a tele-operated mobile ultrasound scanner using a light-weight

50 IEEE TRANSACTIONS ON INFORMATION TECHNOLOGY IN BIOMEDICINE, VOL. 9, NO. 1, MARCH 2005

A Tele-Operated Mobile Ultrasound ScannerUsing a Light-Weight Robot

Cécile Delgorge, Fabien Courrèges, Lama Al Bassit, Cyril Novales, Christophe Rosenberger, Natalie Smith-Guerin,Concepció Brù, Rosa Gilabert, Maurizio Vannoni, Gérard Poisson, and Pierre Vieyres

Abstract—This paper presents a new tele-operated roboticchain for real-time ultrasound image acquisition and medicaldiagnosis. This system has been developed in the frame of theMobile Tele-Echography Using an Ultralight Robot EuropeanProject. A light-weight six degrees-of-freedom serial robot, witha remote center of motion, has been specially designed for thisapplication. It holds and moves a real probe on a distant patientaccording to the expert gesture and permits an image acqui-sition using a standard ultrasound device. The combination ofmechanical structure choice for the robot and dedicated controllaw, particularly nearby the singular configuration allows a goodpath following and a robotized gesture accuracy. The choice ofcompression techniques for image transmission enables a com-promise between flow and quality. These combined approaches,for robotics and image processing, enable the medical specialistto better control the remote ultrasound probe holder system andto receive stable and good quality ultrasound images to make adiagnosis via any type of communication link from terrestrialto satellite. Clinical tests have been performed since April 2003.They used both satellite or Integrated Services Digital Networklines with a theoretical bandwidth of 384 Kb/s. They showed thetele-echography system helped to identify 66% of lesions and 83%of symptomatic pathologies.

Index Terms—Image compression and filtering, medicalrobotics, mobile communication, remote center of motion, ultra-sound images.

I. INTRODUCTION

ROBOTIZED telemedecine offers great medical advan-tages for medical experts who want to perform skilled

actions, from an expert center for the benefit of a remotelylocated patient [1]–[3]. Robotic applications, such as forminimally invasive surgical interventions, help in reducingrisks of damaging delicate anatomical parts; for noninvasiveand invasive techniques such as guided biopsy, teleroboticsbrings accurate displacement of distant tools for the benefitof remotely located patients. Among all medical imagingtechniques, echography examination offers quick and reliablenoninvasive diagnosis for many pathological situations. Itallows a specialist to evaluate the degree of emergency fora patient. However, it is a skilled and “operator-dependent”technique. In areas with poor or reduced medical facilities, inisolated sites, in difficult accessible areas, and sometimes inemergency cases, there is not always an ultrasound specialist onhand to perform the first echography from which an emergency

Manuscript received August 29, 2003; revised May 6, 2004. This work issupported by the European Commission under Contract IST-2001-32516.

The authors are with Laborotoire Vision and Robotics, University of Orleans,Bourges 18020, France (e-mail: [email protected]).

Digital Object Identifier 10.1109/TITB.2004.840062

prediagnosis could be made. For these cases, a proposed alter-native to guarantee a reliable ultrasound examination is to use atele-operated robotized echography system. To guarantee a re-liable tele-examination and, therefore, diagnosis, it is importantfor the medical expert to forget about the distance between himand the patient. As a consequence, the remote control accuracyof the robot, the replica of the expert gestures by the robot,and the quality and flow of the received ultrasound imagesare correlated elements. They are needed by the expert in thefeedback control loop of the overall robotized tele-echographychain and necessary for the feasibility of the diagnosis.

During the last five years, several laboratories have been in-volved with the development of robotic tele-echography appli-cations; for most of these, the challenge has been the combina-tion of the robotic performances or the quality of the transmittedimage [4]–[7]. Most of these projects introduced parallel robotsto fit the medical requirements of a tele-echography examinationover the abdominal area of the remote patient. They are usuallyinstalled on the patient and cover the whole anatomical area.

A different approach is proposed with the Mobile Tele-Echography Using an Ultralight Robot (OTELO) EuropeanProject. The main objectives of the OTELO system are toperform, in real time, a robotized echography examination on aremotely located patient, using any type of communication linkfrom terrestrial to satellite. The main concern is to combine thedevelopment of a light-weight robot with appropriate imagecompression techniques to offer the medical specialist a per-forming tool for an efficient hand-to-eye coordination duringthe robotized tele-echography examination.

Ultrasound images and probe-holder robot are two importantelements of the overall tele-echography chain. They are depen-dent from each other and they contribute to make the systemtransparent for the expert who is the major actor of the tele-operated control loop.

The expert controls the remote probe holder robot by com-bining the one degree-of-freedom (DOF) hands-free input de-vice orientation and the received information. This informationincludes the ultrasound images and the position of the robot onthe patient’s body. When considering an ideal communicationlink, there is no time delay between the emission of the realprobe position data and the reception of the received image.Therefore, the real ultrasound plane position corresponds, atany time, to the desired one given by the input device held bythe expert. In a real tele-operated scenario, one should expecttime delay in the communication link combined with a non-negligible response time of the robotics and electronics system.The received ultrasound images do not correspond any longer to

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DELGORGE et al.: TELE-OPERATED MOBILE ULTRASOUND SCANNER USING A LIGHT-WEIGHT ROBOT 51

Fig. 1. OTELO mobile robotized tele-echography chain.

the desired ultrasound plane position given by the input device.The quality of the ultrasound image can also be altered by thechosen compression technique required by the communicationlink bandwidth. The resulting hand-to-eye coordination is thenhindered.

Therefore, the development of the robotics system is stronglylinked with ultrasound image study when considering the per-formances of the tele-operated global chain. The general spec-ifications of the OTELO system are described in Section II.Sections III and IV present the requirements for the robot me-chanical structure and the control law management. Image pro-cessing techniques chosen for ultrasound images to be sent viathe available communication link are introduced in Section V.Clinical tests were performed in Barcelona Hospital and the re-sults are presented. Conclusions and future work are given inSection VII.

II. OTELO SYSTEM GENERAL ARCHITECTURE

AND SPECIFICATIONS

The OTELO chain consists of three parts (Fig. 1).

1) The expert station where the medical expert remotely con-trols, with a dedicated one-DOF hands-free input device(also called fictive probe) fitted with a six-DOF localiza-tion sensor, the positions and orientations of the distantultrasound probe located on the patient’s skin. The spe-cialist receives, in almost real time depending on the avail-able bandwidth, the patient’s ultrasound images. The in-formation received at the expert station is integrated in anergonomic graphic user interface. Furthermore, a video-conferencing system between the two stations enables theexpert, the paramedic, and the patient to communicatewith each other during the robotized tele-echography ex-amination.

2) The patient station is constituted of a light-weightsix-DOF serial robot that holds the ultrasound probeavailable at the patient site, a compact ultrasound device,a control and communication portable unit, and a video-conferencing system. A paramedic assists the patient. Hepositions the light-weight robot on an anatomic referencepoint on the patient’s skin according to the medicalexpert’s instructions and maintains it during the exam-ination. A strain gauge force sensor, embedded in theprobe holder, measures the contact force between the realprobe and the patient’s skin. The robot controller enables

Fig. 2. Patient and probe positioning for abdominal and renal ultrasoundinvestigations.

to limit this force to 20 N for the patient’s comfort andsafety. Medical images from the ultrasound device arecompressed before being sent to the expert. The patientstation is mobile, that is easily transportable, and can bequickly set up on the spot of use and connected to anyavailable communication infrastructure using transmis-sion control protocol/Internet protocol and unreliabledata protocol modes.

3) The communication link, data exchanged between the twostations, expert and patient, include ultrasound images,robot controls, haptic information, ambient images, andaudio instructions. Most of the bandwidth is used for ul-trasound or ambient image transfer. Terrestrial links [e.g.,Integrated Services Digital Network (ISDN)], fixed andmobile satellite solutions, or 3G technologies (e.g., Uni-versal Mobile Telecommunications System) with variousbandwidth are currently being tested in the frame of theOTELO project.

III. ROBOT SPECIFICATIONS

A. Study of Probe Motion During a Standard Exam

Standard ultrasound examinations have been analyzed inorder to quantify the positions, movements, and velocities ofthe probe used by ultrasound specialists.

Fig. 2 shows the required probe positioning and positions thatthe patient has to be set in for various ultrasound investigations:cardiac, abdominal, and renal. These are prime aspects takeninto account in the design of the serial six-DOF robot for theprobe positioning and for its handling during the robotized tele-echography.

During these specification studies, interesting points havebeen reported: Continuous contact is kept between the probeand the skin, even when the probe is applied on ribs and irreg-ular abdominal skin. The contact force value varies from 5 to20 N. As shown in Fig. 2, the probe is most often held closeto the normal direction of the skin except in some cases, suchas in bladder investigation, where the probe can be tilted up to60 from the normal direction of the skin. Once the probe ispositioned on the area of interest, rotations, inclinations, and


Fig. 3. Kinematics of the OTELO prototype.

Fig. 4. OTELO prototype with its control portable unit and the compact PIEMEDICAL ultrasound device.

small translations are performed around the chosen contactpoint with the skin.

B. Robot Mechanical Specifications

According to the studied ultrasound probe motions, aportable compact six-DOF probe holder robot has been de-signed (Fig. 3) and manufactured with its control and powerportable unit (Fig. 4). It includes the following.

1) Three rotations ( , , and , with their respective ro-tation axes , , and ) with a remote center of motionlocated at the end-tip of the real ultrasound probe allowingthe probe to rotate inside a conical space, with a maximum60 vertex angle.

2) One translation ( ) of 4 cm along the probe axis direc-tion, defined by axis, allows the probe to be continu-ously in contact with the skin.

3) Two translations ( and ) of perpendicular axes allowthe expert to adjust the position (5 5 cm) of the contactpoint above the organ being investigated. The two associ-ated directions and define a plane perpendicular tothe direction of rotation .

4) The mechanical parameter defines the chosen fixedangle between and , and also between and .It allows a maximum tilt of the ultrasound probe of 45with respect to axis.

A compact size and general purpose applications ultrasoundprobe as been chosen for first technical and clinical validations(see Section VI) performed in Barcelona Hospital Clinic sinceApril 2003.

IV. ROBOTIC CONTROL LAW

Due to the serial robot kinematics structure, there is no needto develop and inverse the jacobian matrix as it is possible toobtain a simple analytic expression of the inverse geometricalmodel (IGM). The control laws are obtained by using the IGM[8]. However, the choice of geometrical parameters (e.g., axesranges) imposed by technical constraints (e.g., actuators, sen-sors, and mechanical components dimensions), and by the ne-cessity to have a mechanical equilibrium of mass (robot massover the center of the working space) bring two singular con-figurations inside the conical working space. One correspondsto the boundary configuration, as shown in Fig. 3. The othersingularity occurs when probe holder axes and (corre-sponding, respectively, to rotations and ) are collinear.This latter, corresponds to the probe in a vertical position andis called a wrist singularity or an “uncertain configuration” [9].In this case, large and fast movements of the axes are encoun-tered when moving near the singularity. This is a disturbing sit-uation for the medical expert as the received ultrasound planeis constantly changing. A study of kinematics solutions for therobot has shown that it is possible to design a robot withoutsingular configuration. However, the OTELO prototype bringsbetter performances in terms of weight and size which are oneof the prime user requirements.

The first singularity has been overcome by using mechan-ical structure limitations and software limitations. For the wristsingularity, we developed a specific control law to accuratelyfollow the trajectories in its vicinity and to avoid the speed peaksthat cannot be followed by the actuators. To cope with these lim-itations, two solutions are possible as follows:

1) to track exactly the desired path in the workspace but witha reduced speed;

2) to join the setpoints as quickly as possible for each artic-ulation without worrying about the path.

The second possibility has been chosen as ultrasound exam-ination is noninvasive and as a few degrees of error in the ul-trasound plane orientation can be tolerated without hinderingthe organ search by the expert: As this expert is the main actorof the control loop of the tele-operated chain, he can contin-uously readjust the orientation of the input device accordingto the received image. We use the local redundancy of Axes 1and 3 to make the singular configuration no longer “uncertain.”When the robot reaches the singular configuration, movementis induced to only one of the two locally redundant articula-tion (either Axis 1 or 3). As Axis 1 presents a larger inertia,movements were given to Axis 3 which is controlled to performthe requested movement to obtain the closest orientation of theprobe to the desired one.


Fig. 5. Reference and controlled vector for the ultrasound probe position.

The IGM analysis shows an articular decoupling between theprobe position and rotation parameters which, however, impliesa specific computing process order. The implemented controllaw first computes the rotation parameters then defines the posi-tion parameters. In this chosen mechanical six-DOF serial robot,the wrist singularity only affects the rotation parameters and theoptimization process is, therefore, applied on these parameters.

The desired unit vector of the probe axis is defined as thereference vector. and are the reference articular rotationsof the vector. is the rotation along the axis. isthe unit vector of the probe axis obtained with the optimizationprocess and is defined as the control vector (Fig. 5). It gives thereal controlled position of the ultrasound probe. , , andare the controlled articular rotations determinated by the processwhich will lead to the computation of followed by and .

No tolerance error is considered on the probe nutation whichonly depends on Articulation 2: Therefore, equals . Thedetermination of the control articulation rotation is obtainedby using the following proposed filter:

where is a nonlinear parameter varying with respect to thedistance to the singularity position [10], [11]. is the con-trolled value at , is the reference position at , andis the position of Articulation 1 at .

Finally, the Articulation 3 control is chosen to obtain theorientation of the probe the closest to the referenced one.

The results of the control law management nearby the singu-larity are shown without the controller in Fig. 6(a) and with thecontroller Fig. 6(b). Data are acquired from the robot articularsensors during a real robotic tele-echography examination. Thereference trajectory is generated by a medical ultrasound expertwho moves the one-DOF hands-free input device (fictive probe)in the vicinity of the wrist singularity.

The articular movements managed with the implementedcontroller [Fig. 6(b)] are smoother than the ones obtainedwithout the controller. Notably, for the given input path, Artic-ulation 1 makes almost no move but is actually compensatedby Articulation 3 movements. Furthermore, Articulation 3movements remain smooth and with a smaller magnitude thanthe one observed without the singularity controller [Fig. 6(a)].

This controller enables the specialist to move the remote realultrasound probe within the singularity area offering the de-livery to the expert station of a steady sequence of images even

Fig. 6. Articular trajectory versus time, (a) without singularity processing,(b) with the singularity controller for the same reference trajectory.

when in a normal position to the patient’s skin. In return, thanksto the performances of the singularity controller the remote con-trol of the robot is improved and provides the specialist with areliable tele-echography chain to make a diagnosis.

V. ULTRASOUND IMAGE PROCESSING

Echographic images are grabbed at the patient station usingany ultrasound device and sent to the expert station via a stan-dard communication link for which a good quality of service isensured.

Two kinds of ultrasound image data can be transmitted to theexpert: video and still images. A video compression techniqueis used for the OTELO project in [12]. We focus, in this paper,on the compression of still images.

Ultrasound image sequences can be transmitted followingtwo approaches. When the expert is searching for a specificorgan (liver, kidney, etc.), a high quality image may not be re-quired: Simple compression methods or lossy techniques can


Fig. 7. Comparison between (a) original image and (b) filtered image:PSNR = 56:14 dB.

be applied. When the organ of interest is found, it may be nec-essary to consider lossless compression techniques that wouldbring higher image quality to the expert. This lossless compres-sion can be applied on the whole image or on a region of interest(R.O.I.). This choice also depends on the characteristics of thechosen communication link bandwidth.

In this paper, we first evaluate the contribution of a prefilteringstep in order to facilitate the compression. Then, we determinethe best dedicated compression technique to be applied on ul-trasound images. A comparative study among the most pop-ular compression techniques was performed to determine themethod that would give the optimal transmission time and thebest image quality for the ultrasound specialist. This compara-tive study uses statistical and psychovisual criteria.

A. Preprocessing of Ultrasound Images

The goal of this survey is to improve the ultrasound image,in order to make its compression, and also its transmission,easier. Two different degradations can be detected in an image:the lack of contrast in ultrasound images and the presence ofnoise (speckle). When an ultrasound image has a low contrast,we give the medical expert the choice to adapt this parameter,because automatically changing contrast could affect the diag-nosis. On the other hand, it is well known that ultrasound im-ages are altered by speckle noise. This speckle is generated bythe back-scattered waves due to the heterogeneity of the humantissues. This noise can be reduced without affecting the medicaljudgment of the expert. We propose here to identify the param-eters of this speckle noise, and to apply a filtering method, bestadapted to these parameters, in order to correct the ultrasoundimage, and to improve the compression process.

The system developed in [13] has identified in 73% of theimages a multiplicative noise. The estimation module [14]showed a standard deviation of 0.1. An acquired image islike with the denoisy image and a randomvariable with a unit mean and a standard deviation of 0.1. Withthese parameters, traditional filters, such as Wiener and Kuan,are used to denoise the ultrasound images.

Fig. 7 shows a comparison between original and denoisedimage.

B. Echographic Image Compression

1) Experimental Protocol: The survey was performed ona database composed of 20 ultrasound images of size 768576 similar to the one shown in Fig. 7(a). These images wereacquired by various ultrasound devices (Tringa, Sonosite, or

ESAOTE), then digitized thanks to a grabbing card (MatroxMeteor board, or Matrix MV-Delta).

2) Tested Compression Methods: We compared the fol-lowing techniques: lossless image codings (Huffman, Arith-metic, Lempel Ziv; RLE and Fano codings) with lossy tech-niques (JPEG, JPEG-LS, and JPEG2000). For further details onthis study, one can see [15]. We show the comparison of thesetechniques by using some well-known statistical measures andsome psychovisual judgements.

C. Statistical Comparative Results

To compare the different compression methods and to makethe interest of filtering obvious, the image quality was first eval-uated with respect to four quality measures.

1) The mean square error (MSE) given by

measures the distortion brought by the compression. It isdefined by the mean of the square distances between eachpixel ( ) of the original image and each pixelof the rebuilt image . is the number of rows and

the number of columns.2) The peak signal-to-noise ratio (PSNR)

represents an unbiased measure of the fidelity of the re-built image. More precisely, it represents the MSE, refer-enced with respect to the dynamics of the image in deci-bels. is the maximal intensity. The larger the PSNRis, the smaller the MSE gets, the better the rebuilt imagequality (that is to say faithful to the original image).

3) Compression rate defines the size in bytes of the finalimage over size in bytes of the original image, expressedin percent.

4) Coding times address lossless compression methods;compression and decompression times havebeen computed. For lossy methods, the global compres-sion time has been measured.

The following results represent an average measure of each cri-terion calculated on the original and rebuilt images. Results con-cerning , , and have to be looked at in comparisonwith each other to appreciate the performance of each of thestudied techniques.

1) Lossless Case: It can be concluded that the RLE coding isnot suited to ultrasound image, as its is the largest (Table I).Fano et Huffman algorithms give comparable results in termsof , , and , with poor performances. The Adapta-tive Huffman method presents a compression rate of 54.57%(the final image size is about half of the original one). The lastmethod, based on arithmetic coding, give the best compressionrate, but is associated with larger compression and decompres-sion times.

The Adaptative Huffman method gives the best compromisebetween compression rate and computing times. JPEG-LS gives


TABLE ICOMPARISON BETWEEN COMPRESSION AND DECOMPRESSION

TIME FOR LOSSLESS METHODS

Fig. 8. Comparison between PSNR and CR .

the best compression rate in the near-lossless case (33% versus80%). We can note that JPEG-LS presents a better thanAdaptative Huffman (33% versus 54.57%), for a comparablecompression time.

2) Lossy Case: Fig. 8 presents the PSNR measured for thethree lossy compression methods. A criterion equal to 30 dB isconsidered to be the lower value for a good PSNR.

For a compression rate greater than 5%, JPEG-LS gives thebest image quality, with regard to the PSNR (that confirms theresults in the lossless case). For a rate lower than 5%, JPEG2000becomes the optimal method. Overall JPEG gives the worst re-sults. Table II shows the evolution of the various criteria (quality,time, coding performance) with respect to a very high compres-sion value.

For a high compression rate, JPEG2000 also shows its effi-ciency. Generally, JPEG-LS grants a faster compression, with afactor ranging between 2 and 2.5.

3) Denoising Case: Table III gives the comparison of thequality of images after compression by using the filtering

TABLE IICOMPARISON RESULTS FOR HIGH COMPRESSION RATIO

process. The filtering does not clearly provide an improvementin terms of quality when the compression is low. On the otherhand, for a high compression, the quality seems to be betterwhen a prestep filtering is applied. Fig. 9 illustrates also thistrend for the JPEG2000 method. In fact, until a determinedcompression rate, the filtered image quality is lower than theoriginal one. Conversely, for a higher compression rate, thefiltered image presents better quality than the original one.

This crossing point, called critical rate , is measured witha compression rate of about 4.6% for JPEG2000 (Fig. 9), 6.8%for JPEG, and 4.2% for JPEG-LS. With compression rate lowerthan , filtering contributes to improve the quality of the ul-trasound image. In the JPEG2000 case, this gain is about 0.1dB and for the same quality the size gain is negligible of about0.04%. Despite the small improvements, this might be of in-terest for the telemedicine application.

D. Psychovisual Comparative Results

We propose here to evaluate the quality of the main com-pression techniques (JPEG, JPEG-LS, JPEG2000) accordingto psychovisual receiver operating characteristic (ROC) curvemeasures.

An evaluation campaign ROC started in July 2003. The testwas performed like a “blind test:” The expert looks at differentimages, one by one, without knowing their origin (raw or pro-cessed). The expert gives them a score, ranging from 1 (poorquality) to 5 (very good quality) and normalized to the degreeof severity of each expert with a centered average score. ThisROC survey has been proposed via a web site (programmed inHTML and PHP), which allows the OTELO experts to performthe test whenever and from wherever they want. Results werecollected from four medical experts. We evaluate this qualityscore with respect to the compression rate (Fig. 10).

The quality evaluation given by the experts shows the sametrends of the statistical quality measures. From the expertopinion, JPEG2000 performs a better compression than JPEGand JPEG-LS, especially for a high compression (that is a low

).

VI. CLINICAL RESULTS

Robotized tele-echography tests have been carried out sinceApril 2003 [16], in a clinical environment of the Hospital Clinic(Barcelona, Spain) after authorization obtained from the ethicscommittee of the Hospital Clinic, and signed consent from thepatients. Tele-echography examinations were performed by anexpert situated in the Hospital Casa Maternitat, about 3 km awayfrom the patient station located in the Hospital Clinic. Exami-nations were realized on 32 cases (16 control subjects and


TABLE IIIQUALITY CRITERIA OF FILTERED IMAGES FOR A LOW RATE (75%) AND A HIGH ONE (10%): MEASURED VALUES OF MSE AND PSNR (DECIBELS)

Fig. 9. Filtered images quality in decibels versus the compression rate(percent) for JPEG2000: zoom on crossing point.

16 patients). Twenty-two examinations were done using threeISDN connections, and ten with the satellite connection pro-vided by ELSACOM Spa and with a dynamic allocated band-width of 384 Kb/s. The mean duration of the tele-echographyexamination was of about 21 min (ranging between 15 and 35min). Three echographic devices were used: 14 cases with aTringa, 12 cases with a Toshiba Just-Vision, and 6 cases witha Toshiba SAL 140D. Complete abdominal exams were per-formed including views of liver (left and right lobes), pancreas,portal vein, proximal aorta and distal aorta if necessary, venacava, bladder, uterus/prostate, Douglas, gall bladder, right-leftkidney, and spleen. To make a diagnosis, some parameters weremeasured: size, contour, parenchymal echogenicity, and pres-ence of abnormalities. Experts adopted the following protocolusing the same ultrasound device: A comparison was done be-tween the diagnosis made by the expert from received imagesand the final diagnosis. The final diagnosis was obtained from astandard ultrasound examination performed by a different radi-ologist expert and directly on the patient.

A complete study of the patient has been obtained in 91%of the cases on liver exam, in 85% on kidneys, spleen andgall-bladder exam, 64% on pancreas exam. Simple cyst, liversteatosis, liver tumors, dilated intrahepatic bile ducts, angiomi-olipoma, renal litiasis, pelvic ectasia, and renal cysts have beendetected. The expert remotely controlling the robot was ableto identify 38 out of 57 lesions detected in the 32 subjects(66%). The causes of disagreement with final diagnosis can beclassified as follows:

Fig. 10. Evolution of psychovisual score respect to CR .

1) lesions smaller than 0.4 cm, in seven cases (choles-terolosis, kidney lithiasis, gallbladder polyp);

2) lesions around 1 cm: eight cases (deep angiomiolipoma,kidney lithiasis, liver hemangioma);

3) lesions between 1.5 and 3.8 cm: four cases (cysts, solidrenal mass, multiple focal hiperechoic hepatic lesions).

The impossibility to identify such lesions can be related toa low resolution (eight cases), suboptimal scanning related tothe new technical application (three cases), inadequate imagetransmission (seven cases), and patient bad health condition(one case). Most of the detected lesions were incidental find-ings, without clinical relevance. Twelve patients presentedsymptomatic pathology (jaundice, fever, malaise, etc.) andtele-echography examination enabled to obtain the diagnosisin ten cases (83%). Some difficulties, similar to those observedin a standard examination, arose in performing the robotizedtele-echography when patients were obese, very skinny orelderly people.

VII. CONCLUSION AND PERSPECTIVES

OTELO is an innovative concept designed according to med-ical users specifications for mobile tele-echography examina-tions. The tele-operated echography chain allows an ultrasoundspecialist to perform an echography examination on a remotelylocated patient solely assisted by a paramedic.

The mechanical solution chosen for the OTELO prototype isa serial six-DOF structure with three rotations for the orienta-tion of the probe, two translations for a precise positioning on


the R.O.I., and one translation for maintaining a continuous con-tact force on the patient’s skin. This tele-operated probe holderreproduces on the real probe, and in almost real time, the move-ments performed by the expert with the one-DOF hands-freeinput device at the expert center. The controller implementedin the OTELO prototype permits to have a good path followingeven nearby the singularity.

To overcome the bandwidth limitation of any given communi-cation link, compression techniques and filtering were evaluatedbefore transmission of images to the expert center. When thecompression is high, we showed that a quality gain is obtainedthanks to the filtering step but remains small. Further study willinvolve filtering methods better dedicated to ultrasound imagesthan those currently used such as Wiener and Kuan methods.Both measures of PSNR and Expert Score show that JPEG2000is the most effective compression method in terms of quality forour robotized tele-echographic system. The improved controlof the tele-operated robot combined with stable and good ul-trasound images quality provided the specialist with a reliabletele-echography chain to make a diagnosis.

Clinical evaluations have been carried out on intra-abdom-inal organs by the Hospital Clinic team in Barcelona since April2003. A maximum of three ISDN lines and an Eutelsat Satel-lite link were available for these tests, offering a theoreticalmaximum bandwidth up to 384 Kb/s. Diagnoses obtained withOTELO agreed in 84% of the cases with diagnoses made in clas-sical conditions with the same ultrasound devices. Patients wereconfident during the whole tele-echography protocol and did notsuffer any pain from the robot weight nor from the force exertedon their skin by the probe. The tele-operated robot showed itsability to enable an examination of different parts of a patient’sbody.

The OTELO robotized system is currently used in a regionalhospital near Tours, France, in the frame of a medical pilot phasesince March 4 for a four-month period. The expert center islocated in the main center hospital in Tours. Marketing of thisproduct should begin at the end of 2004.

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[15] C. Delgorge, C. Rosenberger, P. Vieyres, and G. Poisson, “JPEG 2000,an adapted compression method for ultrasound images? A comparativestudy,” in Int. Conf. Systemics, Cybernetics and Informatics, vol. 9, Or-lando, FL, 2002, pp. 536–539.

[16] R. Gilabert, M. Vannoni, F. Courreges, C. Delgorge, C. Novales, G.Poisson, P. Vieyres, and C. Bru, “Clinical validation of a tele-operatedmobile ultrasound scanner using a light weight robot (Otelo project),”in Eur. Congress of Radiology (ECR 2004), Vienna, Austria, Mar. 5–9,2004.

Cécile Delgorge was born in 1976. She receivedthe Engineering Degree in new information andcommunication technologies from Ecole Nouvelled’Ingénieurs en Communication (ENIC), Lille,France, in 1999 and the Master’s Degree in signalsand images in biology and medicine from the Uni-versity of Angers, France, in 2001. She is currentlyworking toward the Ph.D. degree at the Laboratory ofVision and Robotics, University of Orleans, France.

Her Ph.D. work is a contribution to the Europeanproject, Mobile Tele-Echography Using an Ultralight

Robot (OTELO). The research work is in acquisition, compression, and trans-mission techniques for ultrasound images.

Fabien Courrèges has an initial academic educationin general physics from the University of Orleans,France, in 1999. He received the Master’s Degreein mechanics and robotics from the University ofPoitiers, France, in 2000. He is working towardthe Ph.D. degree at the Laboratory of Vision andRobotics, University of Orleans.

His Ph.D. work is a contribution to the devel-opment and the control of three tele-echographyrobotics systems including the Mobile Tele-Echog-raphy Using an Ultralight Robot (OTELO) European

Project. He is currently involved in the OTELO project within the KingstonUniversity as a postdoctorate fellow.


Lama Al Bassit received the Diploma in mechanicsand the Master degree in robotics from Ecole NormalSupirieure de Cachan and the University Paris VI,France, in 1992 and 2001, respectively. She was avisiting student at the University McGill, Montreal,Canada, in the spring 2001. She is currently workingtoward the Ph.D. degree at the Laboratory of Visionand Robotics, University of Orleans, France.

From 1994 to 2000, she was a Research andTeaching Assistant at the Height Institute of AppliedSciences and Technology, Damascus, Syria. Her

research interests include medical robots, mechanisms and mechanical design.

Cyril Novales received the Ph.D. degree in roboticsfrom the University of Montpellier, France, in theCNRS Laboratory LIRMM.

He spent two years as postdoctorate in INRIA Lab-oratory, Grenoble, working in autonomous vehicles.He joined the LVR in Bourges in 1998 as an AssociateProfessor. Since 1998, he was involved in research in-cluding autonomous mobile robots and teleoperatedrobotics dedicated to heathcare; in that last topic, heparticipates in the OTELO project.

Christophe Rosenberger received the Ph.D. degreefrom the University of Rennes I, in 1999.

He is an Assistant Professor at ENSI, Bourges,France. He belongs to the Laboratory of Vision andRobotics, Bourges, in the Signal Image and VisionResearch Unit. His research interests concern imageprocessing, texture analysis, and quality control byartificial vision. He also works on the segmentationand interpretation of multispectral images for remotesensing applications.

Natalie Smith-Guerin received the Ph.D. degreefrom the Industrial Automation Laboratory of INSA,Lyon, France, in 2000. Her thesis concerned surgicalrobotics and particularly the study of the robotizationof the corneal grafting including a cut of the softtissues by a surgical low pressure waterjet.

She has been an Assistant Professor at the Univer-sity of Orleans, Bourges, France, since 2001. Since2001, she has worked in the Vision and RoboticsLaboratory of Bourges and works in the teleoperatedrobotics field. She was involved in the OTELO

European project and now she is involved in the TERISS project where she isconcerned with the mechatronics and haptic aspects.

Concepció Brù received the M.D. degree from theUniversity of Barcelona, Spain.

Since 1979, she has been working in the field ofclinical ultrasound at the Hospital Clínic. She is anAssociate Professor of Radiology at the Universityof Bracelona and is Head of the Imaging Departmentof the Hospital Clínic. She joined the research inrobotics applied to ultrasound in 2001 as a clinicalexpert.

Rosa Gilabert received the M.D. degree from theAutonomous University of Barcelona, Barcelona,Spain.

She is a Radiologist and Head of the UltrasoundDepartment, Hospital Clínic, Barcelona. She joinedthe OTELO project as clinical expert.

Maurizio Vannoni is a Radiologist working at theHospital da Santa Casa, Porto Alegre, Brazil. Duringa fellowship in Barcelona, Spain, he participated inthe OTELO project.

Gérard Poisson received the French Agrigation de-gree in mechanics and the Ph.D. degree in mechan-ical engineering and robotics from Orleans Univer-sity, Bourges, France, in 1980 and 1994, respectively.

He is an Associate Professor. He has taken a fullpart in the creation and development of the Labora-tory Vision and Robotics since 1988. For that matter,he has been involved with several projects in indus-trial robotics, mobile robotics, and teleoperation. Heis in charge of one of the three main research themesof the LVR, called Robotics Autonomous and Teleop-

eration (RAT). His research interest concern perception of environment, visionand autonomy for mobile robots, and design and control of dedicated roboticssystems for medical applications.

Pierre Vieyres received the Ph.D. degree in biomed-ical engineering from the University of Tours, France.

He joined the Laboratory of Vision and Robotics,University of Orleans, France, in 1992, where heis an Associate Professor. Since 1995, he has beeninvolved in the development of dedicated robotsfor the medical field and especially for tele-echog-raphy. He is currently the Project Manager of theMobile Tele-Echography Using an Ultralight Robot(OTELO) European Project.

a tele-operated mobile ultrasound scanner using a light-weight

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