Multiparametric CEST and Z-spectrum analysis proton (ZAP) as biomarkers of human brain aging

Abstract

Abstract Chemical exchange saturation transfer (CEST) has been investigated to capture specific hydroxyl, amine, and amide protons. Z-spectrum analysis protons (ZAP) technique quantifies relaxation times of relatively free- ( $$\:{T}_{\:\:2,f}^{ex}$$ ) and restricted exchange proton ( $$\:{T}_{\:\:2,r}^{ex}$$  ) pools, and their fractions (F f and F r ) from a wider frequency range. Aging is related to brain neurodegeneration. However, the relationship between brain aging and macromolecular exchange protons remains unclear. Here we investigated brain aging by combining CEST and ZAP for comprehensive assessment of the macromolecules as potential biomarkers. Forty-three healthy adults (65.6 ± 16.0 years; 24 females) underwent 3-T experiments. Gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) were automatically segmented, and regions of interest were drawn in hippocampus, substantia nigra, globus pallidus, putamen, caudate, and thalamus. Spearman’s rank correlation coefficient analysis revealed significant age-related increases in F f across WM, CSF, hippocampus, substantia nigra, globus pallidus, and putamen (all P  < 0.05), along with elevated  $$\:{T}_{\:\:2,f}^{ex}$$ in the cortical GM, WM, and thalamus (all P  < 0.05). Amine signal in CSF decreased with age ( P  = 0.049). These results suggest age-related macromolecular alterations, highlighting CEST-ZAP metrics as promising biomarkers for brain aging and neurodegeneration.