Abstract: Objective: This study aimed to investigate the application value of virtual monoenergetic (VMI) (≤70 keV) computed tomography angiography (CTA) in imaging small cerebral vessels with dual-layer detector spectral CT. Methods: The imaging data of 52 patients who underwent head and neck CTA using Philips IQon CT were retrospectively analyzed. Conventional 120 kVp mixed energy images and 40~70 keV (10 keV interval) VMI CTA images reconstructed using spectral data were obtained. The CT value, signal-to-noise ratio (SNR), contrast noise ratio (CNR), and CT value and noise (SD) of the paravascular cerebral parenchyma at the same level were measured in the M1 segment of the middle cerebral artery. The image quality of the middle cerebral artery in volume reconstruction (VRT) and lepidopleural artery in maximum density projection (MIP) was scored by two physicians using a 5-point Likert scale. The evaluation results between the different groups were compared. Results: The CT, SNR, and CNR values of blood vessels at 40~70 keV VMI increased with a decrease in energy level, and the SD values increased slightly, with more statistically significant differences compared with conventional images. In the subjective evaluation, the VRT images in the 40 keV and 50 keV groups were 5 (5, 5) and 5 (4, 5), respectively, and the MIP image scores were 4 (3, 4) and 4 (3, 5), respectively. The subjective scores of both groups were better than those of the other groups, with no statistically significant difference. Conclusion: Virtual monoenergetic CTA technology with dual-layer spectral CT <70 keV can effectively improve the display effect of the distal branch of the cerebral small vessels and legume artery, and 50 keV VMI CTA is recommended.