Lüder A. Kahrs

Temporal bone borehole accuracy for cochlear implantation influenced by drilling strategy: an in vitro study

PurposeMinimally invasive cochlear implantation is a surgical technique which requires drilling a canal from the mastoid surface toward the basal turn of the cochlea. The choice of an appropriate drilling strategy is hypothesized to have significant influence on the achievable targeting accuracy. Therefore, a method is presented to analyze the contribution of the drilling process and drilling tool to the targeting error isolated from other error sources.MethodsThe experimental setup to evaluate the borehole accuracy comprises a drill handpiece attached to a linear slide as well as a highly accurate coordinate measuring machine (CMM). Based on the specific requirements of the minimally invasive cochlear access, three drilling strategies, mainly characterized by different drill tools, are derived. The strategies are evaluated by drilling into synthetic temporal bone substitutes containing air-filled cavities to simulate mastoid cells. Deviations from the desired drill trajectories are determined based on measurements using the CMM.ResultsUsing the experimental setup, a total of 144 holes were drilled for accuracy evaluation. Errors resulting from the drilling process depend on the specific geometry of the tool as well as the angle at which the drill contacts the bone surface. Furthermore, there is a risk of the drill bit deflecting due to synthetic mastoid cells.ConclusionsA single-flute gun drill combined with a pilot drill of the same diameter provided the best results for simulated minimally invasive cochlear implantation, based on an experimental method that may be used for testing further drilling process improvements.

Flexible Robot for Laser Phonomicrosurgery

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 obtained from medical image data implementing a mechanical design comprising compliant and flexible sections, actuation unit and multifunctional tip. We present results of a proof of concept experiment using a patient phantom, demonstrating the applicability of our system for laryngeal access.

An experimental evaluation of loads occurring during guided drilling for cochlear implantation

PurposeDuring guided drilling for minimally invasive cochlear implantation and related applications, typically forces and torques act on the employed tool guides, which result from both the surgeon’s interaction and the bone drilling process. Such loads propagate through the rigid mechanisms and result in deformations of compliant parts, which in turn affect the achievable accuracy. In this paper, the order of magnitude as well as the factors influencing such loads are studied experimentally to facilitate design and optimization of future drill guide prototypes.MethodsThe experimental setup to evaluate the occurring loads comprises two six degree of freedom force/torque sensors: one mounted between a manually operated, linearly guided drill handpiece and one below the specimens into which the drilling is carried out. This setup is used to analyze the influences of drilling tool geometry, spindle speed as well as experience of the operator on the resulting loads.ResultsThe results reveal that using a spiral drill results in lower process loads compared with a surgical Lindemann mill. Moreover, in this study, an experienced surgeon applied lower interaction forces compared with untrained volunteers. The measured values further indicate that both the intraoperative handling of the bone-attached drill guide as well as the tool removal after completing the hole can be expected to cause temporary load peaks which exceed the values acquired during the drilling procedure itself.ConclusionsThe results obtained using the proposed experimental setup serve as realistic design criteria with respect to the development of future drill guide prototypes. Furthermore, the given values can be used to parameterize simulations for profound stiffness analyses of existing mechanisms.

Cochlear shape description and analyzing via medial models

ABSTRACT Planning and analyzing of surgical interventions are often based on computer models derived from computedtomography images of the patient. In the eld of cochlear implant insertion the modeling of several structures ofthe inner ear is needed. One structure is the overall helical shape of the cochlea itself. In this paper we analyzethe cochlea by applying statistical shape models with medial representation. The cochlea is considered as tubularstructure. A model representing the skeleton of training data and an atomic composition of the structure is built.We reduce the representation to a linear chain of atoms. As result a compact discrete model is possible. It isdemonstrated how to place the atoms and build up their correspondence through a population of training data.The outcome of the applied representation is discussed in terms of impact on automated segmentation algorithmsand known advantages of medial models are revisited.Keywords: inner ear, segmentation, active shape models, cochlea

Methods for a fusion of optical coherence tomography and stereo camera image data

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 extension of the stereo camera setup with OCT imaging combines the benefits of both modalities. In order to provide the surgeon with a convenient integration of OCT into the vision interface, we present an automated image processing analysis of OCT and stereo camera data as well as combined imaging as augmented reality visualization. Therefore, we care about OCT image noise, perform segmentation as well as develop proper registration objects and methods. The registration between stereo camera and OCT results in a Root Mean Square error of 284 μm as average of five measurements. The presented methods are fundamental for fusion of both imaging modalities. Augmented reality is shown as application of the results. Further developments lead to fused visualization of subcutaneous structures, as information of OCT images, into stereo vision.

Towards Fully Automated Determination of Laryngeal Adductor Reflex Latencies through High-Speed Laryngoscopy Image Processing

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 laryngoscopic high-speed video sequences obtained during and after stimulation of the larynx by water droplet impact. Here, we present a novel image processing algorithm based on difference image calculation and optical flow analysis for a more objective LAR latency determination. To evaluate our prototype algorithm, we compared the results obtained for a set of example sequences with the values given by two expert phoniatricians. The results show a very good LAR stimulation detection performance. LAR onset detection remains challenging for our algorithmic approach as well as for the human perceptive system, as demonstrated by a low inter-rater reliability.

High-accuracy drilling with an image guided light weight robot: autonomous versus intuitive feed control

PurposeAssistance 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 concepts. Regarding the accuracy, they lead to a lower structural stiffness and, thus, to an additional error source. The aim of this contribution is to examine, if an accuracy needed for demanding interventions can be achieved by such a system or not.MethodsFeasible accuracy results of the robot-assisted process depend on each work-flow step. This work focuses on the determination of the tool coordinate frame. A method for drill axis definition is implemented and analysed. Furthermore, a concept of admittance feed control is developed. This allows the user to control feeding along the planned path by applying a force to the robots structure. The accuracy is researched by drilling experiments with a PMMA phantom and artificial bone blocks.ResultsThe described drill axis estimation process results in a high angular repeatability (

Comparative study on surface reconstruction accuracy of stereo imaging devices for microsurgery

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