Implantable dielectrometer

1. Diagnostic apparatus, comprising:

a sealed case, comprising a biocompatible material and configured for implantation within a body of a human subject;

a dielectrometric probe, which is connected to the case and comprises first and second conductors, which are configured to be placed in proximity to a target tissue in the body;

a driving circuit, which is contained in the case and is coupled to apply a radio-frequency (RF) signal to the probe and to sense the signal returned from the probe; and

processing circuitry, which is configured to evaluate, responsively to the returned signal, a dielectric property of the target tissue.

2. The apparatus according to claim 1 , wherein the driving circuit is configured to apply the RF signal to the probe and to sense the returned signal at multiple different frequencies.

3. The apparatus according to claim 1 , wherein the dielectric property evaluated by the processing circuitry comprises a complex permittivity of the target tissue.

4. The apparatus according to claim 3 , wherein the processing circuitry is configured to evaluate the complex permittivity by measuring an impedance between the first and second conductors.

5. The apparatus according to claim 3 , wherein the processing circuitry is configured to evaluate the complex permittivity by measuring a reflection of the signal from the probe, which is indicative of an impedance mismatch at the target tissue.

6. The apparatus according to claim 3 , wherein the processing circuitry is configured to evaluate the complex permittivity by measuring a delay of the signal transmitted through the probe.

7. The apparatus according to claim 3 , wherein the processing circuitry is configured to evaluate the complex permittivity by measuring a resonant frequency of the probe.

8. The apparatus according to claim 1 , wherein the conductors are arranged to provide a coaxial contact to the target tissue at a distal end of the probe.

9. The apparatus according to claim 8 , wherein the coaxial contact comprises a patch, which is configured to be placed against the target tissue.

10. The apparatus according to claim 8 , wherein the coaxial contact comprises a coaxial tip, in which the first conductor is concentrically contained within the second conductor, wherein the tip is configured for insertion into the target tissue.

11. The apparatus according to claim 1 , wherein the conductors are arranged to define a transmission line in proximity to the target tissue.

12. The apparatus according to claim 11 , wherein the transmission line is defined by arranging the first conductor as a ground plane and the second conductor as a microstrip parallel to the ground plane.

13. The apparatus according to claim 11 , wherein transmission line is defined by arranging the first and second conductors as parallel lines.

14. The apparatus according to claim 11 , wherein the transmission line comprises a coplanar waveguide.

15. The apparatus according to claim 1 , wherein the conductors are arranged to define a resonant ring in proximity to the target tissue.

16. The apparatus according to claim 1 , wherein the processing circuitry is configured to derive a measure of a fluid content of the target tissue from the dielectric property.

17. The apparatus according to claim 16 , wherein the processing circuitry is configured to measure the fluid content continuously.

18. The apparatus according to claim 16 , wherein the processing circuitry is configured to measure the fluid content intermittently.

19. The apparatus according to claim 16 , wherein the processing circuitry is configured to measure changes in the fluid content over time.

20. The apparatus according to claim 1 , wherein the case is configured for implantation in a thorax of the subject.