measurements, antenna design and advanced computer modeling for microwave tissue ablation

272 Pages·2005·6.42 MB·English

by  Deshan Yang

MEASUREMENTS, ANTENNA DESIGN AND ADVANCED
COMPUTER MODELING FOR MICROWAVE TISSUE
ABLATION

by

Deshan Yang

A dissertation submitted in partial fulfillment of
the requirements for the degree of

Doctor of Philosophy
(Electrical Engineering)

at the
UNIVERSITY OF WISCONSIN-MADISON
2005

1

© Copyright by Deshan Yang, 2005
All Rights Reserve
MEASUREMENTS, ANTENNA DESIGN AND ADVANCED
COMPUTER MODELING FOR MICROWAVE TISSUE
ABLATION

by

Deshan Yang

A dissertation submitted in partial fulfillment of
the requirements for the degree of

Doctor of Philosophy
(Electrical Engineering)

at the
UNIVERSITY OF WISCONSIN-MADISON
2005
i
Acknowledgements

Thank you to Prof. John G. Webster and Prof. David M. Mahvi for
their continued guidance and support. Thanks to Prof. James A. Will and
Prof. Susan C. Hagness for their suggestions and support. Thanks to Mark C.
Converse, Ann P. O’Rourke and John Bertram for their fruitful collaboration
and suggestions.
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Table of Contents

Acknowledgements..............................................................................................................i
Table of Contents................................................................................................................ii
Abstract.............................................................................................................................vii

Chapter 1 Introduction to microwave tissue ablation......................................................1
A Liver cancer and treatments........................................................................................2
B Microwave tissue ablation fundamentals....................................................................3
C Current research status for MWA...............................................................................7
C.1 Current clinical trials...........................................................................................7
C.2 Problems and challenges of current MWA technologies....................................8
D References.................................................................................................................12

Chapter 2 Theories and fundamental physics...............................................................14
A Electromagnetism and microwave-tissue interaction...............................................15
A.1 Maxwell’s equations.........................................................................................15
A.2 EM waves in material medium.........................................................................18
A.3 Power flow of EM waves..................................................................................21
A.4 Interactions of microwave and biological materials.........................................22
B Dielectric properties of biological tissues.................................................................23
B.1 Frequency dependence......................................................................................23
B.2 Temperature dependence..................................................................................28
B.3 Tissue water content dependence......................................................................29
B.4 Dielectric properties of liver tumor tissues.......................................................35
C Thermal responses of biological tissues during MWA.............................................36
C.1 Tissue responses versus temperature................................................................36
C.2 Tissue damage versus thermal dose..................................................................37
C.3 Pathological analysis.........................................................................................38
D Heat transfer and the bioheat equation......................................................................39
D.1 The bioheat equation.........................................................................................39
D.2 Blood perfusion and effects..............................................................................41
D.3 Thermal properties and dependent factors........................................................41
E References.................................................................................................................42

Chapter 3 Preliminary Studies and Results....................................................................46
A Review of current antenna designs...........................................................................47
A.1 Monopole coaxial antenna................................................................................47
A.2 Dipole antenna..................................................................................................49
A.3 Slot antenna.......................................................................................................52
A.4 Tri-axial antenna...............................................................................................53
A.5 Cap-choke antenna............................................................................................54
A.6 Other antennas..................................................................................................55
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A.7 Antenna array....................................................................................................56
B Antenna fabrication procedure..................................................................................57
C Basic MWA Experiments and Results......................................................................60
C.1 Ex-vivo Experiments........................................................................................60
C.2 In-vivo Experiments..........................................................................................62
C.3 Basic observations of ablated liver tissue.........................................................63
C.4 Measurements of lesion size and volume.........................................................64
C.5 Basic tissue temperature measurement.............................................................66
C.6 Tissue dielectric property measurement...........................................................67
C.7 Antenna S11 measurement versus frequency...................................................68
D Basic computer simulations for MWA.....................................................................69
D.1 Axial-symmetry computer models....................................................................69
D.2 The basic EM model.........................................................................................71
D.3 Compute the antenna frequency response with the basic EM model...............77
D.4 The basic thermal model...................................................................................79
E References.................................................................................................................84

Chapter 4...........................................................................................................................86
Tissue water content movement during MWA and the expanded bioheat equation........86
A Tissue water content and thermal energy movement during MWA.........................87
A.1 The hypothesis about tissue water and thermal energy movement during MWA
88
A.2 Effects and significances...................................................................................89
B Expanding the bioheat equation to cover tissue water evaporation..........................91
B.1 Theoretical solution of tissue water evaporation with the bioheat equation.....92
B.2 Discussion about the expanded bioheat equation.............................................95
C References.................................................................................................................98

Chapter 5 Measurement and Analysis of Tissue Water Content during MWA...........100
A Method....................................................................................................................101
A.1 The wet-dry procedure....................................................................................101
A.2 Basic experiment setup and procedures..........................................................102
A.3 Detail procedures and explanations................................................................104
A.3.1 Tissue preparation...................................................................................104
A.3.2 Ablation procedure..................................................................................105
A.3.3 Handing ablated tissue............................................................................105
A.3.4 Special attention......................................................................................108
A.3.5 Weighing.................................................................................................109
A.3.6 Drying.....................................................................................................110
A.4 Results.............................................................................................................110
A.5 Discussion and conclusions............................................................................110
A.6 Discussion about the experimental design, restrictions and system errors.....112
B References...............................................................................................................114

Chapter 6 Measurement and analysis of tissue temperature during MWA..................115
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A Method....................................................................................................................117
B Results.....................................................................................................................119
C Discussion...............................................................................................................123
C.1 Differences between regions...........................................................................123
C.2 Tissue temperature versus tissue water content..............................................126
C.3 Free water versus bounded water....................................................................128
D Conclusion..............................................................................................................128
E References...............................................................................................................129

Chapter 7 Design, verification and theoretical analysis of the floating sleeve coaxial
antennas...........................................................................................................................130
A The design of a floating sleeve antenna..................................................................131
B Computer simulation...............................................................................................134
B.1 The computational electromagnetics (CEM) model.......................................134
B.2 Frequency sweep for antenna power reflection..............................................137
C Experimental validation..........................................................................................139
D The theoretical analysis...........................................................................................141
D.1 The theory of two field interference...............................................................141
D.2 Verification with computer simulation...........................................................143
E Analysis of the antenna design...............................................................................149
E.1 The length of the sleeve..................................................................................149
E.2 The thickness of the Teflon gap layer.............................................................151
E.3 The Teflon layer covering the sleeve and its thickness..................................152
E.4 The sleeve position.........................................................................................152
E.5 Other observations:.........................................................................................153
F Alternative designs..................................................................................................154
F.1 With and without Teflon coverage on the sleeve............................................154
F.2 With larger and smaller coaxial cable.............................................................154
F.3 Dipole sleeve antenna versus slot sleeve antenna...........................................155
G Further study...........................................................................................................155
G.1 Using high permittivity material for coverage layer.......................................155
G.2 Optimization for changed tissue dielectric properties....................................157
H References...............................................................................................................158

Chapter 8 Comprehensive computer simulation for MWA..........................................159
A Introduction.............................................................................................................160
B Tissue water dependencies of tissue properties......................................................161
B.1 Tissue density..................................................................................................162
B.2 Tissue heat capacity........................................................................................163
B.3 Tissue thermal conductivity............................................................................165
B.4 Tissue dielectric properties.............................................................................166
C Overview.................................................................................................................167
C.1 Explanation of important interactions.............................................................169
C.2 Implementation and work flow.......................................................................171
C.3 Finite difference method.................................................................................173
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C.4 Goals of the advanced computer model..........................................................174
D Implementation.......................................................................................................174
D.1 Finite element models.....................................................................................174
D.2 Special considerations.....................................................................................175
D.2.1 Approximation of water vapor condensation..........................................175
D.2.2 Tissue water diffusion and adjustments..................................................177
D.3 Computer simulation procedures and configurations.....................................179
E Experiment verifications.........................................................................................182
F Results.....................................................................................................................185
F.1 Lesion size and shape comparison..................................................................185
F.2 Temperature history comparison....................................................................187
F.3 Temperature distribution comparison.............................................................189
F.4 Tissue water distribution comparison.............................................................191
G Discussion and conclusion......................................................................................193
H References...............................................................................................................197

Appendix 1 A Floating Sleeve Antenna Yields Localized Hepatic Microwave Ablation
I. Abstract...................................................................................................................199
II. INTRODUCTION..................................................................................................200
III. Design of the floating sleeve antenna.................................................................202
IV. Computer Simulation and Experimental Results................................................203
A. The computational electromagnetics (CEM) model...........................................204
B. Frequency sweep for antenna power reflection..................................................205
C. Ex-vivo experiments and results.........................................................................206
V. Discussion and conclusion......................................................................................207
Acknowledgment............................................................................................................208
References.......................................................................................................................208

Appendix 2 Expanding the bioheat equation to include tissue internal water evaporation
during heating.................................................................................................................216
1 Abstract...................................................................................................................216
2 Introduction.............................................................................................................216
3 Methods...................................................................................................................219
3.1 Theoretical solution of tissue water evaporation with the bioheat equation...219
3.2 Numeric Simulation........................................................................................221
3.3 Experiment setup and procedures...................................................................226
4 Results and Discussion...........................................................................................227
5 Conclusion..............................................................................................................231
6 References...............................................................................................................232

Appendix 3 Measurement and Analysis of Tissue Water Content during Microwave
Tissue Ablation...............................................................................................................234
1. Abstract...................................................................................................................234
2. Introduction.............................................................................................................234
3. Experimental setup..................................................................................................236
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4. Results.....................................................................................................................237
5. Discussion and conclusion......................................................................................238
6. References:..............................................................................................................240

Appendix 4 Measurement and Analysis of Tissue Temperature during Microwave Liver
Ablation...........................................................................................................................244
1 Abstract...................................................................................................................244
2 Introduction.............................................................................................................244
3 Experiment setup....................................................................................................245
4 Results.....................................................................................................................248
5 Discussion...............................................................................................................252
5.1 Differences between regions...........................................................................252
5.2 Tissue temperature versus tissue water content..............................................253
6 Conclusion..............................................................................................................256
7 References:..............................................................................................................257

Appendix 5 Computer Simulation of Microwave Liver Ablation..................................258

Appendix 6 MATLAB and FEMLAB programs for the comprehensive computer models
.........................................................................................................................................259