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

3

Purpose

Temperature

monitoring

MR

Ultrasound

MicrowaveEIT

NIR

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

5

Principles in Microwave Imaging

6

Relationship between Dielectric Properties and Temperature

In literature Liver tissue

ex vivo @915MHz

@2.45GHz

Susan C. Hagness et al. (2006)

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

8

HIFU Heating

Cyril Lafon et al. (2001)

13 W

8 W

9

Microwave imaging system

10

Integrating MW Imaging and HIFU Heating

11

System Setup

Phantom

12

Difference Image

T = ti T = t0 Difference Image

13

Difference image Circle

Courtesy of Shireen Geimer

Conductivity Difference Image

14

Difference image C-circle

Conductivity Difference Image

15

Difference image Spirals

Conductivity Difference Image

16

Spatial Registration

Conductivity Difference Image

17

Temporal Registration

Temperature

Normalizedconductivity

(1100MHz)

24

25

26

27

28

29

0 500 1000 1500 2000 2500

Time (seconds)

Te

mp

era

tu

re

(C

)

TC0

TC2

TC6

Center

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0 500 1000 1500 2000 2500

Time (seconds)

No

rm

alize

d C

on

du

ctivity (S

/m

)

TC0

TC2

TC6Center

18

Conductivity vs. Temperature Change Conductivity

24 24.5 25 25.5 26 26.5 27 27.5 28 28.50.75

0.8

0.85

0.9

0.95

1(Tcond-7.5,Tcond+7.5)

slope= -0.012933, R2= 0.78877, TempAcc= 0.29208

slope= -0.011089, R2= 0.75808, TempAcc= 0.30793

slope= -0.010414, R2= 0.86939, TempAcc= 0.34109

TC0

TC2TC6

Center

Temperature (°C)

19

New Configuration for Integration

Waveform

Generator

Waveform

Generator

Power

Amp.

Power

Amp.

Temp.

Meter

Temp.

Meter

Thermal couples

Stepper

Controller

Stepper

Controller

HIFU transducer

MW antenna

DMAS

System

DMAS

System

Beam focus

New Configuration for Integration

20

Transducer

Phantom

heated

plane

focal zone scan path

Focus

21

Steerable HIFU Transducer

22

Cross Section of a Focal Beam

1X power level

1.5X power level

23

Cross Section of a Focal Zone

Permittivity

Permittivity

Conductivity

Conductivity

24

Animal Experiment

25

Challenges 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.DShireen GeimerMargaret Fanning Lincoln Potwin Tim Raynolds

Dartmouth Hitchcock Medical CenterP. Jack Hoopes, D.V.M., PH.D

Susan Kane NIH

Phantom experiment

Relationship between Dielectric Constant and Temperature

27

23.5

24.5

25.5

26.5

27.4

28.5

29.5

30.5

31.5

32.5

33.5

34.6

-2

-1

0

1

2

3

4

delta perm. vs temp

300 MHz1 GHz3 GHz8 GHz

delt

a ɛ

23.5

24.5

25.5

26.5

27.4

28.5

29.5

30.5

31.5

32.5

33.5

34.6

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

delta cond. vs temp

300 MHz1 GHz3 GHz8 GHz

delt

a σ

Temperature (C) Temperature (C)