medical textiles with embedded fiber optic sensors for monitoring of respiratory movement
TRANSCRIPT
246 IEEE SENSORS JOURNAL, VOL. 12, NO. 1, JANUARY 2012
Medical Textiles With Embedded Fiber Optic Sensorsfor Monitoring of Respiratory Movement
Jens Witt, François Narbonneau, Marcus Schukar, Katerina Krebber, Julien De Jonckheere, Mathieu Jeanne,Damien Kinet, Bernard Paquet, Annick Depré, Lorenzo T. D’Angelo, Torsten Thiel, and Regis Logier
Abstract—For patients under Magnetic Resonance Imaging(MRI) spontaneous respiration is constantly at risk of beingimpaired by anesthetic drugs or by upper airway obstruction.Therefore, continuous monitoring of the breathing activity isneeded to assess adequate ventilation or to detect specific ob-struction patterns. The paper describes three MRI compatiblerespiration sensors based on pure optical technologies developedwithin the EU FP6 project OFSETH. The sensors are based onfiber Bragg gratings, optical time-domain reflectometry and mac-robending effects. The developed smart medical textiles can senseelongation up to 3% while maintaining the stretching properties ofthe textile substrates for patient’s comfort. The OFSETH harnessallows a continuous measurement of abdominal and thoracicrespiration movement while all vitals organs are free for medicalstaff actions. The sensors were tested in MRI environment and onhealthy adults.
Index Terms—Fiber optic sensor, polymer optical fiber (POF)sensor, respiratory sensor, smart medical textile.
I. INTRODUCTION
R ESPIRATION monitoring is one of the most importantelements of assessing the physiological state. Respira-
tory failure can be difficult to predict. In just a few minuteslife-threatening conditions can arise. Thus, continuous moni-toring of respiratory activity is of great importance in several
Manuscript received November 15, 2010; revised April 20, 2011; acceptedMay 03, 2011. Date of publication June 02, 2011; date of current version De-cember 01, 2011. This work has received research funding from the EU 6thFramework Programme under contract number IST-2004-027869. The viewsexpressed here are those of the authors only. The Community is not liable forany use that may be made of the information contained therein. This is an ex-panded paper from the Fourth European Workshop on Optical Fibre Sensors(EWOFS 2010) Conference. The associate editor coordinating the review ofthis paper and approving it for publication was Dr. William MacPherson.
J. Witt, M. Schukar, and K. Krebber are with the Federal Institute for Mate-rials Research and Testing, 12205 Berlin, Germany (e-mail: [email protected];[email protected]; [email protected]).
F. Narbonneau is with Multitel, INITIALIS Science Park, Rue Pierre et MarieCurie 2, 7000 Mons, Belgium (e-mail: [email protected]).
J. De Jonckheere, M. Jeanne, and R. Logier are with INSERM CIC-IT807, CHRU de Lille, 59037 Lille, France (e-mail: [email protected];[email protected]; [email protected]).
D. Kinet is with Multitel, 7000 Mons, Belgium (e-mail: [email protected]).He is also with the Université de Mons, Faculté Polytechnique 31, 7000 Mons,Belgium, (e-mail: [email protected]).
B. Paquet is with Centexbel, 4650 Herve (Chaineux), Belgium (e-mail:[email protected]).
A. Depré is with Elasta, 8790 Waregum, Belgium (e-mail: [email protected]).L. T. D’Angelo is with Institute of Micro Technology and Medical Device
Technology, Technische Universität München, 85748 Garching, Germany(e-mail: [email protected]).
T. Thiel is with Advanced Optics Solutions GmbH, 01067 Dresden, Germany(e-mail: [email protected]; Fax: +49 351 4960 194).
Digital Object Identifier 10.1109/JSEN.2011.2158416
medical applications, e.g., monitoring of anaesthetized patients,of infants susceptible to Sudden Infant Death Syndrome (SIDS)or of patients with sleep apnea.
Respiration can be monitored by analyzing different physi-ological parameters (Fig. 1) [1]. Oxygenation is the degree towhich the oxygen-carrying capacity of hemoglobin is utilized.It can be measured invasively with an arterial blood sampleand non-invasively, which is the taken standard method formonitoring of anesthetized patients. The non-invasive methodmeasures the absorption of specific light wavelengths passingthrough the finger bed, and is very accurate for oxygen satu-rations over 70%. Capnometry is the measurement of exhaled
, which is important for keeping the blood’s pH constant.It must be measured on non polluted expiratory gases, whichmakes a tracheal intubation necessary. The tidal volume is thevolume of air breathed in and out, and can also be measuredreliably during anesthesia only using tracheal intubation. Chestmovement monitoring is also feasible. It is not possible toassert that movement leads to efficient ventilation even if boththoracic and abdominal respiration movements are monitoredtogether. However, the lack of movement is a clear signal of arespiratory incident.
Commercially available equipment for sleep monitoring ofinfants usually measure thoracic and/or abdominal movements,and are integrated into the mattress or are attached to the infantduring sleep. It is possible to measure heart rate and respira-tion using capacitive elongation sensors and electrodes [2] orto integrate conductive fibers to measure analog physiologicalsignals [3]. The system [4] monitors heart beat rate, breathing,body temperature and body humidity using elastic sensors. Theinclusion of the system in a shoe to monitor pulse oximetry, ac-timetry and the position of infants is another approach [5].
Other devices using conductive wires and electrodes assensor elements were developed for monitoring of adults [6].The T-shirt described in [7] monitors various cardiovascular,respiratory, motoric and experiential responses. It consists of agarment with an embedded inductive plethysmography sensor,a single-channel electrocardiogram, an accelerometer and ahandheld computer for the capture of tome-stamped experiencedata. Within the scope of the VTAM project [8], a T-shirt proto-type was developed which incorporates four electrocardiogramelectrodes, a shock or fall sensor, a breathing rate sensor, twotemperature sensors and a GPS receiver. Kept in a belt andconnected to the T-shirt through a micro connector there is amother board, a power supply and a GSM/GPRS module fordata transmission and hands-free communication. A wearable
1530-437X/$26.00 © 2011 IEEE
WITT et al.: MEDICAL TEXTILES WITH EMBEDDED FIBER OPTIC SENSORS 247
Fig. 1. Overview of the possible respiratory state detection parameters and their measurement.
system [9] developed for recording of cardio respiratory andmotion signals is composed of a vest including sensors for ECGand breathing frequency detection and a portable electronicboard for motion assessment, signal preprocessing and wirelessdata transmission to a remote computer.
For monitoring of anaesthetized patients during MRI, sensorsincluding metallic parts or electrical conductive wire are inap-propriate, since they disturb the imaging process and can causeburns on the patient’s skin [10]. In addition, the patients cannotbe monitored during the transport in or out of the MRI roomsince the MRI compatible monitoring systems are not easilytransportable and often exclusively used for MRI examinationdue to their cost and the few MRI monitors available at the hos-pital. Fiber optic sensors are advantageous because of their elec-tromagnetic immunity which they have already demonstrated inmany applications. Furthermore due to their fibrous nature, op-tical fibers are well suited for integration into textiles.
OFSETH “Optical fiber sensors embedded into technical tex-tiles for healthcare”, a European project supported by the EU6th Framework Programme, investigated how various vital pa-rameters such as respiratory movement, cardiac rate and pulseoximetry can be measured using fiber optic embedded into med-ical textiles [11]–[13]. The developments were targeted on themonitoring of sedated or anaesthetized patients under MRI. OF-SETH investigated several fiber optic sensing techniques formonitoring of respiratory movement. The main developments[14]–[17] are a macrobending sensor based on bending effects,a sensor based on fiber Bragg gratings (FBG), and a sensorwhich uses the optical time-domain reflectometry (OTDR) inpolymer optical fiber (POF). All sensors measure body circum-ference changes due to respiratory movement. While feasibilityof sensing respiration was demonstrated for macrobending sen-sors [18]–[21] and FBG sensors [22]–[24] in the past, OFSETHpresented the first sensor for monitoring of respiratory move-ment based on POF OTDR. One important point during the de-velopment of the OFSETH sensors was to keep the handling ofthe sensors easy for the medical staff.
In this paper it is reported how pure optical sensing tech-nologies for respiratory movement monitoring can successfullysense textile elongation up to 3%, while maintaining thestretching properties of the textile substrates used as layout.Considering the influence of different patient’s morphology aswell as textile integration issues to let free all vital organs formedical staff actions during incident or respiratory accidents,the sensors are integrated to a harness allowing an efficient han-dling and continuous measurement of respiratory movement.
Fig. 2. Sensing harness for MRI application. A Thoracic respiration sensor isintegrated into the black part (upper right); An abdominal sensor is integratedinto the white part (lower middle).
II. SENSOR DESIGN
A. Sensing Harness
European norms in terms of textile and the medical specifica-tion were taken into account, for the design of a sensing harnesswhere the sensors are strategically placed for measurement ofthoracic and abdominal movements caused by the breathing ac-tivity without corruption of one signal by another (Fig. 2) Thisdesign is composed of adjustable parts in order to fit the max-imum of morphologies and to be worn both by men or women.The harness design kept some places free, like the pre-cordiumin order to facilitate resuscitation in case of cardiac arrest orhemodynamical failure, and give vital information on hemody-namical status during resuscitation. Access to the intra-venousinfusion line should also be kept clear, for easy access duringanesthesia or for resuscitation purpose. It must be ensured thatthere is no pressure on venous or arterial blood vessels whichcould obstruct the regular blood flow.
To reduce the number of connections and optical fibers, a du-plex optical connector was used. The connector was prototyped
248 IEEE SENSORS JOURNAL, VOL. 12, NO. 1, JANUARY 2012
Fig. 3. Schematic of the prototyped duplex connector.
especially for this application (Fig. 3) as conventional connec-tors include metallic parts and consequently are not MRI com-patible. The core of the connector is composed of two ceramicferrules integrated into a plastic housing. Male and female con-nectors were designed to assure a definite connection.
The elongation of the harness belt caused by the respiratorymovement was measured using different fiber optic sensingprinciples. The OFSETH sensors developments are based onfiber Bragg gratings, optical time-domain reflectometry, andmacrobending effects. The abdominal movement cause elonga-tions of about 1–3%, which is much higher than for the thoracicmovement which cause only a fractional percentage change.Therefore, the FBG sensor which has high accuracy but a lowstrain limit was used for the thorax while for the abdomen theless accurate POF OTDR and macrobending sensors were used,which have a much higher strain limit.
B. Abdominal Sensors
For larger movements where accuracy is not needed buthigher elongations occur, a bending sensor was used. Thebending design has the advantage that the integration of theoptical fibers into textile fabrics is relatively straightforward,owing to their simple design. The bending design also ensuresthat the optical fiber is not damaged at high strain either. Due tothe amplitude of the abdominal movement the signal-to-noiseratio is high enough to monitor the respiration using a simpleunit which consists of a 1550 nm ELED module and a photo-diode from Teradian Inc. (TAP4NN3) which comes with withsilica single-mode fiber pigtail. In addition to this classicalmacrobending sensor approach, a second sensor (POF OTDRsensor) was developed. Based on a special bending design andusing polymer optical fibers, a real-time OTDR unit was usedfor monitoring of the sensor textiles. The advantage of usingOTDR is the distributed measurement. Using a single fiber,strain can be measured at different locations along the fiber.Using a sensitive and fast OTDR unit it would be possible tomeasure the thoracic and abdominal respiration movementswith only a single fiber and monitoring unit. Another advantageis that it is possible to focus just on the bending part of thefiber to neglect loss contributions and signals from non-sensingparts. The OTDR sensor is based on POF as there are someadvantages compared to silica fibers. POF has higher elasticityand higher breakdown strain than silica fiber. Therefore, they
Fig. 4. Final design of the macrobending sensor. The silica optical fiber wasembedded into elastic fabric during the industrial crochet fabrication process.
are well suited for integration into technical textiles. Anotherhighly important criterion is their biocompatibility, especiallyin the case of fiber breakage.
The macrobending sensor is based on the well-knownbending effect of optical fiber [25]. Bends cause light couplingfrom guided modes into radiation modes and thus some poweris lost. When the sensor textile is stretched, the curvatureradius increases, and the bending loss reduces. Therefore, theintensity variations at the output of the optical fiber will reflectthe relative variation of the sensor textile length. Macrobendingsensors have the advantages that their interrogation is verysimple. The macrobending sensor requires measuring intensitychanges, so the main components needed are the ELED sourceand a photodiode. Due to this fact a compact design is possible.The components are available for less than 150 Euro thereforethe sensor is really low-cost compared to the price of more than10 kEuro for an OTDR unit or a FBG interrogator. Anywaythe signal analysis is not straight forward. When the bendingradius of an optical is changed synchronous mode coupling canoccur, which leads to constructive interference which reducesthe loss induced by the bending [26], [27]. Therefore, severalsources (LED, SLED, ELED, Fabry-Perot) with wavelength of525 nm, 660 nm, 850 nm, 1310 nm and 1550 nm were testedwith polymer and silica fibers from different manufacturers indifferent loop configurations to find a combination and sensorlayout which gives a quite linear relation between sensor elon-gation and attenuation to avoid complicate signal processing.
The optical fiber was integrated into the elastic fabric, pro-duced by crochet, during the industrial process. Changing thethickness of the yarn in warp and weft gives a different compo-sition, look and feel of the finished fabric. The thickness definesthe fabric hardness at equal tension and equal needles numbersin the fabric. The degree of elasticity is defined by the number ofrubber threads. Increasing the number of rubber threads trans-lates into higher rigidity of the fabric and thus more force isneeded for the textile extension. In conclusion, while the dy-namics of sensor is improved by increasing the thickness of thetextile and thus reducing the period of the bending, the signal-to-noise ratio is enhanced by increasing the elasticity of the fabric.A standard single-mode fiber compatible with ITU-T G.652 wasused in the tests. The fiber bend radius at zero strain was opti-mized to keep the total loss compatible with the power budgetof the measuring system. The final design of the sensor is pre-sented in Fig. 4.
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Fig. 5. POF OTDR sensor textile with 500 �m POF. The black part is elasticand contains the sensing fiber. The rest of the belt is non-elastic.
The POF OTDR sensor is based on the measurement of timeand intensity. Short light pulses are launched into a fiber beingtested and due to refractive index changes (Fresnel reflection)and microscopic inhomogenities (Rayleigh scattering) light isscattered back and detected by the instrument.
The POF OTDR sensor textiles are based on bare 500 mPMMA step-index POF (Mitsubishi ESKA CK20) with a fibercore diameter of 0.486 mm. The fiber has been stitched to anelastic fabric by hand. The POF OTDR sensor layout develop-ment started as a series of several equally spaced 180 bends(Fig. 5) similar to the macrobending layout. After several im-provements the final design comprises of a layout with severalsharp edged 90 bends [28].
The elastic sensor textile containing the optical fiber is elon-gated with non-elastic belts. Thus, the sensor textiles are dividedinto two sections: a short elastic part whose length changesduring the respiration and a longer non-elastic part. Due to thedesign of the sensor the abdomen circumference change onlyelongates the elastic part of the sensor belt, thus the strain whichoccurs at the elastic part is much higher than the percental cir-cumference change. Changing the length of the elastic part andthus the length ratio between elastic and the inelastic part allowsit to adjust the sensor parameters like strain ratio, sensitivity ormaximum elongation. The elastic part of the final sensor designhas a length of about 1 cm.
Elongation of the POF OTDR sensor textiles changes thebending radius of the fiber and thus a change of fiber attenu-ation can be measured behind the bending part of the fiber. Forthe sensor a different effect was used. Due to the bending lightscattering occurs. As the amount of backscattered light dependson the bending radius it is possible to measure the elongationof the sensor textile [29]. The respiratory sensor signal is calcu-lated by integration of the OTDR backscattering signal using awindow width of 100 cm. The window is centered on the loca-tion of the bending structure.
C. Thoracic Sensor
For monitoring of the thoracic respiration movement a fiberoptic sensor based on fiber Bragg gratings was developed. TheFBG is made using UV interferometry, inducing a refractiveindex modification in the core of the optical fiber. The FBGreflects a particular wavelength of light (the Bragg wavelength
) and transmits all others as a filter. This particular sensorpresents the advantage of being sensitive to strain which applied
Fig. 6. Final design of the FBG sensor. The silica optical fiber was stitched tothe textile by hand.
to it. So if elongation (compression) is applied, a shift of theBragg wavelength towards longer (shorter) wavelengths can beobserved. The main advantage of using such an optical fibersensor is its linear sensitivity to longitudinal mechanical stresseswith a slope around 1.2 pm .
We used standard silica fiber Bragg gratings. Thus, forwriting the grating the coating is removed and after inscrip-tion the fiber is recoated. During the time without coating,the fiber is weakened, which reduces facilities for integrationand manipulation. For this reason, only optical fibers withsufficient robustness should be used and conventional textilefabrication processes as opted for the macro bending sensor areinadequate for FBG integration. The optical fiber with the FBGphoto-written was thus stitched directly on an elastic fabric.The robustness of the sensor is guaranteed by an additionalsilicone coating and polymer attachment points on both sidesof the FBG are glued around the fiber for a better adhesion ofthe sensor on the fabric and easy stitching without impairingthe sensor properties (Fig. 6). Because of their mechanicalproperties the use of POF FBGs was taken into account duringthe project, but as there are no commercially available POFFBGs and due to the lack of suitable single-mode POF thesensor was finally realized with silica FBGs.
D. Monitoring Units
To ensure a continuous monitoring of the patient both beforeand after the MRI scan, a mobile and transportable monitoringunit is needed. The macro bending sensor unit is a 7relativelysimple construction as it only needs to monitor the intensityfluctuations induced by the bending variations. The unit is basedon a SLED source operating around 1550 nm and a photodiode.
Regarding the FBG-based sensor, signal analysis is some-what more complex as the mechanical strain induced on thesensing bandage is converted to a wavelength shift. This shiftcan be measured by using an Optical Spectrum Analyzerand a broadband source but for a mobile and/or ambulatoryapplication, interrogation has to be redesigned to respond tothe mobility constraints as well as being cost efficient. As analternative method, a monitoring setup based on an opticalbroadband source coupled to a linear optical filter acting asa wavelength-into-intensity converter was used. The setupused a low power SLED source from EXALOS operating at1550 nm with a bandwidth of about 50 nm. The photodiode(TERADIAN TAP4NN3) showed a low noise dark current and
250 IEEE SENSORS JOURNAL, VOL. 12, NO. 1, JANUARY 2012
Fig. 7. Schematic of the combined intensity and FBG monitor.
was sensitive enough to operate the LED un-cooled at a verylow operational current of 50 mA. A chirped FBG was used asa linear optical filter.
The wavelength repeatability is about 5 pm at a comparedto 1 pm for the Micron Optics sm130 used in our laboratory.The price of a spectrometer based FBG interrogator is typicallyabout 10–35 kEuro while the converter solution costs about5 kEuro per channel. One disadvantage is that only one sensorcan be measured per channel, while for a spectrometer type in-terrogator typically 32 to 64 sensors can be measured.
In Fig. 7 the complete scheme of the opto-electronicalinterrogator module is shown, which converts the opticalsensor signal into electrical signals. The electrical signals areprocessed by a data acquisition module based on the Phys-iotrace system. Physiotrace is an acquisition and treatmentboard, based on hardware components (Microchip PIC 16 F),a DSP software component library and a visual programminglanguage, allowing users to model, test and perform all kindof digital signal processing algorithms for all kind of biomed-ical signals [30]. The internal microprocessor A/D converter(12 bits, 250 Hz sampling rate) was used for sampling of theanalog signal.
As the acquisition module and the monitor contain electroniccomponents, they need to be placed out of the MRI field. Thetransmission between the garment and the acquisition moduleis achieved using optical fibers. Both waveform and value aredisplayed on the monitor, as shown in Fig. 8. Finally, the systemis completed by a wireless transmission system from nanotron(nanoLOC AVR, 2.4 GHz ISM band) to transfer all vital data tothe medical staff while the patient stays alone in the MRI roomduring the examination.
Fig. 8. Monitor used for the MRI application.
For the POF OTDR sensor no cost efficient and portable tech-nology is commercially available on the market. Therefore, areal-time laboratory OTDR unit (OFM 20) from Tempo wasused for the sensor. The unit operates at 650 nm and is opti-mized for 500 m POF. The pulse repetition rate is 250 kHz.With 120 pulses per sweep and point the unit has an update rateof about 8 Hz. The number of internal averages was set to 16.This correspond to a measurement rate of 2 Hz. However theGPIB connection limited the measurement rate to 1.2 Hz. Dueto this low rate the OTDR sensor only allows measuring the res-piratory rate (during normal breathing) and not the respiratorywaveform. For measuring the waveform the OTDR unit shouldhave a measurement rate of at least 100 Hz.
A modified firmware should allow to get the full 8 Hz viaEthernet. For getting higher measurement rates one approachcould be to reduce the number of points per trace.
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Fig. 9. Simulator (left) Schematic (right).
Fig. 10. Sensitivity test with amplitude of 2% and initial force of 1.5 N goingthrough 172800 cycles in 192 hours.
III. EXPERIMENTAL RESULTS
A. Robustness Tests
All sensors have been tested on linear and expanding chestsimulators to evaluate the stability of the signals after severalelongation cycles. The tests were in part made in climate cham-bers to characterize the humidity and temperature behavior ofthe sensors. The expanding chest simulator as shown in Fig. 9 isdriven by a step motor. The amplitude and frequency are chosento simulate a real breathing activity. Also tests of washing sensortextiles were performed.
The POF OTDR sensor was subjected to a 120-hours simu-lated respiratory movement test. The respiratory frequency was10 cpm with elongation changing between 0% and 3%. Thesensor allows measuring strain up to 10% before the fiber fails.The signal shape did not change during the test, but the systemshowed a slow drift up and down. During a 2 hours period thesignal DC offset changes about 10%. The absolute change issimilar to the peak to peak amplitude of the simulated respi-ratory movement. Tests without the sensor in neutral positionshowed, that the drift was caused by the monitoring unit. Thewindow position is changing with time and thus calculation ofthe sensor signal leads to a drift. As the relative amplitude isconstant the signal can be easily corrected by applying a highpass filter.
The macrobending sensor response measured as voltage be-hind the photodiode is linear within the range from 0% to 5%elongation with a gradient of about 3 mV/%, varying slightlywith different samples. In Fig. 10 the sensitivity, calculated aspeak-to-peak difference of the voltages given by the photodiode,during a 172800 cycle test run over 192 hours with an elonga-tion of 2% can be seen. The sensor has a constant sensitivity ofabout 5.5 mV with variations below 10%. These tests have been
Fig. 11. Relative amplitude of the FBG sensor during the last 90-hour periodof the long-term test. The applied elongation was about 0.9%. After 20 hoursthe sensor was reattached to the simulator.
Fig. 12. POF OTDR respiratory sensor signal and spirometer signal for anormal breathing adult.
Fig. 13. Complete setup of the MRI-compatible simulator of CIC-IT de Nancy.
performed for different elongations from 2 to 32%. The resultsshow that the sensor retains its sensitivity/stability performancesfor elongations from 2 to 15%.
Tests of the FBG sensor which uses a Bragg grating with awavelength 1547.77 nm, a spectral width of 0.114 nm,and a reflectivity of 95 (measured at room temperature),showed, that the sensor textile can be stretched up to 3% elon-gation without degradation of the optical fiber. Larger elonga-tions are possible but not realistic in the configuration of mon-itoring thoracic respiration. The so-formed optical gauge has asensitivity of 0.32 nm/% substrate elongation. Thus, even whenassuming a low resolution of 20 pm for a low-cost FBG in-terrogator, the measurement accuracy will be better than 0.1%.This value is definitely compliant with the detection of thoracicmovement. The mechanical robustness of the sensor was testedwith more than 90000 cycles in 129 hours with a simulatedbreathing rate between 10 cpm and 12 cpm. In Fig. 11 the rela-tive amplitude during a 90-hour period of the test is shown. Thedrift of about 15 pm in the first 3 hours of testing is caused bya change of temperature in the laboratory room. The FBG has
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Fig. 14. Large picture: Test of the FBG sensor in MRI environment. The first two curves are related to the respiration simulator, the third curve shows the FBGsensor response and the last three curves are related to the magnetic gradients of the MRI equipment. Small picture: Typical abdominal and thoracic respirationsignals during a test on healthy volunteers.
a temperature sensitivity of about 10 pm/K. After 20 hours thesensor was reattached to the simulator.
To fulfill the real conditions of cleansing, the standardizedmethod (BS5651) used by a hospital for normal laundry pro-cedures was considered. This procedure is performed at theminimum disinfecting temperature of 71 in a mechanicalwashing machine having a horizontal rotating cage. Aftercleansing, the sample was dried in normal air conditions. Thistest was done only with a single respiratory sensing belt and notwith the complete harness, to avoid a possible damage of theprototype. To prevent damage to the optical fiber and connec-tors, the sample was inserted in a plastic container with largeopenings, allowing washing water to enter the box. The samplewas locked in this cage in such a way that optical connectors cannot move during centrifugation in the washing process. After6 washing cycles, the sensitivity of the sensor was reduced byabout 30%, but measurement of respiration movement was stillpossible as the signal-to-noise ratio remained sufficient (before:28 dB, after: 18 dB). Washing tests with the complete sensingharness have to be done in future, but according to the results itis expected that harness could be disinfected and reused severaltimes.
B. Clinical Investigations and Test on Healthy Adults
The POF OTDR sensor was tested on a normal breathinghealthy human adult to compare the OTDR sensor signal withthe measurements made by a spirometer. The OTDR was con-nected via computer and D/A converter to the Physiotrace dataacquisition system. Simultaneously the respiration air flow wasmeasured using a spirometer, which also was connected to thePhysiotrace system. The measured air flow data was summed
to calculate the total amount of air breathed in and out, becausethe circumference changes measured by the POF OTDR sensorsshould correlate with the breathed air volume. Fig. 12 shows thecorrelation between both sensor signals. During the respirationthe breathing frequency and depth were changed. As the com-mercial sensor measures the volume of air which is breathed inand out, the OTDR sensor measures the circumference change atthe abdomen. Therefore, both traces in Fig. 12 differ. In contrastto the spirometer the OTDR sensor signal responds different toabdominal and thoracic respiration.
A harness based on the macrobending and FBG sensors wasvalidated on a simulator in MRI environment. As the simulatorshown in Fig. 9 is not MRI compatible a different simulatorbased on a movable table was used (Fig. 13). The displacementof the table was realized by a balloon connected to the medicalrespirator allowing air-flow circulation by controlling the am-plitude and frequency of the movement through the volume orair injected. The signals of the respirator, the sensor responseand the gradient signals emitted by the MRI were measured inreal-time. It is also possible to synchronize these signals withthe MRI acquisition.
Several configurations in terms of volume and/or frequency,in or out of the MRI tube and in presence of or without the MRIgradient were simulated and tested. As results it was demon-strated that the displacement of the movable table is detected interms of amplitude and frequency. The signal of the sensor isnot degraded even when the system is submitted to the gradientof the MRI equipment in and out of the magnetic field (insideand outside the MRI tube respectively) as shown in Fig. 14. Atthe same time, a clinical investigation of the system was carriedout at the hospital of Lille (France) on several healthy volunteers
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and real patients of the hospital’s intensive care unit. For this in-vestigation, the sensors developed in the project were comparedwith commercial sensors available at the hospital. shows the typ-ical signal patterns for both thoracic and abdominal movementfor healthy adults.
IV. CONCLUSIONS
A novel non-intrusive monitoring system for continuous mea-surement of abdominal and thoracic respiratory movement wasdeveloped within the OFSETH FP6 EU project. Based on pureoptical fiber sensors using macrobending effects, fiber Bragggrating and optical time-domain reflectometry, the system hasbeen successfully tested on simulators, in climate chambers andon several healthy volunteers. Its design makes it possible tocover a wide field of applications from hospitalization e.g., themonitoring of patients during imaging scans to homecare.
The system is fully MRI compatible and enables the contin-uous measurement of respiratory movement. It is easy to placearound patients and provides free access to all vital organs formedical staff actions. Unlike many existing systems, our systemexhibits the main advantage that it not only measures the respira-tory signal frequency (as for resistive-based systems) but it alsoallows the analysis of the patient’s respiratory cycle. Finally, oursystem offers the advantage of providing reliable and accurateinformation about the extent of respiratory motion magnitude.
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Jens Witt received the degree in physics in 2002 and the Ph.D. degree in elec-trical engineering from the Technical University of Berlin, Germany in 2006.He received the qualification “European Laser Engineer” from the TechnicalUniversity of Vienna, Austria.
Since 2003, he has been with BAM Federal Institute for Materials Researchand Testing, Berlin, Germany. He was involved in the groups “Visual Methodsand Image Reproduction in Non-Destructive Testing (NDT)” and “Fibre OpticSensors”. Currently he is involved in the group “Distributed and Polymer Op-tical Fibre Sensors” within the framework of national and European researchprojects. He is author and coauthor of more than 20 scientific papers.
François Narbonneau received the Engineer degree in optronics from EN-SSAT (Ecole Nationale Supérieure des Sciences Appliquées et de Technologie),Lannion, France, in 2001 and the Ph.D. degree in physics from the UniversityRennes I, France, in 2007.
Since 2007, he is involved in the Fiber Optics Sensors Group of the AppliedPhotonics Department of Multitel in Belgium as Researcher and as coordinatorof the project OFSETH. Working in the field of optical sensors based on opticalfibres, he is author and coauthor of more than 20 scientific papers.
254 IEEE SENSORS JOURNAL, VOL. 12, NO. 1, JANUARY 2012
Marcus Schukar studied Microsystems Technology at the University of Ap-plied Sciences FHTW, Berlin, Germany. He received his graduate engineer de-gree in 2006 with a diploma thesis on the monitoring of ionising radiation onelectron storage beams with Fiber Bragg grating sensors.
Since 2006 he is engaged as an engineer at the BAM Federal Institute for Ma-terials Research and Testing, Berlin, where he works on a number of nationaland European research projects dealing with the development of distributedfibre optic sensors, polymer fibre optic sensors and FBG sensors for differentapplications.
Katerina Krebber studied physics and received the Ph.D. degree in electricalengineering from the University in Bochum, Germany with a dissertation aboutdistributed fibre optic sensors based on nonlinear effects.
She has more than 15 years experience with the development of fibre opticsensors. In the past she was with Siemens AG and the Fraunhofer-Gesellschaft,Germany. Since 2004 she has been with BAM Federal Institute for MaterialsResearch and Testing, Berlin. At BAM she is head of the working group “Dis-tributed and Polymer Optical Fibre Sensors” and leader of a number of RTDprojects. She is an author and a coauthor of more than 60 scientific publicationsincluding invited talks at international conferences and patents.
Julien De Jonckheere received the M.S. degree in automatic and informaticsfrom the Techniques and Sciences University of Lille, France, in 2003 and thePh.D. degree from the Techniques and Sciences University of Lille in 2007.
He is a biomedical researcher in the field of biomedical sensors and moni-toring systems at the INSERM CIC-IT 807 research centre in Lille, France. Heis specialized in real time systems development for biomedical signals acquisi-tion and processing.
Mathieu Jeanne as anaesthesiologist in 2004 at the University of Lille, France,and received the Ph.D. degree from the Unviersity of Lille2, Lille, France, in2008, for his development of a heart rate variability related analysis for assessingpatient’s pain and wellbeing during general anaesthesia.
Since then, he has been working at the Pôle d’Anesthésie Réanimation of theUniversity Hospital of Lille.
Damien Kinet received the License in physics (oriented surface studies) fromthe Facultés Universitaires Notre de Dame de la Paix à Namur, Belgium, in1993 and the Special License in nuclear sciences from the Université de Liège,Belgium, in 1994. He is currently pursuing the Ph.D. student in the Electromag-netism and Telecommunication Department of the University of Mons, France,where he studies the behaviour of optical fiber sensors embedded into compositematerials.
From 2001 to 2008, he was a member of the research staff (Research Engi-neer) in the Applied Photonic Department of Multitel, Mons, France. Its workwas oriented to the design of fiber Bragg grating, the photosensitivity and theeffect of gamma radiation in optical glasses and he was involved in a Europeanproject (OFSETH). He is (co)-author of several scientific publications and in-ternational presentations.
Mr Kinet is a Student Member of SPIE.
Bernard Paquet received the M.S. degree in electricity and electronic engi-neering at the High School for Industrial Engineers, Liège, Belgium, in 1983.
He was then involved in nondestruction testing research activities for luggagecontrol in a R&D Department of private company. Since 1989, he is employedas a Researcher at Centexbel, the Belgian Textile Research Centre, where he wasproject leader of many projects as well as for the European project OFSETH. Hisresearch activities are in area of sensor integration in fabrics and smart textileapplications.
Annick Depré is with Elasta, Waregum, Belgium.She coordinates research and development projects within the company.
Elasta is a narrow fabric manufacturer, weaving, knitting, and braiding bands,straps, and cords. Her previous working experience is situated in market devel-opment, marketing, and communication in the telecommunication, financial,and textile industries. She has an experienced team of mechanical and machineoperators in the development of research projects.
Lorenzo T. D’Angelo studied mechanical engineering with focus on mecha-tronics at the Technical University of Karlsruhe, Germany. He received theDipl.-Ing. degree in 2006.
He is currently working toward the Doctorate degree at the Department ofMicro Technology and Medical Device Technology of the Technical Univer-sity of Munich, Germany. His research interests include the development ofintelligent textiles, mobile assistant devices for elderly people and embeddedprevention.
Torsten Thiel received the Diploma degree in electrical engineering in 2001from the Technical University of Dresden, Germany, where he had worked inthe scientific team of the Photonics group since 1998.
Since 2001, he has been with the Advanced Optics Solutions GmbH, Dresden,Germany. Currently he is part of the AOS research and development team andthe leader for national and European research projects. He is author and coauthorof more than 10 scientific papers in the fields of fiber optics applications andsensing and holds a couple of patents.
Regis Logier is a Medical Researcher at the University Hospital of Lille, France,in the field of Biosensors and e-Health.
He is the coordinator of the Clinical Investigation Centre – Innovative Tech-nologies (Inserm CIC-IT 807) and the Scientific Director of the University Hos-pital Research Commission. He holds a great experience in the field of the man-agement of technological projects, clinical research support, dissemination andexploitation of the research results.