Method for Navigation and Control of a Magnetically Guided CapsuleEndoscope in the Human Stomach

Henrik Keller, Aleksandar Juloski, Hironao Kawano, Mario Bechtold, Atsushi Kimura, Hironobu Takizawaand Rainer Kuth

Abstract— The use of flexible endoscopes is the standardscreening method for the upper gastrointestinal tract today.Disadvantages for the patient, due to the insertion process andoften applied sedation, can be overcome with wireless capsuleendoscopy (WCE). But WCE is not suited for the stomach asit can not guarantee a complete screening having no activeguidance. With the magnetically guided capsule endoscopy(MGCE) a novel minimal invasive screening method for thegastrointestinal tract is being developed. With its current focuson the human stomach comes the need for a navigation andcontrol method that is specialized for this application and itsconstraints. We present a new method for screening a water-filled stomach with 10 functions for basic capsule movements,special maneuvers and mode-changes. Its evaluation was donein a clinical study consisting of 53 patient and volunteercases. The individual evaluation of each function included astatistical analysis and an operators’ survey. The functionsproved sufficient to reach all parts of the stomach and to acquireclose-up views of the mucosa.

I. INTRODUCTIONThe standard examination procedure for the upper gas-

trointestinal tract (GI) today is gastroscopy with flexibleendoscopes. But this procedure has disadvantages for thepatient, due to the insertion process and the often applied se-dation. With the introduction of wireless capsule endoscopy(WCE) in 2001 a new screening method with high patientcomfort became available [1]. A small capsule with camerasinside is swallowed and transmits its images to a storagedevice outside the body. But WCE is mainly used for thesmall intestine [2] and is not suited for stomach screening.Reason is the passive motion of the capsule by peristalsisand gravity with no control over its position or orientation.This control is necessary as the large volume of the stomachdoes not guarantee a full examination when relying solelyon random positioning. A promising approach is the useof magnetic forces to steer capsules in the GI tract. Mostresearch on this topic concentrates primarily on the intestineas in [3], [4], [5], [6], [7], but some works focus solely

The authors would like to thank J.F. Rey, I. Pangtay (Institut ArnaultTzanck, Saint-Laurent-du-Var, France), H. Ogata, N. Hosoe, T. Hibi (KeioUniversity School of Medicine, Tokyo, Japan), K. Ohtsuka, N. Ogata, S.Kudo (Showa University Northern Yokohama Hospital, Yokohama, Japan),K. Ikeda, H. Aihara and H. Tajiri (The Jikei University School of Medicine,Tokyo, Japan) for conducting the clinical study and their helpful support.

H. Keller is with Institut for Process Control and Robotics, KarlsruherInstitut for Technology, Karlsruhe, Germany and Siemens Healthcare, Er-langen, Germany

A. Juloski, M. Bechtold, R. Kuth are with Siemens Healthcare, Erlangen,Germany

H. Kawano, A. Kimura and H. Takizawa are with Olympus MedicalSystems Corp., Tokyo, Japan

Corresponding author: H. Keller (keller.h@gmail.com)

on the stomach [8], [9]. With their minimal invasivenessthese solutions are actively contributing to the research-fieldof medical micro-robotics, which future heavily relies on aversatile steering mechanism as discussed in [10], [11] andwith further approaches published in [12], [13], [14], [15].

In this work we present a new method for navigationand control in Magnetically Guided Capsule Endoscopy(MGCE) used in a prototype system jointly developed byOlympus Medical Systems Corp. and Siemens Healthcare.The system includes a guidance magnet designed to generatea magnetic field of low intensity to steer a capsule endo-scope with two cameras in a water-filled human stomach.For the presented method the unique characteristics of thestomach were analyzed to create automated field sequencesas guidance functions, which on one side allow capturingoverview and close-up images of the whole stomach wall andon the other side give intuitive control over the system witha corresponding user interface. The resulting 10 functionsinclude basic capsule movements, special maneuvers andmode-changes. They are based on 5+1 degrees of freedom(DOF) of which the magnetic steering can be done in fivedegrees and one is achieved by turning the patient in theguidance magnet. To evaluate the prototype system and thepresented method a clinical study was conducted. It consistedof 53 patient and volunteer cases. With the medically relevantresults published in [16] and [17] the performance of thenavigation and control method is presented here.

a)

b) c)

Fig. 1. MGCE prototype with a) capsule endoscope b) guidance magnetand c) user interface

The Fourth IEEE RAS/EMBS International Conferenceon Biomedical Robotics and BiomechatronicsRoma, Italy. June 24-27, 2012

978-1-4577-1198-5/12/$26.00 ©2012 IEEE 859

II. NAVIGATION CONCEPT AND CONTROLDESIGN

A. MGCE System

The MGCE system is a joint development of OlympusMedical Systems Corp. and Siemens Healthcare. It consistsof the capsule endoscope, the guidance magnet and the userinterface (see Fig.1). The guidance magnet with a footprintof about 1m x 2m has a patient table attached that can beautomatically or manually driven inside the bore to positionthe patient’s stomach in the center of the working volume.

1) Guidance Magnet: The guidance magnet consists of anassembly of electromagnetic coils surrounding the workingvolume. Its development at Siemens started based on thework in [18], [19]. It is designed for the guidance in thehuman stomach, where the concept of the capsule’s move-ment is based on using a liquid as the travelling medium.Water is used to expand the stomach and has the additionaleffect of reducing friction forces on the wall. In comparisonto a conventional MRI system (3T) the necessary magneticflux density is about 30 times smaller with a maximum of100mT. This also reduces the MRI-typical risks of bringingferro-magnetic objects near the system significantly.

The guidance magnet produces the external magnetic fieldB described with its components Bx, By and Bz . Here x,y and z indicate the axes of the Cartesian coordinate systemdefined in relation to the coil assembly. If a permanentmagnet with its dipole moment m is placed somewhere in theworking volume a torque T = m×B tries to align it parallelto the direction of B at this point. As the magnetic element isfixed to the capsule endoscope the direction of B allows thecontrol of the capsule’s rotation in 2DOF. A third rotationalDOF is not available as the rotation around m can not bemagnetically controlled. By overlaying a field gradient on thebase magnetic field B an additional force F can be producedthat can be used for the capsule’s translational movement inanother 3DOF. In this case is

F = (∇B) ·m =

∂Bx

∂x∂By

∂x∂Bz

∂x∂Bx

∂y∂By

∂y∂Bz

∂y∂Bx

∂z∂By

∂z∂Bz

∂z

·mx

my

mz

(1)

For our application’s calculations the magneto-static casecan be assumed as the magnetic field does not change rapidly.In this case the Maxwell Equations state that the rotation anddivergence of B are zero which implies matrix ∇B to besymmetric and trace-free:

∂Bx

∂y =∂By

∂x , ∂Bx

∂z = ∂Bz

∂x ,∂By

∂z = ∂Bz

∂y , ∂Bz

∂z = −∂Bx

∂x −∂By

∂y

(2)

⇒ F =

mx∂Bx

∂x +my∂By

∂x +mz∂Bz

∂x

mx∂By

∂x +my∂By

∂y +mz∂Bz

∂y

mx∂Bz

∂x +my∂Bz

∂y −mz∂Bx

∂x −mz∂By

∂y

(3)

The magnetic field produced by the coils can be calculatedwith the Biot-Savart law for fixed points in space. The fieldand its partial derivatives depend here linearly on the coils’

currents I = (I1, . . . , In)T for a number of n coils. With

V ∈ R8×n a new matrix is defined for this calculation:(Bx By Bz

∂Bx

∂x∂By

∂x∂Bz

∂x∂Bz

∂y∂By

∂y

)T= V · I

(4)So matrix V depends on the coils’ geometry and their

arrangement as well as on the point in the working volumethis calculation is done for. This point should typically be theposition of the capsule, which would have to be tracked. Butit is possible to lose this requirement by using one static pointin the center of the working volume for the calculations. Thisresults in a smaller effective working volume in which themagnetic field and field gradients are homogenous enoughfor the capsule guidance. But it reduces the complexity ofthe system and the single-use capsule significantly.

Finally it is possible to describe the relation between thecurrents I to B and F in one equation:BxByBzFxFyFz

=

1 0 0 0 0 0 0 00 1 0 0 0 0 0 00 0 1 0 0 0 0 00 0 0 mx my mz 0 00 0 0 0 mx 0 mz my

0 0 0 −mz 0 mx my −mz

·V ·I(5)

Fig. 2. Schematic illustration of the guidance magnet as a 12-coil system.The numbers indicate the different electromagnetic coils (source: [20]).

In conclusion the design of the guidance magnet dependson the desired effective working volume and on the realiza-tion of the three B components and the five partial derivatesneeded for the gradient field producing F .

Fig.2 shows a schematic illustration of the guidance mag-net as a 12-coil system matching these requirements. Thepatient lies along the z-axis and the working volume iscentered between coils 1-6. All coils are paired, indicated byconsecutive numbers. The pair of coils 1-2 allows to generateBx and ∂Bx/∂x, coils 3-4 generate By and ∂By/∂y, andcoils 5-6 the needed Bz . Coils 7-8 are used for ∂By/∂x, coils9-10 for ∂Bz/∂y, and coils 11-12 for ∂Bz/∂x. Equation (5)is for the wanted six values of B and F an underdeterminedsystem with an infinite number of solutions. This allows

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imposing additional conditions to obtain a unique solutionfor the coil currents, such as minimizing dissipated power.

On this basis the further development of the presentedmethod consisted on defining automated series of magneticfields described by B and F , which depend on the currentsystem state and an additionally to define possible user input.

2) Capsule: The capsule endoscope is in size 31mmlong and 11mm in diameter and is designed for single use.It has two CCD chip sensors each located at one of itstransparent ends and each surrounded by six white LEDsproviding light by flashing. The sensors take images in turnproducing together 4 frames per second (fps). Typical imagesof the stomach and pathologies can be seen in Fig.3. Thecapsule further includes batteries, a processing chip anda radio transmitter to send the data to antennas fixed tothe patient’s torso. A small permanent magnet is the lastimportant component inside the capsule, enabling the controlwith the magnetic field in 5DOF. If no magnetic forcesare applied the capsule is designed to swim upright withone sensor facing up- and one downwards. This way thecapsule is kept stable in the third rotational degree that isnot magnetically controllable.

3) Graphical User Interface: For the operator a graphicaluser interface (GUI) is available that spreads over twomonitors (Fig.1c). The right one shows the images takenby the capsule simultaneously side by side. It updates theimages in turn, displaying the 2fps for each sensor. It alsogives different examination specific information with e.g. theduration or the patient data. The left one gives additionalinformation useful for the navigation such as the capsule’sorientation as expected with the known B-field.

Fig. 3. Images taken with the guided capsule endoscope showing a)overview on stomach body, b) close-up view on mucosa, c) close-up viewon cardia, d) multiple ulcers, e) gastritis and white mucus, f) polyps

B. Application Analysis for Stomach Screening

For the development of a suitable method for navigationand control for the MGCE different aspects had to be takeninto account.

With the described magnetic field the steering of thecapsule can be done in 5 degrees of freedom, consistingof 2 rotational and 3 translational DOF. Without capsuleposition tracking its orientation is being assumed by the

direction of the B-field at its fixed calculation point. Aspecial characteristic of MGCE is that by turning the patientto different lying positions, the workspace itself can berotated. This gives one more degree of freedom. As thepatient does not require any sedation for the MGCE, theturning can be done without help and the examination timeis not lengthened significantly.

The workspace of the MGCE is the human stomach withunique characteristics. With its form shaped like a “J” itsinner walls are round and covered with folds. When fillingthe stomach with water these folds extend and flatten out butdo never vanish completely (see Fig.3a). When turning thepatient the weight of the water extends the lowest part ofthe stomach the most. So depending on the patient positiondifferent regions of the stomach can be examined better.The water is also used as the travelling medium for thecapsule endoscope. With its help the capsule’s buoyancyreduces the effect of gravity and friction against the mucosa,so forces of less than 1mN are usable for the translationalmovement. In general is a slow movement speed of thecapsule advantageous for a stable navigation with 4fps. Butthe stomach contracts from time to time as part of thedigestive process. Depending on the contraction’s strengththis can effect the capsule’s position.

These constraints had influence on the development of thecapsule movement design and the user interface as discussedin the following section.

C. Design of Capsule Movements and Maneuvers

The different capsule movements and maneuvers as illus-trated in Fig.4 were designed under the requirement to cap-ture overview images and if necessary close-up screenings ofthe whole stomach wall, the mucosa. At the same time theresults had to allow a compatible user interface for intuitivecontrol and short examination times.

As discussed earlier a static point in the center of theworking volume is used for the magnetic field calculationsso tracking of the capsule position is not necessary. With in-creasing distance to this point the field varies from its desiredvalues, which can result in unwanted translational drifts ofthe capsule. In a series of phantom and pig stomach studies itwas shown that with the capsule in contact with the mucosait can be kept stable allowing it to tilt and rotate withoutdrifting away from the observation position. Following thisconclusion the decision was made to constantly generate avertical force with Fy that either pulls the capsule down-(Bottom-mode) or upwards (Top-mode) against the mucosa.The force needs to be strong enough to keep a stable position,but weak enough to still allow horizontal movement alongthe wall. This concept relies on the possibility to turn thepatient, so the side walls can become top and bottom.

The Top- and Bottom-mode in general are the basis for thecapsule control concept. To create an intuitive user interfaceit is important that now one of the translational DOF isreduced to discrete states that can be controlled with digitalbuttons. This way the use of a single joystick with only 2-axes and a minimum of 5 digital buttons became possible

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θ φ

Fig. 4. Capsule movements and maneuvers (all in Bottom-mode exceptTop-mode drawing). Approach is illustrated with upper camera active.

for the basic capsule movements. The left-right axis of thisjoystick can now be used to control the Rotation around thevertical y-axis with angle θ allowing the user to look leftor right and the forward-backward axis of the joystick cancombine the horizontal translational DOFs Fx and Fz . Bymaking them depend on θ the motion’s direction is alongthe cameras’ optical axes projected on the x-z-plane resultingin a Forward/Backward move from the camera’s perspective.With the joystick handle the horizontal force can be graduallyincreased to adjust to the capsule’s friction and frame rate.From the camera’s perspective the Tilting move is the way tolook further up or down. In the studies it proved helpful tostart the examination with a capsule’s tilting angle φ of 45◦

so the user gets an intuitive feeling for what is forward andbackward. Angle φ can be raised or lowered with two digitalbuttons that integrate its value over the time they are pressed.Both capsule camera views are displayed simultaneously onthe GUI and the user can focus on any of them for thenavigation. But Forward/Backward and Tilting up/down arereversed in those views. For this reason a Camera Selectionbutton became necessary that inverts these movements. Theremaining two buttons are needed for the Top- and Bottom-mode. Two instead of one button were chosen as they canturn one mode on and when kept pressed can generate anincreased force for the vertical motion.

Pig stomach studies showed that in some situation the ba-sic movements were not sufficient for a complete screening.For this reason special maneuvers were developed. The firstmaneuver became necessary as stomach folds do not vanishcompletely in an extended stomach. To pass those folds andother anatomical obstacles a Jump maneuver was introduced,that can also be used to move along a steep wall and reachhigher or lower areas of interest. The longer the associatedbutton is pressed the higher the jump. While in Bottom-mode

the jump is upwards it is downwards in Top-mode. The onlyforce component changed when jumping is Fy . The x-z-forces are still controllable with the joystick handle, whichallows the user to influence the horizontal direction of thejumps. While jumps can also be used to quickly observe aclose-up view from some more distance, changing the jumpsspeed became of interest. With two buttons the speed can beset in 10 steps, where 10 is the fastest and default setting.

A second special maneuver is Approach. When triggeredby pressing and holding a button, F is calculated with:FxFy

Fz

=

gx · cos(φ− π2 −

π4 · Joyy) · cosθ

gy · sin(φ− π2 −

π4 · Joyy)

gz · cos(φ− π2 −

π4 · Joyy) · sinθ

(6)

This results in a movement of the capsule along theoptical axis of the currently selected camera. The vectorg = (gx, gy, gz)

T represents the maximal forces for eachF component and depends on the camera. For the uppercamera it differs from the lower in being negated and havinga reduced norm. Joyy is the joystick input in [−1, 1] forBackward/Forward. The maneuver was developed to acquireclose-up images of areas which are hard to reach with theother functions. They are typically convex regions like thelesser curvature near the stomach entrance. Such areas onlyhave to be put in the center of the vision by adjusting φ and θbefore approaching. When Approach is active, changes canstill be made to the tilting and rotating angle to influencethe direction of the optical axis and adjust the approachedposition for a better close-up view.

A third maneuver is Parking. After pressing the designatedbutton an automated series of magnetic fields is activated.First the direction of B described by angles θ and φ is resetto default values of 90◦ and 45◦ with which the lower camerafaces in the direction of the patient’s head. Further a shortpull up of the capsule to move it into Top-mode is applied,after which a magnetic gradient field is generated thatindependently of the current capsule’s positions steers it withlow force toward the center of the working volume. Parkingthe capsule this way allows restarting the examination froma predefined position and orientation of the capsule.

D. Joystick Layout and Function Mapping

Fig. 5. The two 2-axes joysticks of the MGCE prototype

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To remain versatile and allow testing of further functionsthe use of two 2-axes joysticks with each having 14 but-tons was chosen for the MGCE prototype (see Fig.5). Thejoysticks are medically approved input devices developed bySiemens and connected to the control system with a CAN-bus using the CANopen protocol. They each offer 5 buttonsat the joystick handle bar and 9 more arranged as a 3x3 arrayon the joysticks’ base. The latter are flat round buttons forwhich icons were designed as part of this work representingtheir functionality. Each button has one or more underlyingLEDs which were programmed to give different feedback ifand how a function is currently in use.

The mapping of the functions is shown in Fig.6. Twofunctions seen here were not explained so far. In the centertop of each button array, the On/Off -buttons are located thatcontrol if magnetic forces are generated or not. The ImageCapture-buttons on the top of the handle bars can be usedto capture a still image of the current capsule view for laterreviews. The right joystick is mapped with all main functionsdescribed in the previous section. The left joystick offersthe additional functionality of the sideways movement whenmoving the handle left/right and two buttons on the joysticksbase serve for setting the jump speed.

Fig. 6. Mapping of the functions on the right joystick

III. EVALUATION IN CLINICAL STUDY

The method for navigation and control was developedand evaluated in several steps. Concepts were first evolvedwith virtual reality simulations of the MGCE. Testing andfurther development were done using the MGCE prototypewith aquariums and silicon-based stomach phantoms. Theresults were then finalized in repeated trials with pig-stomachpreparations to allow their use in the clinical study withpatients and volunteers.

The clinical study was conducted at the Institut ArnaultTzanck, Saint-Laurent-du-Var, France in collaboration withthree Japanese institutions, namely the Keio University

School of Medicine, Tokyo, the Showa University NorthernYokohama Hospital, Yokohama, and The Jikei UniversitySchool of Medicine, Tokyo. The medically relevant resultsare published in [16]. The study included 53 cases with 29volunteers (23 men, 6 women; mean age 42 years, range24-60) and 24 patients (19 men, 5 women, mean age 52years, range 25-74). The participant preparation started withfasting from the previous midnight on. At 75 minutes beforethe examination the volunteer or patient would drink 500mlclear water of room temperature and around 60min lateranother 400ml, shortly after followed by 400ml at bodytemperature (1.3 liters in total). Then the activated capsulewas swallowed. With the antenna pads attached, the partic-ipant laid down on the patient table and was driven insidethe guidance magnet to a predefined position centering thestomach horizontally. The procedure started with the patientturned to the left-lateral position. After sufficient image datawas collected the position was turned to supine (lying onback) and later to right-lateral. Sometimes additional positionchanges took place to achieve better results by extending thestomach differently.

During the examination all system states and outputs givento the user were logged as well as all inputs of the twojoysticks. A statistical analysis of all examinations was doneto evaluate the navigation and control. Apart from theseobjective facts a survey was done with the eight participatingdoctors to get their subjective feedback as operators. Lastlythe doctors also documented the visualization completenessof the different parts of the stomach after each examination.

A. Results of Method in Clinical Study

All navigation and control functions worked in the humanstomach according to their design. Difficulties in their usearouse in two cases when strong stomach contractions oc-curred, that changed the capsules’ positions and narrowed thespace for capsule movement. In the other examination casesthe stomach was expanded wide enough for all functionsto work. Additional water was given only to a few patientsto re-expend the stomach. In three cases high amounts ofmucus limited the capsule’s view or movement. Turning thepatient, drinking more water or moving the capsule rapidlysolved similar problems in other cases where less mucus waspresent. In one case technical defects did not allow adequatevisualization. Leaving this case aside the visualization wasdue to the mentioned difficulties complete with 96% forgastric pylorus, 98% for antrum, 96% for body, 73% forfundus, and 75% for the cardia (cf. [16]).

1) Statistical Analysis: The statistical analysis of the userinputs is summarized in Table I. It lists for all availablefunctions five results: 1. The mean number of uses in anexamination shows how frequent a function was activated.2. The mean amount of time the function was used in anexamination gives the information on how long the functionwas used after activation. 3. The usage percentage is the timethe function was used over the length of all examinations.4. The uses per minute show how often a function wasactivated in average per minute. 5. The number of patient

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TABLE ISTATISTICAL RESULTS OF METHOD IN CLINICAL STUDY

Function # uses use time usage uses unused in(mean) (mean) (%) per min # exams

Rotate 146.9 552.0s 33.3 5.32 1 (1.9%)

Tilt 76.9 80.3s 4.8 2.78 2 (3.8%)

Fwd/Bck 92.4 406.2s 24.5 3.35 1 (1.9%)

Sideways 11.1 14.9s 0.9 0.40 23 (43.4%)

Top/Bottom 12.1 n/a n/a 0.43 0 (0.0%)

Camera 10.0 n/a n/a 0.36 5 (9.4%)

Jump 16.9 31.7s 1.9 0.61 3 (5.7%)

Approach 15.3 61.8s 3.7 0.56 9 (17.0%)

Park 0.45 3.6s 0.2 0.02 41 (77.3%)

Jump Force 2.7 n/a n/a 0.09 38 (71.7%)

and volunteer cases the function was unused is an importantindication on the necessity of a function to complete anexamination. Results 2. and 3. could not be measured forthree functions, as these change a setting or mode and donot have a duration.

Fig. 7. Typical stable capsule positions with the new navigation methodsimulated in virtual reality [21] (patient in left-lateral): a) Bottom-mode ongreater curvature, b)/c) Top-Mode in fundus/antrum, d) reached with Jump,e) cardia reached with Approach

The functions used the most were Rotate and For-ward/Backward (Fwd/Bck) as the usage of 33.3% and 24.5%clearly shows. Both remained unused in only one case, whichhad to be cancelled early due to a technical defect. The thirdhighest used function is Tilting with a much lower usage of4.8%. These results are partly due to the fact that the threefunctions are placed directly on the right joysticks handle,making their use easy to access. But the main reason is thatover the time of the clinical study an effective new methodfor navigation became commonly used by the operators. Theoperator would use Fwd/Bck to reach a position where thecapsule could be kept stable and use Rotate there to orientate,to screen the area, and to decide on the next position toreach. Fig.7 shows such positions with the patient in left-lateral position. With a default tilting angle of 45◦ andthe wide camera angle, tilting was not always necessary toacquire sufficient images. After screening in this position

TABLE IISURVEY RESULTS OF CLINICAL STUDY

Function How much is this How many timesfunction needed to do you use thisto complete a full function during

examination? one examination?1=no need, 5=high need 1=never, 5=very often

Rotate 5.00 5.00

Tilt 4.88 4.88

Fwd/Bck 4.75 4.63

Sideways 2.75 2.63

Top/Bottom 4.63 3.75

Camera 4.63 4.63

Jump 3.25 2.88

Approach 4.88 4.63

Park 2.13 1.38

Jump Force 3.00 2.13

Fwd/Bck would be used again to get to the next stableposition. With enough positions reached the operator wouldswitch Top-/Bottom-mode to repeat this navigation method inthe other mode, before turning the participant’s to the nextposition. Although the mean number of uses for the Top-/Bottom-mode is with 12.1 rather low, it was used in everyexamination of the study, showing its importance. For thisnavigation method the used camera was switched in average10 times per exam or about every 3 minutes.

The special capsule maneuvers produced mixed results.The most accepted maneuvers were Jump and Approach with16.9 and 15.3 mean uses per case. Since Approach can beactive for a long time to stay at one position its mean use timeand usage percentage are almost twice as high compared tojumping, which is usually a rather short maneuver. Jumpingproved helpful in cases the capsule was stuck in or at gastricfolds and was used in almost all examinations. Approach onthe other hand became the method of choice when observingthe stomach entrance, the cardia. With the patient in the left-lateral position, the capsule would be navigated in Bottom-mode to the greater curvature where by selecting and aimingthe upper-camera at the cardia, Approach was activated tocapture a close-up view as seen in Fig.3c). Parking wasthe least used special maneuver with 0.2% usage. In 77.3%of all examinations it was not activated once. Also oftenunused remained the functions on the left joystick. Settingthe jump force was not used in 71.7% and moving thecapsule sideways in 43.4% of all examinations.

2) Operator Survey: The result of the operators surveyare summarized in Table II. The survey was done after all53 cases of the clinical study were completed. It consistedof two questions. The first was “How much is this functionneeded to complete a full examination?”. It had to beanswered for all joystick functions on a scale from 1 “notat all needed” to 5 “always needed”. Similar answers had tobe given for the second question “How many times do youuse this function during one examination?”. The scale herewas from 1 “never” to 5 “very often”. The survey’s resultsstrengthen most of the statistical results with the subjective

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view of all eight operators participating in the study. Rotate,Tilt and Fwd/Bck rank very high as most needed and usedfunctions, while Sideways, Park and Jump Force are lowest.In the statistical results Jumping and Approach had quiteequal results. In the survey the results differ. Here Jumpingwas rated quite low (3.25, 2.88). Approach (4.88, 4.63) onthe other hand ranks almost as high as Tilting, showing thatit was received well by the operators.

IV. CONCLUSIONS AND FUTURE WORK

With the magnetically guided capsule endoscopy a novelminimal invasive screening method for the gastrointestinaltract is being developed. With its current focus on stomachexaminations comes the need for a new navigation andcontrol method that is specialized for this application andits constraints. The newly developed method presented hereincludes 10 functions for basic capsule movements, specialmaneuvers and mode-changes. By purposely excluding cap-sule position tracking, the complexity of the guidance magnetand capsule is reduced. The disadvantages are unwantedcapsule drifts in the outer parts of the working volume. Theseare compensated by introducing Top-/Bottom-mode to keepthe capsule in contact with the mucosa for stability.

In a clinical study consisting of 53 cases, the functionsproved sufficient to reach all parts of the stomach and toacquire close-up views of any part of the mucosa. Difficul-ties remained though when the stomach was not expandedenough or mucus was blocking the view or movement. Theseproblems need to be solved and might require a change inpatient preparation, as they can only be partially addressedby an improved control method. The statistical analysisand the operator’s survey showed that the functions Rotate,Forward/Backward, Tilt, and Top-/Bottom-mode are in thisorder the most necessary ones for a complete examination.The Camera Selection function was important for intuitivecontrol with the simultaneous display of two views. Of thespecial maneuvers Approach had the best survey results, as itallows quick captures of close-ups, especially of the cardia.The Jump function, although often used, received decentresults in the survey. The functions sideway movement, Parkand Jump Force setting received the lowest statistical andsurvey results and, if kept, need to be improved.

The results of this work are the basis for the currentlyinvestigated improvements of the navigation and controlmethod. But very importantly they define the requirementsfor the future development of an autonomous control systemwhich requires a most robust capsule guidance to automat-ically scan the whole organ. Here the combination withimage processing as e.g. demonstrated in [22] for automaticpathology detection will be one more step towards this goal.

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