| 1. |
- Alonso, Fabiola, 1980-
(författare)
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Models and Simulations of the Electric Field in Deep Brain Stimulation : Comparison of Lead Designs, Operating Modes and Tissue Conductivity
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Deep brain stimulation (DBS) is an established surgical therapy for movement disorders such as Parkinson’s disease (PD) and essential tremor (ET). A thin electrode is implanted in a predefined area of the brain with the use of stereotactic neurosurgery. In the last few years new DBS electrodes and systems have been developed with possibilities for using more parameters for control of the stimulation volume.In this thesis, simulations using the finite element method (FEM) have been developed and used for investigation of the electric field (EF) extension around different types of DBS lead designs (symmetric, steering) and stimulation modes (voltage, current). The electrode surrounding was represented either with a homogeneous model or a patient-specific model based on individual preoperative magnetic resonance imaging (MRI). The EF was visualized and compared for different lead designs and operating modes.In Paper I, the EF was quantitatively investigated around two lead designs (3389 and 6148) simulated to operate in voltage and current mode under acute and chronic time points following implantation.Simulations showed a major impact on the EF extension between postoperative time points which may explain the clinical decisions to change the stimulation amplitude weeks after implantation. In Paper II, the simulations were expanded to include two leads having steering function (6180, Surestim1) and patient-specific FEM simulations in the zona incerta. It was found that both the heterogeneity of the tissue and the operating mode, influence the EF distribution and that equivalent contact configurations of the leads result in similar EF. The steering mode presented larger volumes in current mode when using equivalent amplitudes. Simulations comparing DBS and intraoperative stimulation test using a microelectrode recording (MER) system (Paper III), showed that several parallel MER leads and the presence of the non-active DBS contacts influence the EF distribution and that the DBS EF volume can cover, but also extend to, other anatomical areas.Paper IV introduces a method for an objective exploitation of intraoperative stimulation test data in order to identify the optimal implant position in the thalamus of the chronic DBS lead. Patient-specific EF simulations were related to the anatomy with the help of brain atlases and the clinical effects which were quantified by accelerometers. The first results indicate that the good clinical effect in ET is due to several structures around the ventral intermediate nucleus of the thalamus.
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| 2. |
- Hentschel, Gesine, et al.
(författare)
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Destruction of Unresectable Brain Tumors : Simulation of Thermal Spread and Tissue Damage During MRI-Guided Laser Ablation
- 2021
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Ingår i: Springer Proceedings in Physics. - Cham : Springer. - 9783030811181 - 9783030811198 ; , s. 301-315
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Konferensbidrag (refereegranskat)abstract
- Laser induced thermal therapy (LITT) emerged in recent years as a minimal invasive treatment method for otherwise oftentimes inoperable brain tumors, such as glioblastomas. During the thermal ablation process, the procedure carries the risk of destroying healthy brain tissue adjacent to the tumor. Limitations in the spatial distribution of the real-time monitoring MR thermography system currently allow only a rough representation of the damage zone during surgery. For this reason, improved pre-operative simulations of tissue heating and the resulting tissue damage could be valuable to optimize clinical treatment protocols while minimizing the risks of the procedure. In this study a method is presented, to simulate the ablation process of the LITT with the finite elements method (FEM) using the simulation software COMSOL MULTIPHYSICS. Thereby the temperature distribution is displayed and, based on this, the extent of the tissue damage during the process is simulated. Therefore, relevant parameters for the ablation process, such as optical and thermal properties, blood per-fusion, and the interface between healthy and tumor tissue were investigated and their influence on temperature distribution and extent of tissue damage was described.
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| 3. |
- Johansson, Johannes D., 1977-, et al.
(författare)
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Combined diffuse light reflectance and electric impedance measurements for navigation aid in deep brain surgery
- 2009
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Ingår i: Stereotactic and Functional Neurosurgery. - Basel : S. Karger AG. - 1011-6125 .- 1423-0372. ; 87:2, s. 105-113
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Tidskriftsartikel (refereegranskat)abstract
- Aim: The aim of this study is to investigate reflected light intensity combined with impedance for navigation aid during stereotactic neurosurgery.Methods: During creation of 21 trajectories for stereotactic implantation of deep brain stimulation electrodes in the globus pallidus internus or subthalamus (zona incerta or subthalamic nucleus), impedance at 512 kHz and reflected light intensity at 780 nm were measured continuously and simultaneously with a radio frequency electrode containing optical fibres. The signals were compared with anatomy determined from pre- and postoperative MRI and CT. The measurements were performed within minutes and signal analysis was done post-operatively.Results: Reflected light intensity was low from cortex, lateral ventricle, caudate nucleus and putamen. It was intermediate from globus pallidus and thalamus while it was high from subcortical white matter, internal capsule and the subthalamus. The electric impedance was less consistent but generally low in the cortex, intermediate in subcortical white matter, the putamen, the globus pallidus and the thalamus and high in the internal capsule and the subthalamus.Conclusion: Reflected light intensity and electric impedance give complementary information about passed tissue and the combination seems promising for navigation aid during stereotactic neurosurgery.
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| 4. |
- Johansson, Johannes D., 1977-, et al.
(författare)
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Diffuse Reflectance Spectroscopy During Experimental Radio Frequency Ablation
- 2008
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Ingår i: 14th Nordic-Baltic Conference on Biomedical Engineering and Medical Physics. - Heidelberg : Springer Berlin/Heidelberg. - 9783540693666 - 9783540693673 ; , s. 371-374
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Bokkapitel (refereegranskat)abstract
- The aim of the study was to investigate the spectral changes during heating and to estimate threshold temperatures for initiation of the thermal coagulation. A brain electrode with optical fibers was used to generate lesions in ex-vivo porcine white and gray matter as well as in fat and meat from pork chop. Radio frequency ablation (60 s, 48–90 °C, steps of 2-10 °C) was performed while simultaneous spectroscopy measurements were made in the range 490–900 nm.The optical signal recorded from porcine gray and white brain matter was unstable with the reflected light intensity fluctuating a lot. Nevertheless an abrupt increase in light intensity during coagulation in gray matter was found at 48 ± 6 °C (n = 21), probably indicating onset of coagulation. The reflected light intensity from white matter showed no consistent behavior during coagulation.The results for pork chop meat and fat were considerably more consistent. The reflected light intensity from pork chop meat stayed stable up to a mean temperature of 42.5 ± 3.5 °C (n = 11). Above this temperature it abruptly increased for all wavelengths. The reflected light intensity from pork chop fat dropped over all wavelengths immediately as the temperature increased and remained low as the fat cooled (n = 8).In conclusion diffuse reflectance spectroscopy appears to be suitable to detect onset of coagulation in muscle tissue and gray matter. The estimated initiation temperature of coagulation varied and was dependent on tissue type.
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| 5. |
- Johansson, Johannes D., 1977-, et al.
(författare)
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Impact of cysts during radio frequency (RF) lesioning in deep brain structures : a simulation and in-vitro study
- 2007
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Ingår i: Journal of Neural Engineering. - : Institute of Physics Publishing (IOPP). - 1741-2560 .- 1741-2552. ; 4:2, s. 87-95
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Johansson, Johannes D, 1977-, et al.
(författare)
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Open Access Software for Patient-Specific Deep Brain Stimulation Simulations: ELMA and DBSim
- 2020
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Deep brain stimulation (DBS) is a technique for disruption of pathological activity in the brain by the use of chronically implanted electrodes in the central parts of the brain. DBS is used in e.g. Parkinson’s disease, essential tremor and dystonia and is under investigation for severe cases of Tourette syndrome and obsessive-compulsive disorder. While DBS is nowadays a well-established technique, optimal targeting of brain structures is still not fully known. One way to investigate this is to perform finite element method (FEM) simulations of the activated tissue around the active DBS electrode contacts. The FEM simulations can then be compared with the clinical outcomes of symptom improvement and potential detrimental side effects in the patients. A gratis open access software package for patient-specific FEM simulations based on pre-complied modules is presented. It is based on tissue classification from preoperative magnetic resonance imaging. In the first part, ELMA, the tissue is classified into grey matter, white matter, blood and cerebrospinal fluid. Electric conductivity is assigned based of tissue type and is then used in the second part, DBSim, where patient-specific FEM simulations of the electric field around the DBS electrodes are performed. These simulations can then be used to estimate the volume of tissue activated directly from the electric field magnitude thresholds for different axon diameters or be exported for direct simulation of axon activation in other software. The software package is available for free download at https://liu.se/en/article/ne-downloads
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| 7. |
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| 8. |
- Johansson, Johannes D, 1977-, et al.
(författare)
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Patient-Specific Simulations of Deep Brain Stimulation Electric Field with Aid of In-house Software ELMA
- 2019
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Ingår i: 2019 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC). - : IEEE. - 9781538613115 - 9781538613122
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Konferensbidrag (refereegranskat)abstract
- Deep brain stimulation (DBS) is an established technique for reduction of symptoms in movement disorders. Finite element method (FEM) simulations of the electric field magnitude (EF) are useful for estimating the affected tissue around the DBS lead and this can help optimize the therapy. This paper describes how patient-specific FEM models can be set up with the aid of the Matlab-based in-house software tool ELMA. Electrode placement is determined from two coordinates in postoperative medical imaging and electric conductivity is assigned from preoperative magnetic resonance imaging (MRI) and patient-specific DBS data. Simulations are performed using the equation for steady currents in Comsol Multiphysics (CM). The simulated EF is superimposed on the preoperative MRI for evaluation of affected structures. The method is demonstrated with patient-specific simulations in the zona incerta and a globus pallidus example containing cysts with higher conductive which causes considerable distortion of the EF. The improved software modules and precise lead positioning simplifies and reduces the time for DBS EF modelling and simulation.
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| 9. |
- Johansson, Johannes D, 1977-, et al.
(författare)
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Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity : modelling, simulation and analysis of parameter influence and interaction
- 2006
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Ingår i: Medical and Biological Engineering and Computing. - Heidleberg : Springer. - 0140-0118 .- 1741-0444. ; 44:9, s. 757-766
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Johansson, Johannes D., 1977-, et al.
(författare)
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Simulation of reflected light intensity changes during navigation and radio frequency lesioning in the brain
- 2009
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Ingår i: Journal of Biomedical Optics. - : SPIE - International Society for Optical Engineering. - 1083-3668 .- 1560-2281. ; 14:044040
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Tidskriftsartikel (refereegranskat)abstract
- An electrode with adjacent optical fibers for measurements during navigation and radio frequency lesioning in the brain was modeled for Monte Carlo simulations of light transport in brain tissue. Relative reflected light intensity at 780 nm, I780, from this electrode and probes with identical fiber configuration were simulated using the intensity from native white matter as reference. Models were made of homogeneousnative and coagulated gray, thalamus, and white matter as well as blood. Dual layermodels, including models with a layer of cerebrospinal fluid between the fibers andthe brain tissue, were also made. Simulated I780 was 0.16 for gray matter, 0.67 forcoagulate gray matter, 0.36 for thalamus, 0.39 for coagulated thalamus, unity forwhite matter, 0.70 for coagulated white matter and 0.24 for blood. Thalamic matterhas also been found to reflect more light than gray matter and less than white matterin clinical studies. In conclusion the reflected light intensity can be used todifferentiate between gray and white matter during navigation. Furthermore,coagulation of light gray tissue, such as the thalamus, might be difficult to detectusing I780, but coagulation in darker gray tissue should result in a rapid increase of I780.
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