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Real-Time Fiber-Optic Intubation Simulator with Force Feedback* Ankur R. Baheti, Robert Hafey, Sneha Pai, Jose Gomez, Yuri Millo, and Jaydev P. Desai
Abstract—Fiber-optic intubation is an emergency procedure that can be performed to intubate a patient when the patient has serious difficulty breathing normally. The existing simulators for fiber-optic intubation procedure provide haptic feedback to the user when there is contact with the vocal cord section, but they do not capture the grazing effect of the endoscope along the inner walls of the airway. The grazing on the inner walls of the airway, if not well controlled, could lead to unnecessary trauma for the patient. Hence, there is a need to provide this force feedback in a fiber-optic intubation simulator. We have built a fiber-optic intubation simulator with force feedback. This system is composed of a software simulation coupled with a physics-based simulation which enhances the visual experience. The software simulation is connected to a haptic feedback device. The device provides force feedback when contact is made with the any section of the airway. The force feedback varies based on the position of contact and intensity of contact. We use a PD controller to obtain force feedback at the vocal cord section and a variable magnetic field to capture the grazing effect of the endoscope along the inner walls of the airway. The movements of the endoscope are captured using rotary encoders (which read the insertion and the tip bend) and a compass module (which reads the twist angle of the endoscope along the long axis). These movements are used to navigate the virtual airway using a virtual endoscope. When collisions are encountered the physics library evaluates the position of contact and the force with which contact is made. Force feedback is generated due to the interaction of the solenoids with the permanent magnets at the tip of the endoscope. This information helps the software to actuate the right combination of solenoids. The simulator will help to train all aspects of fiber-optic intubation, namely: 1) developing the necessary psychomotor skills to successfully navigate the airway with minimal or no damage to the airway or vocal cords and 2) cognitive skills to perform the procedure fast and effectively. Index Terms—Fiber-optic intubation, Endoscopy trainer, Bronchoscopy, Haptic feedback.
I. I NTRODUCTION
F
IBER-OPTIC intubation is an emergency procedure that is performed to intubate a patient when the patient has serious difficulty breathing normally. An endoscope is used to deploy a tube in the trachea of the patient to aid breathing. Manuscript received March 17, 2010. This work was supported in part by SiTEL, part of Medstar Health’s Institute of Innovation (MI2). Ankur R. Baheti, Robert Hafey, Sneha Pai, Jose Gomez, and Yuri Millo are with Simulation and Training Environment Laboratory, Medstar Health, Washington DC 20008 USA (email: ankurbaheti013@gmail.com, rob.hafey@gmail.com, snehapai.us@gmail.com, jfgomez21@gmail.com, and yuri.millo@medstar.net). Jaydev P. Desai is with the Robotics, Automation and Medical Systems (RAMS) Laboratory in the Department of Mechanical Engineering, and Maryland Robotics Center at University of Maryland, College Park MD, 20742 (email: jaydev@umd.edu). *A portion of the content of this paper has been published in 2010 Haptics Symposium (with IEEE VR).
Intubation is also performed on patients undergoing bronchoscopies, biopsies and similar procedures. The procedure must be performed within a certain amount of time (subject to the patient’s condition) to avoid the risk of fatality. The most common errors in performing the procedure include: a. Grazing the inner walls of the airway which can lead to excessive bleeding: During the actual procedure, the effect of grazing is often overlooked by novices. Left unchecked, it results in excessive bleeding, and can even prove fatal [8]. b. Intubating the oesophagus: The oesophagus is often intubated in error as it is often more easily accessible than the vocal cords. c. Damaging the vocal cords through repeated contact while trying to force the scope down: Contact made anywhere in the vicinity of the vocal cords section; i.e. epiglottis, oesophagus or the vocal cords itself, can cause excessive coughing and gagging. This makes the intubation difficult as the vocal cords open and close rapidly. Trying to force the scope in may result in damage to the vocal cords or other sections or it could result in the endoscope getting stuck or damaged. Also, if the patient is not intubated fast enough, it could be fatal. Hence, there is a need to train healthcare professionals in efficient administration of these procedures, and to minimize the risk of injury and death. The AccuTouch System (Immersion Medical) [1] is currently a commercially available simulator that is used to train in this procedure. There have been several studies to evaluate this simulator [2] [3] [4]. The studies use expert bronchoscopists to evaluate the performance of novices and to determine the learning curve. The studies prove that the AccuTouch system is an effective trainer; however, it does not provide realistic force feedback when the scope grazes the inner walls of the airway. The Virtual Fiberoptic Intubation (VFI) software was developed by the Institut de Recherche contre les Cancers de l’Appareil Digestif (IRCAD), Strasbourg, France [15]. This software simulator focuses on understanding altered airway anatomy and studies have shown improved performance by the group trained on VFI [16]. In this paper, we present a fiber-optic intubation simulator, which integrates haptic feedback with the graphics environment. This is an extension of our prior work [22], which was primarily related to the development of the haptic feedback device. The system is designed to train healthcare professionals to perform the procedure accurately and avoid abrasive errors in a specified time-limit. The simulator comprises of a software system, which consists of a graphical simulation coupled with a physics-based simulation and a hardware system which
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consists of a prototype endoscope and a device, into which the endoscope is inserted. The software simulation displays a virtual airway navigated using a virtual endoscope. The prototype endoscope houses a compass module to measure the twist angle about the long axis of the endoscope and a digital encoder to measure the bending angle of the tip. The tip of the scope has a sleeve of magnets attached to it. The device provides force feedback whenever the virtual scope makes contact with the airway. The haptic feedback is provided by the interaction between a stationary array of solenoids and permanent magnets on a prototype endoscope. The simulation begins with the insertion of the prototype endoscope into the device. The graphical simulation begins at the tip of tongue. The insertion of the prototype scope into the device leads to corresponding insertion of the virtual scope into the airway in the simulation environment. While navigating through the airway, if the virtual endoscope makes contact with the airway, the physics library determines the force at which the contact is made and the point of contact. The software uses this information to: 1) compute the intensity of contact, 2) combination of solenoids to actuate and 3) the speed at which solenoid assembly should move to correlate accurately with the graphics environment. Based on these parameters the device provides the necessary force feedback. The combination of solenoids is obtained from the minimum coil set technique [5].
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also been used for hybrid locomotion design of a miniature endoscopic capsule [19]. This system combines an on-board legged actuation mechanism with an external magnetic field that guides the capsule motion through a permanent magnet embedded in the device. Apart from these, research has also been done to compare and evaluate the forces generated while doing a task actually versus doing the same task virtually using the principle of magnetic levitation to render force feedback [14]. Computer-based training systems have been developed to simulate surgical procedures such as inserting a catheter into the cystic duct using a pair of laparoscopic forceps, a procedure performed during laparoscopic cholecystectomy to search for gallstones in the common bile duct [20]. Force feedback devices have also been employed to develop telerobotic systems for the operating room [21]. The system incorporates a workstation where information is provided to and received from the operator. The surgeon controls the robotic system using two force feedback hand controllers based on visual information from a stereoscopic viewing device and two liquid crystal displays. III. M ATERIALS AND M ETHODS
II. BACKGROUND Electromagnetism can be utilized to generate haptic feedback. There has been considerable research on implementing Haptics using electromagnetic actuators [9] [10] [11] [13] [14] [17] [18] [22]. They have been used in developing a wide variety of haptic displays. BubbleWrap, used as a haptic display consists of a matrix of electromagnetic actuators, enclosed in fabric, with individually controllable cells that contract and expand. It provides both active and passive feedback [13]. Haptics has also been widely used in surgical simulations and effectiveness of haptic feedback in open surgery simulation, where the haptic feedback was primarily created by magnetic force on a surgical tool, has also been evaluated [9]. Magnetorheological (MR) fluid actuators have been developed to display force feedback at the fingertip of a human user [10] [12] as well as in other haptic displays [17]. A MR position-feedback actuator functions as the human interface module, through which users can feel the virtual resistance and generate reaction forces in the virtual environment. Their property of changing the rheological behavior by tuning an external magnetic field is used to generate the desired effect. Lorentz force magnetic levitation can also be used for haptic interaction. Lorentz force magnetic levitation has been used to develop a haptic interface device integrated with real-time 3D rigid-body simulations for detailed, responsive interaction with dynamic virtual environments [18]. One of the drawbacks of Lorentz force magnetic levitation is low translational and rotational motions. To overcome this, a new coil configuration was developed and incorporated in a device which resulted in a higher translational and rotational motion [11]. Electromagnetism has
Fig. 1. Haptic feedback enabled fiber-optic intubation device along with the prototype scope.
The fiber-optic intubation simulator with force feedback consists of two modules as shown in Figure 1: the first module is the instrumented scope, and the second module is the device which houses all the components for the haptics. A. Prototype scope movements
(a)
(b)
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(c) Fig. 2. Illustrated movements of the scope during a typical intubation procedure [8]. a) Roll along the long axis clockwise b) roll along the long axis counter clockwise and c) tip bend.
The actual endoscope is a flexible tube with a camera at the end which provides imaging capability during the procedure. It also has two point lights at the end of the tube which light up the airway. The tip has a capability to bend about an axis pivoted at one inch from the tip. It is capable of bending 90 degrees on one side and 120 degrees on the other. The surgeons navigate the airway using a combination of movements. They orient the scope by rotating the handle about the long axis of the scope (see Figure 2(a) and 2(b)) and bend the tip to navigate around bends and corners (see Figure 2(c)). For our haptic feedback enabled fiber-optic intubation system, we built a prototype scope (see Figure 3(a)). The scope is fitted with a sleeve of magnets at the tip (see Figure 3(a)), a compass module inside the handle and a digital encoder at the top (see Figure 3(b)). The sleeve has a series of N52 grade neodymium magnets (K and J Magnetics Inc). The interaction of these magnets with the stationary electromagnet array in the haptic feedback device provides the necessary force feedback to the user.
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2(b)). The OS5000-US compass module (see Figure 3(b)) is a three-axis compass with tilt compensation. It uses a USB interface for communication. The orientation of the scope can be obtained as an angle in degrees using the API provided by the manufacturer. The tip bend is captured using a digital encoder (see Figure 2(c) and 3(b)). The swivel knob on the handle moves through 40 degrees when the tip moves through 120 degrees and the swivel knob moves through 30 degrees when the tip moves through 90 degrees. Hence, for every degree the swivel knob moves the tip swivels by 3 degrees. The S4 encoder has a resolution of 360 counts per revolution. Hence, for every degree the swivel knob moves, the angle is given by: θ =E×3 (1) where, θ is the angle of tip bend, E is the actual encoder reading and 3 is the scale factor. Determination of the angle of rotation : The angle of rotation about the long axis of the scope is measured using the OS5000-US compass module, which is a compass module with tilt compensation [23]. The sensor uses a Honeywell twoaxis Automated Meter Reading (AMR) sensor for X-Y plane sensing and a Honeywell z-axis AMR sensor as magnetic sensors, a three-axis accelerometer (ST Microelectronics) as the tilt sensor, and a 50 MIPS (Millions of Instructions Per Second) processor as the microprocessor. The sensor can be mounted in six different orientations and calibrated to read the angle of interest. The sensor is mounted in the right orientation and calibrated to measure the twist angle. The scope is inserted at the opening (see (1) in Figure 4(a)). The scope passes through a set of two pulleys (see (2) in Figure 4(a)). The lower pulley is connected to a S4 digital encoder that measures the absolute depth of insertion of the scope. The depth of insertion is given by: N πD (2) 360 where, z is the depth of insertion, N is the number of counts of the encoder, the encoder resolution is 360, and D is the diameter of the lower pulley. z=
(a)
B. Haptic feedback device
(b) Fig. 3. a) Instrumented scope with a sleeve of magnets b) the handle housing the compass module and a digital encoder.
To capture the motion of the scope on the proximal end, the handle of the scope houses an OS5000-US compass module (ocean Server Inc.) and an S4 digital encoder (US Digital Inc). The compass module is used to measure the angle of rotation of the scope about its long axis (see Figure 2(a) and
(a)
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infinitesimal element, ds, from the point P ) from the point P and is given by: r 2 = x2 + R 2
(4)
where R is the radius of the loop. Hence, the magnitude of dB due to current in any infinitesimal element, ds, is given by: dB = (b) Fig. 4. a) The haptic feedback device consists of: 1) opening for scope insertion, 2) the pulley system to measure the depth of insertion, 3) the solenoid assembly, 4) the linear rail system with an AC stepper motor and an encoder and 5) the airway channel. (b) The solenoid assembly.
Behind the pulleys are a set of four electromagnets (see Figure 4(a) and Figure 4(b)). The electromagnets are coils made of 194 turns of 16 gauge copper wire wound around an iron core made of Ferroxcube 3C90. The outer diameter of the coil is 0.0508 meters and the length of the coil is 0.04445 meters. The diameter of the core is 0.0254 meters. The solenoids are arranged between two square sections as shown in Figure 4(b). The grazing of the endoscope against the inner walls of the airway is simulated by changing the velocity of the rails and the magnetic field in the airway channel surrounded by the solenoids. The speed of rails and current in the solenoids are varied based on the intensity of the grazing. Thus, the solenoids are actuated in pairs, groups or individually with varying current intensities, thereby producing varying force outputs to simulate grazing effect on the walls of the airway. M odel f or estimating the f orces generated by solenoids : The magnetic field surrounding a thin straight conductor can be given by the Biot-Savart Law [6] [7]. Consider a circular loop of radius R located in the yz plane carrying a steady current I (see Figure 5). Consider the loop to be made of small current elements of length ds. Thus, for every element
Circular conductor carrying current.
π = ds (3) 2 where rb is the unit vector. Also, all the infinitesimal arclengths, ds, are at the same distance r (distance of every ds × rb = (ds)(1) sin
(5)
where, dB is the magnetic field at the point and, µ0 is the permeability of free space. The direction of dB is perpendicular to the plane formed by rb and ds, as shown in Figure 5. We can resolve this vector into components, dBx and dBy along the x and y axes respectively. When the components dBy are summed over all elements around the loop, the resultant y-component of B is zero. Hence, the x-component of the magnetic field is the only contributing component to the effective magnetic field at P . Since, dBx = dB cos θ. i.e., B = Bx i, we get: I I dscosθ µ0 I (6) Bx = dBcosθ = 4π x2 + R 2 where the integral is over the entire loop. Since θ, x, and R are constants for all elements of the loop, we obtain: I µ0 IR2 µ0 IR ds = Bx = (7) 3 2(x2 + R2 ) 32 4π(x2 + R2 ) 2 Equation (7) gives the magnetic field due to a single loop of wire carrying current. Consider a conductor with multiple loops of wire carrying current. Figure 6 shows a cross section of a part of a conductor, with multiple loops of wire, carrying current.
Fig. 6.
Fig. 5.
µ0 I ds µ0 I |ds × rb| = 4π r2 4π (x2 + R2 )
Solenoid carrying current.
Consider a rectangular path of length l and width w. We can apply Amperes law [6] to this path by evaluating the integral of Bds over each side of the rectangle. As it is an ideal solenoid, the contribution of B from side 3 is zero. Also, the contribution along path 2 and 4 are zero as they are parallel to the direction of current, and side 1 gives a contribution of B.l to the integral because along this path, B is uniform and parallel to ds. Hence, the integral over the
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closed loop gives: I
I B · dl = B
dl = Bl
(8)
If N is the number of turns in the length l, then the total current in the rectangle is N I. Hence Amperes law gives: µ0 N I l Force exerted by a magnetic field is given by: B=
(9)
2
B A (10) 2µ0 where, A is the area of cross-section of the core. However, the above equations are inapplicable when most of the field is outside the core. In such cases the force can be obtained by using the Magnetic Pole Model or the Gilberts Model [7], which is given by: F =
N IA (11) L where m is the pole strength of the solenoid, and L is the length of the core. The force, F , exerted by the solenoid is given by: m=
µ0 m1 m2 (12) 4πr2 where m1 and m2 are the pole strengths of the solenoids. Using this formula the magnetic field between two solenoids placed directly opposite to each other was evaluated and the plot is as shown in Figure 7.
(a)
(b)
Fig. 8. Graphs depicting the position and velocity tracking of the rails based on the PD controller: (a) position tracking of the rails and (b) velocity tracking of the rails.
endoscope insertion is a proportional + derivative (PD) control scheme. The proportional gain of the system is 1250 and the derivative gain of the system is 0.01. Although, 1000Hz is the preferred update rate for realistic haptic interaction, our system is currently able to achieve 100Hz which was found to be sufficient for detecting collisions with the airway walls and obstructions. The Sensoray card controls the AC signal required to run the stepper motor through the D/A channels on the card. The position and velocity of the rails is tracked using a PD control scheme (see Figure 8).
F =
Fig. 7.
IV. S OFTWARE The procedure screen is divided into four parts, namely: a) the objectives window, b) the actual procedure window, c) the vital stats monitor window, and d) the side view of the insertion (see Figure 9).
Theoretical magnetic field generated due to the solenoids.
The endoscope is always positioned at the center of the assembly, in the airway channel, with the help of an aluminum tube (see Figure 4(b)). The end of the tube has a rubber stopper that is used for the haptic feedback when contact is made with any section of the model. The entire assembly of solenoids is mounted on a linear rail system (Haydon Kerk Inc.)(see (4) in Figure 4(a)). The linear rail system consists of a slider on which the assembly of solenoids is mounted. The slider slides on a lead screw, which is connected to an AC stepper motor with a resolution of 0.0015875 meters per step and 200 steps per revolution, and the AC motor is connected to a digital encoder. The assembly of solenoids moves along with the endoscope. The algorithm implemented to move the rails along with the
Fig. 9. The display screen as seen by the user during the procedure. a) The rectangular window on the left is the objectives window, b) the circular window at the center is the actual procedure window, c) the rectangular window at the bottom-right is the vital signs monitor, and d) the circular window on the top-right is the side view of insertion. Also, an animation of the scope is placed just below the procedure window, so that the trainee can see the orientation of the scope on the screen.
The objectives window displays information about the task to be performed. The procedure window displays the actual simulation. It displays the view as seen from the camera at the tip of the endoscope. The vital stats monitor shows the heart rate, the blood pressure, and the SPO2 levels. These levels vary based on the patient condition which depends on the performance of the user.
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The software framework can be divided into three categories: a) the graphical interface, b) the physics interface, and c) the device interface. The graphical visualization uses the Microsoft XNA framework for the Xbox and Windows. The animated 3D models of the airway, vocal cords, and the trachea are modeled using 3D Studio Max. The library imports these 3D models and renders them on the screen in real time at 60Hz. The animations include opening and closing of the vocal cords (due to coughing or gagging of the patient), the opening and closing of the oesophagus (due to the swallowing by the patient), and the movement of trachea (due to the breathing). The anatomically correct models are created using 3DStudio Max and exported as .FBX files. These files contain the geometric data, the texture mapping information, and the animation data of the models. The XNA framework imports the data and provides the visualization of the airway. Custom shaders are written to provide the special effects like lighting using the lights at the tip of the virtual endoscope, the surface wetness of the inner walls of the airway, vocal cords, and trachea, and other visual effects like mucus, blood, tumors, etc. The JigLibX library is used for the physics-based model in the simulation. The library is written in C# and is integrated with the XNA library. The physics-based model controls the dynamics of the system. It provides accurate physical responses as the endoscope interacts with the walls of the airway, the vocal cords, and the trachea. In order to navigate the scope through the anatomy it is necessary to provide an accurate animating collision mesh and a representation of the scope which has accurate dimensions and can simulate scope bending. Further the scope representation needs to be efficient enough to run on the target base hardware, the XBOX 360 within the JiglibX physics engine. Scope M odel :
Fig. 10.
Chain of spheres depicting the virtual endoscope model.
The physics-based model of the endoscope is a chain of linked spheres as shown in Figure 10. The scope is modeled as a chain of thirty rigidbody spheres. We choose thirty spheres because the Xbox hardware does not have sufficient performance to handle more spheres. The diameter of the Physics spheres is equal to the diameter of the endoscope. These spheres are linked together with revolute joints. The first sphere is designated as the anchor point (see Figure 10). The insertion force is applied at the anchor point which moves the chain of spheres (virtual endoscope) in the airway model. The revolute joints are modeled by a series of constraints (two side constraints, and one mid constraint) which does not allow the spheres to separate. The constraints ensure that the forces are transmitted from one sphere to the next. This transfer of forces and bending allows the chain of spheres shown in Figure
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10 to bend when the spheres collide with the mesh. The last five spheres are used to simulate the tip bending motion. To simulate the forced bending effect at the scope tip, the spheres can be rotated up to 20 degrees relative to the previous sphere. This allows the scope to have variable bending. Collision M odel and Response : The JigLibX physics library is designed for games and only supports rigidbody modeling. Hence, both the airway model and the endoscope model are defined as rigidbodies. The Physics engine provides a callback for collisions between each of the spheres and the collision model. At every frame, the force vectors generated due to collisions are summed to an average force vector for each sphere. The intensity of the force vector depends on the velocity of impact. As the velocity of impact increases, the magnitude of the force vector increases and vice-versa. This variable force vector produces varying degrees of frictional force. The resultant force vector is used to provide input for haptic feedback, as well as, determine when the scope is going to penetrate the model so that we can stop the forward motion of the scope. Simulation : The user controls the wire movement in the anatomy. The system needs three input parameters: depth of insertion, rotation of the scope along the long axis and the bend angle at the tip of the scope. The physics-based system translates these parameters into movement of the chain anchor point. The bending angle of the scope tip bends the spheres at the tip of the chain in relation to the others. This forms the bend in the chain. The rendering camera is attached at the tip of the wire i.e. at the tip of the last sphere on the chain. The wire moves through the geometry thereby changing the viewpoint as the position and the orientation of the wire changes. During insertion, if the wire interacts with the anatomical geometry, the movement of the wire is restricted. Each of the spheres is tested against the geometry for collisions. The collisions with the geometry provide a realistic torque effect on the sphere chain creating a bending effect along the entire length of the wire. Resultant force vectors are generated as the wire collides with the anatomical model. These vectors are used to determine the position and the force of contact. The device interface communicates with the haptic control DLL. The interface queries the device for the various input parameters (insertion, rotation about the long axis and scope tip bend) of the endoscope, processes them and passes them to the physics-based model. The physics library processes the inputs and if a collision is encountered, it communicates the position and intensity of contact to the DLL through the interface. Figure 11 shows a flowchart of the software architecture for the entire system. V. R ESULTS Once the prototype endoscope is inserted in the device airway channel the simulation begins (see Figure 4 and Figure 9). The simulation begins at the tip of the mouth. As the prototype scope is inserted into the device the user starts navigating the virtual airway using a combination of movements of the
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Fig. 11.
Flowchart depicting the flow of control through the simulation.
prototype scope. The slider on the linear rail system starts to move along with the endoscope. If the virtual endoscope makes contact with any section of the airway, vocal cords or trachea, the physics library evaluates the force with which the endoscope makes contact and the position of contact. This is communicated to the software that evaluates the intensity of contact and the exact position of contact. This is then passed as an output to the device through the interface. If the user grazes the inner walls, the physics-based model calculates the frictional force and slows the insertion of the virtual endoscope. This is communicated to the software which evaluates the intensity and point of contact and communicates to the DLL. The DLL evaluates the speed at which the actual endoscope is being inserted through a PD controller and down the rail. It also actuates the right combination of solenoid coils which results in a force due to the interaction of the permanent magnets in the sleeve at the tip of the scope and the solenoids. The force generated is controlled by the amount of current flowing through the solenoids. The current is regulated based on the intensity of contact. The repulsive force between the electromagnets and the permanent magnets on the tip of the scope (see Figure 3(a)) causes the end of the scope to move toward the tube where the contact is made. As the intensity of grazing changes, the physics library calculates the changing frictional force. The software evaluates the changing intensity of contact and the position and communicates the same to the DLL. The DLL evaluates and adjusts the speed of the rail, combination of solenoids actuated, and changes the intensity of current flowing through them. If contact is made with any section of the airway model such that further insertion is not possible, the physics library evaluates the force which is a very high value and thus, the intensity evaluated is a very high value and this brings the rails to a stop. At the end of the procedure when the endoscope is retracted from the device, the device resets to the initial home position. The results of the procedure
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are then displayed. We performed tests to evaluate the efficacy of the system. The first test determined the magnetic field inside the system and compared it to the theoretical magnetic fields at the poles of the solenoids. The second test compared the forces at the tip of the scope. The comparison was based on the interaction of the magnets at the tip of the scope with forces produced by the physics engine. A Hall Effect sensor was used to determine the magnetic field and the forces due to the field using a combination of magnets. The resultant magnetic field is the vector sum of the magnetic fields generated by the individual solenoids. Using the magnetic field, the force generated inside the system can be evaluated. Figure 12(a) shows the variation of the force with the current while Figure 12(b) shows the variation of force inside the airway channel as the distance of the scope increases from one end of the airway channel to the other and Figure 12(c) is a schematic representation of the solenoid assembly and the airway channel. Forces F x and F y are due to the individual solenoids S1 and S2 respectively while F r is the resultant of these two forces and the direction is as shown in Figure 12(c). The resultant force F r varies with the distance and it reduces as the scope moves away from the actuating solenoids.
(a)
(b)
(c) Fig. 12. a) The actual variation of force with current through the solenoid, b) the actual variation of the force with distance inside the airway channel (aluminum tube) and c) airway channel. Fr is the direction of the resultant force when solenoids S1 and S2, for example, are actuated.
A series of procedures were performed on the simulator from the beginning to the end. Whenever a collision was encountered, the force value generated by the physics engine was noted and the current applied to the electromagnets was measured. Using the current value, the force generated by
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(a)
(b) Fig. 13. a) Forces at points of collision in the anatomy, and b) forces at points of collision in the anatomy.
the electromagnets was calculated. A graph of the forces calculated in the physics engine and the actual forces generated in the electromagnets were plotted against the corresponding position of the scope in the anatomy. The plots of the forces at various points of collision in the anatomy are as shown in Figures 13(a) and 13(b). From the Figures 13(a) and 13(b) it was evident that the forces computed by the physics engine matched closely with the forces generated by the electromagnetic model. VI. C ONCLUSIONS AND FUTURE WORK We have developed a fiber-optic intubation simulator that replicates all the movements of the scope, namely insertion, rotation, and the bending at the tip. The haptics part includes capturing of the grazing effect when the tube makes contact with the inner wall, and the force feedback when the tube makes contact with the vocal cord section. The simulator thus works as a training tool for navigating the airway, as well as learning the different aspects of the procedure. We are currently running tests to determine the efficacy of the system as a training tool for residents to become more proficient with the intubation procedure and this would be the focus of our future submissions in this area. ACKNOWLEDGMENT The research was funded in part by SiTEL, part of Medstar Health’s Institute of Innovation (MI2). R EFERENCES [1] Immersion Corporation http://www.immersion.com/
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