Axel Follmann

A novel concept for smart trepanation.

Abstract Trepanation of the skull is a common procedure in craniofacial and neurosurgical interventions, allowing access to the innermost cranial structures. Despite a careful advancement, injury of the dura mater represents a frequent complication during these cranial openings. The technology of computer-assisted surgery offers different support systems such as navigated tools and surgical robots. This article presents a novel technical approach toward an image- and sensor-based synergistic control of the cutting depth of a manually guided soft-tissue–preserving saw. Feasibility studies in a laboratory setup modeling relevant skull tissue parameters demonstrate that errors due to computed tomography or magnetic resonance image segmentation and registration, optical tracking, and mechanical tolerances of up to 2.5 mm, imminent to many computer-assisted surgery systems, can be compensated for by the cutting tool characteristics without damaging the dura. In conclusion, the feasibility of a computer-controlled trepanation system providing a safer and efficient trepanation has been demonstrated. Injuries of the dura mater can be avoided, and the bone cutting gap can be reduced to 0.5 mm with potential benefits for the reintegration of the bone flap.

Robot- and computer-assisted craniotomy (CRANIO): from active systems to synergistic man-machine interaction.

Abstract Computer and robot assistance in craniotomy/craniectomy procedures is intended to increase precision and efficiency of the removal of calvarial tumours, enabling the preoperative design and manufacturing of the corresponding implant. In the framework of the CRANIO project, an active robotic system was developed to automate the milling processes based on a predefined resection planning. This approach allows for a very efficient milling process, but lacks feedback of the intra-operative process to the surgeon. To better integrate the surgeon into the process, a new teleoperated synergistic architecture was designed. This enables the surgeon to realize changes during the procedure and use their human cognitive capabilities. The preoperative planning information is used as guidance for the user interacting with the system through a master—slave architecture. In this article, the CRANIO system is presented together with this new synergistic approach. Experiments have been performed to evaluate the accuracy of the system in active and synergistic modes for the bone milling procedure. The laboratory studies showed the general feasibility of the new concept for the selected medical procedure and determined the accuracy of the system. Although the integration of the surgeon partially reduces the efficiency of the milling process compared with a purely active (automatic) milling, it provides more feedback and flexibility to the user during the intra-operative procedure.

User-Interaction of a Semiautomatic Trepanation System

During trepanation, a neurosurgical procedure for opening the skull, the protection of the underlying dura mater and a minimized loss of bone are major concerns. A concept for a novel trepanation system has been developed in order to open the skull less invasively and more safely. This trepanation system is based on a soft tissue preserving cutting tool and an autonomous control of the cutting depth.

Concept and evaluation of a synergistic controlled robotic instrument for trepanation in neurosurgery

A robotic instrument which synergistically cooperates with the surgeon for opening the skull in neurosurgery is proposed. To reduce frequent complications of this intervention, tear of the dura mater and bad reintegration of the skull bone a soft tissue preserving saw is combined with automatic depth regulation on the basis of a priori acquired medical imaging data (CT/MRI). By fusing the individual capabilities of the surgeon and a robotic device, it is possible to design an instrument which is significantly smaller than a fully autonomous system. The acceptance is enhanced by the integration of the surgeon into the process with direct control over the procedure. During the intervention, the instrument is manually guided by the surgeon on a freely defined trajectory. To be able to control this instrument, a method for real-time depth regulation, medical imaging data pre-processing and reduction as well as appropriate interfaces for the surgeon have been developed. In an experimental setup with phantom skull caps the system has been evaluated and has shown promising results, with a mean error of 0.62mm. Future work will include a detailed analysis of the persisting errors, integration of different sensors to control the instrument and preclinical trials.

Real-time determination of skull thickness for a manually-navigated synergistic trepanation tool

Trepanation of the skull is a common procedure in neurosurgery with the problems of dural tears and wide cutting gaps. A hand-guided instrument containing a soft-tissue preserving saw whose cutting depth is automatically adapted on the basis of a-priori data (CT, MRI) is envisioned to reduce these problems.

Smart Trepanation System: Preclinical Analysis of Safety, Efficiency, and User Satisfaction

BACKGROUND/OBJECTIVE To reduce the risk of dural tears during craniotomies and the associated complications, we developed the Smart Trepanation System (STS) that provides an image- and sensor-based automatic control of the cutting depth of a manually guided soft tissue preserving saw. This article presents the results of an initial user-centered evaluation. METHODS Interactive usability tests with six neurosurgeons were conducted. Resection time and accuracy were recorded in a standardized laboratory setting and compared with a standard craniotome. User satisfaction and subjective workload were assessed using the National Aeronautics and Space Administration Task Load Index scale and a questionnaire regarding intuitiveness, fault tolerance, learnability, and user satisfaction. RESULTS The mean resection time after getting used to the STS was 36.4 ± 9.2 second longer than with the conventional craniotome. All task load indexes except for the temporal demand were rated higher when using the STS, but all were rated smaller than 3 and thus classified as only a small extra task load. The questionnaire showed that the system is not only feasible but also accepted by surgeons and that the user interaction seems to be designed as intuitive, fault tolerant, and easy to learn. CONCLUSION Although the conventional craniotome seems to perform a trepanation faster and with less workload, the advantage of performing a dura-preserving trepanation with significantly smaller cutting gaps outweighs those disadvantages. For validation of those promising in vitro results, further studies have to be conducted in a fresh human cadaver model or in a clinical setting.

Evaluation of a synergistically controlled semiautomatic trepanation system for neurosurgery

One of the most common procedures in neurosurgery is the trepanation of the skull. In this paper, a synergistically controlled handheld tool for trepanation is introduced. This instrument is envisioned to reduce problems of dural tears and wide cutting gaps by combining a soft tissue preserving saw with an automatic regulation of the cutting depth. Since usability and safety of the semi-automatic handheld device are of utmost importance, the complex interaction between the user and the system has been analyzed extensively. Based on prospective usability evaluation the user interaction design and the corresponding user-interface were developed. The compliance with the relevant factors effectiveness, efficiency, error tolerance, learnability and user satisfaction was measured in user-centered experiments to evaluate the usability of the semiautomatic trepanation system. The results confirm the user interaction design of the semiautomatic trepanation system and the corresponding safety strategy. The system seems to integrate itself smoothly into the existing workflow and keeps the surgeon aware of the process.

Optical sensors for a synergistically controlled osteotomy system

Cutting bone is an important task in many surgical interventions (e.g. orthopedic surgery, neurosurgery). However it is often performed close to critical structures such as vessels or central nervous structures with an inherent high risk of serious damage. In this paper a concept for improving the safety of these surgical procedures is presented, by combining a soft tissue preserving saw with optical sensors in a semiautomatic controlled instrument. A real-time system acquires and analyses the data from an optical sensor and allows a indirect detection of the actual local bone thickness and the automatic adjustment of the sawing depth. To determine material characteristics (e.g. soft tissue, bone) a color sensor has been used in combination with a hysteresis controller. To show the feasibility of this concept a simple prototype has been built and evaluated with bone samples and parts of an artificial Sawbones skullcap. The system performed well with different materials and geometries, but further research has to be directed towards sensor integration and dynamic performance.

Analyse der Regelungsstrategien eines Osteotomie-Instruments auf Basis multimodaler Informationen / Analysis of the Control Strategies of an Instrument for Osteotomy on the Basis of Multimodal Information

Zusammenfassung Um den Chirurgen bei der Eröffnung des Schädels in der Neurochirurgie oder des Brustbeins in der Herz- und Thoraxchirurgie zu unterstützen, wurde ein semiautomatisches, handgeführtes Sägeinstrument entwickelt. Die Schnitttiefe wird auf Basis von drei unterschiedlichen Messverfahren (Computertomographie, Ultraschall, Licht) automatisch geregelt. Nach erfolgreichen Machbarkeitsstudien zu den einzelnen Ansätzen wird in diesem Beitrag darauf aufbauend ein detaillierter Vergleich der Verfahren mit einer Untersuchung der strukturellen Vor- und Nachteile sowie Optimierungspotentiale durchgeführt. Summary To support the surgeon during opening of the skull in neurosurgery or of the sternum in cardiothoracic surgery, a semiautomatic, hand guided saw was developed. The cutting depth is automatically controlled on the basis of three different modalities (computed tomography, ultrasound, light). In addition to the general successful proof of general feasibility, the present paper provides the results of a detailed comparison of the different systems in combination with an analysis of the structural advantages and disadvantages and their individual optimization potential.