Real-Time Fiber-Optic Intubation Simulator

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Real-Time Fiber-Optic Intubation Simulator withForce Feedback*

Ankur R. Baheti, Robert Hafey, Sneha Pai, Jose Gomez, Yuri Millo, and Jaydev P. Desai

Abstract—Fiber-optic intubation is an emergency procedurethat can be performed to intubate a patient when the patienthas serious difficulty breathing normally. The existing simulatorsfor fiber-optic intubation procedure provide haptic feedback tothe user when there is contact with the vocal cord section, butthey do not capture the grazing effect of the endoscope alongthe inner walls of the airway. The grazing on the inner wallsof the airway, if not well controlled, could lead to unnecessarytrauma for the patient. Hence, there is a need to provide thisforce feedback in a fiber-optic intubation simulator. We havebuilt a fiber-optic intubation simulator with force feedback. Thissystem is composed of a software simulation coupled with aphysics-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 withthe any section of the airway. The force feedback varies basedon the position of contact and intensity of contact. We use aPD controller to obtain force feedback at the vocal cord sectionand a variable magnetic field to capture the grazing effect of theendoscope along the inner walls of the airway. The movementsof the endoscope are captured using rotary encoders (which readthe insertion and the tip bend) and a compass module (whichreads the twist angle of the endoscope along the long axis). Thesemovements are used to navigate the virtual airway using a virtualendoscope. When collisions are encountered the physics libraryevaluates the position of contact and the force with which contactis made. Force feedback is generated due to the interaction ofthe solenoids with the permanent magnets at the tip of theendoscope. This information helps the software to actuate theright combination of solenoids. The simulator will help to trainall aspects of fiber-optic intubation, namely: 1) developing thenecessary psychomotor skills to successfully navigate the airwaywith 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, Bron-choscopy, Haptic feedback.

I. INTRODUCTION

F IBER-OPTIC intubation is an emergency procedure thatis performed to intubate a patient when the patient has

serious difficulty breathing normally. An endoscope is used todeploy a tube in the trachea of the patient to aid breathing.

Manuscript received March 17, 2010. This work was supported in part bySiTEL, part of Medstar Health’s Institute of Innovation (MI2).

Ankur R. Baheti, Robert Hafey, Sneha Pai, Jose Gomez, and YuriMillo are with Simulation and Training Environment Laboratory, MedstarHealth, Washington DC 20008 USA (email: [email protected],[email protected], [email protected], [email protected], [email protected]).

Jaydev P. Desai is with the Robotics, Automation and Medical Systems(RAMS) Laboratory in the Department of Mechanical Engineering, andMaryland Robotics Center at University of Maryland, College Park MD,20742 (email: [email protected]).

*A portion of the content of this paper has been published in 2010 HapticsSymposium (with IEEE VR).

Intubation is also performed on patients undergoing bron-choscopies, biopsies and similar procedures. The proceduremust be performed within a certain amount of time (subjectto the patient’s condition) to avoid the risk of fatality. Themost common errors in performing the procedure include:

a. Grazing the inner walls of the airway which can leadto excessive bleeding: During the actual procedure, the effectof grazing is often overlooked by novices. Left unchecked, itresults in excessive bleeding, and can even prove fatal [8].

b. Intubating the oesophagus: The oesophagus is oftenintubated in error as it is often more easily accessible thanthe vocal cords.

c. Damaging the vocal cords through repeated contactwhile trying to force the scope down: Contact made anywherein the vicinity of the vocal cords section; i.e. epiglottis,oesophagus or the vocal cords itself, can cause excessivecoughing and gagging. This makes the intubation difficult asthe vocal cords open and close rapidly. Trying to force thescope in may result in damage to the vocal cords or othersections or it could result in the endoscope getting stuck ordamaged. Also, if the patient is not intubated fast enough, itcould be fatal.

Hence, there is a need to train healthcare professionals inefficient administration of these procedures, and to minimizethe risk of injury and death.

The AccuTouch System (Immersion Medical) [1] is cur-rently a commercially available simulator that is used totrain in this procedure. There have been several studies toevaluate this simulator [2] [3] [4]. The studies use expertbronchoscopists to evaluate the performance of novices andto determine the learning curve. The studies prove that theAccuTouch system is an effective trainer; however, it doesnot provide realistic force feedback when the scope grazesthe inner walls of the airway. The Virtual Fiberoptic In-tubation (VFI) software was developed by the Institut deRecherche contre les Cancers de l’Appareil Digestif (IRCAD),Strasbourg, France [15]. This software simulator focuses onunderstanding altered airway anatomy and studies have shownimproved 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 environ-ment. This is an extension of our prior work [22], which wasprimarily related to the development of the haptic feedback de-vice. The system is designed to train healthcare professionalsto perform the procedure accurately and avoid abrasive errorsin a specified time-limit. The simulator comprises of a softwaresystem, which consists of a graphical simulation coupled witha physics-based simulation and a hardware system which


consists of a prototype endoscope and a device, into whichthe endoscope is inserted. The software simulation displaysa virtual airway navigated using a virtual endoscope. Theprototype endoscope houses a compass module to measurethe twist angle about the long axis of the endoscope anda digital encoder to measure the bending angle of the tip.The tip of the scope has a sleeve of magnets attached toit. The device provides force feedback whenever the virtualscope makes contact with the airway. The haptic feedbackis provided by the interaction between a stationary array ofsolenoids and permanent magnets on a prototype endoscope.The simulation begins with the insertion of the prototypeendoscope into the device. The graphical simulation beginsat the tip of tongue. The insertion of the prototype scopeinto the device leads to corresponding insertion of the virtualscope into the airway in the simulation environment. Whilenavigating through the airway, if the virtual endoscope makescontact with the airway, the physics library determines theforce at which the contact is made and the point of contact.The software uses this information to: 1) compute the intensityof contact, 2) combination of solenoids to actuate and 3) thespeed at which solenoid assembly should move to correlateaccurately with the graphics environment. Based on theseparameters the device provides the necessary force feedback.The combination of solenoids is obtained from the minimumcoil set technique [5].

II. BACKGROUND

Electromagnetism can be utilized to generate haptic feedback.There has been considerable research on implementing Hapticsusing electromagnetic actuators [9] [10] [11] [13] [14] [17][18] [22]. They have been used in developing a wide variety ofhaptic displays. BubbleWrap, used as a haptic display consistsof 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 hasalso been widely used in surgical simulations and effectivenessof haptic feedback in open surgery simulation, where thehaptic feedback was primarily created by magnetic force on asurgical tool, has also been evaluated [9]. Magnetorheological(MR) fluid actuators have been developed to display forcefeedback at the fingertip of a human user [10] [12] as well asin other haptic displays [17]. A MR position-feedback actuatorfunctions as the human interface module, through which userscan feel the virtual resistance and generate reaction forcesin the virtual environment. Their property of changing therheological behavior by tuning an external magnetic field isused to generate the desired effect. Lorentz force magneticlevitation can also be used for haptic interaction. Lorentz forcemagnetic levitation has been used to develop a haptic interfacedevice integrated with real-time 3D rigid-body simulationsfor detailed, responsive interaction with dynamic virtual en-vironments [18]. One of the drawbacks of Lorentz forcemagnetic levitation is low translational and rotational motions.To overcome this, a new coil configuration was developedand incorporated in a device which resulted in a highertranslational and rotational motion [11]. Electromagnetism has

also been used for hybrid locomotion design of a miniatureendoscopic capsule [19]. This system combines an on-boardlegged actuation mechanism with an external magnetic fieldthat guides the capsule motion through a permanent magnetembedded in the device. Apart from these, research has alsobeen done to compare and evaluate the forces generated whiledoing a task actually versus doing the same task virtually usingthe principle of magnetic levitation to render force feedback[14].

Computer-based training systems have been developed tosimulate surgical procedures such as inserting a catheter intothe cystic duct using a pair of laparoscopic forceps, a proce-dure performed during laparoscopic cholecystectomy to searchfor gallstones in the common bile duct [20].

Force feedback devices have also been employed to developtelerobotic systems for the operating room [21]. The systemincorporates a workstation where information is provided toand received from the operator. The surgeon controls therobotic system using two force feedback hand controllersbased on visual information from a stereoscopic viewingdevice and two liquid crystal displays.

III. MATERIALS AND METHODS

Fig. 1. Haptic feedback enabled fiber-optic intubation device along with theprototype scope.

The fiber-optic intubation simulator with force feedback con-sists of two modules as shown in Figure 1: the first module isthe instrumented scope, and the second module is the devicewhich houses all the components for the haptics.

A. Prototype scope movements

(a) (b)


(c)

Fig. 2. Illustrated movements of the scope during a typical intubationprocedure [8]. a) Roll along the long axis clockwise b) roll along the longaxis counter clockwise and c) tip bend.

The actual endoscope is a flexible tube with a camera at theend which provides imaging capability during the procedure.It also has two point lights at the end of the tube which lightup the airway. The tip has a capability to bend about an axispivoted at one inch from the tip. It is capable of bending 90degrees on one side and 120 degrees on the other.The surgeons navigate the airway using a combination ofmovements. They orient the scope by rotating the handle aboutthe long axis of the scope (see Figure 2(a) and 2(b)) and bendthe tip to navigate around bends and corners (see Figure 2(c)).

For our haptic feedback enabled fiber-optic intubation sys-tem, we built a prototype scope (see Figure 3(a)). The scopeis fitted with a sleeve of magnets at the tip (see Figure 3(a)), acompass module inside the handle and a digital encoder at thetop (see Figure 3(b)). The sleeve has a series of N52 gradeneodymium magnets (K and J Magnetics Inc). The interactionof these magnets with the stationary electromagnet array in thehaptic feedback device provides the necessary force feedbackto the user.

(a)

(b)

Fig. 3. a) Instrumented scope with a sleeve of magnets b) the handle housingthe compass module and a digital encoder.

To capture the motion of the scope on the proximal end, thehandle of the scope houses an OS5000-US compass module(ocean Server Inc.) and an S4 digital encoder (US DigitalInc). The compass module is used to measure the angle ofrotation of the scope about its long axis (see Figure 2(a) and

2(b)). The OS5000-US compass module (see Figure 3(b)) isa three-axis compass with tilt compensation. It uses a USBinterface for communication. The orientation of the scope canbe obtained as an angle in degrees using the API providedby the manufacturer. The tip bend is captured using a digitalencoder (see Figure 2(c) and 3(b)). The swivel knob on thehandle moves through 40 degrees when the tip moves through120 degrees and the swivel knob moves through 30 degreeswhen the tip moves through 90 degrees. Hence, for everydegree 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 isgiven by:

θ = E × 3 (1)

where, θ is the angle of tip bend, E is the actual encoderreading and 3 is the scale factor.

Determination of the angle of rotation : The angle ofrotation about the long axis of the scope is measured usingthe OS5000-US compass module, which is a compass modulewith tilt compensation [23]. The sensor uses a Honeywell two-axis Automated Meter Reading (AMR) sensor for X-Y planesensing and a Honeywell z-axis AMR sensor as magneticsensors, a three-axis accelerometer (ST Microelectronics) asthe tilt sensor, and a 50 MIPS (Millions of Instructions PerSecond) processor as the microprocessor. The sensor can bemounted in six different orientations and calibrated to read theangle of interest. The sensor is mounted in the right orientationand calibrated to measure the twist angle. The scope is insertedat the opening (see (1) in Figure 4(a)). The scope passesthrough a set of two pulleys (see (2) in Figure 4(a)). The lowerpulley is connected to a S4 digital encoder that measures theabsolute depth of insertion of the scope. The depth of insertionis given by:

z =NπD

360(2)

where, z is the depth of insertion, N is the number of countsof the encoder, the encoder resolution is 360, and D is thediameter of the lower pulley.

B. Haptic feedback device

(a)


(b)

Fig. 4. a) The haptic feedback device consists of: 1) opening for scopeinsertion, 2) the pulley system to measure the depth of insertion, 3) thesolenoid assembly, 4) the linear rail system with an AC stepper motor and anencoder and 5) the airway channel. (b) The solenoid assembly.

Behind the pulleys are a set of four electromagnets (seeFigure 4(a) and Figure 4(b)). The electromagnets are coilsmade of 194 turns of 16 gauge copper wire wound aroundan iron core made of Ferroxcube 3C90. The outer diameterof the coil is 0.0508 meters and the length of the coil is0.04445 meters. The diameter of the core is 0.0254 meters.The solenoids are arranged between two square sections asshown in Figure 4(b). The grazing of the endoscope againstthe inner walls of the airway is simulated by changing thevelocity of the rails and the magnetic field in the airwaychannel surrounded by the solenoids. The speed of rails andcurrent in the solenoids are varied based on the intensity of thegrazing. Thus, the solenoids are actuated in pairs, groups orindividually with varying current intensities, thereby producingvarying force outputs to simulate grazing effect on the wallsof the airway.

Model for estimating the forces generated by solenoids :The magnetic field surrounding a thin straight conductor can

be given by the Biot-Savart Law [6] [7]. Consider a circularloop of radius R located in the yz plane carrying a steadycurrent I (see Figure 5). Consider the loop to be made ofsmall current elements of length ds. Thus, for every element

Fig. 5. Circular conductor carrying current.

ds× r̂ = (ds)(1) sinπ

2= ds (3)

where r̂ is the unit vector. Also, all the infinitesimal arc-lengths, ds, are at the same distance r (distance of every

infinitesimal element, ds, from the point P ) from the pointP and is given by:

r2 = x2 +R2 (4)

where R is the radius of the loop.Hence, the magnitude of dB due to current in any infinites-

imal element, ds, is given by:

dB =µ0I

4π

|ds× r̂|r2

=µ0I

4π

ds

(x2 +R2)(5)

where, dB is the magnetic field at the point and, µ0 is thepermeability of free space. The direction of dB is perpendic-ular to the plane formed by r̂ 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 componentsdBy are summed over all elements around the loop, theresultant y-component of B is zero. Hence, the x-componentof the magnetic field is the only contributing component tothe effective magnetic field at P . Since, dBx = dB cos θ. i.e.,B = Bxi, we get:

Bx =

∮dBcosθ =

µ0I

4π

∮dscosθ

x2 +R2(6)

where the integral is over the entire loop. Since θ, x, and Rare constants for all elements of the loop, we obtain:

Bx =µ0IR

4π(x2 +R2)32

∮ds =

µ0IR2

2(x2 +R2) 32(7)

Equation (7) gives the magnetic field due to a single loopof wire carrying current. Consider a conductor with multipleloops of wire carrying current. Figure 6 shows a cross sectionof a part of a conductor, with multiple loops of wire, carryingcurrent.

Fig. 6. Solenoid carrying current.

Consider a rectangular path of length l and width w. Wecan apply Amperes law [6] to this path by evaluating theintegral of Bds over each side of the rectangle. As it is anideal solenoid, the contribution of B from side 3 is zero.Also, the contribution along path 2 and 4 are zero as theyare parallel to the direction of current, and side 1 gives acontribution of B.l to the integral because along this path, Bis uniform and parallel to ds. Hence, the integral over the


closed loop gives:∮B · dl = B

∮dl = Bl (8)

If N is the number of turns in the length l, then the totalcurrent in the rectangle is NI . Hence Amperes law gives:

B =µ0NI

l(9)

Force exerted by a magnetic field is given by:

F =B2A

2µ0(10)

where, A is the area of cross-section of the core. However,the above equations are inapplicable when most of the fieldis outside the core. In such cases the force can be obtainedby using the Magnetic Pole Model or the Gilberts Model [7],which is given by:

m =NIA

L(11)

where m is the pole strength of the solenoid, and L is thelength of the core. The force, F , exerted by the solenoid isgiven by:

F =µ0m1m2

4πr2(12)

where m1 and m2 are the pole strengths of the solenoids.Using this formula the magnetic field between two solenoidsplaced directly opposite to each other was evaluated and theplot is as shown in Figure 7.

Fig. 7. Theoretical magnetic field generated due to the solenoids.

The endoscope is always positioned at the center of theassembly, in the airway channel, with the help of an aluminumtube (see Figure 4(b)). The end of the tube has a rubberstopper that is used for the haptic feedback when contact ismade with any section of the model. The entire assembly ofsolenoids is mounted on a linear rail system (Haydon KerkInc.)(see (4) in Figure 4(a)). The linear rail system consistsof a slider on which the assembly of solenoids is mounted.The slider slides on a lead screw, which is connected to an ACstepper motor with a resolution of 0.0015875 meters per stepand 200 steps per revolution, and the AC motor is connectedto a digital encoder.

The assembly of solenoids moves along with the endoscope.The algorithm implemented to move the rails along with the

(a) (b)

Fig. 8. Graphs depicting the position and velocity tracking of the rails basedon the PD controller: (a) position tracking of the rails and (b) velocity trackingof the rails.

endoscope insertion is a proportional + derivative (PD) controlscheme. The proportional gain of the system is 1250 and thederivative gain of the system is 0.01. Although, 1000Hz isthe preferred update rate for realistic haptic interaction, oursystem is currently able to achieve 100Hz which was foundto be sufficient for detecting collisions with the airway wallsand obstructions. The Sensoray card controls the AC signalrequired to run the stepper motor through the D/A channelson the card. The position and velocity of the rails is trackedusing a PD control scheme (see Figure 8).

IV. SOFTWARE

The procedure screen is divided into four parts, namely: a) theobjectives window, b) the actual procedure window, c) the vitalstats monitor window, and d) the side view of the insertion (seeFigure 9).

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 circularwindow at the center is the actual procedure window, c) the rectangularwindow at the bottom-right is the vital signs monitor, and d) the circularwindow on the top-right is the side view of insertion. Also, an animation ofthe scope is placed just below the procedure window, so that the trainee cansee the orientation of the scope on the screen.

The objectives window displays information about the taskto be performed. The procedure window displays the actualsimulation. It displays the view as seen from the camera atthe tip of the endoscope. The vital stats monitor shows theheart rate, the blood pressure, and the SPO2 levels. Theselevels vary based on the patient condition which depends onthe performance of the user.


The software framework can be divided into three cate-gories: a) the graphical interface, b) the physics interface,and c) the device interface. The graphical visualization usesthe Microsoft XNA framework for the Xbox and Windows.The animated 3D models of the airway, vocal cords, and thetrachea are modeled using 3D Studio Max. The library importsthese 3D models and renders them on the screen in real timeat 60Hz. The animations include opening and closing of thevocal cords (due to coughing or gagging of the patient), theopening and closing of the oesophagus (due to the swallowingby the patient), and the movement of trachea (due to thebreathing). The anatomically correct models are created using3DStudio Max and exported as .FBX files. These files containthe geometric data, the texture mapping information, and theanimation data of the models. The XNA framework importsthe data and provides the visualization of the airway. Customshaders are written to provide the special effects like lightingusing the lights at the tip of the virtual endoscope, the surfacewetness of the inner walls of the airway, vocal cords, andtrachea, and other visual effects like mucus, blood, tumors,etc.

The JigLibX library is used for the physics-based model inthe simulation. The library is written in C# and is integratedwith the XNA library. The physics-based model controlsthe dynamics of the system. It provides accurate physicalresponses as the endoscope interacts with the walls of theairway, the vocal cords, and the trachea. In order to navigatethe scope through the anatomy it is necessary to provide anaccurate animating collision mesh and a representation of thescope which has accurate dimensions and can simulate scopebending. Further the scope representation needs to be efficientenough to run on the target base hardware, the XBOX 360within the JiglibX physics engine.

Scope Model :

Fig. 10. Chain of spheres depicting the virtual endoscope model.

The physics-based model of the endoscope is a chain oflinked spheres as shown in Figure 10. The scope is modeledas a chain of thirty rigidbody spheres. We choose thirtyspheres because the Xbox hardware does not have sufficientperformance to handle more spheres. The diameter of thePhysics spheres is equal to the diameter of the endoscope.These spheres are linked together with revolute joints. Thefirst sphere is designated as the anchor point (see Figure 10).The insertion force is applied at the anchor point which movesthe chain of spheres (virtual endoscope) in the airway model.The revolute joints are modeled by a series of constraints (twoside constraints, and one mid constraint) which does not allowthe spheres to separate. The constraints ensure that the forcesare transmitted from one sphere to the next. This transfer offorces and bending allows the chain of spheres shown in Figure

10 to bend when the spheres collide with the mesh. The lastfive spheres are used to simulate the tip bending motion. Tosimulate the forced bending effect at the scope tip, the spherescan be rotated up to 20 degrees relative to the previous sphere.This allows the scope to have variable bending.

Collision Model and Response : The JigLibX physicslibrary is designed for games and only supports rigidbodymodeling. Hence, both the airway model and the endoscopemodel are defined as rigidbodies. The Physics engine providesa callback for collisions between each of the spheres and thecollision model. At every frame, the force vectors generateddue to collisions are summed to an average force vector foreach sphere. The intensity of the force vector depends on thevelocity of impact. As the velocity of impact increases, themagnitude of the force vector increases and vice-versa. Thisvariable force vector produces varying degrees of frictionalforce. The resultant force vector is used to provide input forhaptic feedback, as well as, determine when the scope is goingto penetrate the model so that we can stop the forward motionof the scope.

Simulation : The user controls the wire movement in theanatomy. The system needs three input parameters: depthof insertion, rotation of the scope along the long axis andthe bend angle at the tip of the scope. The physics-basedsystem translates these parameters into movement of the chainanchor point. The bending angle of the scope tip bends thespheres at the tip of the chain in relation to the others. Thisforms the bend in the chain. The rendering camera is attachedat the tip of the wire i.e. at the tip of the last sphere onthe chain. The wire moves through the geometry therebychanging the viewpoint as the position and the orientationof the wire changes. During insertion, if the wire interactswith the anatomical geometry, the movement of the wire isrestricted. Each of the spheres is tested against the geometryfor collisions. The collisions with the geometry provide arealistic torque effect on the sphere chain creating a bendingeffect along the entire length of the wire. Resultant forcevectors are generated as the wire collides with the anatomicalmodel. These vectors are used to determine the position andthe force of contact. The device interface communicates withthe haptic control DLL. The interface queries the device forthe various input parameters (insertion, rotation about the longaxis and scope tip bend) of the endoscope, processes themand passes them to the physics-based model. The physicslibrary processes the inputs and if a collision is encountered,it communicates the position and intensity of contact to theDLL through the interface. Figure 11 shows a flowchart ofthe software architecture for the entire system.

V. RESULTS

Once the prototype endoscope is inserted in the device airwaychannel the simulation begins (see Figure 4 and Figure 9).The simulation begins at the tip of the mouth. As the prototypescope is inserted into the device the user starts navigatingthe virtual airway using a combination of movements of the


Fig. 11. Flowchart depicting the flow of control through the simulation.

prototype scope. The slider on the linear rail system startsto move along with the endoscope. If the virtual endoscopemakes contact with any section of the airway, vocal cords ortrachea, the physics library evaluates the force with which theendoscope makes contact and the position of contact. Thisis communicated to the software that evaluates the intensityof contact and the exact position of contact. This is thenpassed as an output to the device through the interface. Ifthe user grazes the inner walls, the physics-based modelcalculates the frictional force and slows the insertion of thevirtual endoscope. This is communicated to the software whichevaluates the intensity and point of contact and communicatesto the DLL. The DLL evaluates the speed at which the actualendoscope is being inserted through a PD controller and downthe rail. It also actuates the right combination of solenoid coilswhich results in a force due to the interaction of the permanentmagnets in the sleeve at the tip of the scope and the solenoids.The force generated is controlled by the amount of currentflowing through the solenoids. The current is regulated basedon the intensity of contact. The repulsive force between theelectromagnets and the permanent magnets on the tip of thescope (see Figure 3(a)) causes the end of the scope to movetoward the tube where the contact is made. As the intensity ofgrazing changes, the physics library calculates the changingfrictional force. The software evaluates the changing intensityof contact and the position and communicates the same to theDLL. The DLL evaluates and adjusts the speed of the rail,combination of solenoids actuated, and changes the intensityof current flowing through them. If contact is made with anysection of the airway model such that further insertion is notpossible, the physics library evaluates the force which is a veryhigh value and thus, the intensity evaluated is a very high valueand this brings the rails to a stop. At the end of the procedurewhen the endoscope is retracted from the device, the deviceresets to the initial home position. The results of the procedure

are then displayed.We performed tests to evaluate the efficacy of the system.

The first test determined the magnetic field inside the systemand compared it to the theoretical magnetic fields at the polesof the solenoids. The second test compared the forces at thetip of the scope. The comparison was based on the interactionof the magnets at the tip of the scope with forces producedby the physics engine.

A Hall Effect sensor was used to determine the magneticfield and the forces due to the field using a combination ofmagnets. The resultant magnetic field is the vector sum of themagnetic fields generated by the individual solenoids. Usingthe magnetic field, the force generated inside the system canbe evaluated. Figure 12(a) shows the variation of the forcewith the current while Figure 12(b) shows the variation offorce inside the airway channel as the distance of the scopeincreases from one end of the airway channel to the other andFigure 12(c) is a schematic representation of the solenoidassembly and the airway channel. Forces Fx and Fy are dueto the individual solenoids S1 and S2 respectively while Fris the resultant of these two forces and the direction is asshown in Figure 12(c). The resultant force Fr varies withthe distance and it reduces as the scope moves away from theactuating 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 resultantforce when solenoids S1 and S2, for example, are actuated.

A series of procedures were performed on the simulatorfrom the beginning to the end. Whenever a collision wasencountered, the force value generated by the physics enginewas noted and the current applied to the electromagnets wasmeasured. Using the current value, the force generated by


(a)

(b)

Fig. 13. a) Forces at points of collision in the anatomy, and b) forces atpoints of collision in the anatomy.

the electromagnets was calculated. A graph of the forcescalculated in the physics engine and the actual forces generatedin the electromagnets were plotted against the correspondingposition of the scope in the anatomy. The plots of the forcesat various points of collision in the anatomy are as shownin Figures 13(a) and 13(b). From the Figures 13(a) and13(b) it was evident that the forces computed by the physicsengine matched closely with the forces generated by theelectromagnetic model.

VI. CONCLUSIONS AND FUTURE WORK

We have developed a fiber-optic intubation simulator thatreplicates all the movements of the scope, namely insertion,rotation, and the bending at the tip. The haptics part includescapturing of the grazing effect when the tube makes contactwith the inner wall, and the force feedback when the tubemakes contact with the vocal cord section. The simulator thusworks as a training tool for navigating the airway, as wellas learning the different aspects of the procedure. We arecurrently running tests to determine the efficacy of the systemas a training tool for residents to become more proficient withthe intubation procedure and this would be the focus of ourfuture submissions in this area.

ACKNOWLEDGMENT

The research was funded in part by SiTEL, part of MedstarHealth’s Institute of Innovation (MI2).

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Documents

Real-Time Fiber-Optic Intubation Simulator