`International Bureau
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`(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY(PCT)
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`Lain5>
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`(10) International Publication Number
`(43) International Publication Date
`WO 2011/051888 A2
`5 May 2011 (05.05.2011)
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`(51)
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`International Patent Classification:
`AG61B 5/00 (2006.01)
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`(21)
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`International Application Number:
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`PCT/IB2010/054858
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`(22)
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`International Filing Date:
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`27 October 2010 (27.10.2010)
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`(25)
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`(26)
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`(30)
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`(71)
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`(72)
`(75)
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`Filing Language:
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`Publication Language:
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`English
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`English
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`Priority Data:
`09174732.9
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`2 November 2009 (02.11.2009)
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`EP
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`Applicant(for all designated States except US): KONIN-
`KLIJKE PHILIPS ELECTRONICS N.V.
`[NL/NL];
`Groenewoudseweg 1, NL-5621 BA Eindhoven (NL).
`
`Inventors; and
`Inventors/Applicants (for US only): ACKERMANS,
`Paul, Anton, Josef [NL/NL]; c/o High Tech Campus
`Building 44, NL-5656 AE Eindhoven (NL). KASSIES,
`Roelf [NL/NL]; c/o High Tech Campus Building 44,
`NL-5656 AE Eindhoven (NL).
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`(74)
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`Agents: VAN VELZEN, Maaike, M.et al.; High Tech
`Campus, Building 44, NL-5656 AE Eindhoven (NL).
`
`(81) Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ,
`CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM, DO,
`DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT,
`HN, HR, HU, ID, IL, IN,IS, JP, KE, KG, KM,KN,KP,
`KR, KZ, LA, LC, LK, LR, LS, LT, LU, LY, MA, MD,
`ME, MG, MK, MN, MW, MX, MY, MZ, NA, NG, NL
`NO, NZ, OM,PE, PG, PH, PL, PT, RO, RS, RU, SC, SD,
`SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN, TR,
`TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW.
`
`(84) Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LR, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG,
`ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU,TJ,
`TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK,
`EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU,
`LV, MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SL, SK,
`SM, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ,
`GW,ML, MR,NE, SN, TD,TG).
`Declarations under Rule 4.17:
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`as to applicant's entitlement to apply for and be granted
`a patent (Rule 4.17(ii))
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`[Continued on next page]
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`(57) Abstract: The medical optical sensor (10)
`comprises at least one light emitter (20) for emit-
`ting light (21) directed to a part of the skin (50)
`ofa patient and at least one photo- detector (30)
`for detecting light (31) reflected from the skin
`(50). A housing (40) for carrying theat least one
`light emitter (20) and the at least one photo-de-
`tector (30) is provided, where the housing (40)
`has a contact area with the skin (50). The atleast
`one light emitter (20) is positioned within the
`housing (40) such that emitted light (21) im-
`pinges on the skin (50) in a central part of the
`contact area. The at least one photo-detector (30)
`is positioned in a peripheral part of the housing
`(40) such that light reflected (31) from the skin
`(50) to the outer part of the contact area is de-
`tectable by the at least one photo-detector (30).
`
`(54) Title: MEDICAL OPTICAL SENSOR
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`
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`APPLE 1011
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`WoO2011/051888A2[IITANNIETMTIITAARAMMMTU
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`APPLE 1011
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`1
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`WO 2011/051888 A2 IIfMIINI TMNT IAAT AA ACTAA AAA
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`Published:
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`—_without international search report and to be republished
`upon receipt ofthat report (Rule 48.2(g))
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`2
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`WO 2011/051888
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`PCT/IB2010/054838
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`Medicaloptical sensor
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`FIELD OF THE INVENTION
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`The invention relates to the field of medical sensors, and in particular to the
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`field of medical optical sensors and systems that make use of one or more of these sensors.
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`The invention further relates to methods for measuring the blood oxygenation level by using
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`these sensors.
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`BACKGROUNDOF THE INVENTION
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`Optical sensors are widely used to determine physiological parameters of
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`patients in medical care. The non-invasive measurement of the oxygen saturationin arterial
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`10
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`blood, also called pulse oximetry, is an application of optical medical sensors of particular
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`importance. In pulse oximeters the oxygensaturation in arterial blood (SpO2), sometimes also
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`referred to as blood oxygenation level, is determined by measuring the absorption of light
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`caused by oxy- (HbO2) and deoxyhemoglobin (HHb). Usually, the absorption is measured at
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`two different wavelengths where the extinction coefficients of HbO2 and HHbdiffer
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`15
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`significantly, for example at wavelengths of 660 nanometers (nm) and 940 nm.In addition to
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`measuring the oxygenation level of blood, pulse oximeters also provide a pulse signal for
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`determining a heart rate of a patient.
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`The light emitter and photo-detector that are used as the light source and the
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`light detector in a pulse oximeter can either be placed opposite of each other for measuring
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`20
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`the transmission oflight through the skin tissue, or adjacent to each other, measuring the
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`diffuse reflection of light from the skin tissue. Suitable measurementlocationsare for
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`example fingertips, toes, earlobes and the forehead.
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`With an increasing integration level of signal processing electronics and the
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`recent advancesin wireless transmission technology, wearable pulse oximeters are available
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`25
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`that allow measurements to be taken while a patient is free to move around. An example of a
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`wearable pulse oximeter is disclosed in the document US 2009/0240125 Al. The document
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`describes a pulse oximeterthat uses an optical sensor of the transmission type. An integrated
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`circuit including signal processing elements required to convert the detected light signals into
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`a pulse oximetry measurement is integrated into a carriage housing ofthe optical sensor.
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`3
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`WO 2011/051888
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`PCT/IB2010/054858
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`In optical measurements on the skin, motionartifacts are a serious point of
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`concern. Movements of a patient could lead to a movementof the sensor with respect to the
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`skin, which, in turn, leads to a change in the optical coupling between the sensor and the skin.
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`Sensor movements can also lead to pressure variations between the sensor and the skin,
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`which could cause perfusion variations in the skin underneath the sensor, resulting in signal
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`artifacts. Furthermore, the signal quality is inherently position sensitive for physiological
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`reasons, for example due to the small size of blood vessels.
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`It would therefore be advantageous to provide for medical optical sensors and
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`medical optical sensor systemsthat are less sensitive to motion artifacts.
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`SUMMARYOF THE INVENTION
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`The present application contemplates a medical optical sensor, a medical
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`optical sensor unit, a medical optical sensor system, and a method of measuring the blood
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`oxygenation level with a medial optical sensor address the abovementioned objects.
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`According to the invention, a medical optical sensor comprisesat least one
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`light emitter for emitting light directed to a part of the skin of a patient and at least one photo-
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`detector for detecting light reflected from the skin. A housing for carrying theat least one
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`light emitter and the at least one photo-detector is provided, where the housing has a contact
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`area with the skin. The at least one light emitter is positioned within the housing such that
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`10
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`15
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`20
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`emitted light impinges on the skin in a central part of the contact area. The at least one photo-
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`detector is positioned in a peripheral part of the housing such that light reflected from the
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`skin to the outer part of the contact area is detectable by the at least one photo-detector. This
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`way, a compact andlightweight sensor can be built.
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`In a preferred embodiment, the housing comprises an outer ring and an inner
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`25
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`ring. Both rings are concentric to each other. The outer ring has a rim that defines the outer
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`perimeter of the contact area with the skin. The innerring has a rim that defines the perimeter
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`of the central part of the contact area with the skin. The housing further comprises a base
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`plate for supporting the ringsat a side of the rings opposite of the respective rims and
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`wherein the at least one photo-detector is mounted between the outer ring and the innerring.
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`30
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`This way, the light emitter and the photo-detector are arranged concentric to each other ina
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`compact waythat allows obtaining a high signal quality.
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`Further according to the invention, a medical optical sensor unit comprises a
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`plurality of sensors as described above, which are arranged in form of a matrix and are
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`4
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`3
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`connected to each other by web members,such that the sensors and the web members form a
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`web-like structure with openings.
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`Further according to the invention, a medical optical sensor system comprises
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`at least one sensor as described aboveorat least one sensor unit as described above. The
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`medical optical sensor system furthermore comprises a control unit for operating the sensor
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`or the sensor unit. Flexible electrical connectors are present for connecting the sensor or the
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`sensor unit with the control unit.
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`Further according to the invention, a method of measuring the blood oxygen
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`level with a medical optical sensor comprises the following steps. Light is emitted by at least
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`10
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`one light emitter and directed to a part of a patient's skin. The light is then reflected by the
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`patient's skin and received by at least one photo-detector. Electrical signals from the at least
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`one photo-detector are processed in order to determine an oximetry value.
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`The basic idea behind all mentioned aspects of the invention is that
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`mechanical forces acting on the sensor which lead to pressure variations between the sensor
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`15
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`and the skin or even to a dislocation of the sensor with respect to the skin are minimized. One
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`type of force acting on the sensoris inertial force. Inertial forces result from an acceleration
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`of the inert mass of the sensor. Acceleration of the sensor is unavoidable if a patient moves.
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`For a given acceleration, the force acting on the sensoris proportional to the massof the
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`sensor. The small and compact design of the medical optical sensor according to the
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`20
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`invention allows building a lightweight sensor that accordingly only experiences small
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`acceleration forces and is well suited for wearable systems. Furthermore, the separation of
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`the electronic control unit and the sensor in the medical optical sensor system according to
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`the invention also minimizes the weight of the sensor and thus the acceleration forces that act
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`on the sensor. A coupling ofa plurality of sensors to form a sensorunit accordingto the
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`25
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`invention opensthe possibility to have a lightweight sensor arrangementwith a low position
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`sensitivity, i.e. the performanceof the sensor arrangementis less influenced by the position
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`of the sensor on the patient.
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`Anothertype of force acting on the sensorarises from theelectrical
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`connections use for operating the sensor. The mechanical decoupling of the sensor from the
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`30
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`electronic control unit due to the flexible electrical connection furthermore minimizes the
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`forces acting on the sensor.
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`Advantageous embodiments are provided in the respective dependent claims.
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`Still further advantages and benefits of the present invention will become apparent from and
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`WO2011/051888
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`elucidated with reference to the embodiments described hereinafter in connection with the
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`drawings.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`Fig. 1 showsa first embodiment of a medical optical sensorin a three-
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`dimensional sectional schematic drawing;
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`Fig. 2 shows a second embodiment of a medical optical sensor positioned on a
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`patient's skin in a schematic drawing;
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`Fig. 3 is a schematic illustration of the influence of the lateral separation of a
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`10
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`light emitter and a photo-detector on the origin of the detected light in a medicaloptical
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`sensor;
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`Fig. 4 showsa first embodiment of a medical optical sensor unit in a schematic
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`drawing seen from above;
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`Fig. 5 showsa side view of a second embodiment of a medical optical sensor
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`15
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`unit in a schematic drawing;
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`Fig. 6 showsa first embodimentof a medical optical sensor system in a
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`sectional schematic drawing; and
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`Fig. 7 showsa side view a second embodimentof a medical optical sensor
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`system in a sectional schematic drawing.
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`20
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`DETAILED DESCRIPTION OF EMBODIMENTS
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`With reference to Figure 1, a medical optical sensor 10 is shownthat
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`comprises a light emitter 20 for emitting light 21, a photo-detector 30 for detecting reflected
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`light 31 and a housing 40 thatis basically cylindrical in shape. The housing 40 includes an
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`25
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`outer ring 41 having a rim 42 and an innerring 43 having a rim 44. On the side opposite of
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`the rims 42,44, the rings 41, 43 are attached to a commonbaseplate 45. On the side opposite
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`of the rings 41, 43, the base plate 45 provides an emitter mount 46 for holding the light
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`emitter 20. The base plate 45 has a central opening that extends the opening ofthe innerring
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`through the base plate 45. The opening in the base plate 45 allows emitted light 21 to leave
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`30
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`the housing 40 through the innerring 43. The photo-detector30 is circular in shape and
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`mounted in the circular groove formed by the base plate 45, the outer ring 41 and the inner
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`ring 42.
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`The medicaloptical sensor 10, also abbreviated as sensor 10 in the following,
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`is designed to be attached to the skin with at least the rims 42 and 44 touching the skin. The
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`emitted light 21 is directed onto the skin and partly penetrates into the skin whereit interacts
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`with the skin tissue and in particular with blood vessels contained in the skin. A part of the
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`light leaves the tissue again after one or more scattering events and enters the photo-detector
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`30 as the reflected light 31. Due to the diffuse reflectance, the area of the skin through which
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`the reflected light 31 leaves the skin is by far larger than the entrance spot of the emitted light
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`21 on the skin. Since, in first order, the light is scattered isotropically in all directions in the
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`diffuse reflectance process, the area through whichthe light leaves the skin is essentially
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`circular in shape. The sensor 10 andthe circular shaped photo-detector 30 accountfor this
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`effect, which leads to a high detection efficiency.
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`10
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`In the embodiment shown,the rims 42 and 44 are positioned in the same
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`plane. The circularly shaped photo-detector 30 is mounted recessed from this plane in a
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`direction way from the skin. In this configuration, the inner ring 43 shadowsthe photo-
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`detector 30 from emitted light 21 shining directly onto the photo-detector 30, thereby
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`overwhelmingthe signal of the reflected light 31 which is much lowerin intensity. In an
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`15
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`alternative configuration, the photo-detector 30 could also be mounted withits light entrance
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`surface positioned within the plane defined by the rims 42 and 44. In orderto protect the light
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`emitter 20 and the photo-detector 30 and in order to have a planar contact area between the
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`sensor 10 and the skin,it is possible to fill the remaining parts of the inner andthe outer rings
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`41 and 43 with a transparent resin. For reasons of biocompatibility and hygiene, a medical-
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`20
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`grade resin suitable for medical applicationsis preferred.
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`In orderto attach the sensor 10 to a patient's skin, a medical-grade optically
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`transparent adhesive can be used. This can either be an adhesive gel or a double-sided
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`adhesive tape. In particular if the sensor 10 does not have a planar contact area for contacting
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`the skin, for exampleif no resin is usedto fill the rings 41 and 43, a gel is suitable to ensure a
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`25
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`good optical transition of light between the skin and the light emitter 20 or the photo-detector
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`30. In all cases, the contact area is defined to be the area that is delimited by the perimeter of
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`the outer ring 41.
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`The close integration of the light emitter 20 and the photo-detector 30 into the
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`compact housing 40, which can be made with a very light weight by using a one piece
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`30
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`extraction molded material, leads to a medical optical sensor 10 that only experiences very
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`small acceleration forces. As a result, the movements of the sensor with respect to the
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`underlying skin are minimized andthe signal delivered by the photo-detector 30 is less
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`affected by movementartifacts.
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`Both light emitter 20 and photo-detector 30 can be semiconductor devices, for
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`example based on silicon (Si), gallium nitride (GaN)or gallium arsenide (GaAs) or a
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`combination thereof. A light emitting diode (LED)or laser diode (LD) can be used as the
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`light emitter 20. The light emitting diode could comprise more than one die, which offers the
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`possibility of emitting light at different wavelengths. Alternatively, the emitter mount 46 of
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`the housing 40 could be designed such that more than one LEDs or LDs could be mounted,
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`either for the option of having light of different wavelengths available, or for the option of
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`providing emitted light 21 at a single wavelength, but with increased power or powerdensity.
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`A photodiode can be used as the photo-detector 30. As an alternative to the
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`10
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`ring shapedcircular single photo-detector 30 shownin Fig. 1, a plurality of smaller photo-
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`detectors could be used, for example small photodiodesthat are arranged between the inner
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`ring 43 and the outer ring 41. However, a single photo-detector 30, in particularifit fills the
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`available space betweenthe inner and the outer rings 41, 43, would offer the best detection
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`sensitivity.
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`15
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`A typical application of the shownoptical medical sensor 10 could be the
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`measurementof the oxygenation level of blood in a pulse oximeter. In this case, a light
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`emitter 20 is used that emits light at two different wavelengths, usually around 660 nm and
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`940 nm.
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`Figure 2 shows another embodiment of a medical optical sensor 10. Elements
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`20
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`having the same or comparable functions are denoted by the same reference numeralsin all
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`figures.
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`The optical medical sensor 10 of Fig. 2 is attached to a skin 50 of a patient by
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`using a medical transparent adhesive 60, a double-sided transparent adhesive tape in this
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`case. In accordance with the embodiment shownin Fig. 1, the medical optical sensor 10 of
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`25
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`Fig. 2 comprises a housing 40 with an outer ring 41 and an innerring 43 andrespective rims
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`42, 44. It also comprises a light emitter 20 for emitting light 21 impinging on the skin 50
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`within the vicinity of the inner ring 43. As in the embodimentof Fig. 1, the photo-detector 30
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`is a single circular shaped photo-detectorfilling almost the entire available space between the
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`innerring 43 and the outer ring 41. In contrast to the embodiment shownin Fig.1, the light
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`30
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`emitter 20 is mounted within the ring 43 rather than on top ofthe base plate 45, thereby
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`reaching a very high level of integration. Both the light emitter 20 and the photo-detector 30
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`are mounted recessed from the plane defined by the rims 42 and 44. Asa result, the inner ring
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`43 prevents light emitted by the light emitter 20 from shining directly into the photo-detector
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`30. In the embodiment shown,the light emitter 20 and the photo-detector 30 are embedded
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`into a transparent medical resin 47. Thus, the resin 47 does notonly fill the remaining parts
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`of the inner and the outer rings 41 and 43 to protect the light emitter 20 and the photo-
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`detector 30, but also fixes them.It is possible to mount the light emitter 20 and the photo-
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`detector 30 by this meansonly.
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`Figures 3A and 3B illustrate the dependenceofthe origin ofthe reflected light
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`31 from the lateral distance between emitted light 21 entering the skin andreflected light 31
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`emerging from the skin 50. The skin 50 comprises three sub-layers, called epidermis layer
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`51, dermis layer 52 and fat layer 53. The dermis layer 52 contains a dense network of small
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`blood vessels andis the layer of the main interest for medical optical measurements.
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`10
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`In Figs. 3 A and B, r denotes the mean distance between the entrance spot of
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`light 21 entering the skin and the area through whichreflected light 31 leaves the skin. A
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`small aperture for the entrance and the exit area is assumed. The vertically hedged u-shaped
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`area schematically indicates the detection volume32, being the volumeofthe skin 50,in
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`which one or morescattering events occur for leading light from the entrance aperture to the
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`15
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`detection aperture. Accordingly, the detection volume 32 can be regardedasthe part of the
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`skin, for which physiological information can be obtained. In the figures, d denotes the depth
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`with respect to the surface of the skin 50 down to which the detection volumereaches.
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`Fig. 3A showsthe situation for a distance r of approximately 1 mm.It is
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`apparentthat the detection volume 32 just overlaps with the upper part of the dermis layer 52.
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`20
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`Fig. 3B showsthesituation for a distance r of approximately 3 mm.Here, the
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`detection volume 32 just reaches down to the fat layer 53.
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`The figures show that a distance r between approximately 1 mm and 3 mm is
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`well suited to perform medical optical measurementsof the reflection type, since then the
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`dermis layer 52, which is of major physiologicalinterest, is being sampled. Accordingly, for
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`25
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`a sensor 10 with a concentric arrangementofthe light emitter 20 and the photo-detector 30,
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`as for example shownin the embodiments of Figs. 1 and 2, an inner ring 43 with a radius of
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`approximately one mm andan outer ring 41 with a radius of approximately 3 mm radiusis
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`advantageous.
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`Figure 4 showsa schematic drawing ofa first embodiment of a medical optical
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`30
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`sensor unit 100 seen from above. The medical optical sensor unit 100, also abbreviated as
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`sensor unit 100 in the following, is depicted from a top view with its invisible down side
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`intended to be attachedto the skin ofa patient.
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`The sensor unit 100 comprises a plurality of sensors 10, which are in this
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`embodimentarranged in a regular matrix with a hexagonallattice structure. Adjacent sensors
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`9
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`10 are connected to each other by web members 110, some of which furthermore have
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`integrated electrical connections 112. For a clear depiction, only some of the mentioned
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`elements carry reference numerals in Fig. 4. The web members110 are deliberately narrow in
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`order to leave openings 120 between adjacent sensors 10 and the connecting web members
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`110. Through the openings 120, the skin ofthe patient is partly exposed to the environment,
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`such that an exchangeofair and in particular moisture is possible. The web members 110 are
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`in addition recessed from the skin to expose the skin even more and enhance the exchange of
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`air and moisture. The resulting open matrix structure enables a long term andirritation-free
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`use on the patent's skin. At least some of the web members 110 can be madeofa flexible
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`10
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`material such that the sensor unit 100 easily adapts to the surface structure and to the
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`curvature ofthe skin.
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`The type of the sensors 10 used in the sensor unit 100, their numberandthe
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`geometry of their arrangement of the embodiment shownin Fig. 4 are only exemplary. While
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`the embodiment of Fig. 4 makes use of a cylindrical sensor 10 with concentric light emitter
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`15
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`and photo-detector and a circular contact area with the skin, a matrix-like sensor unit 100
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`could comprise medical optical sensor having a different outline and/or light emitters and
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`photo-detectors that are positioned differently with respect to each other, for example
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`mounted side by side in a rectangular shaped housing. Furthermore, the sensor unit 100 is not
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`limited to medical optical sensors. It is also possible to combine other medical sensors to
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`20
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`build a medical optical sensor unit, for example medical electrical sensors like electrodes for
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`use in electroencephalography (EEG)or electrocardiography (ECG).
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`Sensor units with more or less than the shown numberof sensors are
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`conceivable as well. Also other arrangements than the shown hexagonalstructure, such as for
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`example linear, triangular, rectangular or quadratic arrangements are possible.
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`25
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`By combining a plurality of sensors 10 within the sensor unit 100,
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`measurements can be performed at a numberoflocations on the skin simultaneously. The
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`derived signals of the plurality of photo-detectors contained in the sensors 10 can be
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`processed further and analyzed in order to receive a maximal signal amplitude and quality.
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`For example, the electrical signals of the photo-detectors could be averaged in order to
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`30
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`minimize the position sensitivity that a single sensor inherently shows. This is particularly
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`important for small sized sensors, where a single sensor could be positioned above a spot of
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`the skin with a low perfusion. Whenaveraging the signals derived by the different photo-
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`detectors, a weighting factor could additionally be used to accountfor the signal quality of
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`the individual single signals. In this way well-positioned photo-detectors that provide a signal
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`10
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`with a high signal-to-noise ratio are preferred over less well-positioned sensors 10 that only
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`provide a signal with a low signal-to-noiseratio.
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`Figures 5A and 5B each showasection of a second embodimentof a medical
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`optical sensor unit 100. As in the embodiment shownin Fig.4, a plurality of sensors 10 is
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`provided for, of which two are depicted in the figure. The two adjacent sensors 10 are
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`connected to each other with a web member 110. In contrast to the embodiment shown in
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`Fig. 4, the sensor unit 100 additionally comprises stands 130 that are equalin size to the
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`sensors 10, but do not provide any electrical functioning. The stands 130 are connected to the
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`adjacent sensors 10 by flexible and elastic web members 111. These flexible and elastic web
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`10
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`members 111 are slightly slanted such that the stands 130 lie in a planethat is vertically
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`dislocated from the plane in which the sensors 10 are arranged. In this way a corrugated
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`matrix is formed.
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`Fig. 5A depicts a situation, in which the sensor unit 100 is put on a patient's
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`skin 50 without applying any force to the sensor unit 100. Asa result of the corrugation of
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`the matrix, the stands 130 float above the skin 50, whichis indicated by a height h larger
`zero.
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`Fig. 5B showsa situation, in which an external force directed towards the skin
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`is applied to the stands 130, such that the stands 130 do touch the skin as indicated by a
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`height h equal to zero. Due to the corrugation, the flexible and elastic web members 111
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`press the shown sensors 10 onto the skin 50. The force applied on the sensor 10 by the
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`flexible and elastic web members 111 is predetermined and can be controlled by using an
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`appropriate material and an appropriate dimensioning for the flexible and elastic web
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`members 111. This makes the applied force an inherent parameter of the device and
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`independent of the way a user applies the device.
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`Asit is the case in the embodiment shownin Fig. 4, also here the type of the
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`sensors 10 used in the sensor unit 100, their number and the geometry of their arrangementis
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`only exemplary. The same holdstrue for the stands 130. In particular the number and
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`geometry of the stands 130 and the ratio between the numberof sensors 10 and stands 130, is
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`not limited to the embodiment shown. Also the sensors 10 and the stands 130 can be of the
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`same shapeas in the showncase, but could alternatively also differ in size and shape.
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`Furthermore, stands 130 could be positioned at regular lattice positions of the matrix and, in
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`this sense, replace sensors 10. Alternatively or additionally, stands 130 could be positioned
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`dislocated from regular lattice positions in so called lattice interstitial positions.
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`Fig. 6 showsa first embodiment of a medical optical sensor system attached to
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`the skin 50 of a patient in a side view.
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`The system comprises a medical optical sensor unit 100 containing of medical
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`optical sensors 10, two of whicharevisible in the figure, and web members 110 connection
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`the sensors 10. The system further comprises an electric control unit 70 with a powersupply
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`71 and a wireless transmitter 72 explicitly shown. Further electrical elements, for example for
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`driving the light emitters of the sensor unit 100 and for receiving and processing the electrical
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`signals of the photo-detectors of the sensor unit 100, are not explicitly shown. The control
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`unit 70 and the sensor unit 100 are electrically connected via a flexible electrical connector
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`10
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`80.
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`The control unit 70 and the sensor unit 100 are individually and separately
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`attached to the skin 50. In both cases, an adhesive could be used for that purpose.
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`Alternatively, only the sensor unit 100 could be attached to the skin 50 by an adhesive, while
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`the control unit 70 is attached to the skin 50 by meansofan elastic band.
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`Theflexible electric connector 80 could, for example, be a ribbon cable with
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`very thin stranded wires, or a flexible flat cable with multiple electrical conductors bonded or
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`evaporated on a thin insulating plastic film base. Using thin and flexible materials for the
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`flexible electric connector 80 results in a mechanical decoupling of the sensor unit 100 from
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`the control unit 70. In this way vibrationsor dislocations of the relatively heavy control unit
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`70 are not transferred onto the sensor unit 100, thereby not disturbing the signal quality.
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`The separation of the control unit 70 and the sensor unit 100 further keeps the
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`inert mass of the sensor unit 100 small compared to systems wherethe electronics and
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`probably even the power supply unit are integrated into the sensor unit. Thisis particularly
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`important for systems that use convenient but power-consuming wireless technology for
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`transmitting the measured physiological parameters to a monitor station, or for systemsthat
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`are designed for a long-term observation of the patient, since in such cases a power supply
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`unit with a sufficient battery capacity and an according heavy weight would haveto be
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`provided.
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`Figure 7 shows a second embodiment of a medical optical system. The system
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`comprises a frame 90 with a roundring-like base and a traverse 91 spanning overthe base.
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`The frame 90 is shaped in form of a wristwatch and attachable to the skin 50 of a patient with
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`an elastic band 92, for example an arm wrist. An electric control unit 70, by way of example
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`depicted as a printed connector board (PCB) with a battery as a power supply 71, is rigidly
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`attached to the frame 90. A medicaloptical sensor 10 is positioned at the center of the frame
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`90 underneath the traverse 91 and mechanically attached to the traverse 91 by a spring 93.
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`The sensor 10 and the control unit 70 are electrically connected via a flexible electrical
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`connector 80.
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`In this embodiment, the sensor 10 is pressed onto the skin 50 by a force thatis
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`defined by the spring constant of the spring 93 and the geometry of the frame 90. Thelarge
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`supporting surface of the frame 90 on the skin 50 leads to a defined height of the traverse 91
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`above the skin 50. Accordingly, the sensor 10 is pressed onto the skin 50 with a relatively
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`constant and predetermined force. At the sametime, the sensor 10 is mechanically decoupled
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`from the frame 90 and the control unit 70, in particular concerning slight lateral movements
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`10
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`of the frame 90 on the skin. As an alternative or in addition to the elastic band 92, the frame
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`90 could be attached to the skin 50 by a medical grade adhesive. In one embodiment, the
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`adhesive could be transparent and fix the sensor 10 as well as the frame 90. In another
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`embodiment, the adhesive could be provided with a central opening that leaves the vicinity of
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`the sensor 10 on the skin blank and only fixes the frame 90. In the letter case, the adhesive
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`does not haveto be transparent.
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`In all embodiments shownor described in connection with Figs. 6 and 7, one
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`or more sensors 10 could be used in the system,either individually attached to the skin 50 or
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`combined together as one or more sensor units 100.
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`The sensors used in the system could be medical optical sensors 10 as
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`described in connection with the Figs. 1 and 2. However, the shown separation of the sensors
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`and the control unit, and the mechanical decoupling due to the usage ofthe flexible electrical
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`connection in the sensor system is also applicable to medical sensors having a different form
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`and/or function than the ones described in connection with Figs. 1 and 2.
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`While the invention has bee