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

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.

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 −6 /° 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.