Depth Scanning Oxygen Sensor

Abstract

An oxygen scanning device includes a console unit. The console unit includes a light source emitting excitation radiation and a detector configured to receive and detect phosphorescence radiation. The device includes a needle sensor operably, optically coupled to the console unit by an optical fiber movably received within a transparent tube housing the optical fiber, the transparent tube being coated by an oxygen-sensitive dye material on an outer side thereof. The optical fiber is terminated by a 45 degree reflecting surface at a distal end thereof wherein excitation radiation is directed to the oxygen sensitive dye material and phosphorescence radiation from the oxygen sensitive material is returned from the oxygen sensitive material to the detector.

Claims

1. An oxygen scanning device, comprising: a console unit, the console unit including a light source emitting excitation radiation and a detector configured to receive and detect phosphorescence radiation; a needle sensor operably, optically coupled to the console unit by an optical fiber movably received within a transparent tube housing the optical fiber, the transparent tube being coated by an oxygen-sensitive dye material on an outer side thereof; the optical fiber being terminated by an angled reflector at a distal end thereof wherein excitation radiation is directed to the oxygen sensitive dye material via the optical fiber and phosphorescence radiation from the oxygen sensitive material is returned via the optical fiber from the oxygen sensitive material to the detector.

2. The oxygen scanning device of claim 1, in which oxygen-sensitive material is a dye embedded in a polymer matrix.

3. The oxygen scanning device of claim 1, wherein the oxygen sensitive material is coated by a protection layer of an oxygen-permeable material.

4. The oxygen scanning device of claim 1, wherein the transparent housing comprises a tube housed in a needle.

5. The oxygen scanning device of claim 2, further comprising a second dye mixed into the polymer matrix, the second dye having pH dependent fluorescence.

6. The oxygen scanning device of claim 2, wherein the light source of the console emits radiation that excites the pH-sensitive dye and the oxygen-sensitive dye and the detector receives both the phosphorescence and fluorescence radiation returned from the polymer matrix and the controller is programmed with an algorithm that evaluates both oxygen pO2 and pH level.

7. The oxygen scanning device of claim 5, further comprising a second dye mixed into the polymer matrix, the second dye having fluorescence or phosphorescence dependent on the presence of a target substance chosen from a group consisting of carbon dioxide, calcium ion and magnesium ion.

8. The oxygen scanning device of claim 2, further comprising a second dye mixed into the polymer matrix, the second dye having temperature dependent fluorescence.

9. The oxygen scanning device of claim 2, wherein the light source of the console emits radiation that excites the temperature-sensitive dye and the oxygen-sensitive dye and the detector receives both the phosphorescence and fluorescence radiation returned from the polymer matrix and the controller is programmed with an algorithm that evaluates both oxygen pO2 and temperature.

10. The oxygen scanning device of claim 1, wherein light source emits radiation that excites endogenic fluorophores at a first wavelength that is transmissible through the oxygen-sensitive dye and the detector detects light returned from fluorescence emission by the endogenic fluorophores at a second wavelength that is transmissible through the oxygen-sensitive dye.

11. The oxygen scanning device of claim 8, wherein the endogenic fluorophores comprise NADH.

12. The oxygen scanning device of claim 8, wherein the light source emits excitation radiation at a wavelength of 340 nm and the detector detects fluorescence radiation at a wavelength of 445 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 is a schematic depiction of a depth scanning oxygen sensing system according to an example embodiment of the invention; and

[0046] FIG. 2 is a schematic depiction of a console unit of a depth scanning oxygen sensing system according to an example embodiment of the invention; and

[0047] FIG. 3 is a schematic depiction of a needle oxygen probe according to an example embodiment of the invention.

DETAILED DESCRIPTION

[0048] Referring to FIGS. 1, 2, and 3, depth scanning oxygen sensing system generally includes base console 20 and needle sensor 23, connected by a single optical fiber assembly 21 and a connector 22. pO2 values are obtained by measuring phosphorescence lifetime of an oxygen-sensitive dye and using the Stern-Volmer equation relating excitation lifetime and pO2 in the micro-environment of the dye.

[0049] Referring particularly to FIG. 2, base console 20 generally includes excitation light source 17, light detector 16, fiber optic coupler 15, motorized translation stage 14, motorized rotation stage 13, motor driver unit 19, and a controller 18.

[0050] Excitation light source 17 emits an appropriate wavelength of light to excite a selected phosphorescent dye. Excitation light source 17 emits excitation light coupled into an optical fiber and connected to a fiberoptic coupler 15. The coupler directs part of the excitation light to optical fiber 1. Phosphorescence or fluorescence light is collected by the needle sensor 23 and propagates back in the optical fiber 1 and is coupled to the coupler 15. The phosphorescence or fluorescence light is directed by the coupler to the detector 16. A controller 18 (typically a digital microcontroller such as PIC18F24K40 manufactured by Microchip Inc.) is used to control the output power of the excitation light source 17 and to record the electronic signals of the light detector 16. The controller is also used to control the motorized translation stage and the motorized rotation stage by sending appropriate electronic signals to the motor driver unit 19. The motor driver 19 supply appropriate electrical current signals to the motors in the translation stage 14 and the rotation stage 13 causing the fiber 1 to translate and rotate such that its distal tip inside the needle sensor 23 is positioned appropriately to emit and collect light to and from a desired position along the sensitive dye-doped layer 4. The controller is also equipped with a bidirectional data channel to a user interface device 24 (such as a computer) allowing the user to operate the scanner.

[0051] Translation stage 14 supports the rotation stage 13 which in turn supports the optical fiber 1. Operating the translation stage causes optical fiber 1 to move along a straight line path without rotating optical fiber 1. Operating the rotation stage 13 causes the optical fiber 1 to rotate.

[0052] Controller 18 is operably coupled to input/output terminal 24, motors driver unit 19, light detector 16 and excitation light source 17. Controller 18 is programmed with appropriate algorithms to control excitation light source 17 and to receive and process information from light detector 16 and to control motors driver unit 19 which in turn controls motorized scanning device 14 and rotation stage 13.

[0053] Input/output terminal 24 is coupled to controller 18 and presents, for example, a graphical user interface by which an operator can input and receive information related to base console 20 and needle sensor 23. The controller 18 records and analyze digital signals acquired from the light detector 16 and then sends the processed signals to the user interface unit 24 for further processing and display.

[0054] Base console 20 is operably coupled to needle sensor 23 at least by optical fiber assembly 21 which includes an optical fiber 1, tight coating 6, and loose sleeve 7 (details shown in FIG. 3).

[0055] Referring particularly to FIG. 3, needle sensor 23 generally includes optical fiber 1, capillary glass tube 3, syringe needle 2, fiber sleeve 7, dye doped polymer layer 4 and thin protection layer 5. Optical fiber 1 is housed within capillary glass tube 3 which is, in turn, housed within syringe needle 2. Optical fiber 1 terminates at angled end 48. Angled end 48 is angled appropriately to cause total internal refraction of both excitation light and phosphorescence or fluorescence light. In an example embodiment, angled end 48 is terminated and polished at an angle of 45 degrees. The angled end 48 delivers excitation light to an oxygen sensing layer composed of a thin layer of dye-doped polymer layer 4. The dye-doped polymer layer 4 is coated on the outer wall of a sealed capillary glass tube 3. Phosphorescence light is generated in the sensing layer 4. Part of the phosphorescence emission is collected by the angled fiber end 48 and delivered to the detection section by the optical fiber 1. The glass capillary is housed in a stainless steel syringe needle 2 that has a side-window allowing physical contact between the sensing layer and the tissue. The optical fiber can be translated horizontally with respect to the static fiber sleeve 7 and the glass capillary 3 by pulling or pushing the back end of the fiber by the translation stage in unit 20 (shown in FIG. 2). This allows for optical probing of any point at the sensing layer and within the side opening in the needle shaft 2. The fiber 1 may have a tight coating 6 to enhance its mechanical properties allowing for better force and torque transmission from the translation and rotation stage in unit 20 to the front angled end of the fiber 48. In this case parts 1 and 6 are in tight contact such that they move together. A connector 22 composed of two parts (8 and 9) allows disconnecting the needle assembly (parts 2, 3, 4, 5, and 9) from the fiber assembly (parts 1, 6, 7, and 8) once the fiber assembly is completely retracted and positioned in the sleeve 7. This feature allows exchanging the needle unit for sterilization or replacement. A thin protection layer of oxygen-permeable layer 5 is deposited by dip coating to prevent degradation of the sensing layer. In addition to translation the fiber can also be rotated by rotating the back end of the fiber. Rotation is necessary for aligning the fiber illumination and receiving direction with the side window in the needle 2.

[0056] Syringe needle 2 may be formed, for example, of stainless steel or another rigid biocompatible material and is perforated by sensing window 50. According to an example embodiment, sensing window 50 may be approximately twenty mm long, though sensing window 50 may be longer or shorter as desired or necessary. Syringe needle 2 according to an example embodiment may have an outside diameter of 0.46 plus or minus 0.02 mm though size can vary.

[0057] Dye doped polymer layer 4 overlies capillary glass tube 3 at least in the vicinity of sensing window 50. Thin protection layer 5 in turn covers dye doped polymer layer 4. Thin protection layer 5 is oxygen permeable and may be applied, for example, by dip coating to prevent degradation of dye doped polymer layer 4.

[0058] Sensing window 50 is structured to allow physical contact between thin protection layer 5 and surrounding tissue into which needle sensor 23 is inserted. Thus, dye doped polymer layer 4 (or protection layer 5 if it is applied) is in direct oxygen sensing contact with surrounding tissue into which needle sensor 23 is inserted.

[0059] Optical fiber 1 is positioned within capillary glass tube 3 so that angled end 48 is directed toward sensing window 50 (light emitted from the fiber tip is directed toward the sensing window 50).

Oxygen Transduction

[0060] Oxygen sensitive dye in dye doped polymer layer 4 is excited by an optical pulse emitted from angled end 48. In case of a dye of high quantum yield for inter-system crossing, a significant part of the dye molecules will be excited to the first triplet state. The dynamics of the relaxation back to the ground state depends on oxygen concentration. The decay is exponential having a lifetime t.sub.1. The lifetime t.sub.1 depends on oxygen partial pressure according to Stern-Volmer equation, H. Boaz and G. K. Rollefson, The Quenching of Fluorescence. Deviations from the Stern-Volmer Law, J. Am. Chem. Soc. 72(8), p. 3435-3443 (1950), as follows:

[00001]$\begin{array}{cc}\frac{I_0}{I_{1.Math.}}=\frac{t_0}{t_{1.Math.}}=1+k_{O.Math..Math.2}+t_0.Math.p& \left(1\right)\end{array}$

where I.sub.0 and I.sub.1 is mean phosphorescence intensity in zero oxygen and at oxygen partial pressure of p respectively, t.sub.0 is the lifetime at zero oxygen conditions, t.sub.1 is the lifetime at p partial oxygen pressure, and k.sub.O2 is the quenching rate coefficient.

[0061] Following optical excitation of a photosensitizer dye, phosphorescence intensity decays exponentially. This decay can be described by the following expression.

I(t)=I.sub.PHexp(t/t.sub.1)(2)

where I.sub.PH is the initial phosphorescence intensity immediately after excitation illumination stops. By measuring the temporal decay of the phosphorescence (I(t)), and fitting the measured data points at a set of discrete time intervals to an exponential function, the lifetime (t.sub.1) can be extracted. Equation 1 is then used to evaluate the oxygen partial pressure.
Error Analysis: The dominant source for systematic measurement error is attributed to the dependence of phosphorescence lifetime on temperature. Coyle and Gouterman in L M. Coyle, and M. Gouterman, Correcting lifetime measurements for temperature, Sensors and Actuators B 61, p. 92-99 (1999), have measured the temperature dependence of phosphorescence lifetime in platinum meso-tetra (pentafluorphenyl) porphyrin (Pt-TFPP). They have found that lifetime decreases at a rate of 0.3%/ C. in the temperature range of 10-50 C. Similar temperature dependence of phosphorescence lifetime has been measured by Zelelow et. al. in B. Zelelow, G. E. Khalil, G. Phelan, B. Carlson, M. Gouterman, J. B. Callis, and L. R. Dalton Dual luminophor pressure sensitive paint: II. Lifetime based measurement of pressure and temperature. Sensors and Actuators B: Chemical 96.1, p. 304-314 (2003) for platinum-tetra(pentafluorophenyl)porpholactone (Pt-TFPL). In a typical application of a device described here, the oxygen probe will be inserted in a living tissue (animal or human) where temperature range is within the range of 32 C. to 42 C. If the tissue temperature is not measured, this uncertainty will lead to a systematic error of up to 3% in pO2 estimation.

Example Device Embodiment Configuration

[0062] Optical fiber 1 may be a multimode, having a 105 m core size, 125 m cladding size and 250 m jacket size, and a numerical aperture (NA) of 0.22. To form angled end 48 a distal end of the fiber can be terminated by 45 degree polishing.

[0063] Excitation light source 17 can be a Nd:YAG CW frequency doubled laser, 532 nm, 200 mW, Square wave modulated. Light detector 16 can be a detector: Avalanche Photodiode integrated with a transimpedance amplifier (100 kOhm).

[0064] An example oxygen sensitive dye can be PtOEP.

[0065] A polymer matrix for dye doped polymer layer 4 and thin protection layer 5 can be formed of cellulose butyrate (CAB).

[0066] Syringe needle 2 can be formed from a syringe needle gauge 26, length 1.5.

[0067] Capillary glass tube 3 can have an inside diameter of 0.15 and an outside diameter of 0.25 mm.

[0068] Information related to partial pressure of oxygen may be presented as absolute values as a function of depth or distance along sensing window 50 within the tissue or as relative values.

[0069] According to another example embodiment, the oxygen sensitive dye is mixed into a polymer matrix such as, but not limited to, cellulose acetate butyrate (CAB). Other polymer matrices may be selected on the basis of permeability to oxygen or other materials that are to be detected and other factors such as biocompatibility.

[0070] The polymer matrix may also incorporate a further dye or dyes mixed into the polymer matrix or otherwise on the exterior of capillary glass tube 3. The further dye may have a pH dependent fluorescence. In the case of this embodiment, excitation light source 17 emits radiation at one or several wavelengths that excites the pH-sensitive dye to fluorescence and the oxygen-sensitive dye to phosphorescence and the detector receives both the phosphorescence and fluorescence radiation returned from the polymer matrix and the controller is programmed with algorithms that operate to evaluate both oxygen pO2 and pH level.

[0071] Similarly, the polymer matrix may include dyes sensitive to the presence of carbon dioxide (CO.sub.2), calcium ion (Ca.sup.++) and/or magnesium ion (Mg.sup.++). In each of these, the light source emits radiation at a wavelength appropriate to excite the dye and the detector is structured to detect radiation returned from the dye by fluorescence or phosphorescence. Controller 18 is configured with hardware or software to resolve signals from light detector 16 to determine and display a concentration of the target substance which can then be determined as a function of depth or distance along the length of sensing window 50.

[0072] Similarly, the polymer matrix may also incorporate a further dye or dyes mixed into the polymer matrix or otherwise on the exterior of capillary glass tube 3. The further dye may have a temperature dependent fluorescence. In the case of this embodiment, excitation light source 17 emits radiation at one or several wavelengths that excites the temperature-sensitive dye to fluorescence and the oxygen-sensitive dye to phosphorescence and the detector receives both the phosphorescence and fluorescence radiation returned from the polymer matrix and the controller is programmed with algorithms that operate to evaluate both oxygen pO2 and temperature.

[0073] According to another example embodiment, excitation light source 17 emits light to excite endogenic fluorophores such as, but not limited to, NADH at a wavelength that is transmissible through the oxygen-sensitive dye and to record fluorescence emission in wavelengths that are transmissible through the oxygen-sensitive dye. Here, for example, NADH is excited at a wavelength of 340 nm and detected at a wavelength of 445 nm. PtOEP oxygen dye, for example, is transparent to both of these wavelengths.

[0074] Accordingly, the invention also includes a method of determining tissue oxygen level over a linear distance and presenting tissue oxygen level graphically or numerically and in absolute values or relative values.

[0075] An example method, includes inserting a needle sensor 23 into a tissue to be evaluated as to oxygen level so that a sensing window 50 having a dye doped polymer layer 4 is in close apposition to the tissue; translating the angled end 48 of an optical fiber 1 inside of the dye doped polymer layer 4 to illuminate the dye doped polymer layer 4 with excitation radiation and to receive phosphorescence radiation from the dye doped polymer layer 4; receiving the phosphorescence radiation at a light detector 16; sending signals from the light detector 16 to a controller and processing the signals using the Stern-Volmer equation relating excitation lifetime and pO2 in the micro-environment of the dye.

[0076] In operation, needle sensor 23 is inserted into a tissue, the partial pressure oxygen profile of which is desired to be determined. The tissue makes contact with thin protection layer 5 and dye doped polymer layer 4 via sensing window 50 in syringe needle 2. Oxygen molecules can diffuse through thin protection layer 5 to dye doped polymer layer 4 to physically interact with dye molecules in layer 4.

[0077] Excitation light source 17 is activated to emit excitation light which travels via optical fiber 1 to illuminate dye doped polymer layer 4. Phosphorescence light emitted by dye doped polymer layer 4 is received by angled end 48 of optical fiber 1 and returned via optical fiber 1 to light detector 16. Actuator 19 may be actuated to operate translation stage 14 which scans optical fiber 1 longitudinally thus causing angled end 48 to move within capillary glass tube 3. As angled end 48 moves relative to dye doped polymer layer 4, accordingly, partial pressure of oxygen within the tissue may be sensed along a linear depth as long as sensing window 50.