Objectives <p>To evaluate the correlation of cerebral perfusion parameters and iodine density (ID) map between conventional CT perfusion (CTP) and dual-layer spectral-detector CT (DLCT) in patients with cerebrovascular diseases.</p> Materials and methods <p>This study enrolled 163 patients with cerebrovascular disorders who received CTP and CT angiography examination by DLCT. Conventional CTP (cCTP), spectral virtual monochromatic images (VMIs) CTP (sCTP, from 40 keV to 70 keV in 10 keV increments, and 100 keV), and ID maps were reconstructed. CTP parameters included cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), and time to peak (TTP) were generated from cCTP and sCTP. The differences and consistency between the cCTP and sCTP parameters were compared by the Kruskal–Wallis Test and Bland–Altman plots. The correlations between the ID maps and the cCTP or sCTP parameters were analyzed by the Spearman test.</p> Results <p>Significant differences were observed in both sides of CBV, MTT, TTP, and left-sided CBF between cCTP and sCTP (<i>p</i> &lt; 0.05). Bland–Altman plots demonstrated that the absolute values of CBF, CBV, MTT from 60 keV VMIs and nearly all relative sCTP values had good consistency with cCTP (<i>p</i> ≥ 0.05). Correlation analysis revealed that relative ID exhibited good correlation with relative CBF from cCTP (<i>r</i> = 0.673, <i>p</i> &lt; 0.001), 50 keV (<i>r</i> = 0.604, <i>p</i> &lt; 0.001), 60 keV (<i>r</i> = 0.628, <i>p</i> &lt; 0.001), and 70 keV (<i>r</i> = 0.614, <i>p</i> &lt; 0.001) VMIs.</p> Conclusions <p>Cerebral perfusion parameters from sCTP show good consistency with those from cCTP. Additionally, the relative ID maps demonstrate good correlations with the relative CBF.</p> Key Points <p><Emphasis Type="BoldItalic">Question</Emphasis> <i>Conventional brain CT perfusion is limited by high radiation dose, while quantitative dual-layer spectral-detector CT has been investigated as a low-dose alternative to perfusion measurement.</i></p> <p><Emphasis Type="BoldItalic">Findings</Emphasis> <i>Dual-layer spectral detector CT-derived perfusion parameters showed good consistency with conventional brain CT perfusion, with the highest correlation with relative iodine density.</i></p> <p><Emphasis Type="BoldItalic">Clinical relevance</Emphasis> <i>This study shows that dual-layer detector spectral CT-derived perfusion parameters, especially iodine density, have potential value to evaluate cerebral hemodynamics with less radiation dose and rapid imaging speed compared with conventional cerebral CTP.</i></p> Graphical Abstract <p></p>