistic visual and physics...

Surgical tasks such as tissue retraction, tissue exposure, and needle suturing remain challenging in autonomous surgical robotics. One challenge in these tasks is nonprehensile manipulation such as pushing tissue, pressing cloth, and needle threading. In this work, we isolate the problem of nonprehensile manipulation by implementing a vision-based...

Skin flap is a common technique used by surgeons to close the wound after the resection of a lesion. Careful planning of a skin flap procedure is essential for the most optimal functional and aesthetic outcome. However, currently surgical planning is mostly done based on surgeons’ experience and preferences. In this paper, we introduce a finite ele...

Research in surgical robotics and automation has made remarkable advancements in recent years thanks to new methods in computer vision, control, and deep learning. Autonomous end-effector manipulation is a challenging task in surgical robotics, and cutting with scissor tools is largely unexplored. A concurrent work explored path and trajectory gene...

This paper introduces the SurgT MICCAI 2022 challenge and its first results. There were two purposes for the creation of this challenge: (1) the establishment of the first standardised benchmark for the research community to assess soft-tissue trackers; and (2) to encourage the development of unsupervised deep learning methods, given the lack of an...

Objective: To present the design choices, modelling of bending stiffness and experimental validation of a novel notched Nitinol compliant wrist that enables tip articulation and suction during endoscopic and robotic middle ear surgery. Methods: The wrist consists of an inner wrist tube (IWT) assembled within an outer wrist tube (OWT). The OWT was s...

The da Vinci Research Kit (dVRK) [1], a hardware and software stack for research development, implements the teleoperation control of the Patient Side Manipulators (PSMs) using the Master Tool Manipulators (MTMs), with the original capabilities of the da Vinci Surgical System such as input device clutching, rotated vision perspective control, and i...

Laser microsurgery is the current gold standard surgical technique for the treatment of selected diseases in delicate organs such as the larynx. However, the operations require large surgical expertise and dexterity, and face significant limitations imposed by available technology, such as the requirement for direct line of sight to the surgical fi...

The laryngeal adductor reflex (LAR) is a vital reflex of the human larynx. LAR malfunctions may cause life-threatening aspiration events. An objective, noninvasive, and reproducible method for LAR assessment is still lacking. Stimulation of the larynx by droplet impact, termed Microdroplet Impulse Testing of the LAR (MIT-LAR), may remedy this situa...

Purpose: It is not always possible to create linear access to the larynx using a rigid operating laryngoscope for microlaryngoscopy. In this study, we evaluate the usability of a novel curved surgical prototype with flexible instruments for the larynx (sMAC) in a simulation dummy and human body donor. Methods: In a user study (n = 6), head and ne...

Hypothesis: This study compares the reaching ability of two classes of transcanal endoscopic ear surgery (TEES) instruments when operating on difficult to access anatomical targets; two novel instruments with steerable flexible tips (SFT-A and SFT-B) and suction capability are compared with standard commercially available tools. Background: TEES...

The consideration of predictive uncertainty in medical imaging with deep learning is of utmost importance. We apply estimation of both aleatoric and epistemic uncertainty by variational Bayesian inference with Monte Carlo dropout to regression tasks and show that predictive uncertainty is systematically underestimated. We apply sigma scaling with a...

The consideration of predictive uncertainty in medical imaging with deep learning is of utmost importance. We apply estimation of both aleatoric and epistemic uncertainty by variational Bayesian inference with Monte Carlo dropout to regression tasks and show that predictive uncertainty is systematically underestimated. We apply $ \sigma $ scaling w...

Purpose: We explain our concept for customization of a guidance instrument, present a prototype, and describe a set of experiments to evaluate its positioning and drilling accuracy. Methods: Our concept is characterized by the use of bone cement, which enables fixation of a specific configuration for each individual surgical template. This well-est...

This European patent concerns an integrated hardware/software system for targeted endoscopic application of a fluid droplet for medical purposes. See all documents related to this patent here: https://worldwide.espacenet.com/patent/search?q=pn%3DEP3536226B1

Laser microsurgery is the current gold standard surgical technique for the treatment of selected diseases in delicate organs such as the larynx. However, the operations require large surgical expertise and dexterity, and face significant limitations imposed by available technology, such as the requirement for direct line of sight to the surgical fi...

This work presents the design of a novel compliant steerable tip (CST) instrument to facilitate transcanal (or totally) endoscopic ear surgery (TEES). The evolution of the instrument's design is shown, where prototypes were evaluated by surgeons and their feedback was used to inform the design changes for the next prototype iteration. The final pro...

Despite great efforts, transoral robotic laser surgery has not been established clinically. Patient benefits are yet to be proven to accept shortcomings of robotic systems. In particular, laryngeal reachability and transition from microscope to accurate endoscopic laser ablation have not been achieved. We have addressed those challenges with a high...

This work presents a droplet applicator module to generate stable droplets with different muzzle energies for the reproducible endoscopic stimulation of the laryngeal adductor reflex (LAR). The LAR is a protective reflex of the human larynx; an abnormal LAR performance may cause aspiration pneumonia. A pathological LAR can be detected by evaluating...

Objectives Transoral surgery of the larynx with rigid instruments is not always possible. This may result in insufficient therapy or in an increased need for open surgery. For these patients, alternative surgical systems are needed. Here, we demonstrate a curved prototype for laryngeal surgery equipped with flexible instruments. Study Design Pre‐c...

Purpose: This study aims to determine Euclidean distances between landmark structures in the larynx and pharynx to optimize endoscope shaft designs with regard to gentle and patient-oriented handling. Methods: Four Euclidean distances between landmarks in the larynx and pharynx were analyzed based on CT data of 66 patients. Distance (1): labium...

Cleft palate is a congenital defect that affects approximately 1 in 800 births worldwide. A robotic approach for cleft palate repair is desired due to the potential ergonomic, vision and accessibility improvements in the small workspace of the oral cavity. This paper presents a 3 mm, 4-degree-of-freedom instrument for use with the widely available...

The laryngeal adductor reflex (LAR) is an important protective function of the larynx to prevent aspiration and potentially fatal aspiration pneumonia by rapidly closing the glottis. Recently, a novel method for targeted stimulation and evaluation of the LAR has been proposed to enable non-invasive and reproducible LAR performance grading and to ex...

In this work, we discuss epistemic uncertainty estimation obtained by Bayesian inference in diagnostic classifiers and show that the prediction uncertainty highly correlates with goodness of prediction. We train the ResNet-18 image classifier on a dataset of 84,484 optical coherence tomography scans showing four different retinal conditions. Dropou...

Hintergrund: Zum Routine-Screening und zur weiteren Charakterisierung des laryngealen Adduktionsreflexes (LAR) wurde eine Reflexauslösung durch den Abschuss von Mikrotropfen und die zeitsynchrone Aufzeichnung einer Hochgeschwindigkeits-Endoskopiesequenz vorgeschlagen. Dieses sogenannte Microdroplet Impulse Testing of the LAR (MIT-LAR) wurde durch d...

In the last decade, focused laser radiation has become an alternative instrumentation for soft tissue surgery due to precise ablation with simultaneous coagulation. However, adjustment of the focal position with respect to the tissue surface is crucial for optimal energy input and minimised trauma. Advantageous laser delivery without tissue contact...

Purpose Minimally invasive cochlear implant surgery is a challenging procedure due to high demands on accuracy. For clinical success, an according assistance system has to compete against the traditional approach in terms of risk, operating time and cost. It has not yet been determined what kind of system is the most suited. The purpose of this stu...

Noise in speckle-prone optical coherence tomography tends to obfuscate important details necessary for medical diagnosis. In this paper, a denoising approach that preserves disease characteristics on retinal optical coherence tomography images in ophthalmology is presented. We propose semantic denoising autoencoders, which combine a convolutional d...

According to the World Health Organization, 285 million people worldwide live with visual impairment. The most commonly used imaging technique for diagnosis in ophthalmology is optical coherence tomography (OCT). However, analysis of retinal OCT requires trained ophthalmologists and time, making a comprehensive early diagnosis unlikely. A recent st...

In microsurgery, lasers have emerged as precise tools for bone ablation. A challenge is automatic control of laser bone ablation with 4D optical coherence tomography (OCT). OCT as high resolution imaging modality provides volumetric images of tissue and foresees information of bone position and orientation (pose) as well as thickness. However, exis...

Accepted for publication at 33rd international conference on Computer Assisted Radiology and Surgery (CARS) 2019.

Purpose: The facial recess is a delicate structure that must be protected in minimally invasive cochlear implant surgery. Current research estimates the drill trajectory by using endoscopy of the unique mastoid patterns. However, missing depth information limits available features for a registration to preoperative CT data. Therefore, this paper ev...

Purpose The facial recess is a delicate structure that must be protected in minimally invasive cochlear implant surgery. Current research estimates the drill trajectory by using endoscopy of the unique mastoid patterns. However, missing depth information limits available features for a registration to preoperative CT data. Therefore, this paper eva...

Purpose Automated segmentation of anatomical structures in medical image analysis is a prerequisite for autonomous diagnosis as well as various computer- and robot-aided interventions. Recent methods based on deep convolutional neural networks (CNN) have outperformed former heuristic methods. However, those methods were primarily evaluated on rigid...

In laser microsurgery, image-based control of the ablation laser can lead to higher accuracy and patient safety. However, camera-based image acquisition lacks the subcutaneous tissue perception. Optical coherence tomography (OCT) as high-resolution imaging modality yields transsectional images of tissue and can provide the missing depth information...

Optical coherence tomography (OCT) is a noninvasive medical imaging modality, which provides highresolution transectional images of biological tissue. However, its potential is limited due to a relatively small field of view. To overcome this drawback, we describe a scheme for fully automated stitching of multiple 3D OCT volumes for panoramic imagi...

Purpose: Automated segmentation of anatomical structures in medical image analysis is a key step in defining topology to enable or assist autonomous intervention robots. Recent methods based on deep convolutional neural networks (CNN) have outperformed former heuristic methods. However, those methods were primarily evaluated on rigid, real-world en...

Background: The implantation of the acetabular cup essentially determines the clinical outcome of total hip arthroplasty. To address this issue, the aim of this study was to build patient-specific instruments (PSIs) with various reference surfaces, followed by in vitro investigations to examine the inter- and intra-operator reliability as well as...

Protective reflexes of the larynx help to avoid intrusion of foreign particles into the lower airways, which can lead to aspiration pneumonia. These protective mechanisms include the Laryngeal Adductor Reflex (LAR), a rapid adduction of the vocal folds. Up to now, the LAR latency could only be determined manually by visually assessing laryngoscopi...

This report deals with intra-operative surface reconstruction from stereo operating microscope images providing metric measurement for application in neurosurgery. During an astrocytoma resection surgery, images were captured with a Haag-Streit HS 5-1000 microscope and processed on its accompanying image processing unit, equipped with an additional...

This report deals with intra-operative surface reconstruction from stereo operating microscope images providing metric measurement for application in neurosurgery. During an astrocytoma resection surgery, images were captured with a Haag-Streit HS 5-1000 microscope and processed on its accompanying image processing unit, equipped with an additional...

The so-called Laryngeal Adductor Reflex (LAR) protects the respiratory tract from particle intrusion by quickly approximating the vocal folds to close the free glottal space. An impaired LAR may be associated with an increased risk of aspiration and other adverse conditions. To evaluate the integrity of the LAR, we recently developed an endoscopic...

Purpose: Assistance of robotic systems in the operating room promises higher accuracy and, hence, demanding surgical interventions become realisable (e.g. the direct cochlear access). Additionally, an intuitive user interface is crucial for the use of robots in surgery. Torque sensors in the joints can be employed for intuitive interaction concept...

Die Erfindung betrifft ein medizinisches Instrumentarium zur Implantation einer künstlichen Hüftgelenkspfanne bei der patientenindividuellen Hüftgelenksplastik, wobei das Instrumentarium wenigstens ein Referenzinstrument in Form einer patientenindividuell angefertigten Schablone und wenigstens ein Werkzeug zur Bearbeitung des Hüftgelenks aufweist.

Recent research has revealed that image-based methods can enhance accuracy and safety in laser microsurgery. In this study, non-rigid tracking using surgical stereo imaging and its application to laser ablation is discussed. A recently developed motion estimation framework based on piecewise affine deformation modeling is extended by a mesh refinem...

Purpose: Mastoid cells as well as trabecula provide unique bone structures, which can serve as natural landmarks for registration. Preoperative imaging enables sufficient acquisition of these structures, but registration requires an intraoperative counterpart. Since versatile surgical interventions involve drilling into mastoid cells and trabecula...

Malunion after forearm fractures are described to appear in 2% to 10% of cases. Reconstructive surgeries ensure adequate anatomical repositioning. Their importance derives from the fact that malunion can often lead to severe pain as well as deformities causing loss of function and aesthetic issues not only in the forearm, but also the wrist and elb...

A common representation of volumetric medical image data is the triplanar view (TV), in which the surgeon manually selects slices showing the anatomical structure of interest. In addition to common medical imaging such as MRI or computed tomography, recent advances in the field of optical coherence tomography (OCT) have enabled live processing and...

Zusammenfassung Während der Implantation von Cochlea-Implantaten muss eine Verletzung bzw. Reizung des Gehörganggewebes vermieden werden. Ziel der vorliegenden Arbeit ist eine Echtzeitüberwachung der Position eines Cochlea-Implantats basierend auf einer kontinuierlichen Messung der Impedanz zwischen den Elektroden des Implantats während der Inserti...

Introduction Visualization of inner ear structures is a valuable strategy for researchers and clinicians working on hearing pathologies. Optical coherence tomography (OCT) is a high-resolution imaging technology which may be used for the visualization of tissues. In this experimental study we aimed to evaluate inner ear anatomy in well-prepared hum...

Patient specific instruments (PSI) are clinically available to support surgeons in several orthopedic or trauma interventions. They are an alternative to conventional and image-guided surgery techniques. However cost and time efficiency, accuracy, usability and benefit for the patient are still controversial discussed. A special use case is total h...

Patient specific instruments (PSI) are currently used as navigation aid in specific orthopedic interventions. The research for improving those instruments and facilitate further applications is still ongoing. The concept of PSI is, that the surface structure of the bone is known from pre-operative medical imaging and can therefore be used as a mech...

This paper presents a real-time method for interactive focus positioning in laser microsurgery. Registration of stereo vision and a surgical laser is performed in order to combine surgical scene and laser workspace information. In particular, stereo image data is processed to three-dimensionally reconstruct observed tissue surface as well as to com...

Patient-specific instruments (PSIs) are clinically used to support the surgeon during a planned intervention. The planning is typically done based on volumetric image data from medical imaging systems, e.g. computed tomography (CT). The PSI uses the known surface structure of a bone for orientation during the intervention. Some surfaces of human bo...

Purpose Recent research has revealed that incision planning in laser surgery deploying stylus and tablet outperforms micromanipulator control. However, vision-based adaption to dynamic surgical scenes has not been addressed so far. In this study, scene motion compensation for tablet-based planning by means of tissue deformation tracking is discusse...

GMS Curr Posters Otorhinolaryngol Head Neck Surg 2016;12:Doc113

The introduction of Er:YAG lasers for soft and hard tissue ablation has proven promising results over the last decades due to strong absorption at 2.94 μm wavelength by water molecules. An extension to endoluminal applications demands laser delivery without mirror arms due to dimensional constraints. Therefore, fiber-based solutions are advanced to...

Purpose: Minimally invasive cochlear implantation is a novel surgical technique which requires highly accurate guidance of a drilling tool along a trajectory from the mastoid surface toward the basal turn of the cochlea. The authors propose a passive, reconfigurable, parallel robot which can be directly attached to bone anchors implanted in a pati...

Introduction:Visualization of inner ear structures is an useful subject for researchers and clinicians working on hearing pathologies. Optical Coherence Tomography as a high resolution imaging technology is applicable for visualization of surface and subsurface structures. In this experimental study, we aimed to evaluate inner ear anatomy in well p...

Laparo-endoscopic surgery is the treatment of choice in a variety of intra-abdominal interventions, leading to lower infection risk, shorter recovery time, and smaller scars. This paper presents a method for quantifying workspaces of instruments in laparoscopic surgery. In contrast to most existing approaches, the proposed performance criterion com...

Laser surgery is an established clinical procedure in dental applications, soft tissue ablation, and ophthalmology. The presented experimental set-up for closed-loop control of laser bone ablation addresses a feedback system and enables safe ablation towards anatomical structures that usually would have high risk of damage. This study is based on c...

Processing stereoscopic image data is an emerging field. Especially in microsurgery that requires sub-millimeter accuracy, application of stereo-based methods on endoscopic and microscopic scenarios is of major interest. In this context, direct comparison of stereo-based surface reconstruction applied to several camera settings is presented. A meth...

Planning and analyzing of surgical interventions are often based on computer models derived from computed tomography images of the patient. In the field of cochlear implant insertion the modeling of several structures of the inner ear is needed. One structure is the overall helical shape of the cochlea itself. In this paper we analyze the cochlea b...

This work investigates combination of Optical Coherence Tomography and two cameras, observing a microscopic scene. Stereo vision provides realistic images, but is limited in terms of penetration depth. Optical Coherence Tomography (OCT) enables access to subcutaneous structures, but 3D-OCT volume data do not give the surgeon a familiar view. The ex...

Recent research has revealed that incision planning in laser surgery deploying stylus and tablet outperforms stateof-the-art micro-manipulator-based laser control. Providing more detailed quantitation regarding that approach, a comparative study of six tablet-based strategies for laser path planning is presented. Reference strategy is defined by mo...

This work proposes new methods for a microstereotactic frame based on bone cement fixation. Microstereotactic frames are under investigation for minimal invasive temporal bone surgery, e.g. cochlear implantation, or for deep brain stimulation, where products are already on the market. The correct pose of the microstereotactic frame is either adjust...

In this contribution we present a customized flexible robot developed as endoscopic device for laser phonomicrosurgery. Following the idea of soft robotics we describe the conventional clinical setting and adjunct benefits of the proposed assistance device to facilitate gentle surgery and usability in the operating room. Design constraints are obta...

Introduction: Internal auditory canal (IAC) tumors are one of the most common lesions in the skull base area. Image guided surgery significantly improved the safety and accuracy of surgery and decreased the complications. Available image guided systems do not provide submillimeteric accuracy in standard setting, as required for skull base surgery....