Conductivity-To-Tissue Volume Ratio: Imaging Biomarker for the Alzheimer's Disease Continuum

While hippocampal volume and tissue conductivity are independent markers of neurodegeneration, their integrated diagnostic utility in Alzheimer's disease remains underexplored. This prospective cross-sectional study evaluated a novel conductivity-to-tissue volume ratio index across the Alzheimer's disease continuum. Overall, 110 participants-30 cognitively normal adults, 52 with amnestic mild cognitive impairment, and 28 with Alzheimer's disease-underwent magnetic resonance electrical properties tomography and 3D T1-weighted imaging. Three ratio indices were calculated from conductivity and regional tissue volume in the insula and hippocampus. After age adjustment, all indices showed a diagnostic gradient across groups. The insular conductivity-to-hippocampal volume ratio showed high discrimination for Alzheimer's disease dementia versus cognitively normal adults, with an area under the curve of 0.917. The indices correlated positively with age and negatively with K-MMSE2 (Korean version of Mini-Mental State Examination, version 2) scores. These findings suggest that conductivity-volume ratio indices may serve as biophysical imaging markers that amplify disease-related contrast across the Alzheimer's disease continuum.