P 39 MRI-based geometric modeling for transcranial current stimulation in mild cognitive impairment converters

Abstract

Question: Transcranial direct current stimulation (tDCS) is a fast-growing field in rehabilitation medicine. However, the stimulation-induced E-field may be uneven on the highly folded cortical surface and thus leads to heterogeneous results in clinical trials. This challenge has been addressed by the analytical methods applicable to quantitatively measure the geometric features derived from the high-resolution structural magnetic resonance imaging (MRI). As a set of novel geometric measures, the geometric features of the folded cortex could be decomposed into scalp-to-cortex distance (SCD), cortical thickness and gyrification. Beyond MRI-based measures, learnings from computational geometric models will be beneficial as this field embraces biophysics and engineering. This study aimed to examine and quantify the cortical morphometry of bilateral dorsolateral prefrontal cortex (DLPFC) and its impact on the E-field during pathological ageing. Methods: Baseline, 1-year and 3-year follow-up structural magnetic resonance imaging scans from normal ageing (NA) adults (n = 32), and mild cognitive impairment (MCI) converters (n = 22) were drawn from the Open Access Series of Imaging Studies (OASIS-2). The quantitative measures of region-specific morphometry included gyrification, cortical thickness (mm), surface area (mm2) and volume (mm3). Head model was developed to simulate the impact of morphometric changes on the E-field induced by tDCS. Results: Ageing had a nonlinear effect on the changes of volume and cortical thickness in the bilateral DLPFC. A pronounced ageing-related reduction was found in the gyrification of left DLPFC in MCI converters, which could predict the global cognition decline at the 3-year follow-up. Along with the reduced gyrification in left DLPFC, the E-field intensity of tDCS model was consequently decreased in MCI converters. Conclusions: Ageing has a prominent effect on region-specific cortical morphometry that leads to decreased E-field intensity in old adults with cognitive impairments. Our findings have important implications for conducting the transcranial brain stimulation in individuals with brain atrophy, such as Alzheimer’s Disease.