Apparatus and method for high resolution temperature measurement and for hyperthermia therapy

• US 20070156212A1
• Filed: 12/30/2005
• Published: 07/05/2007
• Est. Priority Date: 12/30/2005
• Status: Active Grant

• Current Assignee: Optech Ventures, LLC
• Original Assignee: Optech Ventures, LLC
• Inventors: Mukamal, Harold, Saxena, Indu
• Granted Patent: US 7,717,618 B2
• Time in Patent Office: Days
• US Class Current: 607/102
• CPC Class Codes: A61B 18/18 by applying electromagnetic radiation, e.g. microwaves radiation therapy A61N5/00
• CPC Class Codes: A61B 2017/00057 Light
• CPC Class Codes: A61B 2017/00084 Temperature
• CPC Class Codes: A61B 2017/00274 Prostate operation, e.g. prostatectomy, turp, bhp treatment
• CPC Class Codes: A61B 2018/00547 Prostate
• CPC Class Codes: A61N 1/403 for thermotherapy, e.g. hyperthermia
• CPC Class Codes: A61N 5/025 Warming the body, e.g. hyperthermia treatment

Abstract

An apparatus and method for increasing the resolution of a linear array of fiber Bragg gratings by applying a plastic coating having a high CTE over the optical fiber. Apparatus and method for determining the temperature of each of a succession of points along a tissue portion during hyperthermia treatment includes an optical fiber with a succession of closely spaced fiber Bragg gratings. Each grating is responsive to a different wavelength and is sensitive to ambient temperature to change that wavelength as a function of temperature. A tunable laser operative continuously over a range of wavelengths including those to which the gratings respond is used to interrogate the gratings. Sensitivity-enhancing coatings are used on the fibers and the lasers are tuned over very short time cycles.

Claims

1. A temperature profiling sensor for providing temperature indications over a distance comprising;

an optical fiber having a plurality of linearly spaced apart FBGs formed therealong over a selected length each of said FBGs having a different initial periodicity wherein each FBG is responsive to incident light to produce a reflected wavelength spectrum said wavelength spectra being representative of the ambient temperature proximate to each FBG;

a non-conductive coating in sufficiently strong direct or indirect contact with the optical fiber at least over the selected length such that response to the temperature proximate to each FBG by the coating is substantially transmitted as strain to the selected length of the optical fiber and consequently to the FBGs, said coating having a CTE greater than that of the optical fiber;

whereby expansion or contraction of the coating due to the temperature exterior to the coating, local to each FBG, causes mechanical strain to be transmitted to the FBGs and consequent change in the reflected wavelength of each FBG as a function of the temperature proximate thereto said mechanical strain being greater than the thermal strain that would result alone from the optical fiber being exposed to the same temperature thereby increasing the sensitivity of the optical fiber to temperature changes.

2. The temperature profiling sensor of claim 1 wherein the coating is selected to have a CTE of at least about 2×

10<sup>−

6</sup>/°

C.

3. The temperature profiling sensor of claim 1 wherein the coating is selected to have a CTE sufficient to strain the FBGs to cause a reflected wavelength shift per unit temperature (Kt) of at least about 20 picometers/°

C.

4. The temperature profiling sensor of claim 1 further wherein the FBGs have a separation distance no greater than about 10 micrometers.

5. The temperature profiling sensor of claim 1 wherein the unstrained peak wavelength separation of wavelength adjacent FBGs is greater than (Kt) (Tr)+X in which;

Kt is a desired change in reflected wavelength per unit temperature,

Tr is an expected maximum temperature range, and

X is an expected wavelength change induced by non-thermal effects.

6. The temperature profiling sensor of claim 5 in which Kt is at least about 20 picometers/°

C.

7. The temperature profiling sensor of claim 6 in which Tr is a range from about 20°

C. to about 55°

C.

8. The temperature profiling sensor of claim 1 wherein the FBGs have a collective reflection spectrum from about 1220 nm to about 1680 nm.

9. The temperature profiling sensor of claim 1 wherein the FBGs have individual lengths of about 5 mm or less.

10. The temperature profiling sensor of claim 1 further comprising a light source connected to the optical fiber to provide scanning incident light to the FBGs, the light source having a wavelength range sufficient to obtain a reflection from each FBG.

11. The temperature profiling sensor of claim 3 wherein the FBGs are constructed such that the reflected wavelength shift of at least 20 picometers/°

C. occurs during exposure of the temperature sensor to a temperature range from about 30°

C. to about 55 °

C.

12. The temperature profiling sensor of claim 1 wherein the coating has a glass transition temperature effectively lower or higher than the operating range of the sensor such that the properties of the Young'"'"'s modulus of the coating remain predictable and unchanged in that temperature range

13. The temperature profiling sensor of claim 2 wherein the CTE of the coating is at least about 4 times that of the fiber.

14. The temperature profiling sensor of claim 8 wherein the FBGs are exposed to incident light having a range of about 1500 nm to 1600 nm from a light source having a scanning rate of at least 20 nm/second.

15. The temperature profiling sensor of claim 8 wherein the FBGs have a collective reflection spectrum from about 1540 nm to about 1580 nm.

16. The temperature profiling sensor of claim 10 wherein the FBGs have a collective reflection spectrum from about 1220 nm to about 1680 nm.

17. The temperature profiling sensor of claim 16 wherein the FBGs have collective reflection spectrum from about 1540 nm to about 1580 nm.

18. The temperature profiling sensor of claim 16 wherein the scanning light source has a wavelength range from about 1500 nm to about 1600 nm with a scanning rate of at least about 20 nm/second.

19. The temperature profiling sensor of claim 1 wherein the coating is a material of at least substantially polymer content.

20. The temperature profiling sensor of claim 19 wherein the polymer is selected from the group consisting of,

(a) polystyrene;

(b) polymethylmethacrylate;

(c) polyethylene;

(d) polytetrachloride;

(e) Polytetraflouroethylene; and

(f) combinations of (a), (b), (c), (d) and (e).

21. The temperature profiling sensor of claim 1 wherein the separation of the specified characteristic peak wavelength of each FGB is at least 0.5 nm.

22. The temperature profiling sensor of claim 21 further wherein the reflection spectrum of any FBG has no sideband greater than 10% of the peak intensity of the reflection spectrum.

23. A hyperthermia therapy process comprising;

artificially elevating the temperature of a selected tissue area;

obtaining a continuous or periodic temperature profile for at least the selected tissue area by placing proximate the selected tissue area a length of optical fiber having a plurality of spaced apart FBGs, each FBG providing in response to incident light a different reflection spectrum;

at selected time intervals converting the reflection spectra of the FBGs into a temperature reading for the tissue closely proximate each FBG.

24. A hyperthermia therapy system comprising;

an electromagnetic radiation source adapted to cause increase of the temperature of a selected tissue area upon exposure to the electromagnetic radiation for hyperthermia therapy;

a temperature profiling portion of the system for measuring temperature changes caused by the electromagnetic radiation comprising;

an optical fiber temperature sensor comprising a series of FBGs spaced apart along an optical fiber sensor element, each FBG having a different reflection spectrum and a different specified characteristic peak wavelength adapted to be placed adjacently proximate tissue whose temperature is to be determined and monitored during hyperthermia treatment;

an interrogation portion coupled to the optical fiber temperature sensor comprising a scanning light source having a scanning rate defining scan cycles to send interrogating light to the optical fiber sensor, the scanning light source having a scanning wavelength range sufficiently broad to cause reflection by all of the FBGs such that each scanning cycle updates the reflection spectra of the FBGs;

a detection and processing portion for detecting the reflected light of the FBGs and determining therefrom the temperature and the temperature change locally to each FBG comprising;

a wavelength selective detector element coupled to receive reflected light from the FBGs and operative at a sampling rate to produce a time division electrical signal representative of the spectra reflected from each FBG;

a specially programmed processor in communication with the wavelength selective detector element to control its sampling rate and to convert the time divisions of the time division electrical digital signal to wavelength divisions and to identify wavelength peaks for each FBG in each of said scanning cycles by applying a curve smoothing and curve fitting and peak detection procedure comprising;

sampling the signal at a sampling rate defined by;

$\frac{\mathrm{light}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{source}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{scanning}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{rate}}{\mathrm{desired}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{temperature}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{resolution}\times <br><br>\mathrm{Kt}};<br><br>$

applying the sampling rate to the wavelength selective detector;

defining a bin for each FBG in which each bin has a lower wavelength limit and an upper wavelength limit which is not more than ½

the difference between the specified characteristic peak wavelength of the FBG and the specified characteristic peak wavelength of the next lower and the next higher FBG, respectively;

in each bin selecting a number of data points over which to smooth thereby creating a smoothing window having N data points;

replacing each of the data points in each smoothing window by the mean value of the set of data points consisting of N/2 data points preceding the data point and N/2 data points succeeding the data point defining a second set of data points;

curve fitting the second set of data points to a polynomial curve of order of at least two;

determining the peak of the polynomial curve to define a wavelength peak of each FBG;

taking the difference of the wavelength peak of each FBG at selected time intervals from a predetermined wavelength peak at a base condition and converting that wavelength difference to a temperature difference by multiplying by Kt; and

an output device adapted to provide a temperature profile at each of the selected time intervals comprising the temperature at each FBG and/or the temperature change at each FBG.

25. A method of increasing the temperature resolution of a an optical fiber temperature sensor having at least one FBG comprising;

increasing the sensitivity, Kt, of the optical fiber temperature sensor by coating the optical fiber at least in the portion having the FBG with a plastic material in strong contact with the optical fiber which plastic material has a CTE greater than that of the optical fiber;

interrogating the optical fiber at a selected scanning rate and a scanning range that includes the characteristic wavelength of the at least one FBG;

detecting the reflected light spectrum of the at least one FBG at a sampling rate at least equal to

$\frac{\mathrm{light}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{source}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{scanning}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{rate}}{\mathrm{desired}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{temperature}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{resolution}\times <br><br>\mathrm{Kt}};<br><br>$

applying to the reflection spectrum of the at least on FBG, curve fitting and peak detection algorithms to establish a best fit curve and to determine a peak wavelength;

calibrating the detection of wavelength to temperature; and

converting the peak wavelength to temperature according to the calibration.