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Isodose Mapping of Deep-Brain Electrical Stimulation Using Temporal Interference
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1
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| Subject:
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Clinical Applications of Brain Mappin
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Presenter Author:
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| Name:
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Aidin Niazmand
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Author:
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| Name 1:
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Aidin Niazmand - Corresponding - Presenter
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| Affiliation 1:
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School of Electrical and Computer Engineering, College of Engineering, University of Tehran, Tehran, Iran
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| Name 2:
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Dr. Gholam-Ali Hossein-Zadeh
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| Affiliation 2:
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School of Electrical and Computer Engineering, College of Engineering, University of Tehran, Tehran, Iran
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Abstract
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Original Research
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introduction :
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Alzheimer disease is characterized by progressive cognitive decline, with the hippocampus playing a central role in the memory network and being among the structures affected early in the disease. Because of its deep anatomical location, direct focal targeting of the hippocampus is limited with conventional transcranial magnetic stimulation. Temporal interference (TI) stimulation offers a non-invasive approach for deep-brain targeting by applying two high-frequency electric fields with a small frequency difference. This study investigated whether the minimum conventional TI configuration, consisting of two electrode pairs (four electrodes), can preferentially target the right hippocampus while limiting off-target field exposure.
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Methods:
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A realistic finite-element head model (Ernie) was analyzed using TI-Toolbox. The right hippocampus was defined in subject space using the aparc.DKTatlas+aseg atlas (label 53). Electrode positions were optimized with Flex-Search to maximize the mean maximum TI modulation amplitude (TImax) within the target region. Simulations used isotropic conductivity, 1 mA per channel, elliptical 8×8 mm electrodes, and 4-mm gel thickness. Voxel-based analysis quantified TImax in the hippocampal region of interest (ROI) and gray matter. Three-dimensional field distributions were visualized, and histogram-derived isodose levels were used to evaluate spatial selectivity.
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Results:
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The mean TImax in the right hippocampus was 0.259 V/m, compared with 0.171 V/m in gray matter, corresponding to a focality ratio of 1.524 and an approximately 52% higher mean field in the target. The maximum TImax was 0.391 V/m in the hippocampus and 0.526 V/m in gray matter, indicating that some off-target hotspots remained. The whole-head 99.9th-percentile field was 0.443 V/m. Histogram-derived isodose levels corresponding to 50%, 75%, 90%, and 95% of this value were approximately 0.22, 0.33, 0.40, and 0.42 V/m, respectively. The number of elements above these levels decreased from 120,934 at 0.22 V/m to 1,657 at 0.42 V/m, indicating progressive spatial restriction of higher field intensities.
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Conclusion:
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An optimized four-electrode TI montage can preferentially increase TImax within the right hippocampus in a realistic head model. However, complete confinement of the field to the hippocampus was not achieved. Quantitative focality measures together with three-dimensional field and isodose analysis provide a practical framework for evaluating selective deep-brain targeting and may support future protocol development for hippocampal neuromodulation.
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| Attachment:
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| Keywords:
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Hippocampus; Alzheimer Disease; Electric Stimulation; Computer Simulation;
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| Key message:
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