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Impact of cysts during radio frequency (RF) lesioning in deep brain structures: a simulation and in-vitro study
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology. (MINT)
Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology. (MINT)ORCID iD: 0000-0002-0012-7867
Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
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. Vol. 4, no 2, 87-95 p.
Keyword [en]
Electrosurgery, RF ablation, Brain, Blood perfusion, Finite-element method
National Category
Other Medical Engineering
Identifiers
URN: urn:nbn:se:liu:diva-13997DOI: 10.1088/1741-2560/4/2/009ISI: 000247947300015PubMedID: 17409483Scopus ID: 2-s2.0-34247183212OAI: oai:DiVA.org:liu-13997DiVA: diva2:22414
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
In thesis
1. Impact of Tissue Characteristics on Radio-Frequency Lesioning and Navigation in the Brain: Simulation, experimental and clinical studies
Open this publication in new window or tab >>Impact of Tissue Characteristics on Radio-Frequency Lesioning and Navigation in the Brain: Simulation, experimental and clinical studies
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Radio-Frequency (RF) lesioning, or RF ablation, is a method that uses high frequency currents for thermal coagulation of pathological tissue or signal pathways. The current is delivered from an electrode, which also contains a temperature sensor permitting control of the current at a desired target temperature. In the brain, RF lesioning can e.g. be used for treatment of 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 the central brain.

 

The finite element method (FEM), together with experimental comparisons, was used to study the effects of electric and thermal conductivity, blood perfusion (Paper I), and cerebrospinal fluid (CSF) filled cysts (Paper II) on resulting lesion volume and shape in brain tissue. The influence of blood perfusion was modelled as an increase in thermal conductivity in non-coagulated tissue. This model gave smaller simulated lesions with increasing blood perfusion as heat was more efficiently conducted from the rim of the lesion. If the coagulation was not taken into consideration, the lesion became larger with increasing 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 but this was not true for a heterogeneous surrounding. CSF has a much higher electric conductivity than brain tissue, which focused the current to the cyst if the electrode tip was in contact with both a cyst and brain tissue. Heating of CSF could also cause considerable convective flow and as a result a very efficient heat transfer. This affected both simulated and experimental lesion sizes and shapes. As a result both very large and very small lesions could be obtained depending on whether sufficient power was supplied or if the heating was mitigated over a large volume.

 

Clinical (Paper IV) and experimental (Paper III) measurements were used for investigation of changes in reflected light intensity from undamaged and coagulating brain tissue respectively. Monte Carlo (MC) simulations for light transport were made for comparison (Paper V). For the optical measurements, an RF electrode with adjacent optical fibres was used and this electrode was also modelled for the optical simulations. According to the MC simulations, coagulation should make grey matter lighter and white matter darker, while thalamic light grey should remain approximately the same. Experiments in ex-vivo porcine tissue gave an increase in reflected light intensity from grey matter at approximately 50 °C but the signal was very variable and the isotherm 60 °C gave better agreement between simulated and experimental lesions. No consistent decrease in reflected light intensity could be seen during coagulation of white matter. Clinical measurements were performed during the creation of 21 trajectories for deep brain stimulation electrodes. In agreement with the simulations, reflected light intensity was found to differentiate well between undamaged grey, light grey and white matter.

 

In conclusion, blood perfusion and CSF in particular may greatly affect the lesioning process and can be important to consider when planning surgery. Reflected light intensity seems unreliable for the detection of coagulation in light grey brain matter such as the thalamus. However, it seems very promising for navigation in the brain and for detection of coagulation in other tissue types such as muscle.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 74 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1230
Keyword
Brain, Radio frequency ablation, Finite element method, Monte Carlo simulation, light reflectance
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:liu:diva-15749 (URN)978-91-7393-723-8 (ISBN)
Public defence
2009-01-16, Linden, ingång 65, Campus US, Hälsouniversitetet, Linköpings universitet, Linköping, 09:15 (Swedish)
Opponent
Supervisors
Available from: 2008-12-17 Created: 2008-12-02 Last updated: 2017-02-10Bibliographically approved
2. Thermocoagulation in Deep Brain Structures: Modelling, simulation and experimental study of radio-frequency lesioning
Open this publication in new window or tab >>Thermocoagulation in Deep Brain Structures: Modelling, simulation and experimental study of radio-frequency lesioning
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
Neurosurgery, Radiofrequency ablation, Finite element method, Blood perfusion, Cerebrospinal fluid, Free convection
National Category
Surgery
Identifiers
urn:nbn:se:liu:diva-7406 (URN)91-85643-98-X (ISBN)
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

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