Multimodal validation of temporal interference in a 3D-printed pediatric head phantom
BACKGROUND Transcranial temporal interference stimulation (tTIS) is a technique for generating electric-field envelopes within deep brain structures. Yet, its application in human subjects is limited, particularly in pediatric cohorts. OBJECTIVE To evaluate the validity and accuracy of tTIS envelope reconstruction across beta, gamma, and ripple frequency bands in deep brain structures using a 3D-printed pediatric phantom. METHODS A phantom resembling the conductivity properties of a 3-year-old child's head was implanted with dipoles at six deep-brain locations. Sinusoidal signals were delivered via two optimized scalp electrode pairs, using either a high-frequency carrier (HF-C; f₁ = 2-9 kHz; f₂ = 2.02-9.17 kHz) or a low-frequency carrier (LF-C; f₁ = 20 Hz; f₂ = 40-190 Hz) as a non-equivalent reference condition. Signals were recorded by an oscilloscope connected to dipoles. High-density electroencephalography was acquired as a validation tool for reconstructing stimulation-induced field patterns. Time-frequency analysis and permutation t-tests assessed differences between target and control dipoles within region of interest (ROI). RESULTS HF-C showed smaller Euclidean distances (∼7-23 mm) between target and reconstructed maxima, along with more spatially confined envelope distributions across all targets and frequency bands, with better performance at 7-9 kHz carriers. The LF-C reference produced substantially larger deviations (∼50-64 mm). Permutation t-tests confirmed greater power in ROI compared with non-ROI regions (p < 0.05). CONCLUSION HF-C produced more spatially confined reconstructed envelopes at higher kHz within targeted structures compared with lower kHz conditions. These results indicate improved spatial confinement of envelope reconstruction in the 7-9 kHz range within the phantom.