Electron Density and Effective Atomic Number of Normal-appearing Adult Brain Tissues.xlsx

Objectives Few studies have reported in vivo measurements of electron density (ED) and effective atomic number (Zeff) in normal brain tissue. To address this gap, dual-energy computed tomography (DECT)-derived ED and Zeff maps were used to characterize normal-appearing adult brain tissues, evaluate age-related changes, and investigate correlations with myelin partial volume (Vmy) from synthetic magnetic resonance imaging (MRI). Materials and Methods Thirty patients were retrospectively analyzed. The conventional computed tomography (CT) value (CTconv), ED, Zeff, and Vmy were measured in the normal-appearing gray matter (GM) and white matter (WM) regions of interest. Vmy and DECT-derived parameters were compared between WM and GM. Correlations between Vmy and DECT parameters and between age and DECT parameters were analyzed. Results Vmy was significantly greater in WM than in GM, whereas CTconv, ED, and Zeff were significantly lower in WM than in GM (all p < 0.001). Zeff exhibited a stronger negative correlation with Vmy (r = −0.756) than CTconv (r = −0.705) or ED (r = −0.491). ED exhibited weak to moderate negative correlations with age in nine of the 14 regions. In contrast, Zeff exhibited weak to moderate positive correlations with age in nine of the 14 regions. CTconv exhibited negligible to insignificant correlations with age. Conclusion This study revealed distinct GM–WM differences in ED and Zeff along with opposing age-related changes in these quantities. Therefore, myelin may have substantially contributed to the lower Zeff observed in WM, which underlies the GM–WM contrast observed on non-contrast-enhanced CT.