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