scholarly journals Head phantoms for bioelectromagnetic applications: a material study

2020 ◽  
Author(s):  
Alexander Hunold ◽  
René Machts ◽  
Jens Haueisen
Keyword(s):  
Electrical Conductivity ◽  
Ground Truth ◽  
Transcranial Electrical Stimulation ◽  
Intracranial Volume ◽  
Nacl Solution ◽  
Anisotropic Conductivity ◽  
Conductivity Structure ◽  
Agarose Hydrogel ◽  
Stable Representation ◽  
Material Study

Abstract Background Assessments of source reconstruction procedures in electroencephalography and computations of transcranial electrical stimulation profiles require verification and validation with the help of ground truth configurations as implemented by physical head phantoms. Phantoms provide well-defined volume conduction configurations with realistic geometries.We aim to characterize the electrical conductivity of materials for modeling head compartments to establish reproducible and stable physical head phantoms. We analyzed sodium chloride (NaCl) solution, agarose hydrogel, gypsum and reed sticks as surrogate materials for the intracranial volume, scalp, skull and anisotropic conductivity structures. We measured the impedance of all materials when immersed in NaCl solution using a four-point setup. The electrical conductivity values of each material were calculated from the temperature compensated impedances considering the sample geometries. Results We obtained conductivities of 0.332 S/m (0.17 % NaCl solution), 0.0425 S/m and 0.0017 S/m (gypsum with and without NaCl), 0.314 S/m, 0.30 S/m, 0.311 S/m (2 %, 3 %, 4 % agarose). The reed sticks were tested in longitudinal and transversal direction and showed anisotropic conductivity with a ratio of 1:2.8. Conclusion We conclude that the tested materials NaCl solution, gypsum and agarose can serve as stable representation of the three main conductivity compartments of the head, intracranial volume, skull and scalp. An anisotropic conductivity structure such as a piece of white matter can be modeled using tailored reed sticks inside a volume conductor.

scholarly journals Head phantoms for bioelectromagnetic applications: a material study

2020 ◽  
Author(s):  
Alexander Hunold ◽  
René Machts ◽  
Jens Haueisen
Keyword(s):  
Electrical Conductivity ◽  
White Matter ◽  
Ground Truth ◽  
Human Head ◽  
Transcranial Electrical Stimulation ◽  
Intracranial Volume ◽  
Nacl Solution ◽  
Anisotropic Conductivity ◽  
Synthetic Materials ◽  
Agarose Hydrogel

Abstract Background Assessments of source reconstruction procedures in electroencephalography and computations of transcranial electrical stimulation profiles require verification and validation with the help of ground truth configurations as implemented by physical head phantoms. For these phantoms, synthetic materials are needed, which are mechanically and electrochemically stable and possess conductivity values similar to the modeled human head tissues. Three-compartment head models comprise a scalp layer with a conductivity range of 0.137 S/m to 2.1 S/m, a skull layer with conductivity values between 0.066 S/m and 0.00275 S/m, and an intracranial volume with an often-used average conductivity value of 0.33 S/m. To establish a realistically shaped physical head phantom with a well-defined volume conduction configuration, we here characterize the electrical conductivity of synthetic materials for modeling head compartments. We analyzed agarose hydrogel, gypsum, and sodium chloride (NaCl) solution as surrogate materials for scalp, skull, and intracranial volume. We measured the impedance of all materials when immersed in NaCl solution using a four-electrode setup. The measured impedance values were used to calculate the electrical conductivity values of each material. Further, the conductivities in the longitudinal and transverse directions of reed sticks immersed in NaCl solution were measured to test their suitability for mimicking the anisotropic conductivity of white matter tracts.Results We obtained conductivities of 0.314 S/m, 0.30 S/m, 0.311 S/m (2 %, 3 %, 4 % agarose), 0.0425 S/m and 0.0017 S/m (gypsum with and without NaCl in the compound), and 0.332 S/m (0.17 % NaCl solution). These values are within the range of the conductivity values used for EEG and TES modeling. The reed sticks showed anisotropic conductivity with a ratio of 1:2.8. Conclusion We conclude that agarose, gypsum, and NaCl solution can serve as stable representations of the three main conductivity compartments of the head, i.e. scalp, skull, and intracranial volume. An anisotropic conductivity structure such as a fiber track in white matter can be modeled using tailored reed sticks inside a volume conductor.

scholarly journals Head phantoms for bioelectromagnetic applications: a material study

2020 ◽  
Author(s):  
Alexander Hunold ◽  
René Machts ◽  
Jens Haueisen
Keyword(s):  
Electrical Conductivity ◽  
White Matter ◽  
Ground Truth ◽  
Human Head ◽  
Transcranial Electrical Stimulation ◽  
Intracranial Volume ◽  
Nacl Solution ◽  
Anisotropic Conductivity ◽  
Synthetic Materials ◽  
Agarose Hydrogel

Abstract Background: Assessments of source reconstruction procedures in electroencephalography and computations of transcranial electrical stimulation profiles require verification and validation with the help of ground truth configurations as implemented by physical head phantoms.. For these phantoms, synthetic materials are needed, which are mechanically and electrochemically stable and possess conductivity values similar to the modeled human head tissues. Typical three-compartment head models comprise a scalp layer with a conductivity range from 0.137 S/m to 2.1 S/m, a skull layer with conductivity values between 0.066 S/m and 0.00275 S/m, and an intracranial volume with an often-used average conductivity value of 0.33 S/m. To establish a realistically shaped physical head phantom with a well-defined volume conduction configuration we here characterize the electrical conductivity of synthetic materials for modeling head compartments. We analyze agarose hydrogel, gypsum, and sodium chloride (NaCl) solution as surrogate materials for scalp, skull, and intracranial volume. We measure the impedance of all materials when immersed in NaCl solution using a four-electrode setup. The measured impedance values, temperature compensated to 25°C, were used to calculate the electrical conductivity values of each material. Further, the conductivities in the longitudinal and transversal directions of reed sticks immersed in NaCl solution were measured to test their suitability for mimicking the anisotropic conductivity of white matter tracts.Results: We obtained conductivities of 0.314 S/m, 0.30 S/m, 0.311 S/m (2 %, 3 %, 4 % agarose), 0.0425 S/m and 0.0017 S/m (gypsum with and without NaCl in the compound), and 0.332 S/m (0.17 % NaCl solution). These values are within the range of the conductivity values used for EEG and TES modeling. The reed sticks showed anisotropic conductivity with a ratio of 1:2.8. Conclusion: We conclude that the tested materials agarose, gypsum, and NaCl solution can serve as stable representations of the three main conductivity compartments of the head scalp, skull, and intracranial volume. An anisotropic conductivity structure such as a fiber track in white matter can be modeled using tailored reed sticks inside a volume conductor.

scholarly journals Head phantoms for bioelectromagnetic applications: a material study

2020 ◽  
Vol 19 (1) ◽  
Author(s):  
Alexander Hunold ◽  
René Machts ◽  
Jens Haueisen
Keyword(s):  
Electrical Conductivity ◽  
White Matter ◽  
Ground Truth ◽  
Human Head ◽  
Transcranial Electrical Stimulation ◽  
Intracranial Volume ◽  
Nacl Solution ◽  
Anisotropic Conductivity ◽  
Synthetic Materials ◽  
Agarose Hydrogel

Abstract Background Assessments of source reconstruction procedures in electroencephalography and computations of transcranial electrical stimulation profiles require verification and validation with the help of ground truth configurations as implemented by physical head phantoms. For these phantoms, synthetic materials are needed, which are mechanically and electrochemically stable and possess conductivity values similar to the modeled human head tissues. Three-compartment head models comprise a scalp layer with a conductivity range of 0.137 S/m to 2.1 S/m, a skull layer with conductivity values between 0.066 S/m and 0.00275 S/m, and an intracranial volume with an often-used average conductivity value of 0.33 S/m. To establish a realistically shaped physical head phantom with a well-defined volume conduction configuration, we here characterize the electrical conductivity of synthetic materials for modeling head compartments. We analyzed agarose hydrogel, gypsum, and sodium chloride (NaCl) solution as surrogate materials for scalp, skull, and intracranial volume. We measured the impedance of all materials when immersed in NaCl solution using a four-electrode setup. The measured impedance values were used to calculate the electrical conductivity values of each material. Further, the conductivities in the longitudinal and transverse directions of reed sticks immersed in NaCl solution were measured to test their suitability for mimicking the anisotropic conductivity of white matter tracts. Results We obtained conductivities of 0.314 S/m, 0.30 S/m, 0.311 S/m (2%, 3%, 4% agarose), 0.0425 S/m and 0.0017 S/m (gypsum with and without NaCl in the compound), and 0.332 S/m (0.17% NaCl solution). These values are within the range of the conductivity values used for EEG and TES modeling. The reed sticks showed anisotropic conductivity with a ratio of 1:2.8. Conclusion We conclude that agarose, gypsum, and NaCl solution can serve as stable representations of the three main conductivity compartments of the head, i.e., scalp, skull, and intracranial volume. An anisotropic conductivity structure such as a fiber track in white matter can be modeled using tailored reed sticks inside a volume conductor.

Measurement of electrical conductivity of 0.001 mol NaCl solution under high pressures

1997 ◽  
Vol 42 (18) ◽  
pp. 1563-1566 ◽  
Author(s):  
Zheng Haifei ◽  
Xie Hongsen ◽  
Xu Yousheng ◽  
Song Maoshuang ◽  
Guo Jie ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
High Pressures ◽  
Nacl Solution

Micromachined Electrical Conductivity Probe for RF Ablation of Tumors

2005 ◽  
Author(s):  
Ming Yi ◽  
Hrishikesh V. Panchawagh ◽  
Roop L. Mahajan ◽  
Zhengjun Liu ◽  
S. Nahum Goldberg
Keyword(s):  
Electrical Conductivity ◽  
Saline Water ◽  
Effective Area ◽  
Substrate Material ◽  
Rf Ablation ◽  
Nacl Solution ◽  
In Vivo Tests ◽  
Probe Calibration ◽  
The One

RF ablation is an important technique in cancer treatment. It has been proposed that the effective area treated via RF ablation can be increased by increasing the local electrical conductivity. This is achieved by injection of NaCl solution into the tissue. For an accurate and effective RF ablation treatment using this new method, it is necessary to measure the local electrical conductivity, which varies spatially due to diffusion of sodium chloride. In this paper, we propose a micro probe to measure the local tissue electrical conductivity. The probe consists of two in-plane miniature electrodes separated by a small gap. When the electrodes are in contact with the tissue, the electrical resistance across them can be used to calculate the electrical conductivity. The probe is fabricated by standard photolithography techniques. The substrate material is polyimide and the electrodes are made of gold. A four-electrode probe is used to calibrate the new electrical conductivity micro probe using different concentrations of saline water. The resistance measurements are carried out using an impedance analyzer on different frequencies. The frequency of choice for RF ablation of tumors is 500k Hz and is the one selected for calibration and testing. The micro-probe calibration is then verified by measuring electrical conductivity of a phantom and comparing it with the result measured by the four-electrode probe. Finally, some in vivo tests are performed and the results are compared with literate data.

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