PCT
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`Intematronal Bureau
`
`
`
`9/.
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
` (11) International Publication Number: ‘ WO 96/41566
`(51) International Patent Classification 6 :
`
`A618
`
`
`(43) International Publication Date:
`27 December 1996 (27.12.96)
`
`
`
`
`(21) International Application Number:
`PCT/119000006
`(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,
`6 June 1996 (06.06.96)
`(22) International Filing Date:
`
`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, 'IT, UA, UG, US, UZ, VN, ARlPO patent (KE,
` (30) Priority Data:
`
`LS, MW, SD, 52, 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
`OAPI patent (BF, Bl, CF, CG, CI, CM, GA, GN, ML, MR,
`
`NE, SN, TD, TG).
`
` (71) Applicant (for all designated States except US): CYBRO
`
`Published
`MEDICAL LTD. [IL/IL]; P.0.B. 600, Matam, 31000 Haifa
`
`
`(IL).
`Without international search report and to be republished
`
`
`
`upon receipt of that report.
`
`
`(72) Inventors; and
`
`(75) Inventors/Applicants (for US only): FINE, Ilya [IUIL]; 59/6
`
`Henel Street, 76541 Rehovot (IL). S'I’ERNBERG, Alexan-
`
`der [II/IL]; 31 Harofe Street, 34367 Haifa (IL). KATZ,
`
`Yeshayahu [IIJIL]; 45A Eder Street, 34752 Haifa (IL).
`
`GOLDINOV, Leonid [111m]; 21A/9 Nativ Hen, 32243
`
`Haifa (IL). RAPOPORT, Boris [IL/IL]; 3/12 Nativ Shom-
`ron, 28000 Kiryat Ata (IL).
`
`
`
`
` (74) Agent: COHN, Michael; Reinhold Cohn and Partners, PO. Box
`
`
`
`4060, 61040 Tel-Aviv (IL).
`
`(54) Title: SENSOR, METHOD AND DEVICE FOR OPTICAL BLOOD OXIMETRY
`
`(57) Abstract
`
`
`for
`There is described a new sensor
`optical blood oximetry as well as a method
`and apparatus in which the new sensor is used.
`The new sensor includes two point-like light
`emitters positioned in the center of the device
`in close proximity to each other and at least 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.
`
`amt
`
`
`
`\52K
`
`. \
`‘16:
`
`
`
`
`
`4M
`
`1
`
`1
`
`APPLE 1009
`
`1
`
`APPLE 1009
`
`

`

`3v
`
`
`
`AM
`AT
`AU
`BB
`BE
`BF
`30
`BJ
`BR
`
`Armenia
`Austria
`Australia
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`COte d’Ivoire
`Cameroon
`China
`Czechoslovakia
`Czech Republic
`Germany
`Denmark
`Estonia
`Spain
`Finland
`France
`Gabon
`
`FOR THE PURPOSES OF INFORMATION ONLY
`
`United Kingdom
`Georgia
`Guinea
`Greece
`Hungary
`Ireland
`Italy
`Japan
`Kenya
`Kyrgystan
`Democratic People's Republic
`of Korea
`Republic of Korea
`Kazakhstan
`Liechtenstein
`Sri Lanka
`Liberia
`Lithuania
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`Mali
`Mongolia
`Mauritania
`
`2
`
`MW
`MX
`NE
`NL
`NO
`NZ
`PL
`
`R0
`RU
`
`SE
`SG
`51
`SK
`SN
`SZ
`TD
`T6
`T1
`
`UA
`UG
`US
`UZ
`
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`&idan
`Sweden
`Singapore
`Slovenia
`Slovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Trinidad and Tobago
`Ukraine
`Uganda
`United States of America
`Uzbekistan
`Viet Nam
`
`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 as the
`
`10
`
`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 perfused tissue is illuminated and light
`
`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 determine the characteristic of interest,
`
`i.c. the degree of blood oxygen saturation.
`
`The value of oxygen saturation (SaOz) in arterial blood is defined -
`
`by the following known equation:
`
`20
`
`[HbOZ]
`Sac)2 = —— 1
`[H1502] + [H17]
`
`00%
`
`(1)
`
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`
`where [HbOZ] 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:
`
`the light absorbance of oxygenated hemoglobin is different from
`(a)
`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
`volume of 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 performance of optical pulse oximetry are known in the art, and among
`the known optical sensors those dedicated to measuring the degree of oxygen
`saturation of fetal 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
`
`a finger, an ear or the like by placing a light emitter and the detection of a
`transmissive sensor at two opposite sides of the tissue under examination, as
`described for example in US 4,938,213. In reflection oximetry, on the other
`hand, reflectance or transflectance 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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`Ul
`
`10
`
`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 be successfully 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
`
`commonly resorted 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 means that the
`
`nature of the functional interdependence between a 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 specular reflection created by the superficial layer of
`the tissue.
`
`20
`
`US. 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.
`
`30
`
`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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`WO 96/41566
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`-4-
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`PCT/IL96/00006
`
`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 are siiii point—like and
`accordingly it is practically um" oioablc for an operator to apply it
`to a
`wrong portion of the skin of a fetus.
`
`it is important to recall that the basic assu
`mption underlying the
`theory of transmission and reflection c.”
`imetry is, that optical paths of light
`rays with different wavelengths emitted into the LZ:.""e by different light
`
`assumption of substantial equivalence of optical paths is violated.
`In cases where two or more point—like light sources are used,
`
`red and distributed homoge—
`neously. Thus, if one 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
`but optically different site, then in consequence of different light scattering
`and absorption at the two distinct wavelengths, which occurs from the very
`beginning, the optical paths of the light emitted by the two sourceS CEIIIHOI
`
`adjacent
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`Another drawback of known sensors for blood oximetry is that
`they utilize LEDs as light sources for illuminating a tissue with light having
`two wavelength components. The LED light sources are either installed in
`the probe itself such 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
`for example, a pair of wavelengths of 700 nm and 800 nm
`which are suitable for the purposes of 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 LEDs are incapable of providing
`two wavelengths closer to each other than 100 nm.
`
`may provide,
`
`GENERAL DESCRIPTION OF THE INVENTION
`Against the above background it
`is an object of the present
`invention to provide a novel sensor for 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.
`
`for the performance of optical blood oximetry embodying the novel sensor
`and a method making use thereof.
`
`5
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`WO 96/415“
`
`_ 6 _.
`
`PCT/IL96/00006
`
`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 body tissue.
`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
`opaque obstacles, 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 due to the specific novel configuration of the detector
`terminal and the geometry of the sensor.
`
`i.e.
`that due to the essentially annular,
`It should be noted,
`axisymmetric configuration of the first 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 of the detector and
`the geometry of the sensor ensure the stability of the optical paths for each
`given wavelength.
`
`In a preferred embodiment of the invention the applicator block
`has a second essentially annular light detector terminal Spaced from and
`concentric with said first light detector terminal. 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
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`_7_
`
`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.
`
`The light 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 by say,
`
`10 — 20 nm. Thus, in a preferred embodiment a first laser diode emits at
`
`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 requirement of oximetry,
`
`namely the optical paths equivalence at different wavelengths of radiation.
`
`Preferably the carrier body of a sensor according to 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
`
`perpendicular to said contact surface and holding said 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 to the foregoing
`
`embodiment each 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, whereby a free portion of said annular space constitutes
`a collimator that rejects specular reflection. The distance by which the free
`ends are removed from the contact surface is so selected, that only light
`arriving from a relatively deep layer of the blood perfused tissue and
`
`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
`drops with 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 and fetal monitoring applications.
`In a preferred embodiment of the invention, each light detector
`terminal comprises optical fibers with obliquely cut light-acquiring endsi
`In this way the sensitivity of the sensor is improved whereby a working light
`signal reflected from even relatively deep and remote layers of the tissue
`under investigation can be perceived.
`
`According to the above embodiment it is further preferred that at
`least one of the annular spaces holding said 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
`
`30
`
`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 acquires light
`rays arriving at a part of the end closer to the longer side wall. However,
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`WO 96/41566
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`
`-9-
`
`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
`
`may still 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.
`
`10
`
`Due to their specific construction, the light detector terminals
`
`described hereinabove reject 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 improved sensitivity
`
`without it having been necessary to increase the distance between the light
`
`emitter and detector terminals and consequently also with no need to
`
`increase the prescribed limited size of the sensor body.
`
`In a preferred embodiment of the above sensor,
`
`the detector
`
`terminal constituting optical
`
`fibers each have an obliquely cut,
`
`light—
`
`20
`
`acquiring end inclined towards a plane perpendicular to the longitudinal
`
`fiber axis by an acute angle.
`
`In case of plastic 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 may be of any suitable shape, e.g.
`
`cylindrical, and holds at one end the 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 oximetry light emission and detection
`
`30
`
`occur at the same surface of the tissue.
`
`In both the transmission and
`
`reflection methods, pulsatile changes of the value of absorption of the 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 between intensities of light acquired by at 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 quasi light 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 enables to apply to the reflectance oximetry the well
`known Lambert—Beer law which is used in the transmission oximetry, but
`for a radial direction.
`'
`the novel sensor
`In the context of the above novel method,
`embodiment
`in which the light detector terminals are arranged 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 according to the invention may be described as
`a reflectance sensor that simulates a transmissive one.
`It is to be noted that in a sensor according to the invention having
`two concentric detector terminals, the optical paths of illumination 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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`-11..
`
`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 holding at 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 underlying tissues are to be investigated, with the contact surface facing
`
`the skin;
`
`sequentially emitting from said emitters, light of at least two different
`
`wavelengths;
`
`detecting the intensity of light signals arriving from the tissues under
`
`investigation by integral acquisition thereof through said at least two light
`
`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
`
`such ratios.
`
`In the applicator block used in the performance of the above
`
`method 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.
`
`The above method is applicable for determining oxygen saturation
`
`in the arterial blood.
`
`In this application it
`
`is assumed that a pulsatile
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`component of the light absorbance at each one of the wavelengths results
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`from the fluctuating volume of arterial 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 two sets of measure—
`ments are effected at two points of time, the first being the nil (minimum)
`point and the second being the crest (maximum) point of the pulsatile
`arterial blood pressure component. Each of these 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 — The tissue is 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 — The tissue is illuminated with light of the second wave-
`length, while the light of the first wavelength is off, and light signals are
`recorded simultaneously by the first and second detectors.
`The procedure pursuant to these measurements comprises:
`determining two intensity ratios for each of the said two points, the
`first intensity ratio being between the light signal intensities registered by the
`first and second light detectors at the first wavelength, and the second
`intensity ratio being between the light signal intensities registered by the first
`and second light detectors at the second wavelength;
`computing first and second pulsatile components AC1 and AC2 of the
`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 second constant components DCl and DC2 of the
`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 SaO2 in accordance
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`with the following equation:
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`Sa02 = K]
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`DC] x AC2
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`where K1 and K2 are calibration constants.
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`The departure of the present invention from the prior art will be
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`readily appreciated by a person skilled in the art, when comparing with each
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`other equations (1) and (2) herein.
`
`According to yet another aspect of the invention there is provided
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`an apparatus for noninvasive optical blood oximetry comprising:
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`a sensor having a carrier body with an applicator block having a
`
`contact surface which in operation faces a blood perfused body tissue of a
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`subject under investigation, which applicator block is fitted with at least two
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`point like light emitters positioned in close proximity to each other and each
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`emitting light of a wavelength distinct from that of the other; and at least
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`two, essentially annular light detector terminals concentrically surrounding
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`said at least two light emitter terminals, having a free, light-acquiring end
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`for the acquisition of light arriving from a tissue under investigation;
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`at least two light sources coupled to said light emitter terminals and
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`capable of emitting light at at least two different wavelengths;
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`at least two optical detectors coupled to said at least two, essentially
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`annular detector terminals;
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`control means adapted to cause said at least
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`two light sources to
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`illuminate said tissue sequentially via said emitter terminals and to obtain
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`synchronized measurements of intensity of light acquired by said at least two
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`detectors via said at least two detector terminals; and
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`processor means for determining characteristics of interest from the
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`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 embodiment the light emitters consist
`of a plurality of optical fibers having each one free, light
`coupled via another end to a light detector device.
`
`—acquiring end and
`
`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 Ill—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;
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`20
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`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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`light at two distinct wavelengths. An essentially annular space 6 provided
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`in block 1 and consisting of a number of segments 7 with intermittent
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`braces 8 concentrically surrounds the central bore 3 and accommodates a
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`plurality of optical fibers 9 forming together an annular light detector
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`terminal.
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`Inside the sensor's carrier body optical fibers are assumed to be
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`bundled together in a manner not shown and are coupled to a detector
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`device, e.g. a photodiode, equally not shown.
`
`Braces 8 of block 1 connect the median section 10 and the
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`peripheral section 11 of the block with each other.
`
`The light—acquiring ends of the light detector constituting optical
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`fibers 9 may either be flush with the contact surface 2 or alternatively be
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`removed from the surface inwards by a desired distance.
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`In operation the two light emitter terminals 4 and 5 emit light on
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`to a tissue under investigation, and the detector (not shown) transforms and
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`modulates the light acquired by the light—acquiring ends of the optical fibers
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`9 into an electric signal suitable for further processing.
`
`Figs. 2 and 3 illustrate schematically another embodiment of an
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`applicator block in a carrier body of an Optical sensor according to the
`
`invention. As shown, an applicator block 20 has a contact surface 21 and
`
`a central bore 22 holding two bundles 23 and 24 of optical fibers which
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`constitute two light emitter terminals and which are connected to a pair of
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`light sources (not shown). As shown, the light emitting ends 25 and 26 of
`
`the light emitter terminals 23 and 24 are withdrawn inside bore 22 and are
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`thus removed from the contact surface 21.
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`Block 20 further comprises a first annular space 27 concentric
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`with bore 22 and consisting of four segments 28 with intermittent bracing
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`members 29 linking with each other the core section 30 and median section
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`31 of block 20. The first annular space 27 houses a plurality of optical
`
`fibers 32 constituting together a light detector terminal and have each a
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`light—acquiring end 33.
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`A second annular space 35 surrounds concentrically the first
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`annular space 27 and similar to the latter consists of four segments 36 with
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`SUBSTITUTE S1H7EET (RULE 26W
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`intermittent bracing members 37 connecting the median block section 31
`with a peripheral section 38. The second annular space 35 houses a plurality
`of optical fibers 39 which together constitute a second light detector terminal
`and have each a light—acquiring end 40. As shown in Fig. 3 the light-
`acquiring ends 40 are removed from th