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Thermocoagulation in Deep Brain Structures: Modelling, simulation and experimental study of radio-frequency lesioning
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology. (MINT)
2006 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Radio-frequency (RF) lesioning is a method utilising high frequency currents for thermal coagulation of pathological tissue or signal pathways. The current is delivered from an electrode with a temperature sensor, permitting control of the current at a desired target temperature. In the brain RF-lesioning can e.g. be used for severe chronic pain and movement disorders such as Parkinson’s disease. This thesis focuses on modelling and simulation with the aim of gaining better understanding and predictability of the lesioning process in deep brain structures. The finite element method (FEM) together with experimental comparisons was used to study the effects of electrode dimensions, electrode target temperature, electric and thermal conductivity of the brain tissue, blood perfusion and cerebrospinal fluid (CSF) filled cysts. Equations for steady current, thermal transport and incompressible flow were used together with statistical factorial design and regression analysis for this purpose.

Increased target temperature, electrode tip length and electrode diameter increased the simulated lesion size, which is in accordance with experimental results. The influence of blood perfusion, modelled as an increase in thermal conductivity in non-coagulated tissue, gave smaller simulated lesions with increasing blood perfusion as heat was more efficiently conducted from the rim of the lesion. If no consideration was taken to the coagulation the lesion became larger with increased thermal conductivity instead, as the increase in conducted heat was compensated for through an increased power output in order to maintain the target temperature. Simulated lesions corresponded well to experimental in-vivo lesions.

The electric conductivity in a homogeneous surrounding had little impact on lesion development. However this was not valid for a heterogeneous surrounding. CSF-filled cysts have a much higher electric conductivity than brain tissue focussing the current to them if the electrode tip is in contact with both. Heating of CSF can also cause considerable convective flow and as a result a very efficient heat transfer. This affected simulated as well as experimental lesion sizes and shapes resulting in both very large lesions if sufficient power compared to the cysts size was supplied and very small lesions if the power was low, mitigating the heat over a large volume.

In conclusion especially blood perfusion and CSF can greatly affect the lesioning process and appear to be important to consider when planning surgical procedures. Hopefully this thesis will help improve knowledge about and predictability of clinical lesioning.

Place, publisher, year, edition, pages
Institutionen för medicinsk teknik , 2006. , 44 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1267
Keyword [en]
Neurosurgery, Radiofrequency ablation, Finite element method, Blood perfusion, Cerebrospinal fluid, Free convection
National Category
Surgery
Identifiers
URN: urn:nbn:se:liu:diva-7406ISBN: 91-85643-98-X (print)OAI: oai:DiVA.org:liu-7406DiVA: diva2:22415
Presentation
2006-10-12, IMT 1, plan 13, Campus US, Linköpings universitet, Linköping, 00:00 (English)
Opponent
Supervisors
Available from: 2006-09-25 Created: 2006-09-25 Last updated: 2017-02-16Bibliographically approved
List of papers
1. Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity: modelling, simulation and analysis of parameter influence and interaction
Open this publication in new window or tab >>Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity: modelling, simulation and analysis of parameter influence and interaction
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2006 (English)In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 44, no 9, 757-766 p.Article in journal (Refereed) Published
Abstract [en]

Radio-frequency brain lesioning is a method for reducing e.g. symptoms of movement disorders. A small electrode is used to thermally coagulate malfunctioning tissue. Influence on lesion size from thermal and electric conductivity of the tissue, microvascular perfusion and preset electrode temperature was investigated using a finite-element model. Perfusion was modelled as an increased thermal conductivity in non-coagulated tissue. The parameters were analysed using a 24-factorial design (n = 16) and quadratic regression analysis (n = 47). Increased thermal conductivity of the tissue increased lesion volume, while increased perfusion decreased it since coagulation creates a thermally insulating layer due to the cessation of blood perfusion. These effects were strengthened with increased preset temperature. The electric conductivity had negligible effect. Simulations were found realistic compared to in vivo experimental lesions.

Place, publisher, year, edition, pages
Heidleberg: Springer, 2006
Keyword
Electrosurgery, RF ablation, Brain, Blood perfusion, Finite-element method
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-15926 (URN)10.1007/s11517-006-0098-1 (DOI)000240378700003 ()16941099 (PubMedID)2-s2.0-33748485613 (Scopus ID)
Note

The original publication is available at www.springerlink.com: Johannes D Johansson, Ola Eriksson, Joakim Wren, Dan Loyd and Karin Wårdell, Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity: modelling, simulation and analysis of parameter influence and interaction, 2006, Medical and Biological Engineering and Computing, (44), 9, 757-766. http://dx.doi.org/10.1007/s11517-006-0098-1 Copyright: Springer Science Business Media http://www.springerlink.com/

Available from: 2008-12-16 Created: 2008-12-16 Last updated: 2017-12-14Bibliographically approved
2. Comparison between a detailed and a simplified finite element model of radio-frequency lesioning in the brain
Open this publication in new window or tab >>Comparison between a detailed and a simplified finite element model of radio-frequency lesioning in the brain
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2004 (English)In: 26th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, San Fransisco, USA, 2004, Vol. 4, 2510-2513 p.Conference paper, Published paper (Refereed)
Abstract [en]

A detailed and a simplified model of a lesioning electrode was made using the finite element method. 15 simulations of the lesioning procedure were performed for each model and the resulting lesion volumes were compared in order to investigate if the simplified model is adequate. The simplified model resulted in a very slight overestimation of the volume compared to the detailed model. It was thus concluded that the simplified model is adequate for simulations.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13995 (URN)10.1109/IEMBS.2004.1403723 (DOI)
Available from: 2006-09-25 Created: 2006-09-25 Last updated: 2017-02-22Bibliographically approved
3. Simulations of radio-frequency lesions with varying brain electrode dimensions
Open this publication in new window or tab >>Simulations of radio-frequency lesions with varying brain electrode dimensions
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2005 (English)In: 13th Nordic Baltic conference biomedical engineering and medical physics, Umeå, Sweden, 2005, Vol. 9, 62-63 p.Conference paper, Published paper (Refereed)
Abstract [en]

Radio-frequency (RF) lesioning in the

brain was simulated using the finite element method

(FEM). Heating for 60 s with temperature control in

order to keep the tip at 80 °C was simulated. Length,

L, (2 – 4 mm) and diameter, D, (0.5 – 2.5 mm) of the

electrode tip were varied and the resulting lesion

volumes were used to calculate a regression model:

Lesion Volume = – 13.1D + 15.7LD + 13.1D2 mm3.

The results can be useful for electrode design and

prediction of lesion size.

Keyword
Radio-frequency surgery, Brain, Lesion size, Electrode dimensions, Finite Element Method (FEM)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13996 (URN)
Available from: 2006-09-25 Created: 2006-09-25 Last updated: 2017-02-21Bibliographically approved
4. Impact of cysts during radio frequency (RF) lesioning in deep brain structures: a simulation and in-vitro study
Open this publication in new window or tab >>Impact of cysts during radio frequency (RF) lesioning in deep brain structures: a simulation and in-vitro study
2007 (English)In: Journal of Neural Engineering, ISSN 1741-2560, E-ISSN 1741-2552, Vol. 4, no 2, 87-95 p.Article in journal (Refereed) Published
Abstract [en]

Radiofrequency lesioning of nuclei in the thalamus or the basal ganglia can be used to reduce symptoms caused by e.g. movement disorders such as Parkinson's disease. Enlarged cavities containing cerebrospinal fluid (CSF) are commonly present in the basal ganglia and tend to increase in size and number with age. Since the cavities have different electrical and thermal properties compared with brain tissue, it is likely that they can affect the lesioning process and thereby the treatment outcome. Computer simulations using the finite element method and in vitro experiments have been used to investigate the impact of cysts on lesions' size and shape. Simulations of the electric current and temperature distributions as well as convective movements have been conducted for various sizes, shapes and locations of the cysts as well as different target temperatures. Circulation of the CSF caused by the heating was found to spread heat effectively and the higher electric conductivity of the CSF increased heating of the cyst. These two effects were together able to greatly alter the resulting lesion size and shape when the cyst was in contact with the electrode tip. Similar results were obtained for the experiments.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2007
Keyword
Electrosurgery, RF ablation, Brain, Blood perfusion, Finite-element method
National Category
Other Medical Engineering
Identifiers
urn:nbn:se:liu:diva-13997 (URN)10.1088/1741-2560/4/2/009 (DOI)000247947300015 ()17409483 (PubMedID)2-s2.0-34247183212 (Scopus ID)
Note

Original Publication: Johannes D. Johansson, Dan Loyd, Karin Wårdell and Joakim Wren, Impact of cysts during radio frequency (RF) lesioning in deep brain structures: a simulation and in-vitro study, 2006, Journal of Neural Ingeneering, (4), 2, 87-95. http://dx.doi.org/10.1088/1741-2560/4/2/009 Copyright: Institute of Physics Publishing http://www.iop.org/

Available from: 2008-12-16 Created: 2008-12-16 Last updated: 2017-12-13Bibliographically approved

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