System, method and apparatus for evaluating tissue temperature
Method, system and apparatus for monitoring target tissue temperatures wherein temperature sensors are configured as passive resonant circuits each with a unique resonating signature at monitoring temperatures extending below a select temperature setpoint. The resonant circuits are configured with an inductor component formed of windings about a ferrite core having a Curie temperature characteristic corresponding with a desired temperature setpoint. By selecting inductor winding turns and capacitance values, unique resonant center frequencies are detectable. Temperature monitoring can be carried out with implants at lower threshold and upper limit temperature responses. Additionally, the lower threshold sensors may be combined with auto-regulated heater implants having Curie transitions at upper temperature limits.
1. A temperature responsive untethered sensor implant for evaluating a temperature rise from a monitoring temperature or temperatures to a set point temperature comprising:
a core component exhibiting a relative permeability characteristic elevating in value with a corresponding elevation in monitoring temperatures and exhibiting a Curie temperature above said monitoring temperatures corresponding with said set point temperature;
an inductive winding with turns wound about said core component to define an inductive component;
a capacitor coupled with said inductive winding to define a resonant circuit electromagnetically excitable to have a resonating output at a select resonant center frequency and exhibiting a decrease in the intensity of said resonating output at said select resonant center frequency when at temperatures approaching at said Curie temperature.
2. The implant of claim 1 in which said implant further comprises:
a non-magnetic heater component coupled in heat influencing relationship with said sensor implant at a location substantially non-interfering with said resonating output.
3. The implant of claim 1 in which:
said defined resonant circuit exhibits an absence of said resonating output at said select resonant center frequency when at said Curie temperature.
4. The implant of claim 1 in which:
said core component is formed of ferrite material.
5. The implant of claim 1 in which:
said select resonant center frequency corresponds at least in part with the number of said turns of said inductive winding.
6. The implant of claim 1 in which:
said select resonant center frequency corresponds at least in part with the value of capacitance of said capacitor.
7. The implant of claim 1 in which:
said select center frequency corresponds with both the number of said turns of said inductive winding and with the value of capacitance of said capacitor.
8. The implant of claim 1 in which:
said core component has an outer surface and extends along a component axis between oppositely disposed end surfaces;
further comprising a first electrically insulative sleeve having a first sleeve outer surface and located over said core component outer surface and having oppositely disposed first sleeve ends extending between or beyond said core component end surfaces; and
said inductive winding turns are wound over said sleeve outer surface.
9. The implant of claim 8 in which:
a second electrically insulative sleeve having a second sleeve outer surface located over said inductive winding, having oppositely disposed second sleeve ends extending beyond said first sleeve ends.
10. The implant of claim 9 in which:
said capacitor is mounted within said second sleeve between a said first sleeve end and an adjacent said second sleeve end.
11. The implant of claim 10 in which:
said first and second sleeves are formed of polymeric material; and
said second sleeve is potted with a biocompatible epoxy adhesive.
12. The implant of claim 10 in which said second sleeve, when potted, is coated with an electrically insulative biocompatible conformal layer.
13. The implant of claim 10 in which:
said second sleeve is potted with said biocompatible epoxy adhesive wherein the outwardly disposed surface of said epoxy adhesive is disposed inwardly from at least one of said second sleeve ends to define an anchoring structure for engagement with animal tissue.
14. The implant of claim 10 further comprising:
a biocompatible anchor structure configured for engagement with animal tissue mounted within and extending from at least one of said second sleeve ends.
15. The implant of claim 9 in which said implant further comprises:
a non-magnetic heater component coupled in heat influencing relationship with said sensor implant at a said second sleeve end.
16. The implant of claim 15 in which:
said heater component is configured as an open ended sleeve coupled at the said second sleeve outer surface.
17. The implant of claim 1 in which said implant further comprises:
a thermally activatable release agent supported by said implant and effective to disperse when said implant is within tissue at or below said transition temperature.
18. The implant of claim 1 in which:
said monitoring and said set point temperatures are between about 39° C. and about 70° C.
19. The implant of claim 1 in which:
said monitoring and said set point temperatures are between about 41° C. and about 50° C.
20. The implant of claim 1 in which: said monitoring and said set point temperatures are between about 42° C. and about 45° C.
21. The implant of claim 1 in which: said set point temperature is within a range from about 4° C. to about 13° C. over normal body temperature.
22. The system of claim 1 in which: said set point temperature is within a range from about 2° C. to about 33° C. over normal body temperature.