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Use microwave tomographic imaging for temperature monitoring in thermal therapy
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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
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Relationship between Dielectric Properties and Temperature
In literature Liver tissue
ex vivo @915MHz
@2.45GHz
Susan C. Hagness et al. (2006)
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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
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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
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Transducer
Phantom
heated
plane
focal zone scan path
Focus
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Steerable HIFU Transducer
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Cross Section of a Focal Beam
1X power level
1.5X power level
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Cross Section of a Focal Zone
Permittivity
Permittivity
Conductivity
Conductivity
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Animal Experiment
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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
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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)