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Interactive computer-based simulator for training in bladenavigation and targeting in myringotomy

Brian Wheelera, Philip C. Doyleb,c, Shamir Chandaranac, Sumit Agrawalc,Murad Huseinc, Hanif M. Ladaka,c,d,e,∗

a Biomedical Engineering Graduate Program, The University of Western Ontario, London, Ontario, Canadab Rehabilitation Sciences, The University of Western Ontario, London, Ontario, Canadac Department of Otolaryngology, The University of Western Ontario, London, Ontario, Canadad Department of Electrical and Computer Engineering, The University of Western Ontario, London, Ontario, Canadae Department of Medical Biophysics, The University of Western Ontario, London, Ontario, Canada

a r t i c l e i n f o

Article history:

Received 22 January 2009

Received in revised form 8 June 2009

Accepted 16 September 2009

Keywords:

Myringotomy

Ear surgery

a b s t r a c t

A virtual-reality simulator was developed for the training of Otolaryngology

(Ear–Nose–Throat) surgical residents to perform myringotomy, a relatively common

surgical procedure in which an incision is made in the eardrum mainly to treat middle-ear

infections. The simulator presents the trainee with a three-dimensional (3D) virtual model

of the ear that can be viewed through a mock surgical microscope consisting of a stereo

visor mounted on a custom-designed stand. The trainee interacts with the virtual ear using

a real myringotomy blade, the movements of which are tracked in real time using a stereo

optical tracker. Interactions of the blade with virtual tissues are calculated and rendered

Surgical training

Computer simulation

Virtual-reality

on the visor using freely available physics and graphics software engines. Six experienced

surgical residents and surgeons assessed the effectiveness of the simulator as a viable

training tool by completing a questionnaire designed specifically for this study after using

the simulator. Surgeons and residents were positively impressed by the simulator as a

training tool and would recommend its use as part of training.

1. Introduction

Myringotomy is a surgical procedure in which a small incisionis made in the eardrum through which fluid can be aspiratedfrom an infected middle-ear cavity, medications instilled, andventilation tubes placed. Myringotomy with tube insertionis the most common paediatric surgical procedure in NorthAmerica with more than 1 million operations being performed

annually [1].

The myringotomy procedure is performed using a surgi-cal microscope to allow visualization of the eardrum through

∗ Corresponding author at: Department of Medical Biophysics, Medicalmond Street, Suite 2, London, Ontario, Canada N6A 5C1. Tel.: +1 519 66

E-mail address: hladak@uwo.ca (H.M. Ladak).0169-2607/$ – see front matter © 2009 Elsevier Ireland Ltd. All rights resdoi:10.1016/j.cmpb.2009.09.010

© 2009 Elsevier Ireland Ltd. All rights reserved.

a handheld speculum (funnel) placed in the ear canal. Thespeculum is held by the nondominant hand, leaving thedominant hand free to perform surgical maneuvers such asnavigating a myringotomy blade down the ear canal andmaking the incision using the blade. A high level of manualdexterity and experience are needed to operate under a micro-scope, insert a blade through the narrow ear canal, and createthe incision in a safe and efficient manner. These fundamen-

Sciences Building, The University of Western Ontario, 1151 Rich-1 2111x86551; fax: +1 519 661 2123.

tal operative skills also are essential in performing many othertypes of ear surgery.

Currently, at most institutions surgical residents are taughtthe procedure at a very early stage in their training through

erved.

i n b i o m e d i c i n e 9 8 ( 2 0 1 0 ) 130–139 131

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Fig. 1 – Hardware comprising the myringotomy simulator.The optical tracker is facing the mock microscope. Thecheckered papers labelled M1, M2 and M3 are markersprovided by Claron Technology (Toronto, ON). M1 allowstracking of the position and orientation of the visor. M2defines the location of the virtual ear. M3 allows fortracking of the speculum. The markers are placed within

c o m p u t e r m e t h o d s a n d p r o g r a m s

bservation and practicing directly on patients. This approachan place patients at risk due to inexperience. Possible com-lications of myringotomy caused by inexperience includexcessive trauma to the eardrum, accidental cutting of thear canal, damage to the ossicular chain, and damage to theiddle-ear wall. These complications can result in bleeding,

earing loss, and vertigo for the patients.Several researchers have proposed physical replicas of the

ar canal and eardrum as a means of providing practiceor myringotomy without the risk of harm to patients [2–6].hese generally consist of a straight tube with a circularross-section to represent the ear canal and a flat syntheticembrane (e.g., rubber) attached to one end of the tube

o represent the eardrum. These replicas are placed undersurgical microscope and are operated upon by the resi-

ent. Clearly, these replicas do not accurately represent earanal and eardrum geometries, tissue mechanical properties,r the large variability that exists across patients. Moreover,hen trainees use such replicas, an experienced surgeon must

ssess the quality of the myringotomy which can take awayaluable time from treating patients.

Virtual-reality (VR) technology consisting of computers andD human–computer interfaces has been utilized to simu-ate various surgical procedures for training and planningurposes [7]. By using various human–computer hardware

nterfaces, the user of a VR-based simulator interacts with aD computer model of tissues that look and feel like real tis-ues. Since the patient is replaced by a virtual replica, theres no immediate risk of danger to the patient. Additionally,he benefits of VR-based surgical simulation include broaden-ng surgical training through the provision of different virtualatient types, and its ability to quantify surgical performance

8]. VR-based training also has the potential to reduce costsssociated with surgical training. Given dwindling funds forducation in general, more cost effective and efficient meth-ds are needed in surgical training. Many surgeons believehat VR-based training is the answer. It could hold the sameignificant benefits for myringotomy training.

Although VR simulators have been developed for otherreas of Ear–Nose–Throat (ENT) surgery including virtual oto-copy [9], endoscopic sinus surgery [10], and temporal boneissection [11,12], there are no existing VR simulators foryringotomy training. In this paper, we describe a VR-based

imulator for training residents in navigating a myringotomylade down the ear canal without accidentally cutting the earanal and targeting the correct location on the eardrum for thencision (antero-inferior quadrant). A face validity study wasonducted as described in Section 4 to determine if experi-nced surgeons and residents consider the level of abstractionsed in designing the simulator acceptable for training surgi-al residents on the intended tasks.

. Design considerations

imulation of human anatomy, whether off-line or in real

ime, is a daunting task due to the complex geometry androperties of most tissues. Since the objectives were to designsimulator to allow trainees to practice navigating a myringo-

omy blade down the ear canal without accidentally cutting

view of the optical tracker. The hardware implementationshown above utilizes a laptop.

the canal and to allow targeting the preferred quadrant of theeardrum, static graphical computer models of the eardrumand ear canal were deemed sufficient. Static models do notdeform when contacted by virtual surgical tools. However, rep-resentation of the gross physical geometry is important andphotorealistic rendering of the eardrum is required so traineescan use important landmarks as a guide in making an incisionin the preferred area of the eardrum.

The user’s interaction with virtual tissues should mimic areal surgery as much as possible. Ideally, the trainee should beable to use real surgical instruments to interact with virtualtissues. Moreover, both the virtual tissues and virtual toolsrepresenting the actual surgical tools need to be rendered onan output device that looks and functions like an actual sur-gical microscope. Graphical rendering, including detection ofcollisions between virtual tools and tissues, must be done inreal time. Rendering at a minimum rate of 10 frames per secondis deemed sufficient for smooth animation for VR applications[13]. Force feedback to the trainee when virtual tools touch vir-tual tissues was not deemed critical since the eardrum is verycompliant and provides minimal force feedback. However,contact with the ear canal itself should result in significantreaction forces. Calculating and rendering these forces wasnot deemed necessary by the designers as it does not con-tribute to the training objectives of improving navigation andtargeting. Simply indicating graphically that accidental con-tact was made was thought to be sufficient; however, feedbackfrom users was sought as outlined in Section 4 to determinethe acceptability of this design simplification.

3. Description of simulator

3.1. Overview

The major components of the simulator are shown in Fig. 1and consist of a computer (e.g., a laptop or desktop) running

132 c o m p u t e r m e t h o d s a n d p r o g r a m s i n

Fig. 2 – Trainee using the simulator. The trainee is viewingthe computer-simulated environment (virtual ear canal,eardrum and virtual tools) through the visor. By moving aphysical myringotomy blade in physical space, he is able tomove the corresponding virtual blade so he can interactwith the virtual ear. The styrofoam block permits thetrainee to stabilize his/her hands as done in an actualsurgery. Note the speculum is hidden by the trainee’s lefthand. This particular realization of the simulator uses a

desktop computer.

the simulation software, a mock surgical microscope and anoptical tracker. As shown in Fig. 2, when using the simulatorthe trainee looks through the mock microscope and positions

the microscope and a real speculum so that s/he can clearlysee the virtual eardrum rendered on the microscope by thesimulation software. Fig. 3 shows a sample two-dimensional

Fig. 3 – Simulated environment as seen through oneeyepiece of the visor. During the simulation, the traineeactually sees a 3D stereo display, but only a 2D depiction isshown here. The black part around the eardrum and earcanal is the speculum. At the top left, the current metricsare displayed. The top right contains instructions to thetrainee.

b i o m e d i c i n e 9 8 ( 2 0 1 0 ) 130–139

(2D) view as seen through one liquid crystal display (LCD) ofthe visor; during the simulation, the trainee actually sees a 3Dstereo display, but only a 2D depiction is shown here. Oncethe trainee has an unobstructed view of the eardrum s/hecan slide the mouse to adjust the zoom setting. The traineecan then begin guiding the physical blade through the phys-ical speculum, down the virtual ear canal toward the virtualeardrum. While guiding the blade, the trainee can stabilizehis/her hands on a styrofoam block just as a surgeon wouldstabilize his/her hands on the patient’s head during an actualprocedure. The position and orientation of the physical bladeare continuously measured by the optical tracker and are usedto update the position and orientation of a virtual represen-tation of the blade. A portion of the virtual blade is shown inFig. 3. Once the trainee has made the incision, s/he can signalthe end of the myringotomy procedure by removing the bladefrom the virtual eardrum. During the simulated procedure,errors as described in Section 3.4 are reported to the trainee. Inorder to assist the trainee, an optional cue consisting of threedots on the virtual eardrum can be provided to indicate a linealong which the incision should be made. If the cue is turnedoff, the trainee needs to independently decide the preferredlocation for the incision.

3.2. Tool tracking

For tracking the motion of the surgical instruments (i.e., phys-ical blade, speculum and microscope eyepiece), the ClaronTechnology (Toronto, ON, Canada) MicronTracker 2 S60 is used.This device consists of a pair of cameras for stereo vision.Imaging software provided with the MicronTracker recognizesa visual marker on the actual surgical tool and determines itslocation and orientation in 3D space. The maximum speed ofthe camera is set to 30 frames processed per second. The sim-ulation software runs at 60 frames per second and, therefore,samples tool position data from the camera every other frame.A visual motion tracker allows the simulator the use of a sur-gical tool with minimal modification: The surgical tool simplyneeds a paper marker attached to it so that it can be identifiedby the tracker.

3.3. Mock microscope

The mock microscope consists of a 3D stereo headset mountedon an adjustable stand. The headset used is the eMagin Z8003D visor (Bellevue, WA, USA). It has two LCDs, each of whichrefreshes at 30 Hz, for a total of 60 rendered frames per second.Each display has 800 horizontal by 600 vertical pixels. Since thevisor was originally designed for consumer computer gameplaying, it can render the simulated environment clearly andis inexpensive compared to other stereo visors. The stand towhich the headset is mounted allows the position and angle ofthe visor to be adjusted. The stereo glasses were mounted in amanner so that tilting them would require the same amountof force as when using an actual surgical microscope. Themounting mechanism was designed to subjectively match the

force required when using a real microscope as perceived bythe designers of the simulator. Adjustment of the visor resultsin the optical tracker initiating equivalent adjustments in thesimulation software. This is because the position and angle of

c o m p u t e r m e t h o d s a n d p r o g r a m s i n b

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ig. 4 – Simplified flowchart describing overall operation ofhe simulation software.

he visor are tracked using a marker (M1 in Fig. 1) attached tohe left side of the visor. Marker M2 attached to the speculumracks its position and orientation, and marker M3 denoteshe position and orientation of the virtual ear. The headsetits above and to the right of the motion tracker. This positionllows the tracking camera to observe the mock microscopend surgical instrument at all times while the virtual surgerys being performed. As stated above, magnification of the viewhrough the mock microscope is controlled using the com-uter’s mouse. This allows for a smooth, analogue-style zoom.

.4. Simulation software

ig. 4 shows a simplified flowchart describing the overall oper-tion of the software. The simulation starts when the userresses the spacebar on the keyboard. In the “Initialization”hase, graphical models for each of the simulated objects

eardrum, ear canal, speculum, and myringotomy blade) areoaded into memory and initial conditions such as positionnd orientation are set for all objects, as well as for that of theiewing camera. The starting time is set to zero.

When the simulation is running, the software continuouslyonitors the inputs (optical tracker, keyboard and mouse),

hecks for collisions between virtual tools and virtual tissues,

nd sends output to the visor comprising the mock micro-cope. When running, each display frame is generated sixtyimes every second taking into account the positions and ori-ntations of the simulated objects. The keyboard and mouse

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are monitored every display frame for input from the user,whereas the optical tracker is monitored every other frameto match its sampling rate. Collisions between objects aredetected during each frame.

During the simulation, the user can exit the software atany time through a key press. This unloads all models frommemory and returns control to the operating system. Move-ments of the mouse are also monitored and are used to controlmagnification of the scene.

If movement of the blade is detected by the optical tracker,collisions are checked for between the virtual representationof the blade and that of the virtual ear. If a collision is detected,the two objects that have collided are determined, and theposition and direction of the collision relative to each objectis calculated. From this information, the program decideswhether the collision is an incision or an error. In the caseof an incision of the virtual eardrum, a line is created fromthe initial point of the incision to the current location of theincision collision (i.e., where the blade is currently touchingthe eardrum). When the blade is removed from the virtualeardrum by the trainee, the operation is deemed complete andthe simulation is stopped. All of the metrics are also updatedand displayed upon completion of the operation. Currently,the simulator only displays three metrics: time to complete thesimulated operation, the total number of errors as describedbelow and a graphical rendering of the incision itself and ofthe path taken to navigate down the virtual ear canal to reachthe virtual eardrum. After displaying the metrics, the simula-tor waits for input from the keyboard to indicate if the userwishes to exit the software completely or start another virtualoperation.

If an error rather than an incision collision is detected, thetype of error that has occurred is determined. The appropri-ate feedback is initiated (such as a visual indicator for a wallcontact), and the error count is incremented. In the currentimplementation, three types of errors are considered: acciden-tal contact of the virtual ear canal with the blade, cutting theincorrect location on the eardrum (anything except the antero-inferior region) and inserting the blade too deeply (more than2 mm) beyond the virtual eardrum.

3.5. Software implementation

The simulator is written in C++ using Microsoft’s Visual Studio2005. The simulator has been tested on computers runningMicrosoft Windows XP and Microsoft Windows 2000. TheObject-oriented Graphics Rendering Engine (OGRE) [14] is afreely available software library that is used to display thesimulated scene. This graphical rendering engine can displaytextured triangular mesh representations of the simulatedobjects such as the ear canal, eardrum and surgical tools aswell as two-dimensional text and particle effects such as dots.The Open Dynamics Engine (ODE) [15] is used for collisiondetection. It is a freely available software library. Collisiondetection between the triangular mesh objects is done usingthe actual triangular meshes rather than simplified geometry

such as spheres. This allows for better accuracy in determiningthe location and orientation of collisions.

Input from the keyboard and mouse is monitored and pro-cessed using the Object-oriented Input System (OIS), a free

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object-oriented input system [16]. OIS allows multiple devicesincluding different keyboards to be easily adapted to thesystem. Input from the optical tracker is obtained from thehardware drivers that communicate with the tracker itself.

Graphical output to the visor is expected at a rate of 60frames per second, with frames alternating between the leftand the right display. Thus, the result is two displays eachrunning at 30 frames per second. To handle the two separateviews, the NVidia (Santa Clara, CA, USA) video cards used havesequential stereo drivers that do the sequential stereo outputautomatically. The view in the rendering engine is drawn froma slightly left camera position for one frame, and a slightlyright camera position for the next frame. The frames are thensent to the visor in sequence.

3.6. Anatomical models

The anatomy of the ear and the tools used in the procedureare all modeled using textured 3D triangular meshes. For thisinitial implementation, simplified but useful geometries wereimplemented to represent the eardrum and ear canal. Theeardrum is modeled using a flat circular plate. This plate istextured using an image of an eardrum as seen through anotoscope. The default scenario pictured in this document andused in the evaluation study contains an image from the Wiki-media Commons [17]. The plate representing the eardrum isplaced perpendicular to the virtual ear canal. The ear canalmodel consists of a long cylinder; no attempt was made torender the ear canal photo realistically since the objective wassimply to train residents to avoid cutting it. In the default sce-nario it is simply straight and hollow, with an inner diameter of10.4 mm and a length of 11.5 mm (half the length of an averageadult ear canal) [18]. The length of the ear canal is shortenedto eliminate the portion that would be covered by the specu-lum in a real operation. The speculum is modeled as a hollowtapered cone with the same dimensions as a real speculum.The inner end of the speculum model (the part closest to theeardrum when inserted) is shortened so as not to interferewith the shortened ear canal model. The myringotomy bladeis represented by a model that matches the dimensions of areal blade and is depicted using a metallic texture.

4. Evaluation of simulator

4.1. Development of measurement instrument

In order to evaluate the value of the surgical simulator, aproprietary measurement instrument was developed. Initially,the researchers discussed the varied areas of consideration forsuch a surgical simulation tool. As an outgrowth of this discus-sion, several core areas of concern were noted. Briefly, theseareas included concerns specific to issues of eye–hand coor-dination, skill development, anatomical location and visualand movement realism, perceptions of the “mock” micro-scope itself, and the value of the simulator as a training aid.

Additionally, information on issues such as color, generalizedgeometry of the anatomical structures involved (i.e., the earcanal and eardrum), movement, and visual focus were desired.Lastly, a global judgment of the value of the tool relative to its

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perceived level of difficulty in the hands of those who hadvaried levels of experience was included for evaluation.

From the standpoint of measurement instrument develop-ment, we considered the construct validity of the areas to beaddressed, as well as the content validity of those questions.As part of this process, input was obtained and several lev-els of revision to the structure and content of the questionswere undertaken by those with expertise in the area. An ini-tial core set of questions was streamlined to avoid redundancyor ambiguity. This then led us to determine the best method ofpresenting questions and gathering responses from surgeons.

In developing the measurement tool, several approachesto data acquisition were pursued. Consequently, we ended upwith 23 areas of concern from which a set of questions evolved.We then evaluated this set of questions and worked to deter-mine the ideal format in which the questions should be posed.First, given the nature of the areas to be pursued, 7 ques-tions were assessed by the research team to be best addressedvia a “yes/no” response format. The remaining 16 questionswere judged to be most appropriately assessed using a Likert-style scale. As such, we developed an identical 7-point, equalappearing interval scale for each of these questions.

All scales were constructed to exhibit a range of favourableand unfavourable responses, along with a neutral responsewhich was placed at the midpoint (i.e., “4”) on the scale.Responses of 1, 2, and 3, represented “strongly agree”, “mostlyagree”, and “agree”, respectively. Similarly, responses of 5, 6,and 7 represented “disagree”, “mostly disagree” and “stronglydisagree”, respectively. The use of this scale was deemed to beappropriate and exhibited the potential to be sensitive to theconstructs that were important to evaluate in respect to thesimulator.

4.2. Content of the questionnaire

The complete questionnaire is provided in Appendix A. Inregard to the content areas of the 16 questions, the follow-ing categorization may be offered. Two questions (Q1 andQ2) addressed the perceived value of general opportunities totrain eye–hand coordination; three questions (Q3, Q4, and Q5)addressed issues of skill development specific to the simula-tor under evaluation in this project; one question focused onthe importance of anatomical location (Q6) for the procedureof interest; five questions (Q7, Q8, Q9, Q12, and Q13) addressedaspects of visual realism in the simulator; two questions (Q10and Q11) assessed the “mock” microscope; and finally, 3 ques-tions (Q14, Q15, and Q16) addressed perceptions of the valueof using the present system as part of training.

The remaining seven questions were direct “yes–no” evalu-ations of the respondents’ perceptions of the simulator and itsrelated features and value. As the final part of the assessment,participants were asked to evaluate the comparative level ofdifficulty when using the simulator relative to performing theactual surgical procedure (myringotomy).

4.3. Participants

All available surgeons and surgical residents in London,Ontario, Canada with myringotomy experience were recruitedto evaluate the simulator. Six participants were able to par-

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Table 1 – Summary of results for Sections A and B ofquestionnaire in Appendix A.

Section A

Question number Mean Standard deviation

1 2.0 1.32 1.8 1.23 2.8 1.64 3.5 1.05 3.2 1.06 1.0 0.07 2.3 1.08 3.0 0.99 3.7 1.8

10 3.8 1.211 3.3 0.812 4.8 1.313 3.8 1.014 3.2 0.815 3.2 0.816 2.2 1.2

Section B

Question number No Yes

1 0 62 0 63 0 64 1 5

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icipate, and this participant group included one first-yearesident, two third-year residents, a fifth-year resident, as wells two experienced and board-certified practicing surgeons.

.4. Administering the questionnaire

he simulator was positioned on a table in a room with normaluorescent lighting. Instruction on the use of the simulatoras provided before the participants used the simulator. Eacharticipant was allowed to use the simulator long enough toecome well acquainted with its features. Upon finishing, eacharticipant was provided with as much time as required tonswer the questionnaire.

. Results of questionnaire

uestionnaires were completed by all six respondents. Of thisroup of six, a range of clinical and surgical expertise was rep-esented. In regard to the 16 scaled questions in Section A,atings were collapsed across the six respondents for eachuestion. A summary of the mean (M) and standard devi-tion of scores for each question is provided in Table 1 forection A of the questionnaire, whereas the total number ofyes” and “no” responses are presented for Section B. Basedn data obtained, the perceived value of training eye–hand

oordination revealed favourable responses (M = 2.0 and 1.8,espectively). For questions on skill development, the meanesponse was again favourable (2.8, 3.5, and 3.2); however,t should be pointed out that while the majority of respon-

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dents indicated favourable responses to these questions, onerespondent was unfavourable relative to these three ques-tions. Interestingly, that respondent had the least amount ofexperience within the group of six respondents. In responseto the importance of anatomical location, responses uniformlyexhibited strong agreement. For questions concerning visualrealism, responses indicated a varied range with correspond-ing mean values being less well interpreted. Questions specificto evaluation of the mock microscope demonstrated that 5 of12 responses across the two questions neither agreed or dis-agreed with the statement; of the remaining 7 responses, amore favourable response was common to those with moreexperience, whereas less favourable responses were associ-ated with those exhibiting less surgical experience. Finally,relative to the three questions specific to the value of usingthe simulator in training, mean responses of 3.2, 3.2, and2.2 were obtained. Collectively, analysis of the scaled datasuggest that of the 96 total responses (6 respondents × 16questions), 24 of 96 (25%) were found to neither agree nor dis-agree. For the remaining 72 responses, only 9 (12.5%) reflectedless favourable responses to questions concerning the simu-lator.

Concerning the 7 questions that addressed issues that useda Yes/No response format, four respondents fully agreed (Yes)with all statements. For the remaining two respondents, eachresponded “No” to two of the questions; both responded neg-atively to Q5, while individual responses were revealed for Q6and Q7.

Finally, the last question posed asked respondents to indi-cate the comparative level of difficulty relative to the actualmyringotomy procedure. Four of the six respondents indi-cated that the simulator was “slightly more” difficult, whilethe remaining two indicated it to be “much more” difficult.

6. Discussion

6.1. Implementation issues

Myringotomy surgery is done under a 3D stereo microscope.It requires very fine, delicate movements by the surgeon. Thestudy indicates that the Z800 visor is more than adequate forsimulating the surgical microscope used in the surgery. Forthe surgical tools used and the delicate movements required,the MicronTracker 2 S60 seems acceptable, but it could useimprovement.

The results of the questionnaire suggest several immedi-ate avenues for further improvement to the simulator. Thefirst question of Section B (see Appendix A) and the writtenfeedback provided by the participants who tried the simu-lator indicate that haptics is an important factor that is notcurrently implemented in the simulator. The addition of ahaptic arm to the input system of the simulator would likelysatisfy this deficiency. The haptic arm will allow the sur-geon to manipulate the tool in the operating space and feelappropriate forces when s/he touches the virtual eardrum and

ear canal. Our initial experience with commercially availablehaptic devices indicates that they cannot realistically renderthe small forces associated with myringotomy. Haptic devicesbased on magnetic levitation principles [19] may be capable of

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rendering such small forces and would be useful to test whenthey are commercially available.

The addition of haptics would also serve to solve the prob-lems with the optical tracker. It is difficult to position themarkers on the tools without the trainee’s hands blocking thetracker’s view of the markers and still measure the positions ofthe tools accurately. The farther away from the tip of the toolthe marker is, the more magnified the tracking errors become.Using haptic devices instead of optical tracking would removethese problems completely, as haptic devices track their posi-tions themselves.

The responses to the questions about realism exhibiteda lot of variation. Incorporating varying ear canal geome-tries from computed tomography scans of actual patients mayhelp reduce this variability. Additionally, realistic deformableeardrum models may help in this regard as well. The sim-ulation of other parts of the surgery can be added forcompleteness. Right now, only the myringotomy itself, i.e., themaking of the incision in the eardrum, is simulated. Remov-ing wax from the ear canal, suctioning the incision, insertinga ventilation tube, and placing the speculum are other partsof the surgery which can be added to the simulator.

6.2. Questionnaire results

Most of the participants involved in the study agree that thesimulator may be useful for improving hand-eye coordina-tion and motor skills related to myringotomy surgery. Trainingon the simulator also can be done in a controlled classroomenvironment and it by the users on their own time. Withthe simulator, surgical residents can have unlimited access tosurgery training. Those who need to improve their visual andmotor skills in order to be able to perform surgery can takeevery opportunity to do so using the simulator. The surgeonsand surgical residents that responded to the questionnaireindicated that they would use the simulator and recommendits use to others, and as a result, the use of VR technology maybe of significant benefit in training.

To quantify potential improvements as a result of train-ing on the simulator, two additional validation studies arerequired. An internal validity study would quantify theimprovement in performing the simulated surgery, and wouldrequire tracking the progress of participants as they repeatedlyuse the simulator over a period of time. Although this wouldquantify improvement in performing the simulated task, a VRto OR (operating room) transference study must be done toestablish if the simulator effectively improves the skills of res-idents when doing the actual surgery in the operating room.Internal validity and transference studies require recruitmentof a number of participants who can dedicate significant timeto the studies; these studies are currently being undertaken inour laboratory.

All participants found that the simulated surgery was moredifficult than the actual surgery. In part, this may be due toproblems associated with the optical tracker, issues that aredocumented above in Section 6.1. Modifying the level of dif-

ficulty, or perhaps having a range of difficulty would allowsurgeons to compare their skills to the real procedure and alsogive them sufficient challenge. Some ways to change the dif-ficulty would be to require a less or more accurate incision,

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a change in the size of the ear canal, and by adding morecues or removing some cues (such as the incision placementindicator).

Responses about realism were favourable but varied. Themost variation occurred for the question about the surgicalinstrument. Feedback from the comment section indicatedthat the less positive responses were due to two factors. Thefirst is inherent jitter resulting from the imprecision of theoptical tracker. The second is the lack of any force feedback.Using a haptic arm as an alternative to the optical tracking sys-tem for input would likely help to resolve both of these issues.Most of the other realism questions dealt with the 3D mod-els and their textures. Using realistic geometries taken fromreal patient data would be ideal, and applying textures takenfrom real human ear anatomy would help as well. Geometryfor ear canals can be obtained through computed tomography(CT) [20]. The shape of the tympanic membrane can also bemeasured using moiré topography, a non-contacting opticaltechnique [21].

A single ear canal shape was modeled in the present imple-mentation of the simulator as the goal was to determine if themethodology used in designing the simulator could result ina realistic and useful experience. However, a larger databaseof realistic models is currently being incorporated into thesimulator to encompass the variability in ear anatomy acrossdifferent patients using the methods outlined above that arebased on patient-specific anatomical models derived from CT.Feedback from a staff otolaryngologist on one such modelderived from CT images indicates that CT-derived geometriesrendered with a single skin-tone color provide a realistic expe-rience.

The current study suggests that the simulator may beeffective in training surgeons in some of the skills needed toperform a myringotomy. In order to establish the effectivenessof the simulator in increasing the skills of surgeons, a VR-to-OR transference study must be done. A transference study willreveal if the simulator effectively improves the surgical skill ofthe trainee when doing the actual surgery.

7. Conclusions

The VR system simulates the blade navigation and incisionplacement portions of the myringotomy procedure and isviewed by experienced surgeons and residents as potentiallyuseful for training in hand-eye coordination. The question-naire results suggest that the myringotomy simulator issufficiently realistic and the systems that are modeled areappropriate for the task. The simulator is viewed as a train-ing device that can be used both in structured laboratory andclassroom environments as well as during informal practicesessions. Participants in the study would continue to use thesimulator and would recommend its use.

Conflicts of Interest

None declared.

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c o m p u t e r m e t h o d s a n d p r o g r a m s

cknowledgements

he authors would like to thank the six participants who eval-ated the simulator and Govind Rehal who assisted with thereparation of figures. Funding for this work was providedy the Natural Sciences and Engineering Research Council ofanada to H.M. Ladak to support the stipend of B. Wheeleruring his graduate studies. B. Wheeler also received partialtipend support from the Precarn Scholars Program.

ppendix A.

urgical Simulation ScaleWe are seeking information on a virtual-reality-based sim-

lator for myringotomy training and use of similar training

Section A

1. Surgical residents and medical students should be provided withand-eye coordination prior to operating on patients.

1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disa2. Surgical residents and medical students should be provided withand-eye coordination as part of their medical education.1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disa3. The system that I have been exposed to is a good introduction tas a surgeon.1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disa4. The system that I have been exposed to permits development o

1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disa5. The system that I have been exposed to is useful for improvingmicroscope.1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disa6. Correct anatomical placement of the surgical incision is an imp

1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disa7. The visual representation of the ear drum (tympanic membranskills associated with myringotomy.

1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disa8. The visual representation of the ear canal provides sufficient remyringotomy.

1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disa

i o m e d i c i n e 9 8 ( 2 0 1 0 ) 130–139 137

approaches in medical education, and we are asking for yourinput. In Section A you will find 16 questions. Please provideyour rating to each of the questions using the 7-point scalelocated below the question. The scale ranges from a value of“1” (Strongly Agree) to a rating of “7” (Strongly Disagree); wehave also indicated descriptive terms for all other points onthe scale. Please note that a response of “4” indicates that youdo not agree or disagree with the statement. Your response toeach of these questions should be indicated by either placingand X through the number that best represents your opin-ion about a given question, or by circling that number; pleasechoose only whole numbers (do not provide a response thatfalls between two numbers). Please make sure that you answerall 14 questions. In Section B you will be asked to respond toseven Yes/No questions; please answer all of these questionsby circling your selection.

h structured classroom opportunities to finely develop their

5 6 7

greeDisagree Mostly Disagree Strongly Disagree

h independent, self-directed opportunities to develop

5 6 7

greeDisagree Mostly Disagree Strongly Disagree

o training basic hand-eye coordination skills that I will need

5 6 7

greeDisagree Mostly Disagree Strongly Disagree

f skills for accurate placement of a surgical incision.

5 6 7

greeDisagree Mostly Disagree Strongly Disagree

skills such as using a surgical instrument under a

5 6 7

greeDisagree Mostly Disagree Strongly Disagree

ortant requirement for performing a myringotomy.

5 6 7

greeDisagree Mostly Disagree Strongly Disagree

e) provides sufficient realism for training of basic surgical

5 6 7

greeDisagree Mostly Disagree Strongly Disagree

alism for training of basic surgical skills associated with

5 6 7

greeDisagree Mostly Disagree Strongly Disagree

138 c o m p u t e r m e t h o d s a n d p r o g r a m s i n

Appendix A (Continued )

9. The visual representation of the virtual surgical instrument provassociated with myringotomy.

1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disag10. The “mock” microscope models the important basic features o

1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disag11. The “mock” microscope is an adequate method for training bas

1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disag12. The motion tracker provides an acceptable representation of m

1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disag13. The physical instrument and the visor provide sufficient realis1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disag14. I would continue to use the system for training if it was readily1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disag15. I would recommend use of the system for training medical stu1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disag16. Use of visual simulation is a valuable part of surgical training.1 2 3 4Strongly Agree Mostly Agree Agree Neither

Agree/Disag

Section B

1. Is “force feedback” (feeling contact force) when in the virtual eaYes No

2. Is realistic ear canal geometry important for skill development?

Yes No

3. Is realistic eardrum geometry important for skill development?

Yes No

4. Is realistic simulation of bleeding important for skill developme

Yes No

5. Is the use of realistic colours and textures important for skill deYes No

6. Is realistic simulation of microscope movement important for sk

Yes No

7. Is realistic simulation of the mock microscope’s focus important

Yes No

b i o m e d i c i n e 9 8 ( 2 0 1 0 ) 130–139

ides sufficient realism for training of basic surgical skills

5 6 7

reeDisagree Mostly Disagree Strongly Disagree

f an actual surgical microscope.

5 6 7

reeDisagree Mostly Disagree Strongly Disagree

ic surgical skills.

5 6 7

reeDisagree Mostly Disagree Strongly Disagree

ovements associated with a surgical tool.

5 6 7

reeDisagree Mostly Disagree Strongly Disagree

m for training basic surgical skills.5 6 7

reeDisagree Mostly Disagree Strongly Disagree

available.5 6 7

reeDisagree Mostly Disagree Strongly Disagree

dents and/or surgical residents if it was readily available.5 6 7

reeDisagree Mostly Disagree Strongly Disagree

5 6 7

reeDisagree Mostly Disagree Strongly Disagree

r canal important?

nt?

velopment?

ill development?

for skill development?

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Soc. Am. 120 (2006) 3789–3798.[21] W.F. Decraemer, J.J.J. Dirckx, W.R.J. Funnell, Shape and

c o m p u t e r m e t h o d s a n d p r o g r a m s

Section CPlease circle your response.Which of the following statement best describes the simu-

ator’s level of difficulty in comparison to a real myringotomyrocedure?

Comparative Level of Difficulty

uch Less Somewhat Less Equal Slightly More Much More

lease provide any additional comments:

Thank you for your time and input!

e f e r e n c e s

[1] P.C. Coyte, R. Croxford, C.V. Asche, T. To, W. Feldman, J.Friedberg, Physician and population determinants of rates ofmiddle-ear surgery in Ontario, JAMA 286 (2001) 2128–2135.

[2] S. Baer, H. Williams, A. McCombe, A model for instruction inmyringotomy and grommet insertion, Clin. Otolaryngol.Allied Sci. 15 (1990) 383–384.

[3] A.O. Owa, R.W. Farrell, Simple model for teachingmyringotomy and aural ventilation tube insertion, J.Laryngol. Otol. 112 (1998) 642–643.

[4] M. Duijvestein, J. Borgstein, The Bradford grommet trainer,Clin. Otolaryngol. 31 (2006) 163.

[5] A. Leong, S. Kundu, P. Martinez-Devesa, C. Aldren, Artificial

ear: a training tool for grommet insertion and manualdexterity, ORL J. Otorhinolaryngol. Relat. Spec. 68 (2006)115–117.

[6] T. Walker, S. Duvvi, B.N. Kumar, The Wigan grommet trainer,Clin. Otolaryngol. 31 (2006) 349–350.

i o m e d i c i n e 9 8 ( 2 0 1 0 ) 130–139 139

[7] G. Riva, Applications of virtual environments in medicine,Methods Inf. Med. 42 (2003) 524–534.

[8] S.L. Dawson, J.A. Kaufman, Imperative for medicalsimulation, Proc. IEEE 86 (1998) 479–483.

[9] R.P. Frankenthaler, V. Moharir, et al., Virtual otoscopy,Otolaryngol. Clin. North Am. 31 (1998) 383–392.

[10] C.V. Edmond Jr., G.J. Wiet, B. Bolger, Virtual environments.Surgical simulation in otolaryngology, Otolaryngol. Clin.North Am. 31 (1998) 369–381.

[11] B. Pflesser, A. Petersik, U. Tiede, K.H. Hohne, R. Leuwer,Volume cutting for virtual petrous bone surgery, Comput.Aided Surg. 7 (2002) 74–83.

[12] G.J. Wiet, D. Stredney, Update on surgical simulation: TheOhio State University experience, Otolaryngol. Clin. NorthAm. 35 (2002) 1283–1288.

[13] T.A. Funkhouser, C.H. Sequin, Adaptive display algorithm forinteractive frame rates during visualization of complexvirtual environments, Proc ACM SIGGRAPH 93 Conf ComputGraphics (1993) 247–254.

[14] OGRE 3D: Open source graphics engine, www.ogre3d.org,last accessed on October 14, 2009.

[15] Open Dynamics Engine, http://www.ode.org.[16] Object Oriented Input System,

http://sourceforge.net/projects/wgois/.[17] File: Normales Trommelfell.jpg - Wikimedia Commons,

http://commons.wikimedia.org/wiki/File:NormalesTrommelfell.jpg.

[18] D.H. Keefe, J.C. Bulen, K.H. Arehart, E.M. Burns, Ear-canalimpedance and reflection coefficient in human infants andadults, J. Acoust. Soc. Am. 94 (1993) 2617–2638.

[19] P.J. Berkelman, Z.J. Butler, R.L. Hollis, Design of ahemispherical magnetic levitation haptic interface, in:Proceedings of the ASME Dynamics Systems and ControlDivision, DSC, Vol. 58, 1996, pp. 483–488.

[20] L. Qi, H. Liu, J. Lutfy, W.R.J. Funnell, S.J. Daniel, A nonlinearfinite-element model of the newborn ear canal, J. Acoust.

derived geometrical parameters of the adult, humantympanic membrane measured with a phase-shift moireinterferometer, Hear. Res. 51 (1991) 107–121.