Table Of ContentUNIVERSITAT POLITÈCNICA DE VALÈNCIA
DEPARTAMENTO DE INGENIERÍA ELECTRÓNICA
Computational Models and Experimentation for
Radiofrequency-based Ablative Techniques
“Modelos computacionales y experimentación
para técnicas ablativas por radiofrecuencia”
Ph.D. THESIS
Ana González Suárez
ADVISORS
Dr. Enrique Berjano Zanón
Dra. Macarena Trujillo Guillén
Valencia, January 2014
“I am among those who think that science has great beauty. A
scientist in his laboratory is not only a technician: he is also a child
placed before natural phenomena which impress him like a fairy
tale. We should not allow it to be believed that all scientific progress
can be reduced to mechanisms, machines, gearings, even though
such machinery has its own beauty.”
— Marie Curie. During a debate in Madrid ‘The Future of Culture' (1933)
A mis padres y a Javi
Acknowledgements
In general, I would like to thank everybody who in one or another way has
contributed to the achievement of this PhD Thesis.
Especially, I would like to express my deepest gratitude to my advisors, Enrique
and Macarena, for giving me the wonderful opportunity to start my research work with
them and for their support and invaluable guidance during these years. Without a shred
of doubt, it was a real pleasure for me to work alongside you.
I am most grateful to the external reviewers, Dr. Tobias Preusser, Dr. Dieter
Haemmerich and Dr. Punit Prakash, for their time and effort devoted to review the PhD
Thesis manuscript, and for the valuable suggestions and comments they made, which
unquestionably helped me to improve the quality of this work.
I do not want to forget to express my sincere gratitude to Dr. Walfre Franco for
giving me the opportunity to train and conduct my predoctoral stay at The Wellman
Center for Photomedicine and for his valuable support and help during those months.
Undoubtedly, it was a pleasure for my working with him. I also want to thank Dr. Joel
Jimenez-Lozano for the great help provided with the computational modeling of skin.
Furthermore, I want to mention that one of the best things of my stay in Boston was
undoubtedly the fact of meeting two wonderful people, Enoch and Monica, who they
made me feel at home. I hope to see you both soon, either in Spain, México or USA.
Moreover, I would like to express my gratitude to the Conselleria d’Educació of
the Generalitat Valenciana for the predoctoral grant VaLi+D (ACIF/2011/194), which
provided me the financial support to conduct during these last years the development of
this PhD Thesis and allowed me to participate in several projects (TEC2008-01369,
TEC2011-27133-C02-01, INNOVA11-01-5502, PAID-06-11 Ref. 1988 and UPV-FE-
5040); and also for the predoctoral visiting fellowship (BEFPI/2013/003) that gave me
the financial support to do a stay for 4 months.
Finally, I would like to dedicate my dissertation work to my parents and Javi. I
sincerely believe that I would have not been able to conclude this work without their
infinite patience, support and understanding at all times.
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Abstract
Ablative techniques based on radiofrequency (RF) energy are used to
produce a safe and localized heating of target biological tissue. In recent years there
has been rapid growth in the number of new medical procedures employing these
techniques, accompanied by the emergence of new electrode designs and energy
delivery protocols. However, there are still many unknowns about the true electro-
thermal behavior of energy applicators, along with energy-tissue interaction issues
in specific applications.
The main purpose of this PhD Thesis is to gain a better understanding of the
electrical and thermal phenomena involved in the heating of biological tissues by RF
currents, in order to improve the efficacy and safety of the techniques currently used
in clinical practice in different areas, such as cardiac surgery, oncology and
dermatology. An additional aim is to suggest technological improvements for
designing new applicators. The Thesis combines two methodologies widely used in
the field of Biomedical Engineering: computational modeling (mathematical) and
experimental (ex vivo and in vivo) tests.
Our cardiac research was focused on improving intraoperative ablation of
atrial fibrillation by an epicardial (minimally invasive) approach. To do this, we
used mathematical models to assess an impedance measurement system as a method
of quantifying the amount of epicardial fat present prior to ablation. We also studied
how to improve ablation of the ventricular wall using an endocardial-endocardial
approach (interventricular septum) and an endocardial-epicardial approach
(ventricular free wall). This involved comparing computer simulations of the
efficiency of bipolar and unipolar modes of ablation in terms of the transmurality of
the lesion across the ventricular wall.
Surgical oncology focused on RF-assisted hepatic resection. RF heating
techniques should be able to minimize intraoperative bleeding and seal vessels and
ducts by creating a thermal coagulative necrosis. If this heating occurs in the vicinity
of large vessels, there is a risk of damage to this vessel. Using mathematical models
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and in vivo experiments, we evaluated whether the effect of blood flow within a
large vessel would be able to thermally protect the wall when RF-assisted resection
is performed in the vicinity. We also conducted computational and ex vivo and in
vivo experimental studies on the electro-thermal behavior of bipolar internally
cooled RF applicators. These are a safer alternative to the monopolar applicators due
to the fact that RF currents flow almost exclusively through the biological tissue
between the electrodes.
The dermatological area focused on improving the treatment of disorders of
the subcutaneous tissue (e.g. lipomatosis, lipedema, Madelung disease and cellulite)
by a theoretical study of the optimum dosimetry for each case. For this we evaluated
the electrical, thermal and thermo-elastic effects of two different structures of
subcutaneous tissue during RF heating, as well as the thermal damage to both
structures after heating has been quantified.
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Description:placed before natural phenomena which impress him like a fairy tale by a theoretical study of the optimum dosimetry for each case. For this we
