Measurement of friction on straight catheters in in vitro brain andphantom material

As part of their studies on the magnetic stereotaxis system (MSS), a means of delivering therapies to the bulk brain, the authors have measured the frictional forces on a thin, straight tube used to simulate a catheter. Experiments were done with a spring-loaded, stainless steel tube of 1.9-mm diameter which was passed through 5.5 cm of gelatin phantom or, alternatively, through in vitro calf brain. The dynamic response of the tube to sudden displacement of the outer end of the spring yields estimates of the tube's friction per unit length. Twenty-three runs in the two media were analyzed for the static and dynamic frictional forces exhibited. In these series the static frictional forces were found to be (0.0132±0.0012) N cm^-1 [(1.32±0.12) g cm^-1] of length in the gelatin phantom and (0.0079±0.0008) N cm^-1 [(0.79±0.08) g cm^-1] of length in brain. The kinetic friction coefficient, b, was found to be (8.4±2.1) N s m^-1/cm length of catheter in brain and (16.3±7.6) N s m^-1/cm length of catheter in the phantom material. Based on these figures, the MSS will be capable of moving straight catheters of similar friction that are 20-cm long at rates of displacement of 0.02 to 0.05 cm s^-1 in the white and grey matter of the brain. Future studies will evaluate the forces arising from curved paths. Unanswered questions remain as to the mechanical difference between in vivo and in vitro brain, between animal and human brain, and the involvement of sulci in practical paths of motion     

In vivo mechanical behavior of intra-abdominal organs

For realistic surgical simulation in a virtual environment, in vivo material properties of biological tissues are required for simulating the deformations and the reaction forces from the tool-tissue interactions. In this paper, the in vivo static and dynamic mechanical behavior of the liver and lower esophagus of pigs were presented both in linear and nonlinear regions under compressive and shear indentations. A robotic device was programmed to function as a mechanical stimulator with a 2-mm flat-tipped cylindrical probe attached to its tip. A series of ramp and hold stimuli, as well as sinusoidal indentation stimuli, were delivered to the organs and reaction forces were measured. The conditions for these indentation stimuli were designed such that they were similar to conditions in an operating room. Experiments were also carried out on the organs for ex vivo and in vitro conditions. Results show that the breathing and pulse rate significantly affect the measured force responses of the organs. From the obtained force-displacement relationships, steady-state impedances as well as dynamic impedances of both organs were calculated. The results also show that in vivo steady-state impedance of the lower esophagus is significantly higher than that of the liver. The in vivo steady-state response of the liver, however, exhibits a greater degree of nonlinearity than that of the lower esophagus. The in vivo steady-state response of the lower esophagus in the three orthogonal directions also indicates that the lower esophagus is not significantly anisotropic. The impedance of both organs under sinusoidal indentations (0-5 Hz) are fairly similar each other. Magnitudes of the impedance over the stimulus frequencies are fairly constant. The impedance phase angles decrease over the range of stimulus frequencies applied. Comparison of the measurements obtained from the in vivo, ex vivo, and in vitro experiments shows that the mechanical properties of the biological tissues change significantly after the death of the animal. The tissues generally become stiffer and exhibit greater nonlinearity. The degree of change in their mechanical properties is dependent on the amount of time after the death of the animal. These data can be further utilized in the computing of the material parameters of tissue models for laparoscopic surgery simulators as well as open surgery simulators.     

Technology 1991: medical electronics

1990 saw major advances in medical technology. A combination of technological advances in magnetic resonance imaging (MRI) is unveiling new horizons for brain surgery, providing real-time feedback in the operating room. Computer-based stereotaxic techniques are being used experimentally in surgery, and experiments with robotic surgery are underway. In other developments, a variation on MRI, magnetic resonance spectroscopy, was shown to diagnose coronary artery disease accurately, ultrasonic imaging of blood flow received renewed attention, interest in biomagnetic imaging continued to grow and research cast further doubt on the efficacy of gallstone lithotripsy     

Feasibility of ultrasound hyperthermia with waveguide interstitialapplicator

Interstitial and intracavitary ultrasonic hyperthermia applicators facilitate well-controlled power deposition in tissues. In this paper, analysis of temperature elevation and experimental results in tissue phantom, animal tissue in vivo and animal tissue in vitro are presented for a waveguide applicator intended for treatment of brain tumors. It consisted of a G18 hypodermic needle attached via a conical velocity transformer to a 12.7-mm-diameter piezoelectric disk operated at 1.0 MHz. The axial acoustic pressure distribution had a standing-wave pattern with the four cycles/cm spatial periodicity. This periodicity was absent in the temperature distribution in tissue phantoms. The simulations based on a solution to the effective heat conductivity equation indicated that the hyperthermic range can be reached within a 4- and a 10-mm radius around the applicator for a 21- and a 60-mm sample diameters, respectively, with reasonable input power. The first number corresponded closely to the 5-mm radius observed in porcine brain in vivo and the second one came close to the 9-mm radius in porcine brain in vitro. The presented results demonstrate the potential of the ultrasound waveguide interstitial applicator for hyperthermia of small volume tumors     

Single-port robotic manipulator system for brain tumor removal surgery: SiromanS

The paper presents a new single-port robotic manipulator system (SiromanS) for brain tumor removal surgery. SiromanS is designed to minimize the size of surgical incisions compared to those needed for existing brain tumor removal surgeries. SiromanS consists of two robotic arms, a stereo-endoscope with a light source, and a cylindrical insertion part to house the arms and the endoscope. The stereo-endoscope is used to provide a 3D view of the surgical site to surgeons. The insertion part possesses three channels, through which the two robotic arms and the stereo-endoscope are integrated into SiromanS. One robotic arm of SiromanS has a gripper end-effector and the other has a suction end-effector to remove the brain tumor. This paper presents the robotic arm controlled by a wire-driven mechanism for distal dexterous motion and its miniaturization, and illustrates an actuating module that is separable from the robotic arm for sterilization and tool exchange. The forward/inverse kinematics analysis is also presented. A series of experimental results show that SiromanS’ performance capabilities are promising for brain surgery applications.     

In-vivo implant mechanics of flexible, silicon-based ACREO microelectrode arrays in rat cerebral cortex

The mechanical behavior of an electrode during implantation into neural tissue can have a profound effect on the neural connections and signaling that takes place within the tissue. The objective of the present work was to investigate the in vivo implant mechanics of flexible, silicon-based ACREO microelectrode arrays recently developed by the VSAMUEL consortium (European Union, grant #IST-1999-10073). We have previously reported on both the electrical [1]-[3] and mechanical [4], [5] properties of the ACREO electrodes. In this paper, the tensile and compression forces were measured during a series of in vivo electrode insertions into the cerebral cortex of rats (7 acute experiments, 2-mm implant depth, 2-mm/s insertion velocity). We compared the ACREO silicon electrodes (40 opening angle, 1-8 shafts) to single-shaft tungsten electrodes (3 degrees and 10 degrees opening angles). The penetration force and dimpling increased with the cross-sectional area (statistical difference between the largest and the smallest electrode) and with the number of shafts (no statistical difference). We consistently observed tensile (drag) forces during the retraction phase, which indicates the brain tissue sticks to the electrode within a short time period. Treating the electrodes prior to insertion with silane (hydrophobic) or piranha (hydrophilic) significantly decreased the penetration force. In conclusion, our findings suggest that reusable electrodes for acute animal experiments must not only be strong enough to survive a maximal force that exceeded the penetration force, but must also be able to withstand high tension forces during retraction. Careful cleaning is not only important to avoid foreign body response, but can also reduce the stress applied to the electrode while penetrating the brain tissue.     

Interactive 3D registration of ultrasound and magnetic resonanceimages based on a magnetic position sensor

The use of stereotactic systems has been one of the main approaches for image-based guidance of the surgical tool within the brain. The main limitation of stereotactic systems is that they are based on preoperative images that might become outdated and invalid during the course of surgery. Ultrasound (US) is considered the most practical and cost-effective intraoperative imaging modality, but US images inherently have a low signal-to-noise ratio. Integrating intraoperative US with stereotactic systems has recently been attempted. In this paper, we present a new system for interactively registering two-dimensional US and three-dimensional magnetic resonance (MR) images. This registration is based on tracking the US probe with a DC magnetic position sensor. We have performed an extensive analysis of the errors of our system by using a custom-built phantom. The registration error between the MR and the position sensor space was found to have a mean value of 1.78 mm and a standard deviation of 0.18 mm. The registration error between US and MR space was dependent on the distance of the target point from the US probe face. For a 3.5-MHz phased one-dimensional array transducer and a depth of 6 cm, the mean value of the registration error was 2.00 mm and the standard deviation was 0.75 mm. The registered MR images were reconstructed using either zeroth-order or first-order interpolation     

DFORCE: Delayed FOrce ReferenCE control for master–slave robotic systems

The acceptance of master–slave robotic teleoperated applications in the medical field is related not only to the accuracy and precision of the robotic systems but also to the haptic features. Indeed, the capability to render a good haptic feeling, hence the sensation to drive the real surgical tool, is necessary for reaching an effective interaction between surgeon and robotic system.In this paper an innovative controller for master–slave haptic systems for neurosurgery has been developed by getting inspiration from force reflecting controllers and non-time based control schemes. This new DFORCE (Delayed FOrce ReferenCE) controller is founded on the basic idea to control the position of the device through a system that can generate forces on the master side only when the surgeon is grasping the haptic handle. Thus, when the surgeon is not grasping the haptic handle and external forces are present, the system remains stable.The haptic sensation, the stability and the readiness of the system have been studied and a tuning procedure proposed. Moreover, simulated and experimental tests on a test-bed master system and a haptic master–slave interface for neurosurgical operations have been carried out in order to demonstrate the effectiveness of the controller.     

Investigation of intraoperative brain deformation using a 1.5-Tinterventional MR system: preliminary results

All image-guided neurosurgical systems that the authors are aware of assume that the head and its contents behave as a rigid body. It is important to measure intraoperative brain deformation (brain shift) to provide some indication of the application accuracy of image-guided surgical systems, and also to provide data to develop and validate nonrigid registration algorithms to correct for such deformation. The authors are collecting data from patients undergoing neurosurgery in a high-field (1.5 T) interventional magnetic resonance (MR) scanner. High-contrast and high-resolution gradient-echo MR image volumes are collected immediately prior to surgery, during surgery, and at the end of surgery, with the patient intubated and lying on the operating table in the operative position. Here, the authors report initial results from six patients: one freehand biopsy, one stereotactic functional procedure, and four resections. The authors investigate intraoperative brain deformation by examining threshold boundary overlays and difference images and by measuring ventricular volume. They also present preliminary results obtained using a nonrigid registration algorithm to quantify deformation. They found that some cases had much greater deformation than others, and also that, regardless of the procedure, there was very little deformation of the midline, the tentorium, the hemisphere contralateral to the procedure, and ipsilateral structures except those that are within 1 cm of the lesion or are gravitationally above the surgical site     

Active-Constraint Robotics for Surgery

The concepts and benefits of hands-on robotic surgery and active-constraint robotics are introduced. The argument is made for systems to be cost effective and simple in order that they can be justified for a large range of surgical procedures. The case is made for robotic systems to have a clear justification, with benefits compared to those from cheaper navigation systems. The need to have robust systems, that require little surgical training and no technical presence in the operating room, is also discussed. An active constraint medical robot, the Acrobot System, is described together with its use in a prospective randomized controlled trial of unicondylar knee arthroplasty (UKA), comparing the performance of the Acrobot System with conventional surgery. Twenty-eight patients awaiting UKA were randomly allocated to have the operation performed conventionally or with the assistance of the Acrobot. The results of the trial are presented together with a discussion of the need for measures of accuracy to be introduced so that the efficacy of the robotic surgery can be immediately identified, rather than having to wait for a number of years before long-term clinical improvements can be demonstrated     

The Interconnection of MRI Scanner and MR-Compatible Robotic Device: Synergistic Graphical User Interface to Form a Mechatronic System

MRI scanner and magnetic resonance (MR)-compatible robotic devices are mechatronic systems. Without an interconnecting component, these two devices cannot be operated synergetically for medical interventions. In this paper, the design and properties of a graphical user interface (GUI) that accomplishes the task is presented. The GUI interconnects the two devices to obtain a larger mechatronic system by providing command and control of the robotic device based on the visual information obtained from the MRI scanner. Ideally, the GUI should also control imaging parameters of the MRI scanner. Its main goal is to facilitate image-guided interventions by acting as the synergistic component between the physician, the robotic device, the scanner, and the patient.     

Air cooling for an interstitial microwave hyperthermia antenna:theory and experiment

Microwave antennas are inserted through brachytherapy catheters implanted in a tumor to deliver interstitial hyperthermia cancer therapy. Theoretical calculations show that a cooling rate on the order of 0.1 W/cm length of catheter will significantly improve the radial uniformity of the temperature distribution of single antennas or arrays. Experiments and theoretical calculations show that air passing through the annulus between the antenna and the catheter at 10 L/min or less will produce such a cooling rate in a 2.2-mm OD catheter that has both ends accessible. To maintain uniformity of cooling rate along the catheter, it is better to control the cooling rate by preheating the air entering the catheter to 30-40 degrees C than it is to control the flow rate of room-temperature air. Ohmic heating of the antenna feedline does not confound the air cooling action significantly.     

Automatic detection of conduction block based on time-frequencyanalysis of unipolar electrograms

It is commonly thought that lethal tachyarrhythmias, such as ventricular fibrillation (VF), are perpetuated by functional reentry, which occurs when an activation wave blocks and rotates around tissue that is excitable (i.e., functional block). Electrograms recorded near these regions typically contain two sequential deflections representing activation on either side of the block. By detecting these "double potentials," we hypothesize that functional block can be detected by a single electrode. METHODS: Unipolar electrograms were recorded from a 24 x 21 mapping array on the intact ventricular epicardium of five pigs during electrically-induced VF. The short time Fourier Transform (STFT) of each electrogram was analyzed to identify double potentials. To evaluate the performance of the STFT algorithm, conduction block was located in activation maps using a minimum conduction velocity criterion (10 cm/s) and then compared to the results of the STFT algorithm. RESULTS: The STFT algorithm detected conduction block with a sensitivity of 0.74 +/- 0.12 and a specificity of 0.99 +/- 0.00. CONCLUSION: We have developed an automated algorithm that can detect functional block during VF from a single electrode recording. Possible applications include fast, objective identification of block in mapping data and realtime localization of reentrant substrates using mapping catheters.     

Characterization and experimental results of a novel sensor for measuring the contact force from myenteric contractions

The intraluminal pressures and traction forces associated with the migrating motor complex are well understood; however, the contact forces directly exerted by the bowel wall on a solid, or near solid, bolus have not previously been measured. Quantifying contact forces is an important component to understanding the net force experienced by an in vivo robotic capsule endoscope. In this paper, we develop a novel sensor, the migrating motor complex force sensor (MFS), for measuring the contact force generated by the contracting myenteron of the small intestine. The MFS consists of a perfused manometer connected to four torus-shaped balloons custom formed of natural latex rubber and embedded with temperature and pressure sensors. Force exerted on the balloon causes sensor pressure change. In vivo, the MFS measures the magnitude and axial location of contact pressure exerted by the myenteron. The device is tested in vivo in a live porcine model on the middle small bowel. The mean total force per centimeter of axial length of intestine that occurred over a 16-min interval in vivo was 1.04 N·cm (-1) in the middle region of the small intestine; the measured force is in the range of theoretical values.     

Gecko‐Inspired Dry Adhesive for Robotic Applications

Most geckos can rapidly attach and detach from almost any kind of surface. This ability is attributed to the hierarchical structure of their feet (involving toe pads, setal arrays, and spatulae), and how they are moved (articulated) to generate strong adhesion and friction forces on gripping that rapidly relax on releasing. Inspired by the gecko's bioadhesive system, various structured surfaces have been fabricated suitable for robotic applications. In this study, x–y–z asymmetric, micrometer‐sized rectangular flaps composed of polydimethylsiloxane (PDMS) were fabricated using massively parallel micro‐electromechanical systems (MEMS) techniques with the intention of creating directionally responsive, high‐to‐low frictional‐adhesion toe pads exhibiting properties similar to those found in geckos. Using a surface forces apparatus (SFA), the friction and adhesion forces of both vertical (symmetric) and angled/tilted (x–y–z asymmetric) microflaps under various loading, unloading and shearing conditIons were investigated. It was found that the anisotropic structure of tilted microflaps gives very different adhesion and tribological forces when articulated along different x–y–z directions: high friction and adhesion forces when articulated in the y–z plane along the tilt (+y) direction, which is also the direction of motion, and weak friction and adhesion forces when articulated against the tilt (–y) direction. These results demonstrate that asymmetric angled structures, as occur in geckos, are required to enable the gecko to optimize the requirements of high friction and adhesion on gripping, and low frictional‐adhesion on releasing. These properties are intimately coupled to a (also optimum) articulation mechanism. We discuss how both of these features can be simultaneously optimized in the design of robotic systems that can mimic the gecko adhesive system.     

Evaluating automatic debiting systems by modelling and simulationof virtual sensors

The Dutch government is considering placing Automatic Debiting Systems (ADS) for electronic fee collection (EFC) on the highways. These systems would interact via a transponder in each passing car, and subtract a fee from the driver's credit card. Nonpayers would be photographed and fined. The ultimate goal is to use these systems to influence road usage. It is shown how the concept of virtual sensors, designed for goal-directed sensing in (robotic) autonomous systems, can be used in the design of the simulation. It is also shown how this forces the choice for a discrete event simulation, which in turn affects the implementation of the virtual sensor concept     

Motion and Internal Force Control for Omnidirectional Wheeled Mobile Robots

This paper presents an integrated scheme for motion control and internal force control for a redundantly actuated omnidirectional wheeled mobile robot. The interactive forces between a robot body and its wheels can be reduced into two orthogonal parts: motion-induced forces and internal forces. First, it is shown that the internal forces reside in the null space of the coefficient matrix of the interactive forces and do not affect robotic motion. However, these forces caused by motor torques should be minimized as much as possible to increase the energy efficiency and life span of joint components. With different goals, the control for motion and the control for internal forces can be designed separately. Here, both kinematic and dynamic models of the forces are proposed. A proportional differential plus controller regulates the motion and an inverse dynamic controller tracks it. Then, to minimize the internal forces, an integral feedback internal force controller is used. The motion controller guarantees the robotic motion while the internal force controller minimizes the internal force occurring during robot motion. Simulation results verify the effectiveness of the proposed schemes.     

An intelligent robotic system for rehabilitation of joints andestimation of body segment parameters

An an application of robotics in physical rehabilitation therapy, a robotic system consisting of two planar robot arms, each with two degrees of freedom, is considered. This robotic system, when coupled across a human joint, provides a vehicle for rehabilitation of the joint following surgery or trauma. A novel approach for estimation of body segment parameters is formulated that uses state and output information from the robot system to improve these estimates. In addition, redundant sensors are used to improve the accuracy of the estimates. The dynamic equations for a single robot arm are provided and the system is simulated. Therapeutic applications of the robotic system are discussed and the sensitivity of the measured forces with respect to the robot arm joint angles is studied in order to find an optimum orientation of the system for the best possible estimation. The application of this system to both rehabilitation and sports medicine is also discussed     

Calibration of tracking systems in a surgical environment

The purpose of this paper was to assess to what extent an optical tracking system (OTS) used for position determination in computer-aided surgery (CAS) can be enhanced by combining it with a direct current (DC) driven electromagnetic tracking system (EMTS). The main advantage of the EMTS is the fact that it is not dependent on a free line-of-sight. Unfortunately, the accuracy of the EMTS is highly affected by nearby ferromagnetic materials. The authors have explored to what extent the influence of the metallic equipment in the operating room (OR) can be compensated by collecting precise information on the nonlinear local error in the EMTS by using the OTS for setting up a calibration look-up table. After calibration of the EMTS and registration of the sensor systems in the OR the authors have found the average euclidean deviation in position readings between the DC tracker and the OTS reduced from 2.9±1.0 mm to 2.1±0.8 mm within a half-sphere of 530-mm radius around the magnetic field emitter. Furthermore the authors have found the calibration to be stable after re-registration of the sensors under varying conditions such as different heights of the OR table and varying positions of the OR equipment over a longer time interval. These results encourage the further development of a hybrid magnetooptical tracker for computer-aided surgery where the electromagnetic tracker acts as an auxiliary source of position information for the optical system. Strategies for enhancing the reliability of the proposed hybrid magnetooptic tracker by detecting artifacts induced by mobile ferromagnetic objects such as surgical tools are discussed