PCT
`
`WORLDINTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`(22) International Filing Date:
`
`6 June 1996 (06.06.96)
`
`+s
`
`
`
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
` (11) International Publication Number: — WO 96/41566
`(51) International Patent Classification 6 :
`
`
`
`A61B
`(43) International Publication Date:|27 December 1996 (27.12.96)
`
`
`
`
`
`
`
`(21) International Application Number: PCT/IL96/00006|(81) Designated States: AM, AT, AU, BB, BG, BR, BY, CA, CH,
`CN, CZ, DE, DK,EE, ES,FI, GB, GE, HU,IL,IS, JP, KE,
`
`
`KG, KP, KR, KZ, LK, LR, LT, LU, LV, MD, MG, MN,
`MW,MX, NO,NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK,
`
`TJ, TM, TT, UA, UG, US, UZ, VN, ARIPO patent (KE,
` (30) Priority Data:
`LS, MW,SD, SZ, UG), European patent (AT, BE, CH, DE,
`
`114080
`9 June 1995 (09.06.95)
`IL
`DK,ES, FI, FR, GB, GR,IE, IT, LU, MC, NL, PT, SE),
`
`
`114082
`9 June 1995 (09.06.95)
`IL
`OAPIpatent (BF, BJ, CF, CG, CI, CM, GA, GN, ML, MR,
`
`NE, SN, TD, TG).
`
`
` (71) Applicant (for all designated States except US): CYBRO
`Published
`MEDICALLTD.[IL/IL}; P.O.B. 600, Matam, 31000 Haifa
`
`
`(IL).
`
`Withoutinternational search report and to be republished
`
`
`upon receipt of that report.
`
`
`(72) Inventors; and
`
`(75) Inventors/Applicants (for US only): FINE, Ilya [IL/IL]; 59/6
`
`Herzel Street, 76541 Rehovot (IL). STERNBERG,Alexan-
`
`der [IL/IL]; 31 Harofe Street, 34367 Haifa (IL). KATZ,
`
`Yeshayahu [IL/IL]; 45A Eder Street, 34752 Haifa (IL).
`
`GOLDINOV, Leonid [IL/IL]; 21A/9 Nativ Hen, 32243
`
`Haifa (IL). RAPOPORT,Boris [IL/IL]; 3/12 Nativ Shom-
`ton, 28000 Kiryat Ata (IL).
`
`
` (74) Agent: COHN,Michael; Reinhold Cohn and Partners, P.O. Box
`
`4060, 61040 Tel-Aviv (IL).
`
`
`
`
`
`
`(57) Abstract
` ANTE
`
`
`}
`
` A
`
`for
`There is described a new sensor
`optical blood oximetry as well as a method
`and apparatus in which the new sensoris used.
`The new sensor includes two point-like light
`emitters positioned in the center of the device
`in close proximity to each other andatleast one
`and preferably two annular detector terminals
`concentrically surrounding the light emitters.
`The light sources may, for example, be two
`laser diodes emitting each monochromatic light
`within the range of 670-940 nm. The detector
`devices are, for example, photodiodes.
`
`($4) Title: SENSOR, METHOD AND DEVICE FOR OPTICAL BLOOD OXIMETRY
`
`1
`
`APPLE 1009
`
`1
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`APPLE 1009
`
`

`

` applications under the PCT.
`
`FOR THE PURPOSES OF INFORMATION ONLY
`Codes used to identify States party to the PCT onthe front pages of pamphlets publishing international
`
`a<
`
`MW
`MX
`NE
`NL
`NO
`NZ
`PL
`PT
`RO
`RU
`SD
`SE
`SG
`SI
`SK
`SN
`SZ
`TD
`TG
`TJ
`TT
`UA
`UG
`US
`UZ
`VN
`
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Singapore
`Slovenia
`Slovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Trinidad and Tobago
`Ukraine
`Uganda
`United States ofAmerica
`Uzbekistan
`Viet Nam
`
`AM
`AT
`AU
`BB
`BE
`BF
`BG
`BJ
`BR
`BY
`CA
`CF
`CG
`CH
`cI
`CM
`CN
`cs
`CZ
`DE
`DK
`EE
`ES
`FI
`FR
`GA
`
`Armenia
`Austria
`Australia
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`C&e d'Ivoire
`Cameroon
`China
`Czechoslovakia
`Czech Republic
`Germany
`Denmark
`Estonia
`Spain
`Finland
`France
`Gabon
`
`GB
`GE
`GN
`GR
`HU
`IE
`IT
`JP
`KE
`KG
`KP
`KR
`KZ
`ui
`LK
`LR
`LT
`LU
`LV
`MC
`MD
`MG
`ML
`MN
`MR
`
`United Kingdom
`Georgia
`Guinea
`Greece
`Hungary
`Treland
`Italy
`Japan
`Kenya
`Kyrgystan
`Democratic People’s Republic
`ofKorea
`Republic of Korea
`Kazakhstan
`Liechtenstein
`Sri Lanka
`Liberia
`Lithuania
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`Mali
`Mongolia
`Manritania
`2
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`WO 96/41566
`
`PCT/IL96/00006
`
`SENSOR, METHOD AND DEVICE FOR
`OPTICAL BLOOD OXIMETRY
`
`FIELD OF THE INVENTION
`
`The present invention relates to a novel sensor for non-invasive
`optical blood oximetry, such as blood pulse oximetry effected on a blood
`perfused tissue;
`to a method of optical oximetry; and to a device suitable
`for performing the method.
`
`BACKGROUND OF THE INVENTION
`
`In the prior art there is described a method of measuring the
`degree of oxygen saturation of blood using what is commonly known asthe
`optical pulse oximetry technology. References to that technology may be
`found in US 4,167,331, US 4,938,218,
`in the brochure "Fetal Oxygen
`Physiology" sponsored by NELLCOR LTD., and there are others.
`In
`accordance with this method, a blood perfusedtissueis illuminated andlight
`absorption by the tissue is determined by a suitable light sensor. Pulsatile
`changes in the value of absorption which are caused by cardiovascular
`activity of the blood are then used to determinethe characteristic ofinterest,
`i.e. the degree of blood oxygen saturation.
`The value of oxygen saturation (SaO,) in arterial blood is defined .
`by the following known equation:
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`5aQ
`HbO
`) = —————>__. 100%
`[HbO,] + [Hb]
`
`(1)
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`PCTAL96/00006
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`where [HbO,] is the concentration of oxygenated hemoglobin concentration
`in a unit of
`blood volume and [Hb]
`is the concentration of reduced
`hemoglobin.
`In commonly used methods of pulse oximetry a tissue under
`investigation is illuminated by light having at least two components of
`different wavelengths, and the measurements are based upon the following
`two physical phenomena:
`(a)
`the light absorbance of oxygenated hemoglobin is different from
`that of reduced hemoglobin, at each of the two wavelengths;
`(b)
`the light absorbance of the blood perfused tissue at each
`wavelength has a pulsatile component, which results from the fluctuating
`volumeof arterial blood passing across the tissue between the light source
`and the sensor.
`It is therefore assumed,that the pulsatile absorbance component
`of a tissue layer
`located between the light
`source and the sensor
`characterizes the degree of Oxygen saturation of arterial blood.
`Various types of sensors designed for effecting measurements in
`the performanceofoptical pulse oximetry are knownin the art, and among
`the known optical sensors those dedicated to measuring the degree ofoxygen
`saturation offetal arterial blood constitute a particular group of such devices.
`.
`Basically, the prior art discloses two types of optical sensors
`which are associated with and serve for two modes of performing optical
`blood oximetry:
`transmission pulse oximetry in which so-called
`transmissive sensors are used and reflection pulse oximetry in which so-
`called reflectance or transflectance sensors are used.
`In transmission pulse
`oximetry one measures light passing across a blood perfused tissue such as
`a finger, an earor the like by placing a light emitter and the detection of a
`transmissive sensorat two opposite sides ofthe tissue under examination, as
`described for example in US 4,938,213. In reflection oximetry, on the other
`hand,reflectanceortransflectance sensors can be used which comprise both
`light emitters and light detectors which are accordingly placed on one and
`the same side of the tissue under examination, as described, for example, in
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`US 5,228,440,
`5,247,932, 5,099,842 and in WO 90/01293. Reference to
`the two types of sensors can also be found, for example, in US 5,247,932
`and in "Fetal Oxygen Saturation Monitoring" sponsored by NELLCOR.
`Both the transmission and the reflection modes of operation have
`specific limitations of applicability and their accuracy in general, and in
`specific applications in particular is not satisfactory. Thus, for example, the
`transmission technology can besuccessfully applied only in cases where the
`tissue to be investigated forms a distinctive protrusion which makes it
`possible to apply a light emitter and a light sensor at opposite surfaces.
`It is thus evident that the reflection technology is the one most
`commonlyresorted to, notably in fetal oximetry. Unfortunately, however,
`accuracy of the conventional
`reflection technology is
`rather
`low in
`comparison with that of the transmission one, because the degree of
`diffusion of the emitted light in the tissue is unknown, which meansthatthe
`nature of the functional interdependence betweena light signal received by
`the sensor and the degree of blood oxygen saturation is also unknown.
`Another disadvantage of the known reflection technology is a partial
`shunting of the emitted light on the surface of the tissue between the source
`and the sensor, and a specularreflection created by the superficial layer of
`the tissue.
`
`U.S. Patent No. 5,009,842 describes a sensor with means for
`overcoming the problem of shunting of the emitted light on the outer surface
`of the tissue between the light source and the detector. U.K. Patent
`Application No. 2 269 012 proposes to select and separate light signals
`resulting from light reflection by a superficial layer of a blood perfused
`tissue such as skin or hair, essentially by choosing a particular distance
`between the locations of emitting and detecting optical
`fibers on the
`contacted surface of the tissue under examination.
`Fetal oximeters usually comprise applicators which generally
`include a plate with at least one substantially point-like light source and at
`least one substantially point—like light detector suitably spaced from the light
`source(s). One drawback of such applicators is that if the applicator is
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`applied to a non-uniform section of the skin, such as a hairy portion or a
`birthmark,
`the light Signal received by the detector(s) will be distorted.
`Even in relatively large size oximeters, e.g. of the kind described in
`US 5,099,842 the light sources and detectors 2m sill point—like and
`accordingly it is Practically un’: siaable for an 0Perator to apply it
`to 3
`wrongportion of the skin of a fetus.
`4.45 mnortant to recall that the basic assumption underlying the
`theory of transmission and reflection ovimetry is, that optical paths of light
`Tays with different wavelengths emitted into the <i--ne by different light
`Sources, are substantially equal. However,in actual fact the Jengin UF seh
`an optical path dependson the light scattering coefficient which,in its turn,
`is a function of the wavelength. Accordingly, when the wavelengths ofthe
`light sensors chosen for oximetry measurem
`ents and with them the light
`Scattering coefficients significantly
`from each Other,
`the basic
`differ
`assumption of substantial equivalenceof optical paths is violated.
`In cases where two or more point-
`like light sources are used,
`problems mayarise due to the fact that the ski
`n surface, blood vessels and
`other parts of biological media, are not Structured anddistributed homoge-
`neously. Thus,ifone point—like light source emitting at a given wavelength
`is applied to any site of a non-uniform skin, while the other light source
`emitting at a different wavelength is attached to a topographically adjacent
`but optically different site, then in consequence ofdifferent light sCattering
`and absorption at the two distinct wavelengths, which occurs from
`beginning, the optical paths of the light emitted by the two source
`be equal. Thetotal amountof optical energy acquired by a detect
`or can be
`approximated as being the sum ofthe amounts of
`energy portions carried by
`the Propagating rays reaching the detector.
`As the optical paths of these
`Tays are wavelength-dependent and since eac
`h part of that energy travels to
`the detector through a different Optical path
`, the total attenuation of light
`components with different wavelengths can significantly differ from each
`other, with the Consequence of the occurrence of a random error in the
`evaluation of oxygen blood saturation.
`
`the very
`S cannot
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`Another drawback of known sensors for blood oximetry is that
`they utilize LEDsas light sources for illuminating a tissue with light having
`two wavelength components. The LED light sourcesareeither installed in
`the probeitself suck as, for example,
`in US 4,938,218 or linked to the
`probes via optical
`fibers
`such as,
`for example,
`in US 5,099,842,
`GB-A~-2 269 012, WO 91/18549 and WO 90/01293. Such light sources
`may provide, for example, a pair of wavelengths of 700 nm and 800 nm
`which are suitable for the purposesof blood oximetry. However,although
`it is well known that the accuracy of oximetric measurements increases the
`Closer the two wavelengths are to each other, nevertheless within the
`wavelength range required for oximetry LEDsare incapable of Providing
`two wavelengths closer to each other than 100 nm.
`
`GENERAL DESCRIPTION OF THE INVENTION
`Against the above background it
`is an object of the present
`invention to provide a novel sensorfor optical blood oximetry, free of the
`disadvantages of known technologies.
`It is a further object of the invention to provide a novel method
`of optical blood oximetry,
`It is yet another object of the invention to Provide an apparatus
`for the performance of optical blood oximetry embodying the novel sensor
`and a method making use thereof.
`Essentially, the objects of the present invention are achieved by
`ensuring that the light paths oflight components with different wavelengths,
`emitted by at least two distinct light emitters, will always be substantially
`equal
`to each other irrespective of the nature of the skin and of the
`underlying tissue and also irrespective of variations in physiological
`
`conditions.
`
`According to one aspect of the present invention thereis provided
`a Sensor for noninvasive optical blood oximetry, comprising a carrier body
`with an applicator block having a contact surface which in operation faces
`a blood perfused body tissue of a subject under investigation, which
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`two point-like light emitters
`least
`applicator block is fitted with at
`positioned in close proximity to each other and emitting each light at a
`wavelength distinct from that of the other, and at least a first, essentially
`annular light detector terminal concentrically surrounding said at least two
`light emitters, coupled to a light detector device and having a free, light-
`acquiring end for the acquisition of light arriving from said bodytissue.
`It has been found that even if a sensor according to the invention
`is placed on to the skin without fine adjustment, at least a portion of the
`annular detector will contact the skin without encountering any intervening
`opaqueobstacles, and consequently an emitted light signal will, after passing
`through the tissues, be acquired by the detector terminal.
`In other words,
`the signal—to-noise ratio of a sensor according to the present invention is
`Significantly improved dueto the specific novel configuration ofthe detector
`terminal and the geometry ofthe sensor.
`i.e.
`It should be noted,
`that due to the essentially annular,
`axisymmetric configuration ofthefirst detector in a sensor according to the
`invention, any local disturbances in the tissue structure which in case of a
`prior art point-like detector would result in significant deviation of the
`optical path, will not affect the intrinsic average optical path of light of a
`given wavelength. Put in other words, the annular shape ofthe detector and
`the geometry of the sensor ensure the Stability of the optical paths for each
`given wavelength.
`In a preferred embodimentofthe invention the applicator block
`has a second essentially annular light detector terminal Spaced from and
`concentric with saidfirst light detector termina]. With a sensor having such
`a configuration it
`is possible to perform a modified, new method of
`evaluation of blood oxygen saturation, as will be described further below.
`The said light emitters may each be a light source positioned
`within the applicator block, or alternatively a light emitter terminal having
`a free,
`light emitting end and being coupled via another end to a light
`source. Typically the light emitter terminals are in form of bundles of
`optical fibers.
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`The light detector terminals preferably consist of a plurality of
`optical fibers having each one free, light-acquiring end and coupled via
`another end to a light detector device.
`The provision that the light emitting ends of the light emitter
`terminals should be point-like means that they should each have a small
`area. Typically the two terminals will be complementary to each other
`forming together a circular plate having a diameter of the order of 1 mm.
`Thelight detector(s) of a sensor according to the invention may,
`for example, comprise a plurality of photo—diodes. Examples of light
`sources in a sensor according to the present invention are laser diodes
`capable of producing at least two distinct powerful monochromatic light
`radiation with very close wavelengths, within the range of from 670
`to 940 nm and preferably 750 to 800 nm, differing from each other bysay,
`10 -20nm. Thus, in a preferred embodimenta first laser diode emits at
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`750-760 nm and a second laser diode at 780-800 nm. Such characteristics
`
`are not available in light sources, such as LEDs used in conventional
`oximetry apparatuses. The laser diodes have the further advantage of
`enabling a more linear absorption by the tissues of monochromatic light of
`any wavelength within the intrinsic emission range.
`In view of all this, the use of laser diodes in the optical sensors
`according to the invention enables to fulfil a basic requirementof oximetry,
`namely the optical paths equivalence at different wavelengthsof radiation.
`Preferably the carrier body of a sensor accordingto the invention
`
`is opaque.
`
`In one embodiment, said applicator block in a carrier body of a
`sensor according to the invention comprises an axial, throughgoing bore
`perpendicularto said contact surface and holdingsaid light emitter terminals,
`and at least one substantially annular space concentrically surrounding said
`bore and accommodating each a light detector terminal.
`In one particular design of a sensor according 10 the foregoing
`embodimenteach light detector terminal is placed within said substantially
`annular space of said applicator block such that the free light acquiring ends
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`thereof are sunk within the accommodating annular space and removed from
`Said contact surface, wherebya free portion of said annular space constitutes
`a collimator that rejects specularreflection. The distance by which thefree
`ends are removed from the contact surface is So selected, that only light
`arriving from arelatively deep layer of the blood perfused tissue and
`directed substantially parallel to the axis of the applicator block is acquired,
`while the specular reflection from the superficial layer of the tissue, which
`is substantially divergent from the axis, is rejected.
`It has been found that an increase of the distance between a
`point-like light emitter terminal and a detector terminal helps not only to
`overcome the shunting effect, but also to improve the sensitivity of the
`sensor. On the other hand, however, the intensity of the detected signal
`dropswith an increase of the distance between the light emitter and detector
`terminals, which puts a practical limitation on the distance between the
`emitter and detector terminals. An additional limitation results from the
`requirement of clinicians to minimize the size of the sensor, especially for
`neonatal andfeta] monitoring applications.
`In a preferred embodiment of the invention, each light detector
`terminal comprises optical fibers with obliquely cut light-acquiring ends.
`In this way the sensitivity ofthe sensoris improved whereby a working light
`signal reflected from even relatively deep and remote layers of the tissue
`underinvestigation can be perceived.
`According to the above embodimentit is further preferred that at
`least one of the annular spacesholdingsaid first and second annular detector
`terminals are slanting with their side walls flaring out towards the contact
`surface such that the said obliquely cut light-acquiring ends of the detector
`terminal constituting optical fibers are flush with or parallel to the contact
`
`surface.
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`
`that an optical fiber with an
`is known from the prior art,
`It
`obliquely cut light-acquiring end generally rejects light rays arriving at a
`part of the end close to the shorter side wall of the fiber and acquireslight
`Tays arriving at a part of the end closer to the longer side wall. However,
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`there is no indication in the prior art, that such optical fibers have ever been
`used in sensors for optical blood oximetry.
`In the sensor set out above the geometry of the optical fibers
`enables to increase the area of the tissue at which the light detector terminals
`maystill acquire working optical signals. Where in accordance with the
`invention the optical fibers that constitute an annular light detector terminal
`have obliquely cut light-acquiring ends, the terminal is capable of acquiring
`working signals from an annular detection zone of the tissue that has a
`larger inner radius than that of the detector terminal ring.
`Due to their specific construction, the light detector terminals
`described hereinabovereject the slanting light rays appearing between the
`light emitter and light detector terminals, while at the same time enhancing
`the acquisition of light coming out from relatively deep blood perfused
`layers of the tissue. Accordingly, such a sensor has an improvedsensitivity
`withoutit having been necessary to increase the distance betweenthe light
`emitter and detector terminals and consequently also with no need to
`increase the prescribed limited size of the sensor body.
`the detector
`In a preferred embodiment of the above sensor,
`terminal constituting optical
`fibers each have an obliquely cut,
`light-
`acquiring end inclined towards a plane perpendicular to the longitudinal
`fiber axis by an acute angle.
`In case ofplastic optical fibers this acute angle
`does not exceed about 42°, and is preferably within the range of
`about 20°-22°.
`
`The carrier body of the sensor maybeof any suitable shape,e.g.
`cylindrical, and holdsat one endthe said applicator block so that the contact
`surface of the latter forms one end face of the body.
`As mentioned, in transmission pulse oximetry the emitted light
`passes between opposite surfaces of the blood perfused tissue under
`investigation, while in reflection pulse oximetrylight emission and detection
`occur at the same surface of the tissue.
`In both the transmission and
`reflection methods, pulsatile changes of the value of absorption ofthe light
`by the blood perfused tissue are used to determine the characteristics of
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`interest, the pulsatile changes being conventionally determined on the basis
`of the relationship between the intensity of the emitted light and that of the
`light detected by a single detector.
`In accordance with the present invention, a novel approach has
`been conceived by which the pulsatile changes are determined, on the basis
`of measured relation betweenintensities of light acquired byat least one pair
`of detector terminals differently distanced from the light emitting terminals.
`In this method,the detector terminal closest to the emitter terminals may be
`considered with respect to the second, more distanced detector terminal as
`a quasilight emitter terminal.
`This approach is based on the following physical model. A
`photon,after travelling a certain distance in a sample, is randomly scattered,
`This process is repeated until the photon leaves the sample boundaries. The
`photon travelling in the initial direction is considered as "transmitted"
`photon;
`the photon moving in the opposite direction is a "reflected" photon.
`After 30 to 40 steps any "memory" of the direction of the incident radiation
`is lost and there is no preferred direction of propagation, the light intensity
`decreasing isotropically in all directions. This interpretation of the light
`Propagation behavior enablesto apply to the reflectance oximetrythe well
`known Lambert-Beer law whichis used in the transmission oximetry, but
`for a radial direction.
`Lo
`the novel sensor
`In the coritext of the above novel method,
`embodiment
`in which the light detector terminals are alranged in two
`concentric rings around the light emitter terminals, the detector terminals
`define between them a tubular section of the tissue which is quasi-
`transmissively
`illuminated
`by
`light
`emanating from the
`emitters.
`Accordingly,
`such a sensor accordingto the invention may be described as
`a reflectance sensor that simulates a transmissive one.
`It is to be noted that in a sensor accordingto the invention having
`two concentric detector terminals,the optical pathsofillumination provided
`by the two real emitter terminals are similarly affected by any kind of
`optical disturbance in the annular detection zone,
`independent of the
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`wavelength of the emitted light and of the distance of the emitter terminals
`from the first annular detector terminal. Accordingly, substantial equiva—
`lence of optical traces will automatically be achieved for any location of the
`sensor on the skin and also in case of changing physiological conditions in
`the underlying tissue.
`
`Thus by another aspect
`the invention provides a method of
`noninvasive optical blood oximetry in blood perfused tissues including:
`providing an optical sensor with an applicator block holdingat least
`two light emitters in close proximity to each other and at least two light
`detector terminals concentrically surrounding said at least two light emitters
`and having a contact surface;
`positioning said applicator block on a skin portion of a subject where
`the underlyingtissues are to be investigated, with the contact surface facing
`the skin;
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`sequentially emitting from said emitters, light of at least two different
`wavelengths;
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`detecting the intensity of light signals arriving from the tissues under
`investigation by integral acquisition thereof through said at least twolight
`detector terminals;
`determining the ratios between the intensity of light detected by said
`at least two annular light detector terminals at each of said at least two
`different wavelengths; and
`determining a value of oxygen saturation of the blood on the basis of
`
`suchratios.
`
`In the applicator block used in the performance of the above
`methodthe said light emitters may each be a light source positioned within
`the applicator block, or alternatively a light emitter terminal havingafree,
`light emitting end and being coupled via another end to a light source.
`Typically the light emitter terminals are in form of bundles of opticalfibers.
`The above methodis applicable for determining oxygen saturation
`in the arterial blood.
`In this application it
`is assumed that a pulsatile
`component of the light absorbanceat each one of the wavelengthsresults
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`from the fluctuating volumeofarterial blood in the tissue section between
`the first light detector and the second light detector, and therefore this
`pulsatile absorbance component
`is indicative of the degree of oxygen
`
`saturation.
`
`In the performance of the above method twosets of measure~
`ments are effected at two points oftime, the first being the nil (minimum)
`point and the second being the crest (maximum) point of the pulsatile
`arterial blood pressure component. Each ofthese two sets of measurements
`include the following two Steps assuming that the tissue is illuminated by
`light of two different wavelengths, and that the sensor has only
`
`two detector
`
`terminals:
`
`Step 1— Thetissueis illuminated with light of the first wavelength,
`while light of the second wavelength is off, and light signals are recorded
`simultaneously by the first and second detectors;
`Step 2- Thetissue is illuminated with light of the second wave-
`length, while the light of the first wavelength is off, and light signals are
`recorded simultaneously bythe first and second detectors.
`The procedure pursuant to these measurements comprises:
`determining twointensity ratios for each of the said two points, the
`first intensity ratio being between the light signalintensities registered by the
`first and second light detectors at the first wavelength, and the second
`intensity ratio being betweenthelightsignalintensities registered by the first
`and second light detectors at the second wavelength;
`computing first and second pulsatile components AC] and AC2ofthe
`light signal for each of said first and second wavelengths, being each the
`difference between the intensity ratio calculated at the crest and the nil
`points for the respective wavelength;
`computing first and secondconstant components DCI and DC2ofthe
`light signals for each of said first and second wavelengths, being each the
`average of two intensity ratios calculated at the nil and crest points for the
`two wavelengths; and
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`calculating the oxygen saturation of arterial blood SaO, in accordance
`with the following equation:
`
`SaO, = K] ===="*
`DCI x AC2
`
`where K1 and K2 are calibration constants.
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`The departure of the present invention from the prior art will be
`readily appreciated by a person skilled in the art, when comparing with each
`other equations (1) and (2) herein.
`According to yet another aspect of the invention there is provided
`an apparatus for noninvasive optical blood oximetry comprising:
`a sensor having a carrier body with an applicator block having a
`contact surface which in operation faces a blood perfused body tissue ofa
`subject underinvestigation, which applicator blockis fitted with at least two
`point like light emitters positioned in close proximity to each other and each
`emitting light of a wavelength distinct from that of the other;
`andat least
`two, essentially annular light detector terminals concentrically surrounding
`said at least two light emitter terminals, having a free, light-acquiring end
`for the acquisition of light arriving fromatissue under investigation;
`20
`at least two light sources coupled to said light emitter terminals and
`capable of emitting light at at least two different wavelengths;
`at least two optical detectors coupled to said at least two, essentially
`annular detector terminals;
`two light sources to
`control means adapted to cause said at least
`illuminate said tissue sequentially via said emitter terminals and to obtain
`synchronized measurementsofintensity oflight acquired bysaid at least two
`detectors via said at least two detector terminals; and
`processor means for determining characteristics of interest from the
`results of said synchronized measurements.
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`In accordance with one embodiment the said light emitters are
`light sources positioned within the applicator block.
`In accordance with another embodimentthe light emitters consist
`of a plurality of optical fibers having each onefree,light
`~acquiring end and
`coupled via another end to a light detector device.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`For better understanding the invention will now be further
`described and illustrated by way of non-limiting examples only, with
`reference to the annexed drawings in which:
`Fig. 1 is an enlarged schematic plan view of one embodiment of an
`applicator block in a carrier body of a sensor according to the invention;
`Fig. 2 is an enlarged schematic plan view of another embodiment of
`an applicator block;
`Fig. 3 is a cross—section taken along line II-III of Fig. 2;
`Fig. 4 is an enlarged axial cross-sectional view of a further embodi-
`ment of a carrier body with applicator block in a sensor according to the
`invention;
`Fig. 5 is a diagram explaining the optics at the light-acquiring end of
`one embodiment of an optical fiber in a light detector terminal of a sensor
`according to the invention;
`|
`Fig. 6 is a similar diagram concerning another embodiment of the
`light-acquiring end of an optical fiber; and
`Fig. 7 is a block diagram of an oximeter according to the invention.
`
`DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS
`Fig.
`1 shows the contact surface of an applicator block of a
`Carrier body in a sensor according to the invention. As shown, block 1
`which is assumed to be made from an Opaque material such as a metal, has
`a contact surface 2 and a central bore 3 holding two bundles of optical
`fibers 4 and 5 serving as light emitter terminals. Bundles 4 and 5 are
`coupled each to a laser diode (not shown) and are thus capable of emitting
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`nm
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`light at two distinct wavelengths. An essentially annular space 6 provided
`in block 1 and consisting of a number of segments 7 with intermittent
`
`braces 8