Stroke lesion effects on simulated electric fields induced by tDCS
Poster No:
28
Submission Type:
Late-Breaking Abstract Submission
Authors:
Ikko Kimura1, Daria Antonenko2, Marcus Meinzner2, Agnes Flöel2, Axel Thielscher1
Institutions:
1DRCMR, Copenhagen University Hospital - Amager and Hvidovre, Hvidovre, Denmark, 2University Medicine Greifswald, Greifswald, Germany
First Author:
Co-Author(s):
Introduction:
Transcranial direct current stimulation (tDCS) enhances rehabilitation in stroke patients1. Simulating the tDCS-induced electric field (E-field) in the diseased brain is important for personalising stimulation parameters. A previous study investigated the lesion effect on tDCS-induced E-fields by adding artificial lesions to head models of healthy participants. However, those lesions had simple shapes and were assumed to be homogenously filled with cerebrospinal fluid (CSF)2 while the sizes, geometries and tissue properties of real lesions are more complex and variable3. Here, we evaluated the impact of lesions on tDCS-induced E-fields based on structural and diffusion MRI data from stroke patients (Figs. 1A and B).
·Figure 1
Methods:
We used existing4 (1) T1-weighted (T1w) and diffusion MRI (dMRI) data from stroke patients (n = 14), and (2) T1w from age-matched healthy controls (n = 14). The head models for both groups were generated using SimNIBS 4.1.05. To assess the general effect of lesions on the E-field, manually labelled lesion masks from stroke patients were added to the head models of healthy controls6, after non-linearly co-registering these two heads. In addition, to evaluate the impact of more complex tissue properties within the lesion on the E-field in stroke patients, their conductivities were estimated from the mean diffusivity of dMRI (complex lesion model)7, and simulation results were compared with results when modelling the lesions as homogenous CSF (simple lesion model)6. To compare the E-fields, we simulated four electrode montages ([primary motor cortex (M1) or individual peri-lesional target] x [bipolar or focal [3x1]])4,8. The peri-lesional target was defined by the peak activation of task functional MRI data near the lesion from the previous study4. The magnitude and normal component of the E-field (|E| and nE)9 were compared within the M1 and peri-lesional region-of-interests (ROIs; 12.5 mm spheres8). Spearman's correlation coefficients were calculated to link E-field differences to lesion features (lesion size, distance with region, and mean absolute conductivity difference within the lesion6).
Results:
Figures 2A and B show the differences between the head models with and without lesions in healthy controls. The |E| and nE showed a difference of up to 47% and 87%, respectively, which was higher than previously reported (max: ~30%). The mean absolute difference within the ROI was significantly higher in bipolar montages than in 3x1 for |E| of M1 (P < 0.001) and nE of M1 (P < 0.001) or peri-lesional target (P = 0.013), but not for |E| of peri-lesional target (P = 0.11). The mean absolute |E| and nE changes after adding lesions were positively correlated to the lesion size consistently across montages (r = 0.43 - 0.77), while negatively to the lesion distance (r = -0.48 - -0.93) (Figs. 2C and D).
Figures 2E and F illustrate the difference between the simple and complex lesion models in stroke patients. The |E| and nE differed by up to 35% and 30%, respectively. The mean absolute difference within the ROI was significantly higher in bipolar montages than in 3x1 for M1 (|E|, P < 0.001; nE, P < 0.001) and peri-lesional target (|E|, P = 0.012; nE, P = 0.0024). The mean absolute |E| and nE differences between simple and complex lesion models were positively correlated with the lesion size in some montages (r = 0.18 - 0.75), while negatively with the lesion distance consistently for all montages (r = -0.80 - -0.98) (Figs. 2G and H).
Figures 2E and F illustrate the difference between the simple and complex lesion models in stroke patients. The |E| and nE differed by up to 35% and 30%, respectively. The mean absolute difference within the ROI was significantly higher in bipolar montages than in 3x1 for M1 (|E|, P < 0.001; nE, P < 0.001) and peri-lesional target (|E|, P = 0.012; nE, P = 0.0024). The mean absolute |E| and nE differences between simple and complex lesion models were positively correlated with the lesion size in some montages (r = 0.18 - 0.75), while negatively with the lesion distance consistently for all montages (r = -0.80 - -0.98) (Figs. 2G and H).
·Figure 2
Conclusions:
The effect of lesions on simulated E-field was higher than that expected from a previous simulation study. We also found moderate differences in E-field between the head model with simple and complex lesion models in stroke patients. The sizes of these differences were dependent on the type of montages, lesion size, and lesion distance to the targeted location.
Brain Stimulation:
Non-invasive Electrical/tDCS/tACS/tRNS 1
Disorders of the Nervous System:
Neurodegenerative/ Late Life (eg. Parkinson’s, Alzheimer’s) 2
Modeling and Analysis Methods:
Other Methods
Keywords:
Modeling
MRI
1|2Indicates the priority used for review
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Healthy subjects only or patients (note that patient studies may also involve healthy subjects):
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2. Evans, C. et al. The impact of brain lesions on tDCS-induced electric fields. Sci Rep 13, (2023).
3. Duering, M. et al. Within-lesion heterogeneity of subcortical DWI lesion evolution, and stroke outcome: A voxel-based analysis. Journal of Cerebral Blood Flow and Metabolism 40, (2020).
4. Darkow, R., Martin, A., Würtz, A., Flöel, A. & Meinzer, M. Transcranial direct current stimulation effects on neural processing in post-stroke aphasia. Hum Brain Mapp 38, (2017).
5. Puonti, O. et al. Accurate and robust whole-head segmentation from magnetic resonance images for individualized head modeling. Neuroimage 219, (2020).
6. Handiru, V. S., Mark, D., Hoxha, A. & Allexandre, D. An Automated Workflow for the Electric Field Modeling of High-definition Transcranial Direct Current Stimulation (HD-tDCS) in Chronic Stroke with Lesions. in Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS (2021). doi:10.1109/EMBC46164.2021.9629584.
7. Tuch, D. S., Wedeen, V. J., Dale, A. M., George, J. S. & Belliveau, J. W. Conductivity tensor mapping of the human brain using diffusion tensor MRI. Proc Natl Acad Sci U S A 98, (2001).
8. Niemann, F. et al. Electrode positioning errors reduce current dose for focal tDCS set-ups: Evidence from individualized electric field mapping. Clinical Neurophysiology 162, 201–209 (2024).
9. Antonenko, D. et al. Towards precise brain stimulation: Is electric field simulation related to neuromodulation? Brain Stimul 12, 1159–1168 (2019).