Fig 1.
Measuring circuit of contact impedance.
In this study, an impedance analyzer was used, and the voltage excitation mode (500 mV) was applied.
Fig 2.
The realistic 3D head model with realistic electrode-skin interface including electrode, conductive gel and epidermis.
A stroke lesion with 1.5 cm diameter was modeled.
Fig 3.
The dielectric parameters of head tissues, hemorrhagic tissue and ischemic tissue.
Fig 4.
The procedure to obtain the boundary voltage difference for image reconstruction, where δ represents the different levels of effects of contact impedance and fi denotes the frequency.
Fig 5.
The circuit for assessing the effects of the contact impedance imbalance between two measuring electrodes, in which two resistors simulate the contact impedance.
Fig 6.
(a)(b) The contact impedance of all subjects at all electrodes. The dashed lines represent the measurement results of the electrodes at the forehead. (c)(d) The measurement results of electrochemical impedance and conductive gel impedance in the case of conductive gel with the thickness of 0.4 mm.
Fig 7.
The current distribution beneath Electrode 5 with different contact impedances and the absolute voltage change in Electrode 5.
Fig 8.
The boundary voltage changes (BVC) caused by three levels of contact impedance, ischemic stroke and hemorrhagic stroke.
Fig 9.
Real-part images of the ischemic stroke lesion and the effects of three levels of contact impedance (The reference frequency was 10 Hz).
The physical unit of color bar is S/m in this study.
Fig 10.
Imaginary-part images of the ischemic stroke lesion and the effects of three levels of contact impedance.
Fig 11.
Real-part images of the hemorrhagic stroke lesion and the effects of three levels of contact impedance.
Fig 12.
Imaginary-part images of the hemorrhagic stroke lesion and the effects of three levels of contact impedance.
Fig 13.
The effects of contact impedance on the boundary voltages because of imbalance between contact impedances.
Fig 14.
Reconstructed results of the ischemic stroke and the effects of the contact impedance.
The contact impedance imbalance was simulated by varying the resistor in series with Electrode 1.