Use microwave tomographic imaging for temperature monitoring in thermal therapy

1. Integrated Microwave Thermal Imaging System with Mechanically Steerable HIFU Therapy Device Tian Zhou 01/26/09

2. Outline Purpose Principles of Microwave Imaging Dielectric Properties vs. Temperature Change Integration of Microwave Thermal Imaging and HIFU Heating (Configuration I, II) Challenges 2

3. Purpose 3

4. Principles in Microwave Imaging Dielectric Properties Permittivity, ɛ a measurement of energy storage in a material from an external electric field Conductivity, σ (siemens/m) how dissipative or lossy a material is to an external electric field* *Agilent tech notes 4

5. Principles in Microwave Imaging 5

6. Relationship between Dielectric Properties and Temperature In literature Liver tissue ex vivo @915MHz @2.45GHz Susan C. Hagness et al. (2006) 6

7. Integrating MW Imaging and HIFU Heating Temperature change will alter the dielectric properties of a phantom or tissues Microwave imaging is able to capture the change of the dielectric properties Microwave imaging can be a potential non-invasive tool to provide feedback of the thermal profile in HIFU heating 7

8. HIFU Heating 13 W 8 W Cyril Lafon et al. (2001) 8

9. Microwave imaging system 9

10. Integrating MW Imaging and HIFU Heating 10

11. System Setup 11 Phantom

12. Difference Image 12 T = tiT = t0 Difference Image

13. Difference image Circle Conductivity Difference Image Courtesy of ShireenGeimer 13

14. Difference image C-circle 14 Conductivity Difference Image

15. Difference image Spirals 15 Conductivity Difference Image

16. Spatial Registration 16 Conductivity Difference Image

17. Temporal Registration Temperature Normalized conductivity (1100MHz) 17

18. Conductivity vs. Temperature Change Conductivity Temperature (°C) 18

19. New Configuration for Integration Waveform Generator Power Amp. MW antenna Temp. Meter Stepper Controller HIFU transducer Thermal couples DMAS System Beam focus 19

20. New Configuration for Integration 20 Phantom Transducer heated plane focal zone scan path Focus

21. Steerable HIFU Transducer 21

22. Cross Section of a Focal Beam 22 1X power level 1.5X power level

23. Cross Section of a Focal Zone 23 Permittivity Conductivity Permittivity Conductivity

24. Animal Experiment 24

25. Challenges 25 Spatial Resolution Better with higher frequency, but higher attenuation Compromise between spatial res. and SNR Registered with images which have fine anatomic details Temporal Resolution Currently reconstructed offline Understanding the Relationship between Dielectric Properties and Temperature Change Nonlinear in vivo

26. Acknowledgement Thayer School, Dartmouth College Paul Meaney, PH.D Keith Paulsen, PH.D Shireen Geimer Margaret Fanning Lincoln Potwin Tim Raynolds Dartmouth Hitchcock Medical Center P. Jack Hoopes, D.V.M., PH.D Susan Kane NIH 26

27. Phantom experiment Relationship between Dielectric Constant and Temperature 27 Temperature (C) Temperature (C)