Objective In this study, energy spectrum CT optimal virtual single energy image (VMI) with virtual flat scan (VUE) phase subtraction was compared with the matched mask bone elimination (MMBE) method in the subtraction of head and neck CT angiography (CTA).

Methods This retrospective study comprised 80 patients who underwent head and neck CTA between January 2024 and February 2025 at our institution. Reconstruction of image data was performed at 10- keV intervals, with eleven groups of VMI data from 40~140 keV ultimately reconstructed. The CT values and standard deviations of the common carotid artery (CCA), internal carotid artery (ICA), middle cerebral artery (MCA), and anterior cerebral artery (ACA) were measured, and the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR) were calculated. Then, subjective scoring of the 11 groups of VMI images was performed by two senior attending physicians. The outcomes of the objective evaluation indexes and subjective scoring were statistically analyzed to identify the best VMI images. The subtraction images obtained from the optimal VMI subtraction VUE were compared with the MMBE subtraction images, including arterial and venous system vascularization, debulking, overall image quality grade, and effective radiation dose.

Results The differences in the SNR and CNR of CCA, ICA, MCA, and ACA between the VMIs of each energy level were statistically significant, with the SNR and CNR of 60 keV images found to be higher than those of other VMI images. The radiologists showed good agreement on their subjective evaluations of VMI image quality at each energy level (Kappa>0.61). The differences in subjective scores between the VMI at each energy level were statistically significant, with the 60 keV images showing the highest subjective scores. The subtracted images of ICA intracranial segment, vertebral artery (VA) intracranial segment, and intracranial artery after subtraction of the 60 keV images and VNC were significantly better than those of the MMBE method. The debulking effect of its subtraction was also significantly better than that of the MMBE method. The percentage of the overall image quality of Grade I was 88.75% (71/80), significantly higher than that of the MMBE method (77.50%; 62/80). Its average effective radiation dose was (0.96±0.02)mSv, approximately 44.24% lower than that of the MMBE method-a difference that was statistically significant.

Conclusion We identified 60 keV as the best virtual single energy for displaying head and neck CTA. Its subtracted image was better in terms of head and neck arterial vascular display, debridement effect, and overall image quality grade. This highlights its potential as an alternative to the traditional matched-mask debridement method. By omitting the true flat scan, the radiation dose can be significantly reduced, providing a novel mechanism for the optimization of head and neck CTA.