CA2017740A1 - Fiberoptic probe having waveguide properties - Google Patents
Fiberoptic probe having waveguide propertiesInfo
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- CA2017740A1 CA2017740A1 CA 2017740 CA2017740A CA2017740A1 CA 2017740 A1 CA2017740 A1 CA 2017740A1 CA 2017740 CA2017740 CA 2017740 CA 2017740 A CA2017740 A CA 2017740A CA 2017740 A1 CA2017740 A1 CA 2017740A1
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- optical fiber
- light
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- Investigating Or Analysing Materials By Optical Means (AREA)
- Measuring And Recording Apparatus For Diagnosis (AREA)
- Media Introduction/Drainage Providing Device (AREA)
- Spectrometry And Color Measurement (AREA)
- Investigating Or Analysing Biological Materials (AREA)
- Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
Abstract
ABSTRACT OF THE INVENTION
A fiberoptic probe includes a gas sensor disposed at the distal end of a fiberoptic catheter. The sensor includes a core and a cladding which provide the sensor with waveguide properties. The core is formed from a matrix of fluorophors which fluoresce with an intensity dependent upon the presence of a gas activate such as oxygen. This fluorescence is detected to provide an indication of gas activate concentration.
Spectral and diffuse reflectance means increase the signal-to-noise ratio of the sensor.
A fiberoptic probe includes a gas sensor disposed at the distal end of a fiberoptic catheter. The sensor includes a core and a cladding which provide the sensor with waveguide properties. The core is formed from a matrix of fluorophors which fluoresce with an intensity dependent upon the presence of a gas activate such as oxygen. This fluorescence is detected to provide an indication of gas activate concentration.
Spectral and diffuse reflectance means increase the signal-to-noise ratio of the sensor.
Description
2S3 il~7~
FIBEROPTIC PROBE HAVING WAVEGUIDE PROPERTIES
BACKGROUND OF THE I~ENTI~N
Field of the Invention This 1nvent~on relates generally to f~beroptic probes and more spec~fically to gas sensors used ln such probes.
Discuss~on of the Prior Art The measurement of physiologlcal parameters ~5 1mportant ln many med1cal procedures both d~agnostic and therapeutic. It has been des~rable such procedures to min~m~ze the s1ze of the measurement probes and sensors ~n order to reduce the 1nvaslve trauma to the pat1ent.
The measurement of blood gases ~s of ~nterest ~n almost all surgical procedures. Of pr~mary concern ~s the part~al pressure of oxygen ~n the blood. Th~s quantlty provides an lndication of how well the lungs are performing their function of oxygenating the blood but ~t ~s also representat~ve of the extent to wh~ch that oxygen ~s being perfused to the extremit~es of the body.
Sensors of the past have ~ncluded the optlcal f~ber apparatus d~sclosedby Buckles ~n his U.S. Patent Nos. 4 321 057 and 4 399 099. These patents disclose a fiber which ~s provided w~th an outer sheath of absorptive semipermeable materlal. Inc~dent light which ~s directed ~nto the proximal end of the fiber ~s refracted ~nto the sheath where it reacts w~th fluorescent molecules to emit radiat~on. This rad~ation ~s reflscted ~nto the ~1ber d~statly ahd detected for ~ts ~nformation content. Although th~s apparatus funct~ons w~th a s~ngle fiber there is no attempt to ~ncrease the s~gn~l-to-no~se rat~o of the apparatus by redirect~ng any port~on of the ~nformat~on slgnal back along the same opt~cal f~ber.
Inventor discloses ~n h~s U.S. Patent Appl~cat~on Ser~al No. lOO lOO
f~led on September 21 l9B7 a f1beropt~c probe connector for measur~ng phys~olog~cal parameters. This device consists of an opt~cal fiber and a sleeve connector lncluding a sheath substrate wh~ch def~nes a sensor cav~ty and an annular recess for receiving the fiber core. The sheath compr1ses a gas permeable polymer mater~al wh~ch permits the passage of oxygen lnto th~ sensor reglon. A chem~cal ~nd~cator ~nclud~ng an oxygen quench1ng fluorescent dye 1s d1sposed ~n the sensor reglon wh1ch ls 2~77 lnterrogated by the 11ght from the f1ber. The fluorescent tye 1ncludes a revers1ble chem1cal 1nd~cator havlng fluorophors whlch fluoresce 1n response to 1ncldent llght, ~1th an lntenslty wh1ch 1s dependent upon the concentratlon of oxygen. The fluorescent 11ght 1s then Ineasured to prov1de an lndlcat10n of oxygen concentratlon.
Sensors of the past also 1nclude the opt1cal wavegulde vapor sensor dlsclosed by G~ullan1 1n h1s U.S. Patent No. 4,513,087. Thls dev1ce lncludes a glass cap111ary tube wh1ch ls f11m-coated on 1ts outer surface w1th a dye havlng characterlstlcs for changlng color 1n accordance w1th the concentrat~on of ammonla ln the envlronment. Gull1anl s devlce relles upon absorptlon technology where1n the evanescent component of the lncldent 11ght 1s absorbed by the dye ln an amount dependent upon the concentratlon of ammon1a. The result1ng reduct10n ~n llght energy 1s dependent upon the magn1tude of energy lost 1n the evanescent wave.
S1nce the energy loss 1s dependent upon the degree of color change of the dye, wh1ch 1n turn 1s dependent upon the degree of concentrat10n of ammon1a, 1t follows that thls apparatus can be approprlately cal1brated to provlde an 1nd1catlon of ammon1a concentrat10n.
In U.S. Patent No. 3,584,662 to H1cks et al, a b10electrode 1s d1sclosed for use 1n measur1ng the concentratlon of glucose 1n blood or serum.
Th1s dev1ce 1ncludes a membrane of 1mmobll1zed glucose ox1dase whlch 1s placed 1n contact wlth the blood or tlssue. The glucose and oxygen d1ffuse 1nto the enzyme layer provld1ng an outward flow of hydrogen peroxlde and gluconlc ac1d. The oxygen saturat10n level ls mon1tored and the amount of glucon1c ac1d and perox1de determ1ned to prov1de an lnd1catlon of glucose concentrat10n.
Haase dlscloses 1n h1s U.S. patent no. 4,201,222 a f1beroptic catheter adapted for 1nsert10n 1nto a blood vesse1. The catheter 1ncludes a sem1permeable ~all member wh1ch perm1ts the passage of blood gasses 1nto a sensor reglon.
The problems assoc1ated wlth these dev1ces result 1n part from the small slze des1red for 1nvas1ve appl1cat10ns. Due to the s1ze constralnts the magn1tudes of the 1nformat10n s19nals ava11able for 1nterpretatlon are relatlvely low. When used lnvas1vely, the muscle and other art1fact no1se can be relatlvely h1gh w1th a consequently low s1gnal-to-no1se rat10. For these reasons 1t 1s 1mportant to capture and ma1nta1n as much of the 11ght as poss1ble. Th1s appl1es not only to the 1nc1dent 11ght . .
wh1ch 15 1ntroduced 1nto the sensor, but also the 11ght wh1ch 1s reflected from the sensor.
.
~ ~ 7r~
Part1cularly 1n the case of fluorescent sensors the l~ght ava11ab1e from the fluoresc1ng fluorophors ls relat~vely low 1n magn1tude. In these sensors 1t ~s partlcularly des1rable to enhance the ~avegulde properties of the sensor and to max1m1ze those propert1es w1th respect to the optlcal f1ber. D1rect1ng the 1ncldent l~ght s19nal down an optlcal f~ber and return1ng the 1nformatlon s1gnal back along the same f1ber prov1des an opportun1ty for 1ncreas1ng the s1gnal-to-no~se rat~o of the sensor.
Art of more general lnterest to the present concept 1ncludes the follow1ng patents:
Inventor U.S Patent No.
Peterson 4 476 870 Lubbers 4 003 7D7 SUMMARY OF THE INVENTION
In accordance w1th the present 1nvent10n the respect1ve 1nd1ces of refractlon for the opt1cal f1ber and the them~cal sensor are taken 1nto account tn prov1d1ng a gas permeable cladd1ng for the sensor sleeve. The chem~cal 1nd1cator and the sensor cladd1ng are chosen w1th 1nd1ces of refract10n wh~ch prov1de the sensor w1th 119htgu1de propert1es 1ncluding a cr1t1cal angle wh1ch 1s generally equ1valent to the cr1t1cal angle for the opt~cal flber.
By chooslng a sensor core hav~ng an lndex of refract10ns generally equ~valent to the 1ndex of refract10n for the core of the f1ber the adverse effects on 119ht travell1ng across the f1ber/sensor 1nterface can be s~gn1f1cantly reduced.
It 1s also posslb1e to lncrease the s19nal-to-no1se rat10 of the sensorby prov~d~ng a cap at the dlstal end of the sensor. Thts eap can be provlded wlth a means such as a m1rror for d1rect1ng toward the opt~cal f~ber that port~on of the return s19na1 wh1ch ls travelllng dlstally and therefore would be lost to the measurement process.
These and other features and advantages of the present lnvent10n w111 be more apparent to those skl11ed ln the art wlth a d1scusslon of preferred embod1ments of the 1nvent10n and reference to the assoc1ated draw1ngs.
~ESCRIPTION OF THE DRA~I~GS
F1g. 1 ls a plctorlal 111ustrat10n of a preferred use and d1spos1t10n of the catheter ~nd t1ssue sensor assoc1ated w1th the present lnvent~on;
F~g. 2 ~s a schematlc dlagram of the 119ht source and detectors ~7 assoc1ated w1th a preferred embodlment of th1s 1nvent~on;
F~g. 3 ls an ax~al cross sectlon vlew of the opt~cal f~ber and sensor assoc1ated w~th the present 1nventlon;
F1g. 4 1s a theoret~cal d1agram of a refracted 119ht ray 1mpinging on an 1nterface at an angle less than the cr1t~tal angle;
F1g. 5 1s a theoretlcal d1agram of a 11ght ray 1mp1ng1ng on an 1nterface at an angle equal to or greater than the cr1t1cal angle;
F19. 6 1s an ax~al cross sectlon v~ew of the opt1cal f~ber and sensor s~m11ar to F1g. 3 and 111ustrat1ng the wavegulde propert1es of the opt~cal f1ber;
Flg. 7 1s a theoret1cal d1agram of an opt1cal f1ber and the acceptance Angle assoc1ated w1th that f1ber;
F19. 8 1s an ax1al cross sect10n v1ew s1m11ar to F1g. 3 111ustrat1ng the acceptance angle assoclated w1th the sensor;
F19. 9 1s an ax1al cross sectlon vlew s1mllar to ~19. 3 111ustrating the wavegu1de propert~es of the sensor;
F~g. lO 1s an axlal cross sectlon v~ew s1m~1ar to F~g. 3 lllustrat~ng the effect of a sensor end CAp on the return lnformatlon s19nal; and Flg. ll 1s an ax1al cross sectlon vlew s1m11ar to F19. 3 lllustrat1ng the effect of a p19ment w1th1n the sheath and the return lnformat10n s1gnal as ~t enters the optlcal f~ber.
aE~cRlpTloN OF PREFERRED EMBODIMENTS
It 1s often deslrable to measure the part1al pressure of a gas ~1thln apartlcular flu~d env1ronment. For example the concentrat10ns of oxygen n1trous ox1de ozone and carbon dloxlde wlth1n amblent a1r would be of partlcular 1nterest to envlronmental1sts.
Other env1ronments for measurement are small and somet1mes 1nherently encumbered w1th no1se factors wh1ch degrade the s1gnal-to-no1se ratlo of the measurement. Such ls the case wlth the measurement of gas partlal pressures ln blood or t1ssue. If a measurement 1s taken d1rectly from the body (~n v~vo) 1t ls deslrable that any 1ncls10n be m~n1m1zed ln order to avo1d trauma and to reduce the poss1b111ty of 1nfect10n to the pat~ent. In the measurement of blood gases 1t ~s also des~rable to mln1m1ze the effect of any nolse such as that assoc1ated w1th muscle mot~on art~fact ~nd blood pulse. All of these factors must be addressed ~774~
ln tha present use of cath~ters havlng ~as SQnSOrs dlsposcd at thelr d1stal tlDs. Those c~thQt~rs h~Y~ b~n lnserted 1nto ths arm~ o~
p~tltnts wher0 thq s~nsors havQ bsen lodged 1n tho tlssue bed to measure the concontrat10n ot gases such ~t oxy~n and carbon dloxldo.
Such a procedure ls llluttrated ln F1gure l whsro th~ arm o- tha pat1ent ls dos1gnatod ganQrally by tht rtter~nc~ numeral lO. A ~lberoptlc CathetBr 12 15 connsctQd to a ll~ht sourco and dctactor 14 and has a ~as s~nsor 16 dlsposod at lts d1~tal tlp. ~n uss ths catheter 12 ls lnsart~d through an lnclslon ln thQ arm lO wlth tho sansor 16 c~beddQd ln the tlssue leld subcutan~ously Or th~ arm lO.
The llght source 1n detector 14 ls shown ln ~rc~t~r datall ln Flgura 2 alon~ w1th th~ scnsor 16 whlch 1s 111ustrated to 1ncludc a multlpllclty o~ tluorophors 20 doscr1bad ln graat~r dctall below. Tho llght source ln detector 14 lncludes a lamp 22 whlch provldes a po1nt sourc~ of generally whlte llght. Th1s 11ght ls ~ath~rod by a colllmat1ng lens 24 and dlrsctsd through a color ~llter 26 to p3SS llght ot a des1red wavelength. In ~ pre~Qrr~d ~mbod1mcnt the color of thls 113ht 1s goner~lly blu3 w1th a csntsr wavelength of 4ao nanomators.
Th1s colorod 11ght 1s d1rected alon~ an arrow 2~ onto a be~m spllttzr 30. The spl1ttor s~paratas thc colorad 11~ht dlrectlng a portlon o~ lt alon~ ~n ~rrow 32 lnto ~ black box or llght dump 34. In th1s part1cular embod1mQnt, th~ spllttar 30 ls contl~ured so th~t halr 0~ the 1~plnglng llght paSSQS throu~h the splltter 30 a~on~ an arrow 36 and onto a d1ehrotc tlltQr 38. Thls ~lltor 38 1s cont1gurcd to pass only red llght so tho blue lncldent llght lmplnglng on the tlltar 1s totally ren ected along an arrow 40 and passed through a focuslng lQns 42. The resultlng 11ght 1s d1rected through a shutter 44 and onto a prox1mal and of the f1bcropt1c cath~tar 12. Thls blua llght passQs through the cathster 12 lnto th~ ssnsor 16 whcr~ 1t 1mp1n~6s upon tho mult1pllc1ty of fluorophors 20.
As dlscu3sQd ln grQat6r data11 bslow th~ ~luorophors 20 rcspond to ths1mp1ng1ng blua llght by fluorasc1n~ at a color dcpQnd0nt upon tho chQmlstry o~ tho ~luorophors 20. For oxamplQ 1n a pr~tQrr~d ~mbod1m~nt somo ot thc tluorophors 2D may be prov1ded wlth a chomlstry wh1ch t1UOr~SCQS w1th a g~n~r~lly r~d 11ght havlng a cent~r wavnlQnath ot about 6ZO nanomQters whlle othQr ~1uorophors 20 ~luoresces w1th a genorally gr~Pn llght havlng a c~nt6r ~Av~lcngth o~ 530 nanOmQtarS.
The abl11ty ot thc tluorophors 20 to ~luor~sc~ tonds to dograd~ over tlmc. Thls phenomonon 1s genor~lly ro~orrod to as photo blo~ch1n~. In ordar to 1nhlblt th1s adv~rss a~rnct lt 1s des1rab1e to puls~ thq llght pass1ng through tha cath~t~r 12 ln ord~r to rQducs thQ duty cyc1~ ot thc fluorophors 20. Thls ls th0 prlmary purpos~ ot tha shutt~r 44 whlch ln a prnt0rr0d ambod1mant op~ns and clos~s w1th ~ duty cyclc o~ 4X.
_ 5 _ The fluorescent green and red 119hts emanat1ng from the fluorophors 20 ~ ~ 7 travel back along the f1beroptlc catheter 12 to the shutter 44. S~nce th1s return l~ght occurs 1n such a short per10d of t~me, 1t passes through the shutter 44 w1th~n the per10d of lts duty cycle. The red and green 119hts, represented by an arrow 46 1n F19ure 2, pass through the lens 42 and 1mp~nges on the d1chrolc f11ter 3B. As noted, th1s f11ter 38 ls conf19ured to pass red 11ght, so the red portlon of the return slgnal cont1nues throuQh the f11ter 38, along an arrow 47 and 1nto a red 119ht detector 48.
S1nce the green 119ht cannot pass through the f11ter 3B, 1t 1s reflected along an arrow 50 onto the beam spl1tter 30. The spl1tter 30 d~rects a portlon of the green 11ght along an arrow 52 and 1nto a green 11ght detector 54. The detectors 48 and 54 prov~de an 1ndlcat10n as to the 1ntens1ty of the respect1ve red and green components of the return s19na1. These measurements are related to the 1ntens1ty w1th whlch the respect1ve fluorophors 20 fluoresce. Therefore, the measurement prov1des an 1nd1cat10n of the magn1tude of that fluorescence.
In th1s part1cular system, the fluorescence of the red fluorophors 20 1s quenched tn the presence of oxygen. But th1s 1s not the case w1th the green fluorophors. On the other hand, the fluorescence of both the red and green fluorophors 20 1s ~ffected equally by no1se art1facts such as those caused by muscle mot10n or blood pulsat10ns. G1ven these cons1derat10ns, s1gnals from the red and green detectors, 48 and 54 respect1vely, can be comblned 1n an output c1rcu1t 56 to prov1de an 1nd1cat10n of the concentrat10n of oxygen 1n the sensor 16. Output c1rcu1ts of th1s type are well known to those sk111ed 1n the art.
Of part1cular 1nterest to the present 1nvent10n 1s the catheter 12 and sensor 16 wh1ch are sreatly magn1f1ed 1n F1gure 3. From th1s v1ew 1t can be seen that the f1beropt1c catheter 12 1ncludes an opt1cal flber 70 of the type commonly tonf19ured to lnclude a core 72 and a cladd1ng 74.
The sensor l~ includes an 1nd1cator mater1al d1sclosed by the 1nventor 1n h1s copend1ng Patent Appl1cat10n Ser1al No. lOO,lOO flled on September 21, 1987, and ent1tled F1ber Opt1cal Probe Connector For Physlolog1c Measurement Dev1ces. Th1s tnd1cator mater1al has opt1cal propert1es wh1ch vary tn response to the concentratton of the part1cular gas act1vate, such as oxygen, to be measured. These propert1es are 1nterrogated by the tnc1dent blue 11ght pass1ng through the opt1cal f1ber 70 and the 1nformat10n relat1ng to gas concentratton 1s carr1ed back along the same f1ber 17 to the 11ght source and detector 14.
More spec1f1cally, the sensor 16 can be prov1ded w1th a generally cyl1ndr1cal core 72 and a cladd1ng 74 wh~ch surrounds the core except for an angular recess B2. Th1s recess 82 1s conf1gured to rece1ve the d~stal end of the opt1cal f1ber 70. In the preferred embod~ment, the recess 82 1s cyl1ndrical and ~s conf1gured to recelve the d1stal end of the optical f~ber 70 ~n a close, frlctlon llt. The flber 17 ls held wlth~n the recess 82 ~n order to prov1de a d~rect contact and 1nterface 84 between the core 72 of the f1ber 70 and the core 76 of the sensor 16.
It 1s 1mportant to note that the 11ght assoc1ated w1th the fluorescent return slgnal has a relatlvely low magnttude. In other words, the returnlng lnformatlon slgnal ls relatlvely weak 1n compar1son to the lncldent slgnal. Compoundlng thls problem ls the fact that th~s weak 1nformatlon slgnal must be measured 1n an envlronment where there 1s cons1derable muscle mot10n artlfact and other nolse whlch tends to degrade the s1gnal-to-no1se rat10 of the measurement. It ~s th1s factor wh~ch ~s of partlcular concern to the present lnventlon.
The sensor 16 ls conflgured to reta1n as much of the lnc1dent llght as poss1ble w1th1n the core 76 and to capture as much of the fluorescent return 119ht as poss1ble for return along the f1ber 70. In a preferred embod1ment these ob~ect1ves are accompllshed prlmarlly by max1mlz~ng the opt~cal propertles of the mater1als whlch form the f1ber 70 and the sensor 16.
These optlcal propertles result from several character~st1cs of the materlals 1ncludlng a parameter commonly referred to as an 1ndex of refractlon. Thls lndex ls a dlmenslonless number derlved by d1vldlng the speed of llght ln a vacuum by the speed of 11ght 1n the materlal of 1nterest. The larger the lndex of refractlon for a glven materlal the slower the llght travels through that materlal.
As llght passes from one mater1al to another, lts speed changes result1ng 1n a bendlng or refractlon of the 11ght ray. Th1s phenomenon 1s 111ustrated theoretlcally 1n F19ure 4 where two materlals A and B, having dlfferent lndlces of refractlon, are separated by an lnterface 88. An lncldent 119ht ray 90 bends or refracts as 1t passes through the 1nterface 88 as shown by a refracted ray 92. Measur1ng the angles of the respect1ve rays 90 and 92 relat1ve to a llne 94 normal to the ~nterface BB, produces the respectlve angles e, and ~2. If the 1ndex of refractlon for the materlal A 1s greater than the 1ndex of refractlon for the materlal B, than ~2 wlll be larger than ~l.
It 1s well known that at some angle ~1, the 1nc~dent 119ht ray 90 wlll ~not pass through the 1nterface 88 but wlll be reflected by the 1nterface as 1f lt were a mlrror. Thls angle 1s commonly referred to as the crlt1cal angle and ls lllustrated 1n Flgure 4 where the angles el and ~2 are equal. Thls crlt1cal angle can be calculated 1n accordance wlth the followlng formula: -o ~ Arcs~n NA/NB ~Formula I) 2~77~
where:
NA '5 the lndex of refract1On for the materlal A;
NB ~S the 1ndex of refract1On for the materlal B; and N~ > NA
By way of 111ustrat1On 1t wlll be noted that the llght ray 98 str1kes the 1nterface 96 at a cr1t1cal angle wh1ch, for the f1ber 70, wh1ch 1s des~gnated Of. For the reasons prev~ously dlscussed, th~s 119ht ray 98 w111 rema~n w1th1n the core 72. All other llght rays wh1ch str1ke the 1nterface 96 at an angle greater than the crlt1cal angle Of, as represented by a ray lO0 1n F~gure 6, w111 llkew1se be reflected and rema1n w1th1n the core 72. In contradlstlnctlon, a 119ht ray 102 wh1ch 1s representat1ve of all rays str1klng the tnterface 96 at an angle less than the cr1t1cal angle Of w111 pass through the cladd1ng 74 and be lost from the system.
It can be apprec1ated that 1t 1s des1rable for the flber 70 to have a relat1vely small crltlcal angle Of so that as many light rays as poss1ble are trapped wlth1n the core 72. Th1s of course reduces the amount of 119ht wh1th 1s lost through the claddlng 74 ~nd 1ncreases the amount of llght whlch is reta1ned for contrlbutlon to the qas measurement. Llght rays wh1ch strlke the lnterface 84 at an angle less than thls crltlcal angle Of will pass through the lnterface and be lost exterlorly of the flber 70. However, all 119ht rays strlk1ng the lnterface 84 at an angle greater than thls cr1t1cal angle w111 be repeatedly reflected into the tore 72 as they travel down the flber 70. Th1s princ1pal of total 1nternal reflect1On enables the 11ght to propagate down the optlcal f1ber 70. S1nce the angles of 1nc1dence and reflect1On are equal, as 111ustrated theoret1cally 1n F1gure 5, these rays cont1nue to zlgzag down the length of the core 72 toward the 1nterface 84 w1th the sensor 16 In a preferred embod1ment, the flber 70 1s 300l330 m1cron clad Ens19n 81ckford fiber No. HCR M300T-12. In thls part1cular fiber, the core 72 has an lndex of refract1On Nl equal to 1.45; and the cladd1ng 74 has an 1ndex of refract1On N2 equal to 1.40. Th1s prov1des the Ens19n B1ckford flber 70 wlth a cr1tlcal angle Of equal to 75.0-As the rays 98 and 100 approach the interface 84 between the core 72 of -;
the fiber 70 and the core 76 of the sensor 16, another opt1cal phenomenon takes place. Th1s phenomenon, wh1ch ls based on the ~b111ty of a mater~al to gather or accept llght and dlsburse 1t ts a funct~on of lts ~77 numer~cal aperture tNA). For a structure hav~ng a core and claddlng.
such as the flber 70 and sensor 16 the numer1cal aperture (NA) ls also defined by the respect~ve 1nd~ces of refract~on of the core and c1add1ng.
In add~tion the numer~cal aperture (NA) 1s dependent upon the lndex of refract~on of the mater~al from wh~ch the ray emanates. Spec~f1cally the numer~cal aperture ls def~ned ~n accordance w~th Snell s Law:
t(N3)2 1 (N4)2~X
NA . _ _ _ (FORMULA II) N
where:
N3 ~s the 1nde~ of refract10n for the core of the rece~v~ng structure suth as the core 76; and N4 1s the ~ndex of refractlon for the cladd~ng of the réce~v~ng structure such as claddlng 78: and Nl ~s the 1ndex of refract~on for the mater~al from which the wave emanates such as the core 72.
The hlgher the numer~cal aperture the greater the l~ght gather~ng capab~l~ty of a f~ber structure. G1ven the numer~cal aperture NA an acceptance angle ~ 1s def~ned 1n accordance wlth the follow~ng formula:
~ . Arcs~n NA (FORMULA III) In F~gure 7 the angle ~ 1s 111ustrated theoret1cally by a f~ber 106 hav~ng an end surface 108. The acceptance angle ~ 1s measured from a l~ne llO wh~ch ~s perpend~cular to the end surface 108.
In those cases where the f1ber cross sect~on 1s c~rcular the ~ngle of acceptance def1nes a cone hav~ng an apex or cone angle equal to tw~ce the angle ~. For th~s reason the angle ~ ~s somet~mes referred to as the acceptance half-angle. In F19ures 7 ~nd 8 the cone angle 1s measured between a pa~r of l~nes des~gnated by the reference numberals 72 and 74.
An lmportant aspect of the present lnventlon ls assoc1ated w~th the sensor 16 ~nclud~ng the core 76 and the cladd~ng 78 wh~ch funct~ons as a l~ght gu~de or f~ber. Th~s be~ng the case lt ~s apparent that w~th appropriate indices of refract~on for the core 76 and the cladd~ng 78 an ~7~a acceptance half-angle 05 can be calculated for the sensor 16.
As the l~ght rays travel down the f1ber 70 as prevlously d~scussed w~th reference to Flgure 6 they w~ll pass across the 1nterface 84 and 1nto the core 76 but only 1f they are w~th1n the acceptance cone of the sensor 16. S1nce 1t 1s destrable to max1m1ze the amount of llght passlng 1nto the sensor 16 ~t follows that the angle O ls preferably equal to or greater than 90- m~nus the cr~tlcal angle Of of the f1ber 70. If th1s were not the case some of the 11ght trapped w1th1n the f1ber 70 would not be accepted by the sensor 16 and would therefore be lost from the gas measurement process.
Once the 119ht passes through the 1nterface 84 1nto the core 76 of the sensor 16 1t ls des1rable to reta~n as much o~ th1s 11ght as poss1ble ~n order to 1ncrease the s19nal-to-no1se rat10 of the sensor 16. Referr1ng to F~gure 9 1t w111 be noted that the sensor 16 can be made to function as a 119ht gu1de 1f the 1ndex of refract10n for the core 76 1s greater than the 1ndex of refract10n for the cladd1ng 78.
.
In a preferred embod1ment the core 76 of the sensor 16 1s formed from a solid phase matr1x mater1al cons1st1ng of any d1ffusable hydrophob1c diphenyl-d1methyl mater1al. S11tcone polymers have shown partttular promise; d1phenyl-dtmethyl s110xanes are used 1n the preferred embod1ment. The fluorophors 20 are embedded 1n thls matr1x but do not contr1bute to the 1ndex of refract10n N3 wh1ch 1s 1.479 for the core 76.
The cladd1ng 78 1s formed from d1methys110xane polymer wh1ch has an 1ndex of refractlon N4 of 1.411. These respect1ve 1nd1ces of refract~on for the core 76 and cladd1ng 78 prov1de the sensor 16 w1th a cr1t1cal angle 05 equal to 72.6~. Th1s angle 1s talculated as prev10usly d1scussed 1n accordance w1th Formula I.
Given the respect1ve 1nd1ces of refract10n for the ~1ber core 72 ~Nl .
1.45) the sensor core 76 (N3 . 1.479) and the sensor tladd1ng 78 (N4 .
1.411) Formula II and III tan be appl1ed to show that the sensor 16 1n the preferred embod1ment on numer1cal aperature (NA) of 0.306 and an acceptance half-angle s Of 17.8~. It ls partlcularly des1rable 1n accordance w1th the present 1nvent10n to reduce ~s much as poss1ble the amount of 11ght wh1th passes through the cladd1ng ?B. By reta1n1ng th1s llght w1th1n the core 76 a greater 1ntens1ty of 11ght wtll rema1n enabl1ng the rays to pass further along the core 76. Thls 1s destrable 1n order that the sensor 16 can measure the gas concentrat10n over a greater length and area of the core 76. Th1s trapp1ng of the 11ght w~th1n the core 76 enables the fluorophors 20 to be act1vated even at d1stant locat10ns such as that deslgnated generally by the reference numeral 112.
As the blue 1nc1dence 119ht bombards the fluorophors 20 in the sensor 16 they w111 glow w1th the red color or the green color as prev10usly d~scussed. ~owever, the 1ntens1ty of flu~rescence for the red ~ 77 fluor~phors 1s dependent upon the concentratlon of the gas actlvate, such as oxygen, wh~ch 1s be1ng measured. Only the fluorescence of the red fluorophors ls quenched 1n the presence of oxygen. The yreen fluorophors are not affected by the concentratlon of the gas actlvate and therefore prov~de an excellent reference for the gas measurement. In th1s embod~ment, ~t 1s the 1ntens~ty of the red 11ght, pass~ng rlght to left In Flgure lO wh~ch 1s measured by the 11ght detector 14. ~he greater the gas concentratlon the more the fluorescence of the red fluorophors 20 ls Inhlb~ted. Thus the gas actlvate tends to hive a quench1ng effect whlch reduces the 1ntens1ty of the red color. In Ftgure 10, two of the fluorophors are illustrated generally at 116 and 118. The fluorophor 116 1s lllustrated to be 1n the presence of several oxygen nolecules whlch ~uench or otherw1se reduce the 1ntenslty of the fluorescent red 11ght.
As a partlcular fluorophor (such as the flurophor 118) fluoresces, lt emlts llght ln all dlrectlons; ~n other words, lt 1s 1sotroplc.
Normally, only the llght rays havlng a vector component ln the d~rect10n of the f1ber 70 would have ~ny posslb111ty of returnlng to the llght detector 14. For example, wlth reference to a vert1cal plane 120 pass~ng through the fluorophor 118, only the rays passlng to the left of the plane 120 have any potent1al for return1ng along the f1ber 70. Normally, the rays passlng to the rlght of the plane 120 would have no poss1bll~ty of contr1butlng to the gas actlvate measurement.
Nevertheless, lt ls 1mportant that these llght rays whlch are dlrected away from the flber 70 be retalned ln the gas measurement process ln order to lncrease the magnltude of the return lnformatlon slgnal. For th1s reason, a preferred embod1ment of the sensor 16 ~s prov1ded wlth an end cap lllustrated generally at 124 ~n Flgure 9. On the lnner surface of the end cap 124, 1n ~uxtaposltlon to the core 76, a mlrror 126 or other reflect10n means can be provlded. Thls mlrror 126 funct~ons to reflect the 119ht rays travelllng dlstally of the sensor 16. Thus the r~ys to the r1ght of the plane 120, wh1ch would otherw1se be lost to the measurement process, are reflected by the m1rror 126 back 1n the dlrectlon of the flber 70. It ls apparent that thls m1rror 126 can theoretlcally lncrease the magn~tude of the lnformatlon s'snal by a factor of two. Thls m1rror 126 provldes specular reflectance and ls preferably porous. In a preferred embodlment 1t 1s formed from metall1zed ceramlc whlch ls provlded wlth a poroslty of 20X.
The m~rror 126 prov1des a further advantage w~th respect to the ~ncldent llght. Any photons assoclated wlth the lncldent llght whlch do not fall upon a fluorophor can be reflected by the mlrror 126 back lnto the core 76. On ~ts return path, thls photon of lncldent 119ht w111 have a further opportun~ty to contact a flllorophor that m19ht otherw~se have ~774 been missed. The fluorescense of ~h1s fluorophor w111 1ncrease the magn~tude of the return s1gnal and thereby enhance the s1gnal-to-no1se ratio of the sensor 16.
In a preferred embod1ment the core 76 and the cladd1ng 78 of the sensor16 are cyl~ndr1cal 1n conf19urat10n w1th thelr respect1ve axes co1nc1dent with the long1tud1nal ax1s of the sensor 16. ~n th1s embod1ment the lnterface ~4 between the f1ber 70 and the sensor 16 1s preferably transverse to the axls of the sensor. S1m11arly the end cap 24 and the m1rror 126 are preferably transverse to the ax~s of the sensor 16. It 1s deslrable that the 1nterface 84 and the m1rror 126 be parallel wlth respect to each other; 1n a preferred embod1ment they are both perpend1cular to the ax1s of the sensor 16.
Another means for 1nh1b1t1ng loss of 11ght from the core 76 1s assoc1ated w~th the color and opac1ty of the cladd1ng 78. It has been found that diffuse reflectance results from the prov1s10n of a wh1te or other l~ght colored p19ment 122 1n the cladd1ng 78. In F1gure ll th1s p1gment 122 1s illustrated by a pa1r of part1cles. Any rays wh1ch are not w1th1n the critical angle s ~such as a ray 123 1n F1gure 11) and ~h1ch therefore escape 1nto the cladd1ng 78 would have the poss1b111ty of be1ng scattered back ~nto the core 76 by th1s p1gment 122. Th1s d1ffuse reflectance can also be advantageously prov1ded 1n the end cap 124 part1cularly 1f the m1rror 126 1s om1tted from a part1cular embod1ment. Prov1d1ng a p1gment ln the cladd1ng 78 a~ds not only 1n scatterlng the llght rays back to the core 76, but 1t also opt1cally lsolates the sensor 16 from unwanted amb1ent 11ght. Thus the p1gment tends to functlon as a llght buffer so that relat1vely br1ght surg1cal l~ghts do not 1nterfere w1th the gas measurement. In a preferred embod~ment the wh1te or llght colored p19ment ls prov~ded ~n the form of Tltanlum Dlox1de.
~he 119ht gu1de propert1es of the sensor !6 also have a pos1tlve effect on the abll1ty of the sensor 16 to d1rect the return fluorescent 119ht back to the fiber 70. W1th the claddlng 78 the sensor 16 funct10ns as a 119ht gu1de trapp1ng the return1ng red and green 11ght 1n accordance w1th the cr1t1cal angle ~5 of the sensor 16. By captur1ng more of the 11ght from the fluoresc1ng fluorophors 20 the slgnal-to-no1se rat10 for the sensor 16 1s greatly ~ncreased. Th1s 1s part1cularly ~mportant slnce the fluorescent 11ght ls s1gn1f1cantly reduced 1n 1ntenslty ln compar1son to the lnc1dent llght and th1s relatlvely low 1ntens1ty ~s even further reduced by the ~uench1ng effect of the ~as act1vate.
When the return1ng red and green l~ghts reaches the lnterface 84 as shown ~n F19ure ll the1r ab111ty to enter the flber 70 w~ll depend upon the cone acceptance angle of the f1ber 70. In th1s case the numer1cal aperture 1s also determ1ned by Snell s law as prev10usly appl1ed 1n Formula II to the sensor 16 and as now appl1ed to the f1ber 70.
77~
l(Nl~2 _ N2)2~X
NA . (FORMULA IV) where:
Nl ~s the 1ndex of refract~on for the the f1be~ core such as fcr the core 72; and N2 ~5 the 1ndex of the refractlon for the f1ber cladd~ng such as the cladding 74; and N3 ls the 1ndex of refractlon for the sensor cone such as the core 76.
G~ven the respect1ve lndlces of refractlon for the sensor core 75 (N3 .1.479) the fiber core 72 (Nl ~ 1.45) and the f~ber cladding 74 (N2 -1.40) ~ormula IV can be appl~ed to show that the fiber has a numer~tal aperature (NA) equal to 0.256 and an acceptance half angle ~f equal to 14.82. Th~s angle ls 111ustrated between a pa1r of ltnes 126 and 128 in F1gure ll.
If the acceptance half angle ~f of the flber 70 1s equal to or greater than 90 mlnus the crltlcal angle ~s Of the sensor 16 then all of the 11ght trapped 1n the sensor 16 wlll pass 1nto the ~1ber 70. S1nce th~s return llght contalns the slgnal to be measured 1t 1s deslrable that 1t be permltted to enter the flber 70 and that 1t be trapped w1thln the core 72 for presentat1On to the llght detector 14. Once the return llght ls 1n the core 72 of the flber 70 1t wlll be sub~ect to the same crltlcal angle constra1nts discussed w1th reference to F1gure 6. Any return 11ght rays whlch strlke the 1nterface 96 at an angle less than the cr1t1cal angle Of will pass through the claddlng 74. Only those returnlng llght rays striktng the lnterface 58 at an angle greater than the crlt1cal angle Of wlll be trapped and presented to the llght detector 14 .
Once the sensor 16 has been provlded wlth llght gu1de propert1es 1t lsapparent that a11 of the advantages assoclated w1th flberopt1c technology are ava11able to 1ncrease the eff1c1ency of the gas measurement.
Importantly one of these advantages ls assoclated w1th the fact that the sensor 16 can be bent cons1derably w1thout degrad1ng 1ts h19h signal-to-nolse ratlo. This ls posslble because the 11ght gulde properties of the sensor 16 facllltate retentlon of most of the trapped light w1thln the core 76 even when bent thereby malnta1n1ng the s1gnal avallable for process1ng.
In add~t10n to ~nc~eas~n~ the streng~h of the ~nformatlon s~gnal the ~.~3~r~
light gulde propert~es of the sensor 16 also reduce the effect of no~
In the past muscle mot~on art~fact has phys~cally bent the sensors w~th a consequent 10ss of l~ght from the process. Unfortunately th~s loss has been 1nterpreted as a h19h gas concentrat~on s~gn~f1cantly degrad~ng the accuracy of pr~or sensors. W~th the l~ght gulde characterlst7cs ssoc~ated w1th the present 1nvent~on bend1ng caused by muscle mot~on does not generate nolse. S1m11arly the adverse effects assoclated w~th other phys~cal artlfacts such as blood pulsat~ons are also !S~ gn~f~cantly reduced.
In a preferred embod~ment the 1nd1ces of refract~on for the cores 72 and 76 of the f~ber 70 and sensor 16 respectlvely have been chosen to be relat1vely equal. Th1s reduces the refract~on effect at the ~nterface B4 so the 11ght travel~ng from the flber 70 to the sensor 16 1s relat~vely unrefracted. ln order that the cr1t1cal angles Of and 05 m1ght be equal ~t 1s necessary to choose mater1als for the cladd~ng 74 and the cladding 7B wh1ch have ~nd1ces oS refract10n that are also equal. If the 1ndlces of refract10n for the cores 72 ind 76 are equal and the 1nd1ces of refract~on for the cladd~ngs 56 and 78 are equal 1t follows that the cr~t~cal angles Of and 05 w~ll be equal and the acceptance half angles Of and 05 wlll also be equal. W1th these propertles the greatest retent~on of l~ght w~th~n the f1ber 70 and sensor 16 can be ach1eved. In general ~t has been found that best results are prov~ded when the rat~o of crit~cal angles f/s ~5 w~th1n a range of about 1.10 to 0.90 and the rat10 of core refract~ve 1ndex of f~ber and sensor ~s w1th1n a range of 1.02 to 0.98.
A preferred embod~ment of the sensor 16 measures the concentrat~on of oxygen as prev10usly d1sclosed. However the sensor 16 can be adapted to measure the concentrat~on of other substances ~n a part1cular envlronment by prov~d1ng a convers10n layer 130 around the claddlng 78. Thls layer 130 could ~nclude var~ous chem~cals for convert1ng the substance of ~nterest tnto oxygen. Then as the concentratlon of oxygen ~s mon~tored by the sensor 16 that would prov1de an 1nd1cat10n of concentrat~on for the part~cular substance.
For example the sensor 16 1nclud~ng the conversat10n layer 130 m19ht typ1cally be~ d1sposed ~n the tlssue bed of a pat1ent. In th~s env~ronment 1nclud1ng b100d the subst2nce of ~nterest could be glucose in wh~ch case the convers10n layer 130 m1ght 1nclude glucose ox1dase as d~sclosed 1n appl~cant s co-pend~ng Patent Appl~cat~on Serlal Number lO0 100 prev~ously ment10ned. The conversat10n layer 130 would convert .;
any glucose present 1n the blood envlronment ~nto oxygen. ~he measurement of oxygen by the sensor 16 would then prov~dq an ~nd~cat~on as to the concentrat~on of glucose w~th~n the b100d.
The measurement of gas act1vates other than oxygen, such as carbon d10x~de, when comblned wlth sultable converslon layers, would make the sensor 16 advantageous for measur~ng the concentratlons of many d~fferent substances 1n many dlfferent env1ronments.
Although thls lnvent10n has been d1sclosed ~th reference to a speclfic oxygen sensor adapted for 1n v1vo appl1catlons, 1t will be apparent that the light gu~de qual1t~es assoclated w~th the sensor 16 are advantageous for many other app1~catlons. For example, dlfferent materlals can be used for the core 76, the claddlng 78, and the fluorophors Z0 1n order to provlde for measuremen~ of gases other than oxygen. Slmllarly, gas concentrat~ons can be measured 1n other flu1d env1ronments, both gas and 11qu1d, to prov1de an lnd1catlon of the part1al pressure assoc1ated w1th a part~cular gas act1vate.
It is also apparent that the llght gulde propert1es ssoc1ated w1th thepresent ~nvent10n would be equally appl1cable and advantageous to gas reasurement by way of absorpt10n technology. In any case where lt ls des1rable to reduce 119ht losses w1thln a sensor, an approprlate cladding configurat10n can be added to provlde the sensor wlth 119ht gulde propert1es.
~hese and other features and advantages of the present lnvent10n w111 be apparent to those skllled ln the art so that the scope of th1s lnventlon should be ascertalned only wlth reference to the follow1ng cla~ms.
FIBEROPTIC PROBE HAVING WAVEGUIDE PROPERTIES
BACKGROUND OF THE I~ENTI~N
Field of the Invention This 1nvent~on relates generally to f~beroptic probes and more spec~fically to gas sensors used ln such probes.
Discuss~on of the Prior Art The measurement of physiologlcal parameters ~5 1mportant ln many med1cal procedures both d~agnostic and therapeutic. It has been des~rable such procedures to min~m~ze the s1ze of the measurement probes and sensors ~n order to reduce the 1nvaslve trauma to the pat1ent.
The measurement of blood gases ~s of ~nterest ~n almost all surgical procedures. Of pr~mary concern ~s the part~al pressure of oxygen ~n the blood. Th~s quantlty provides an lndication of how well the lungs are performing their function of oxygenating the blood but ~t ~s also representat~ve of the extent to wh~ch that oxygen ~s being perfused to the extremit~es of the body.
Sensors of the past have ~ncluded the optlcal f~ber apparatus d~sclosedby Buckles ~n his U.S. Patent Nos. 4 321 057 and 4 399 099. These patents disclose a fiber which ~s provided w~th an outer sheath of absorptive semipermeable materlal. Inc~dent light which ~s directed ~nto the proximal end of the fiber ~s refracted ~nto the sheath where it reacts w~th fluorescent molecules to emit radiat~on. This rad~ation ~s reflscted ~nto the ~1ber d~statly ahd detected for ~ts ~nformation content. Although th~s apparatus funct~ons w~th a s~ngle fiber there is no attempt to ~ncrease the s~gn~l-to-no~se rat~o of the apparatus by redirect~ng any port~on of the ~nformat~on slgnal back along the same opt~cal f~ber.
Inventor discloses ~n h~s U.S. Patent Appl~cat~on Ser~al No. lOO lOO
f~led on September 21 l9B7 a f1beropt~c probe connector for measur~ng phys~olog~cal parameters. This device consists of an opt~cal fiber and a sleeve connector lncluding a sheath substrate wh~ch def~nes a sensor cav~ty and an annular recess for receiving the fiber core. The sheath compr1ses a gas permeable polymer mater~al wh~ch permits the passage of oxygen lnto th~ sensor reglon. A chem~cal ~nd~cator ~nclud~ng an oxygen quench1ng fluorescent dye 1s d1sposed ~n the sensor reglon wh1ch ls 2~77 lnterrogated by the 11ght from the f1ber. The fluorescent tye 1ncludes a revers1ble chem1cal 1nd~cator havlng fluorophors whlch fluoresce 1n response to 1ncldent llght, ~1th an lntenslty wh1ch 1s dependent upon the concentratlon of oxygen. The fluorescent 11ght 1s then Ineasured to prov1de an lndlcat10n of oxygen concentratlon.
Sensors of the past also 1nclude the opt1cal wavegulde vapor sensor dlsclosed by G~ullan1 1n h1s U.S. Patent No. 4,513,087. Thls dev1ce lncludes a glass cap111ary tube wh1ch ls f11m-coated on 1ts outer surface w1th a dye havlng characterlstlcs for changlng color 1n accordance w1th the concentrat~on of ammonla ln the envlronment. Gull1anl s devlce relles upon absorptlon technology where1n the evanescent component of the lncldent 11ght 1s absorbed by the dye ln an amount dependent upon the concentratlon of ammon1a. The result1ng reduct10n ~n llght energy 1s dependent upon the magn1tude of energy lost 1n the evanescent wave.
S1nce the energy loss 1s dependent upon the degree of color change of the dye, wh1ch 1n turn 1s dependent upon the degree of concentrat10n of ammon1a, 1t follows that thls apparatus can be approprlately cal1brated to provlde an 1nd1catlon of ammon1a concentrat10n.
In U.S. Patent No. 3,584,662 to H1cks et al, a b10electrode 1s d1sclosed for use 1n measur1ng the concentratlon of glucose 1n blood or serum.
Th1s dev1ce 1ncludes a membrane of 1mmobll1zed glucose ox1dase whlch 1s placed 1n contact wlth the blood or tlssue. The glucose and oxygen d1ffuse 1nto the enzyme layer provld1ng an outward flow of hydrogen peroxlde and gluconlc ac1d. The oxygen saturat10n level ls mon1tored and the amount of glucon1c ac1d and perox1de determ1ned to prov1de an lnd1catlon of glucose concentrat10n.
Haase dlscloses 1n h1s U.S. patent no. 4,201,222 a f1beroptic catheter adapted for 1nsert10n 1nto a blood vesse1. The catheter 1ncludes a sem1permeable ~all member wh1ch perm1ts the passage of blood gasses 1nto a sensor reglon.
The problems assoc1ated wlth these dev1ces result 1n part from the small slze des1red for 1nvas1ve appl1cat10ns. Due to the s1ze constralnts the magn1tudes of the 1nformat10n s19nals ava11able for 1nterpretatlon are relatlvely low. When used lnvas1vely, the muscle and other art1fact no1se can be relatlvely h1gh w1th a consequently low s1gnal-to-no1se rat10. For these reasons 1t 1s 1mportant to capture and ma1nta1n as much of the 11ght as poss1ble. Th1s appl1es not only to the 1nc1dent 11ght . .
wh1ch 15 1ntroduced 1nto the sensor, but also the 11ght wh1ch 1s reflected from the sensor.
.
~ ~ 7r~
Part1cularly 1n the case of fluorescent sensors the l~ght ava11ab1e from the fluoresc1ng fluorophors ls relat~vely low 1n magn1tude. In these sensors 1t ~s partlcularly des1rable to enhance the ~avegulde properties of the sensor and to max1m1ze those propert1es w1th respect to the optlcal f1ber. D1rect1ng the 1ncldent l~ght s19nal down an optlcal f~ber and return1ng the 1nformatlon s1gnal back along the same f1ber prov1des an opportun1ty for 1ncreas1ng the s1gnal-to-no~se rat~o of the sensor.
Art of more general lnterest to the present concept 1ncludes the follow1ng patents:
Inventor U.S Patent No.
Peterson 4 476 870 Lubbers 4 003 7D7 SUMMARY OF THE INVENTION
In accordance w1th the present 1nvent10n the respect1ve 1nd1ces of refractlon for the opt1cal f1ber and the them~cal sensor are taken 1nto account tn prov1d1ng a gas permeable cladd1ng for the sensor sleeve. The chem~cal 1nd1cator and the sensor cladd1ng are chosen w1th 1nd1ces of refract10n wh~ch prov1de the sensor w1th 119htgu1de propert1es 1ncluding a cr1t1cal angle wh1ch 1s generally equ1valent to the cr1t1cal angle for the opt~cal flber.
By chooslng a sensor core hav~ng an lndex of refract10ns generally equ~valent to the 1ndex of refract10n for the core of the f1ber the adverse effects on 119ht travell1ng across the f1ber/sensor 1nterface can be s~gn1f1cantly reduced.
It 1s also posslb1e to lncrease the s19nal-to-no1se rat10 of the sensorby prov~d~ng a cap at the dlstal end of the sensor. Thts eap can be provlded wlth a means such as a m1rror for d1rect1ng toward the opt~cal f~ber that port~on of the return s19na1 wh1ch ls travelllng dlstally and therefore would be lost to the measurement process.
These and other features and advantages of the present lnvent10n w111 be more apparent to those skl11ed ln the art wlth a d1scusslon of preferred embod1ments of the 1nvent10n and reference to the assoc1ated draw1ngs.
~ESCRIPTION OF THE DRA~I~GS
F1g. 1 ls a plctorlal 111ustrat10n of a preferred use and d1spos1t10n of the catheter ~nd t1ssue sensor assoc1ated w1th the present lnvent~on;
F~g. 2 ~s a schematlc dlagram of the 119ht source and detectors ~7 assoc1ated w1th a preferred embodlment of th1s 1nvent~on;
F~g. 3 ls an ax~al cross sectlon vlew of the opt~cal f~ber and sensor assoc1ated w~th the present 1nventlon;
F1g. 4 1s a theoret~cal d1agram of a refracted 119ht ray 1mpinging on an 1nterface at an angle less than the cr1t~tal angle;
F1g. 5 1s a theoretlcal d1agram of a 11ght ray 1mp1ng1ng on an 1nterface at an angle equal to or greater than the cr1t1cal angle;
F19. 6 1s an ax~al cross sectlon v~ew of the opt1cal f~ber and sensor s~m11ar to F1g. 3 and 111ustrat1ng the wavegulde propert1es of the opt~cal f1ber;
Flg. 7 1s a theoret1cal d1agram of an opt1cal f1ber and the acceptance Angle assoc1ated w1th that f1ber;
F19. 8 1s an ax1al cross sect10n v1ew s1m11ar to F1g. 3 111ustrat1ng the acceptance angle assoclated w1th the sensor;
F19. 9 1s an ax1al cross sectlon vlew s1mllar to ~19. 3 111ustrating the wavegu1de propert~es of the sensor;
F~g. lO 1s an axlal cross sectlon v~ew s1m~1ar to F~g. 3 lllustrat~ng the effect of a sensor end CAp on the return lnformatlon s19nal; and Flg. ll 1s an ax1al cross sectlon vlew s1m11ar to F19. 3 lllustrat1ng the effect of a p19ment w1th1n the sheath and the return lnformat10n s1gnal as ~t enters the optlcal f~ber.
aE~cRlpTloN OF PREFERRED EMBODIMENTS
It 1s often deslrable to measure the part1al pressure of a gas ~1thln apartlcular flu~d env1ronment. For example the concentrat10ns of oxygen n1trous ox1de ozone and carbon dloxlde wlth1n amblent a1r would be of partlcular 1nterest to envlronmental1sts.
Other env1ronments for measurement are small and somet1mes 1nherently encumbered w1th no1se factors wh1ch degrade the s1gnal-to-no1se ratlo of the measurement. Such ls the case wlth the measurement of gas partlal pressures ln blood or t1ssue. If a measurement 1s taken d1rectly from the body (~n v~vo) 1t ls deslrable that any 1ncls10n be m~n1m1zed ln order to avo1d trauma and to reduce the poss1b111ty of 1nfect10n to the pat~ent. In the measurement of blood gases 1t ~s also des~rable to mln1m1ze the effect of any nolse such as that assoc1ated w1th muscle mot~on art~fact ~nd blood pulse. All of these factors must be addressed ~774~
ln tha present use of cath~ters havlng ~as SQnSOrs dlsposcd at thelr d1stal tlDs. Those c~thQt~rs h~Y~ b~n lnserted 1nto ths arm~ o~
p~tltnts wher0 thq s~nsors havQ bsen lodged 1n tho tlssue bed to measure the concontrat10n ot gases such ~t oxy~n and carbon dloxldo.
Such a procedure ls llluttrated ln F1gure l whsro th~ arm o- tha pat1ent ls dos1gnatod ganQrally by tht rtter~nc~ numeral lO. A ~lberoptlc CathetBr 12 15 connsctQd to a ll~ht sourco and dctactor 14 and has a ~as s~nsor 16 dlsposod at lts d1~tal tlp. ~n uss ths catheter 12 ls lnsart~d through an lnclslon ln thQ arm lO wlth tho sansor 16 c~beddQd ln the tlssue leld subcutan~ously Or th~ arm lO.
The llght source 1n detector 14 ls shown ln ~rc~t~r datall ln Flgura 2 alon~ w1th th~ scnsor 16 whlch 1s 111ustrated to 1ncludc a multlpllclty o~ tluorophors 20 doscr1bad ln graat~r dctall below. Tho llght source ln detector 14 lncludes a lamp 22 whlch provldes a po1nt sourc~ of generally whlte llght. Th1s 11ght ls ~ath~rod by a colllmat1ng lens 24 and dlrsctsd through a color ~llter 26 to p3SS llght ot a des1red wavelength. In ~ pre~Qrr~d ~mbod1mcnt the color of thls 113ht 1s goner~lly blu3 w1th a csntsr wavelength of 4ao nanomators.
Th1s colorod 11ght 1s d1rected alon~ an arrow 2~ onto a be~m spllttzr 30. The spl1ttor s~paratas thc colorad 11~ht dlrectlng a portlon o~ lt alon~ ~n ~rrow 32 lnto ~ black box or llght dump 34. In th1s part1cular embod1mQnt, th~ spllttar 30 ls contl~ured so th~t halr 0~ the 1~plnglng llght paSSQS throu~h the splltter 30 a~on~ an arrow 36 and onto a d1ehrotc tlltQr 38. Thls ~lltor 38 1s cont1gurcd to pass only red llght so tho blue lncldent llght lmplnglng on the tlltar 1s totally ren ected along an arrow 40 and passed through a focuslng lQns 42. The resultlng 11ght 1s d1rected through a shutter 44 and onto a prox1mal and of the f1bcropt1c cath~tar 12. Thls blua llght passQs through the cathster 12 lnto th~ ssnsor 16 whcr~ 1t 1mp1n~6s upon tho mult1pllc1ty of fluorophors 20.
As dlscu3sQd ln grQat6r data11 bslow th~ ~luorophors 20 rcspond to ths1mp1ng1ng blua llght by fluorasc1n~ at a color dcpQnd0nt upon tho chQmlstry o~ tho ~luorophors 20. For oxamplQ 1n a pr~tQrr~d ~mbod1m~nt somo ot thc tluorophors 2D may be prov1ded wlth a chomlstry wh1ch t1UOr~SCQS w1th a g~n~r~lly r~d 11ght havlng a cent~r wavnlQnath ot about 6ZO nanomQters whlle othQr ~1uorophors 20 ~luoresces w1th a genorally gr~Pn llght havlng a c~nt6r ~Av~lcngth o~ 530 nanOmQtarS.
The abl11ty ot thc tluorophors 20 to ~luor~sc~ tonds to dograd~ over tlmc. Thls phenomonon 1s genor~lly ro~orrod to as photo blo~ch1n~. In ordar to 1nhlblt th1s adv~rss a~rnct lt 1s des1rab1e to puls~ thq llght pass1ng through tha cath~t~r 12 ln ord~r to rQducs thQ duty cyc1~ ot thc fluorophors 20. Thls ls th0 prlmary purpos~ ot tha shutt~r 44 whlch ln a prnt0rr0d ambod1mant op~ns and clos~s w1th ~ duty cyclc o~ 4X.
_ 5 _ The fluorescent green and red 119hts emanat1ng from the fluorophors 20 ~ ~ 7 travel back along the f1beroptlc catheter 12 to the shutter 44. S~nce th1s return l~ght occurs 1n such a short per10d of t~me, 1t passes through the shutter 44 w1th~n the per10d of lts duty cycle. The red and green 119hts, represented by an arrow 46 1n F19ure 2, pass through the lens 42 and 1mp~nges on the d1chrolc f11ter 3B. As noted, th1s f11ter 38 ls conf19ured to pass red 11ght, so the red portlon of the return slgnal cont1nues throuQh the f11ter 38, along an arrow 47 and 1nto a red 119ht detector 48.
S1nce the green 119ht cannot pass through the f11ter 3B, 1t 1s reflected along an arrow 50 onto the beam spl1tter 30. The spl1tter 30 d~rects a portlon of the green 11ght along an arrow 52 and 1nto a green 11ght detector 54. The detectors 48 and 54 prov~de an 1ndlcat10n as to the 1ntens1ty of the respect1ve red and green components of the return s19na1. These measurements are related to the 1ntens1ty w1th whlch the respect1ve fluorophors 20 fluoresce. Therefore, the measurement prov1des an 1nd1cat10n of the magn1tude of that fluorescence.
In th1s part1cular system, the fluorescence of the red fluorophors 20 1s quenched tn the presence of oxygen. But th1s 1s not the case w1th the green fluorophors. On the other hand, the fluorescence of both the red and green fluorophors 20 1s ~ffected equally by no1se art1facts such as those caused by muscle mot10n or blood pulsat10ns. G1ven these cons1derat10ns, s1gnals from the red and green detectors, 48 and 54 respect1vely, can be comblned 1n an output c1rcu1t 56 to prov1de an 1nd1cat10n of the concentrat10n of oxygen 1n the sensor 16. Output c1rcu1ts of th1s type are well known to those sk111ed 1n the art.
Of part1cular 1nterest to the present 1nvent10n 1s the catheter 12 and sensor 16 wh1ch are sreatly magn1f1ed 1n F1gure 3. From th1s v1ew 1t can be seen that the f1beropt1c catheter 12 1ncludes an opt1cal flber 70 of the type commonly tonf19ured to lnclude a core 72 and a cladd1ng 74.
The sensor l~ includes an 1nd1cator mater1al d1sclosed by the 1nventor 1n h1s copend1ng Patent Appl1cat10n Ser1al No. lOO,lOO flled on September 21, 1987, and ent1tled F1ber Opt1cal Probe Connector For Physlolog1c Measurement Dev1ces. Th1s tnd1cator mater1al has opt1cal propert1es wh1ch vary tn response to the concentratton of the part1cular gas act1vate, such as oxygen, to be measured. These propert1es are 1nterrogated by the tnc1dent blue 11ght pass1ng through the opt1cal f1ber 70 and the 1nformat10n relat1ng to gas concentratton 1s carr1ed back along the same f1ber 17 to the 11ght source and detector 14.
More spec1f1cally, the sensor 16 can be prov1ded w1th a generally cyl1ndr1cal core 72 and a cladd1ng 74 wh~ch surrounds the core except for an angular recess B2. Th1s recess 82 1s conf1gured to rece1ve the d~stal end of the opt1cal f1ber 70. In the preferred embod~ment, the recess 82 1s cyl1ndrical and ~s conf1gured to recelve the d1stal end of the optical f~ber 70 ~n a close, frlctlon llt. The flber 17 ls held wlth~n the recess 82 ~n order to prov1de a d~rect contact and 1nterface 84 between the core 72 of the f1ber 70 and the core 76 of the sensor 16.
It 1s 1mportant to note that the 11ght assoc1ated w1th the fluorescent return slgnal has a relatlvely low magnttude. In other words, the returnlng lnformatlon slgnal ls relatlvely weak 1n compar1son to the lncldent slgnal. Compoundlng thls problem ls the fact that th~s weak 1nformatlon slgnal must be measured 1n an envlronment where there 1s cons1derable muscle mot10n artlfact and other nolse whlch tends to degrade the s1gnal-to-no1se rat10 of the measurement. It ~s th1s factor wh~ch ~s of partlcular concern to the present lnventlon.
The sensor 16 ls conflgured to reta1n as much of the lnc1dent llght as poss1ble w1th1n the core 76 and to capture as much of the fluorescent return 119ht as poss1ble for return along the f1ber 70. In a preferred embod1ment these ob~ect1ves are accompllshed prlmarlly by max1mlz~ng the opt~cal propertles of the mater1als whlch form the f1ber 70 and the sensor 16.
These optlcal propertles result from several character~st1cs of the materlals 1ncludlng a parameter commonly referred to as an 1ndex of refractlon. Thls lndex ls a dlmenslonless number derlved by d1vldlng the speed of llght ln a vacuum by the speed of 11ght 1n the materlal of 1nterest. The larger the lndex of refractlon for a glven materlal the slower the llght travels through that materlal.
As llght passes from one mater1al to another, lts speed changes result1ng 1n a bendlng or refractlon of the 11ght ray. Th1s phenomenon 1s 111ustrated theoretlcally 1n F19ure 4 where two materlals A and B, having dlfferent lndlces of refractlon, are separated by an lnterface 88. An lncldent 119ht ray 90 bends or refracts as 1t passes through the 1nterface 88 as shown by a refracted ray 92. Measur1ng the angles of the respect1ve rays 90 and 92 relat1ve to a llne 94 normal to the ~nterface BB, produces the respectlve angles e, and ~2. If the 1ndex of refractlon for the materlal A 1s greater than the 1ndex of refractlon for the materlal B, than ~2 wlll be larger than ~l.
It 1s well known that at some angle ~1, the 1nc~dent 119ht ray 90 wlll ~not pass through the 1nterface 88 but wlll be reflected by the 1nterface as 1f lt were a mlrror. Thls angle 1s commonly referred to as the crlt1cal angle and ls lllustrated 1n Flgure 4 where the angles el and ~2 are equal. Thls crlt1cal angle can be calculated 1n accordance wlth the followlng formula: -o ~ Arcs~n NA/NB ~Formula I) 2~77~
where:
NA '5 the lndex of refract1On for the materlal A;
NB ~S the 1ndex of refract1On for the materlal B; and N~ > NA
By way of 111ustrat1On 1t wlll be noted that the llght ray 98 str1kes the 1nterface 96 at a cr1t1cal angle wh1ch, for the f1ber 70, wh1ch 1s des~gnated Of. For the reasons prev~ously dlscussed, th~s 119ht ray 98 w111 rema~n w1th1n the core 72. All other llght rays wh1ch str1ke the 1nterface 96 at an angle greater than the crlt1cal angle Of, as represented by a ray lO0 1n F~gure 6, w111 llkew1se be reflected and rema1n w1th1n the core 72. In contradlstlnctlon, a 119ht ray 102 wh1ch 1s representat1ve of all rays str1klng the tnterface 96 at an angle less than the cr1t1cal angle Of w111 pass through the cladd1ng 74 and be lost from the system.
It can be apprec1ated that 1t 1s des1rable for the flber 70 to have a relat1vely small crltlcal angle Of so that as many light rays as poss1ble are trapped wlth1n the core 72. Th1s of course reduces the amount of 119ht wh1th 1s lost through the claddlng 74 ~nd 1ncreases the amount of llght whlch is reta1ned for contrlbutlon to the qas measurement. Llght rays wh1ch strlke the lnterface 84 at an angle less than thls crltlcal angle Of will pass through the lnterface and be lost exterlorly of the flber 70. However, all 119ht rays strlk1ng the lnterface 84 at an angle greater than thls cr1t1cal angle w111 be repeatedly reflected into the tore 72 as they travel down the flber 70. Th1s princ1pal of total 1nternal reflect1On enables the 11ght to propagate down the optlcal f1ber 70. S1nce the angles of 1nc1dence and reflect1On are equal, as 111ustrated theoret1cally 1n F1gure 5, these rays cont1nue to zlgzag down the length of the core 72 toward the 1nterface 84 w1th the sensor 16 In a preferred embod1ment, the flber 70 1s 300l330 m1cron clad Ens19n 81ckford fiber No. HCR M300T-12. In thls part1cular fiber, the core 72 has an lndex of refract1On Nl equal to 1.45; and the cladd1ng 74 has an 1ndex of refract1On N2 equal to 1.40. Th1s prov1des the Ens19n B1ckford flber 70 wlth a cr1tlcal angle Of equal to 75.0-As the rays 98 and 100 approach the interface 84 between the core 72 of -;
the fiber 70 and the core 76 of the sensor 16, another opt1cal phenomenon takes place. Th1s phenomenon, wh1ch ls based on the ~b111ty of a mater~al to gather or accept llght and dlsburse 1t ts a funct~on of lts ~77 numer~cal aperture tNA). For a structure hav~ng a core and claddlng.
such as the flber 70 and sensor 16 the numer1cal aperture (NA) ls also defined by the respect~ve 1nd~ces of refract~on of the core and c1add1ng.
In add~tion the numer~cal aperture (NA) 1s dependent upon the lndex of refract~on of the mater~al from wh~ch the ray emanates. Spec~f1cally the numer~cal aperture ls def~ned ~n accordance w~th Snell s Law:
t(N3)2 1 (N4)2~X
NA . _ _ _ (FORMULA II) N
where:
N3 ~s the 1nde~ of refract10n for the core of the rece~v~ng structure suth as the core 76; and N4 1s the ~ndex of refractlon for the cladd~ng of the réce~v~ng structure such as claddlng 78: and Nl ~s the 1ndex of refract~on for the mater~al from which the wave emanates such as the core 72.
The hlgher the numer~cal aperture the greater the l~ght gather~ng capab~l~ty of a f~ber structure. G1ven the numer~cal aperture NA an acceptance angle ~ 1s def~ned 1n accordance wlth the follow~ng formula:
~ . Arcs~n NA (FORMULA III) In F~gure 7 the angle ~ 1s 111ustrated theoret1cally by a f~ber 106 hav~ng an end surface 108. The acceptance angle ~ 1s measured from a l~ne llO wh~ch ~s perpend~cular to the end surface 108.
In those cases where the f1ber cross sect~on 1s c~rcular the ~ngle of acceptance def1nes a cone hav~ng an apex or cone angle equal to tw~ce the angle ~. For th~s reason the angle ~ ~s somet~mes referred to as the acceptance half-angle. In F19ures 7 ~nd 8 the cone angle 1s measured between a pa~r of l~nes des~gnated by the reference numberals 72 and 74.
An lmportant aspect of the present lnventlon ls assoc1ated w~th the sensor 16 ~nclud~ng the core 76 and the cladd~ng 78 wh~ch funct~ons as a l~ght gu~de or f~ber. Th~s be~ng the case lt ~s apparent that w~th appropriate indices of refract~on for the core 76 and the cladd~ng 78 an ~7~a acceptance half-angle 05 can be calculated for the sensor 16.
As the l~ght rays travel down the f1ber 70 as prevlously d~scussed w~th reference to Flgure 6 they w~ll pass across the 1nterface 84 and 1nto the core 76 but only 1f they are w~th1n the acceptance cone of the sensor 16. S1nce 1t 1s destrable to max1m1ze the amount of llght passlng 1nto the sensor 16 ~t follows that the angle O ls preferably equal to or greater than 90- m~nus the cr~tlcal angle Of of the f1ber 70. If th1s were not the case some of the 11ght trapped w1th1n the f1ber 70 would not be accepted by the sensor 16 and would therefore be lost from the gas measurement process.
Once the 119ht passes through the 1nterface 84 1nto the core 76 of the sensor 16 1t ls des1rable to reta~n as much o~ th1s 11ght as poss1ble ~n order to 1ncrease the s19nal-to-no1se rat10 of the sensor 16. Referr1ng to F~gure 9 1t w111 be noted that the sensor 16 can be made to function as a 119ht gu1de 1f the 1ndex of refract10n for the core 76 1s greater than the 1ndex of refract10n for the cladd1ng 78.
.
In a preferred embod1ment the core 76 of the sensor 16 1s formed from a solid phase matr1x mater1al cons1st1ng of any d1ffusable hydrophob1c diphenyl-d1methyl mater1al. S11tcone polymers have shown partttular promise; d1phenyl-dtmethyl s110xanes are used 1n the preferred embod1ment. The fluorophors 20 are embedded 1n thls matr1x but do not contr1bute to the 1ndex of refract10n N3 wh1ch 1s 1.479 for the core 76.
The cladd1ng 78 1s formed from d1methys110xane polymer wh1ch has an 1ndex of refractlon N4 of 1.411. These respect1ve 1nd1ces of refract~on for the core 76 and cladd1ng 78 prov1de the sensor 16 w1th a cr1t1cal angle 05 equal to 72.6~. Th1s angle 1s talculated as prev10usly d1scussed 1n accordance w1th Formula I.
Given the respect1ve 1nd1ces of refract10n for the ~1ber core 72 ~Nl .
1.45) the sensor core 76 (N3 . 1.479) and the sensor tladd1ng 78 (N4 .
1.411) Formula II and III tan be appl1ed to show that the sensor 16 1n the preferred embod1ment on numer1cal aperature (NA) of 0.306 and an acceptance half-angle s Of 17.8~. It ls partlcularly des1rable 1n accordance w1th the present 1nvent10n to reduce ~s much as poss1ble the amount of 11ght wh1th passes through the cladd1ng ?B. By reta1n1ng th1s llght w1th1n the core 76 a greater 1ntens1ty of 11ght wtll rema1n enabl1ng the rays to pass further along the core 76. Thls 1s destrable 1n order that the sensor 16 can measure the gas concentrat10n over a greater length and area of the core 76. Th1s trapp1ng of the 11ght w~th1n the core 76 enables the fluorophors 20 to be act1vated even at d1stant locat10ns such as that deslgnated generally by the reference numeral 112.
As the blue 1nc1dence 119ht bombards the fluorophors 20 in the sensor 16 they w111 glow w1th the red color or the green color as prev10usly d~scussed. ~owever, the 1ntens1ty of flu~rescence for the red ~ 77 fluor~phors 1s dependent upon the concentratlon of the gas actlvate, such as oxygen, wh~ch 1s be1ng measured. Only the fluorescence of the red fluorophors ls quenched 1n the presence of oxygen. The yreen fluorophors are not affected by the concentratlon of the gas actlvate and therefore prov~de an excellent reference for the gas measurement. In th1s embod~ment, ~t 1s the 1ntens~ty of the red 11ght, pass~ng rlght to left In Flgure lO wh~ch 1s measured by the 11ght detector 14. ~he greater the gas concentratlon the more the fluorescence of the red fluorophors 20 ls Inhlb~ted. Thus the gas actlvate tends to hive a quench1ng effect whlch reduces the 1ntens1ty of the red color. In Ftgure 10, two of the fluorophors are illustrated generally at 116 and 118. The fluorophor 116 1s lllustrated to be 1n the presence of several oxygen nolecules whlch ~uench or otherw1se reduce the 1ntenslty of the fluorescent red 11ght.
As a partlcular fluorophor (such as the flurophor 118) fluoresces, lt emlts llght ln all dlrectlons; ~n other words, lt 1s 1sotroplc.
Normally, only the llght rays havlng a vector component ln the d~rect10n of the f1ber 70 would have ~ny posslb111ty of returnlng to the llght detector 14. For example, wlth reference to a vert1cal plane 120 pass~ng through the fluorophor 118, only the rays passlng to the left of the plane 120 have any potent1al for return1ng along the f1ber 70. Normally, the rays passlng to the rlght of the plane 120 would have no poss1bll~ty of contr1butlng to the gas actlvate measurement.
Nevertheless, lt ls 1mportant that these llght rays whlch are dlrected away from the flber 70 be retalned ln the gas measurement process ln order to lncrease the magnltude of the return lnformatlon slgnal. For th1s reason, a preferred embod1ment of the sensor 16 ~s prov1ded wlth an end cap lllustrated generally at 124 ~n Flgure 9. On the lnner surface of the end cap 124, 1n ~uxtaposltlon to the core 76, a mlrror 126 or other reflect10n means can be provlded. Thls mlrror 126 funct~ons to reflect the 119ht rays travelllng dlstally of the sensor 16. Thus the r~ys to the r1ght of the plane 120, wh1ch would otherw1se be lost to the measurement process, are reflected by the m1rror 126 back 1n the dlrectlon of the flber 70. It ls apparent that thls m1rror 126 can theoretlcally lncrease the magn~tude of the lnformatlon s'snal by a factor of two. Thls m1rror 126 provldes specular reflectance and ls preferably porous. In a preferred embodlment 1t 1s formed from metall1zed ceramlc whlch ls provlded wlth a poroslty of 20X.
The m~rror 126 prov1des a further advantage w~th respect to the ~ncldent llght. Any photons assoclated wlth the lncldent llght whlch do not fall upon a fluorophor can be reflected by the mlrror 126 back lnto the core 76. On ~ts return path, thls photon of lncldent 119ht w111 have a further opportun~ty to contact a flllorophor that m19ht otherw~se have ~774 been missed. The fluorescense of ~h1s fluorophor w111 1ncrease the magn~tude of the return s1gnal and thereby enhance the s1gnal-to-no1se ratio of the sensor 16.
In a preferred embod1ment the core 76 and the cladd1ng 78 of the sensor16 are cyl~ndr1cal 1n conf19urat10n w1th thelr respect1ve axes co1nc1dent with the long1tud1nal ax1s of the sensor 16. ~n th1s embod1ment the lnterface ~4 between the f1ber 70 and the sensor 16 1s preferably transverse to the axls of the sensor. S1m11arly the end cap 24 and the m1rror 126 are preferably transverse to the ax~s of the sensor 16. It 1s deslrable that the 1nterface 84 and the m1rror 126 be parallel wlth respect to each other; 1n a preferred embod1ment they are both perpend1cular to the ax1s of the sensor 16.
Another means for 1nh1b1t1ng loss of 11ght from the core 76 1s assoc1ated w~th the color and opac1ty of the cladd1ng 78. It has been found that diffuse reflectance results from the prov1s10n of a wh1te or other l~ght colored p19ment 122 1n the cladd1ng 78. In F1gure ll th1s p1gment 122 1s illustrated by a pa1r of part1cles. Any rays wh1ch are not w1th1n the critical angle s ~such as a ray 123 1n F1gure 11) and ~h1ch therefore escape 1nto the cladd1ng 78 would have the poss1b111ty of be1ng scattered back ~nto the core 76 by th1s p1gment 122. Th1s d1ffuse reflectance can also be advantageously prov1ded 1n the end cap 124 part1cularly 1f the m1rror 126 1s om1tted from a part1cular embod1ment. Prov1d1ng a p1gment ln the cladd1ng 78 a~ds not only 1n scatterlng the llght rays back to the core 76, but 1t also opt1cally lsolates the sensor 16 from unwanted amb1ent 11ght. Thus the p1gment tends to functlon as a llght buffer so that relat1vely br1ght surg1cal l~ghts do not 1nterfere w1th the gas measurement. In a preferred embod~ment the wh1te or llght colored p19ment ls prov~ded ~n the form of Tltanlum Dlox1de.
~he 119ht gu1de propert1es of the sensor !6 also have a pos1tlve effect on the abll1ty of the sensor 16 to d1rect the return fluorescent 119ht back to the fiber 70. W1th the claddlng 78 the sensor 16 funct10ns as a 119ht gu1de trapp1ng the return1ng red and green 11ght 1n accordance w1th the cr1t1cal angle ~5 of the sensor 16. By captur1ng more of the 11ght from the fluoresc1ng fluorophors 20 the slgnal-to-no1se rat10 for the sensor 16 1s greatly ~ncreased. Th1s 1s part1cularly ~mportant slnce the fluorescent 11ght ls s1gn1f1cantly reduced 1n 1ntenslty ln compar1son to the lnc1dent llght and th1s relatlvely low 1ntens1ty ~s even further reduced by the ~uench1ng effect of the ~as act1vate.
When the return1ng red and green l~ghts reaches the lnterface 84 as shown ~n F19ure ll the1r ab111ty to enter the flber 70 w~ll depend upon the cone acceptance angle of the f1ber 70. In th1s case the numer1cal aperture 1s also determ1ned by Snell s law as prev10usly appl1ed 1n Formula II to the sensor 16 and as now appl1ed to the f1ber 70.
77~
l(Nl~2 _ N2)2~X
NA . (FORMULA IV) where:
Nl ~s the 1ndex of refract~on for the the f1be~ core such as fcr the core 72; and N2 ~5 the 1ndex of the refractlon for the f1ber cladd~ng such as the cladding 74; and N3 ls the 1ndex of refractlon for the sensor cone such as the core 76.
G~ven the respect1ve lndlces of refractlon for the sensor core 75 (N3 .1.479) the fiber core 72 (Nl ~ 1.45) and the f~ber cladding 74 (N2 -1.40) ~ormula IV can be appl~ed to show that the fiber has a numer~tal aperature (NA) equal to 0.256 and an acceptance half angle ~f equal to 14.82. Th~s angle ls 111ustrated between a pa1r of ltnes 126 and 128 in F1gure ll.
If the acceptance half angle ~f of the flber 70 1s equal to or greater than 90 mlnus the crltlcal angle ~s Of the sensor 16 then all of the 11ght trapped 1n the sensor 16 wlll pass 1nto the ~1ber 70. S1nce th~s return llght contalns the slgnal to be measured 1t 1s deslrable that 1t be permltted to enter the flber 70 and that 1t be trapped w1thln the core 72 for presentat1On to the llght detector 14. Once the return llght ls 1n the core 72 of the flber 70 1t wlll be sub~ect to the same crltlcal angle constra1nts discussed w1th reference to F1gure 6. Any return 11ght rays whlch strlke the 1nterface 96 at an angle less than the cr1t1cal angle Of will pass through the claddlng 74. Only those returnlng llght rays striktng the lnterface 58 at an angle greater than the crlt1cal angle Of wlll be trapped and presented to the llght detector 14 .
Once the sensor 16 has been provlded wlth llght gu1de propert1es 1t lsapparent that a11 of the advantages assoclated w1th flberopt1c technology are ava11able to 1ncrease the eff1c1ency of the gas measurement.
Importantly one of these advantages ls assoclated w1th the fact that the sensor 16 can be bent cons1derably w1thout degrad1ng 1ts h19h signal-to-nolse ratlo. This ls posslble because the 11ght gulde properties of the sensor 16 facllltate retentlon of most of the trapped light w1thln the core 76 even when bent thereby malnta1n1ng the s1gnal avallable for process1ng.
In add~t10n to ~nc~eas~n~ the streng~h of the ~nformatlon s~gnal the ~.~3~r~
light gulde propert~es of the sensor 16 also reduce the effect of no~
In the past muscle mot~on art~fact has phys~cally bent the sensors w~th a consequent 10ss of l~ght from the process. Unfortunately th~s loss has been 1nterpreted as a h19h gas concentrat~on s~gn~f1cantly degrad~ng the accuracy of pr~or sensors. W~th the l~ght gulde characterlst7cs ssoc~ated w1th the present 1nvent~on bend1ng caused by muscle mot~on does not generate nolse. S1m11arly the adverse effects assoclated w~th other phys~cal artlfacts such as blood pulsat~ons are also !S~ gn~f~cantly reduced.
In a preferred embod~ment the 1nd1ces of refract~on for the cores 72 and 76 of the f~ber 70 and sensor 16 respectlvely have been chosen to be relat1vely equal. Th1s reduces the refract~on effect at the ~nterface B4 so the 11ght travel~ng from the flber 70 to the sensor 16 1s relat~vely unrefracted. ln order that the cr1t1cal angles Of and 05 m1ght be equal ~t 1s necessary to choose mater1als for the cladd~ng 74 and the cladding 7B wh1ch have ~nd1ces oS refract10n that are also equal. If the 1ndlces of refract10n for the cores 72 ind 76 are equal and the 1nd1ces of refract~on for the cladd~ngs 56 and 78 are equal 1t follows that the cr~t~cal angles Of and 05 w~ll be equal and the acceptance half angles Of and 05 wlll also be equal. W1th these propertles the greatest retent~on of l~ght w~th~n the f1ber 70 and sensor 16 can be ach1eved. In general ~t has been found that best results are prov~ded when the rat~o of crit~cal angles f/s ~5 w~th1n a range of about 1.10 to 0.90 and the rat10 of core refract~ve 1ndex of f~ber and sensor ~s w1th1n a range of 1.02 to 0.98.
A preferred embod~ment of the sensor 16 measures the concentrat~on of oxygen as prev10usly d1sclosed. However the sensor 16 can be adapted to measure the concentrat~on of other substances ~n a part1cular envlronment by prov~d1ng a convers10n layer 130 around the claddlng 78. Thls layer 130 could ~nclude var~ous chem~cals for convert1ng the substance of ~nterest tnto oxygen. Then as the concentratlon of oxygen ~s mon~tored by the sensor 16 that would prov1de an 1nd1cat10n of concentrat~on for the part~cular substance.
For example the sensor 16 1nclud~ng the conversat10n layer 130 m19ht typ1cally be~ d1sposed ~n the tlssue bed of a pat1ent. In th~s env~ronment 1nclud1ng b100d the subst2nce of ~nterest could be glucose in wh~ch case the convers10n layer 130 m1ght 1nclude glucose ox1dase as d~sclosed 1n appl~cant s co-pend~ng Patent Appl~cat~on Serlal Number lO0 100 prev~ously ment10ned. The conversat10n layer 130 would convert .;
any glucose present 1n the blood envlronment ~nto oxygen. ~he measurement of oxygen by the sensor 16 would then prov~dq an ~nd~cat~on as to the concentrat~on of glucose w~th~n the b100d.
The measurement of gas act1vates other than oxygen, such as carbon d10x~de, when comblned wlth sultable converslon layers, would make the sensor 16 advantageous for measur~ng the concentratlons of many d~fferent substances 1n many dlfferent env1ronments.
Although thls lnvent10n has been d1sclosed ~th reference to a speclfic oxygen sensor adapted for 1n v1vo appl1catlons, 1t will be apparent that the light gu~de qual1t~es assoclated w~th the sensor 16 are advantageous for many other app1~catlons. For example, dlfferent materlals can be used for the core 76, the claddlng 78, and the fluorophors Z0 1n order to provlde for measuremen~ of gases other than oxygen. Slmllarly, gas concentrat~ons can be measured 1n other flu1d env1ronments, both gas and 11qu1d, to prov1de an lnd1catlon of the part1al pressure assoc1ated w1th a part~cular gas act1vate.
It is also apparent that the llght gulde propert1es ssoc1ated w1th thepresent ~nvent10n would be equally appl1cable and advantageous to gas reasurement by way of absorpt10n technology. In any case where lt ls des1rable to reduce 119ht losses w1thln a sensor, an approprlate cladding configurat10n can be added to provlde the sensor wlth 119ht gulde propert1es.
~hese and other features and advantages of the present lnvent10n w111 be apparent to those skllled ln the art so that the scope of th1s lnventlon should be ascertalned only wlth reference to the follow1ng cla~ms.
Claims (19)
1. A catheter assembly for monitoring the concentration of an analyte in a liquid, physiological environment,comprising:
a source of visible light;
a catheter having a proximal end and a distal end;
an optical fiber disposal within the catheter and extending between the proximal and the distal ends of the catheter the optical fiber communicating with the light source at the proximal end of the catheter;
a sensor disposed to communicate with the optical fiber at the distal end of the catheter;
a core material included in the sensor and having properties variable in response to the concentration of the analyte in the physiological environment;
a cladding material surrounding the core material in the sensor the cladding material being permeable to the analyte and having properties for inhibiting the escape of the light from the core material of the sensor; and means for detecting the variable properties of the core material and for determining the concentration of the analyte in the environment.
a source of visible light;
a catheter having a proximal end and a distal end;
an optical fiber disposal within the catheter and extending between the proximal and the distal ends of the catheter the optical fiber communicating with the light source at the proximal end of the catheter;
a sensor disposed to communicate with the optical fiber at the distal end of the catheter;
a core material included in the sensor and having properties variable in response to the concentration of the analyte in the physiological environment;
a cladding material surrounding the core material in the sensor the cladding material being permeable to the analyte and having properties for inhibiting the escape of the light from the core material of the sensor; and means for detecting the variable properties of the core material and for determining the concentration of the analyte in the environment.
2. The catheter assembly recited in claim 1 wherein:
the optical fiber includes a core material and a cladding material which provide the fiber optic with optical characteristics including a first critical angle;
the core material and the cladding material of the sensor provide the sensor with optical characteristics including a second critical angle; and the ratio of the first critical angle to the second critical angle being within a range of 1.10 to 0.90.
the optical fiber includes a core material and a cladding material which provide the fiber optic with optical characteristics including a first critical angle;
the core material and the cladding material of the sensor provide the sensor with optical characteristics including a second critical angle; and the ratio of the first critical angle to the second critical angle being within a range of 1.10 to 0.90.
3. The catheter assembly recited in Claim 2 wherein the ratio of the first critical angle to the second critical angle is substantially inity, and the ratio of core refractive index of fiber to sensor is unity.
4. The catheter assembly recited in Claim 1 wherein:
the core material of the fiber has a first index refraction;
the core material of the sensor has a second index refraction; and the first index of refraction is substantially equivalent to the second index of refraction.
the core material of the fiber has a first index refraction;
the core material of the sensor has a second index refraction; and the first index of refraction is substantially equivalent to the second index of refraction.
5. An optical waveguide sensor communicating through an optical fiber with a light source and detector the sensor having properties for measuring the concentration of an activate in a fluid environment, comprising:
a core material in a solid phase communicating with the optical fiber and receiving a source light having a first wavelength of interest;
a multiplicity of fluorophors included in the core material and being responsive to the source light to produce a return light at a second wavelength of interest;
the return light being directed through the optical fiber to the detector, and having an intensity dependent upon the concentration of the activate in the fluid environment, the return light being isotropic and including first rays directed toward the optical fiber and second rays directed away from the optical fiber;
a cladding material disposed around the core material and having properties for inhibiting loss of both the source light and the return light from the core material of the sensor;
end cap means included in the cladding material for redirecting the second rays of the return light toward the optical fiber; whereby the redirected second rays of the return light combine with the first rays of the return light to increase the signal-to-noise ratio of the sensor.
a core material in a solid phase communicating with the optical fiber and receiving a source light having a first wavelength of interest;
a multiplicity of fluorophors included in the core material and being responsive to the source light to produce a return light at a second wavelength of interest;
the return light being directed through the optical fiber to the detector, and having an intensity dependent upon the concentration of the activate in the fluid environment, the return light being isotropic and including first rays directed toward the optical fiber and second rays directed away from the optical fiber;
a cladding material disposed around the core material and having properties for inhibiting loss of both the source light and the return light from the core material of the sensor;
end cap means included in the cladding material for redirecting the second rays of the return light toward the optical fiber; whereby the redirected second rays of the return light combine with the first rays of the return light to increase the signal-to-noise ratio of the sensor.
6. The optical wave guide sensor of Claim 5 wherein the end cap means includes a mirror disposed to face the core material and having properties for producing specular reflectance of the second rays of the return light into the core material.
7. The optical wave guide sensor recited in Claim 5 wherein the end cap means includes scattering particles disposed in the cladding material and having properties for producing a diffuse reflectance of the second rays of the return light into the core material.
8. The optical wave guide sensor recited in Claim 7 wherein the scattering particles include Titanium Dioxide.
9. The optical wave guide sensor recited in claim 5 wherein the sensor is disposed in a physiological environment icluding a particular substance and further comprises:
a reaction layer disposed around the cladding material and having properties for producing the activate in a concentration dependant upon the concentration of the particular substance in the physiological environment.
a reaction layer disposed around the cladding material and having properties for producing the activate in a concentration dependant upon the concentration of the particular substance in the physiological environment.
10. The optical wave guide sensor recited in Claim 9 wherein the physiological environment is blood.
11. The optical wave guide sensor recited in claim 10 wherein the particular substance is glucose and the gas activate is oxygen.
12. A gas sensor adapted to receive a first light signal from an optical fiber and having properties for monitoring the concentration of a gas activate in a fluid environment, the sensor including:
a core material communicating with the optical fiber to receive the first light signal and being responsive to the first light signal to provide a second light signal having characteristics variable with the concentration of the gas activate in the fluid environment;
a cladding material disposed around the first core material and having properties for inhibiting the escape of the first and second light signals from the core material;
the core material and the cladding material being configured at a proximal end of the sensor to receive the optical fiber;
end cap means included in the cladding material and disposed at a distal end of the sensor for directing at least a portion of the second light signal back into the optical fiber; whereby the cladding material and the end cap means provide the sensor with an increased signal-to-noise ratio.
a core material communicating with the optical fiber to receive the first light signal and being responsive to the first light signal to provide a second light signal having characteristics variable with the concentration of the gas activate in the fluid environment;
a cladding material disposed around the first core material and having properties for inhibiting the escape of the first and second light signals from the core material;
the core material and the cladding material being configured at a proximal end of the sensor to receive the optical fiber;
end cap means included in the cladding material and disposed at a distal end of the sensor for directing at least a portion of the second light signal back into the optical fiber; whereby the cladding material and the end cap means provide the sensor with an increased signal-to-noise ratio.
13. The gas sensor recited in Claim 12 wherein:
portions of the cladding material define an annular recess configured to received the optical fiber at the proximal end of the sensor;
the core material defines with the optical fiber an interface; and the first light signal passes across the interface from the optical fiber into the sensor and the second light signal passes across the interface from the sensor into the optical fiber.
portions of the cladding material define an annular recess configured to received the optical fiber at the proximal end of the sensor;
the core material defines with the optical fiber an interface; and the first light signal passes across the interface from the optical fiber into the sensor and the second light signal passes across the interface from the sensor into the optical fiber.
14. The gas sensor recited in Claim 13 wherein:
the core material is disposed longitudinally along an axis of the sensor; and the interface and the end cap means are disposed generally transverse to the axis of the sensor.
the core material is disposed longitudinally along an axis of the sensor; and the interface and the end cap means are disposed generally transverse to the axis of the sensor.
15. The gas sensor recited in Claim 14 wherein:
the optical fiber has a longitudinal axis;
the sensor is configured to receive the optical fiber with the axis of the fiber disposed generally parallel to the axis of the sensor; and the interface and the end capped means are disposed generally perpendicular to the axis of the sensor.
the optical fiber has a longitudinal axis;
the sensor is configured to receive the optical fiber with the axis of the fiber disposed generally parallel to the axis of the sensor; and the interface and the end capped means are disposed generally perpendicular to the axis of the sensor.
16. The gas sensor recited in Claim 12 further comprising a dye included in the core material and comprising a multiplicity of fluorophors each having fluorescent properties responsive to the first light signal to emit the second light signal, the intensity of the second light signal being dependent upon the concentration of the gas activate in the fluid environment.
17. The gas sensor recited in Claim 16 wherein the cladding material has properties for inhibiting passage of the fluid in the environment while facilitating passage of the gas activate from the environment into the core material of the sensor.
18. The gas sensor recited in Claim 12 further comprising a mirror included in the end cap means for reflecting at least a portion of the second light signal toward the optical fiber.
19. The gas sensor recited in Claim 12 further comprising means included in the cladding material for reflecting at least a portion of the second light signal into the core material of the sensor.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US35925489A | 1989-05-31 | 1989-05-31 | |
| US07/359,254 | 1989-05-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2017740A1 true CA2017740A1 (en) | 1990-11-30 |
Family
ID=23413020
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2017740 Abandoned CA2017740A1 (en) | 1989-05-31 | 1990-05-29 | Fiberoptic probe having waveguide properties |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH0380835A (en) |
| CA (1) | CA2017740A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9642568B2 (en) | 2011-09-06 | 2017-05-09 | Medtronic Minimed, Inc. | Orthogonally redundant sensor systems and methods |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0627358B2 (en) * | 1985-03-11 | 1994-04-13 | 株式会社日立製作所 | Coated steel and its manufacturing method |
| JP6511303B2 (en) * | 2015-03-13 | 2019-05-15 | テルモ株式会社 | Sensor |
| KR102138308B1 (en) | 2019-03-13 | 2020-08-13 | 울산과학기술원 | Eyelash extension system |
-
1990
- 1990-05-29 CA CA 2017740 patent/CA2017740A1/en not_active Abandoned
- 1990-05-31 JP JP2143250A patent/JPH0380835A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9642568B2 (en) | 2011-09-06 | 2017-05-09 | Medtronic Minimed, Inc. | Orthogonally redundant sensor systems and methods |
| US10194845B2 (en) | 2011-09-06 | 2019-02-05 | Medtronic Minimed, Inc. | Orthogonally redundant sensor systems and methods |
| US11229384B2 (en) | 2011-09-06 | 2022-01-25 | Medtronic Minimed, Inc. | Orthogonally redundant sensor systems and methods |
| US11931145B2 (en) | 2011-09-06 | 2024-03-19 | Medtronic Minimed, Inc. | Orthogonally redundant sensor systems and methods |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0380835A (en) | 1991-04-05 |
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