Ultra-high-resolution imaging of intracranial flow diverters with photon counting CT: A comparative phantom study with flat-panel CT

Abstract

Flow diverters are a crucial element in the treatment of intracranial aneurysms. However, the optimal non-invasive follow-up imaging modality, particularly for the detection of in-stent stenosis, remains uncertain. This study aims to compare the performance of photon-counting detector CT (PCD-CT) in ultra-high-resolution (UHR) mode with flat-panel CT (FP-CT) for the evaluation of intracranial flow diverters. A phantom model for intracranial vessels was used to evaluate 15 flow diverters of various sizes and designs. Imaging was performed using both PCD-CT and FP-CT. Qualitative assessment of the stent lumen was conducted by three experienced neuroradiologists using a 5-point Likert scale. Quantitative analysis included measurements of lumen area, contrast to noise ratio and signal to noise ratio. FP-CT provided a significantly larger assessable stent lumen than PCD-CT at all dose levels (p < 0.05), with no significant differences between PCD-CT dose levels (p = 0.999). Increasing PCD-CT dose did not improve lumen visualization. SNR and CNR increased with PCD-CT dose (p < 0.001), peaking at CTDI 20, but showed diminishing returns beyond CTDI 10. Flow diverter diameter correlated positively with SNR and CNR (p < 0.05). Subjective image quality improved with PCD-CT dose (p < 0.001) but showed no significant difference beyond 10 mGy (p > 0.05). FRED devices had the lowest ratings, independent of imaging modality (p = 0.80). Our study demonstrated that while FP-CT provided superior visualization of the flow diverter lumen in a head phantom vessel model, subjective assessability ratings were comparable between FP-CT and PCD-CT when evaluated by experienced readers. PCD-CT at a CTDIvol of 10 mGy offered the best balance between image quality and radiation dose, making it a viable alternative for post-interventional assessment of flow diverters.

Keywords: Artifacts; Flat-panel CT; Flow diverter; Image quality; Ultra-high-resolution imaging.

Fig. 1

Flat panel CT (A, B) and photon-counting detector CT (CTDIvol 20 mGy; C, D) with axial and sagittal reconstructions of a Silk Vista 2.5 × 15 mm flow diverter. Compared to FP-CT, PCD-CT shows a smaller apparent lumen and a hypodense artifact adjacent to the stent wall (arrowheads). Window settings were manually optimized for contrast: A, B) W: 700 HU, L: 2000 HU; C, D) W: 250 HU, L: 700 HU.

Fig. 2

Assessable luminal area across scan modalities, radiation doses, and different flow diverter models.

Fig. 3

Relative beam hardening artifact width in PCD-CT imaging of flow diverters. Scatter plot showing the strong negative correlation between nominal stent diameter and relative artifact width (ρ = − 0.91, p < 0.001). Artifact width was defined as the distance between the contrast-filled lumen and the inner stent contour and normalized to device diameter. Smaller flow diverters exhibited proportionally greater artifact burden, consistent with reduced assessable lumen.

Fig. 4

Box plots of contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) across scan modalities and radiation dose levels.

Fig. 5

Flat panel CT (A, C) and photon-counting detector CT (CTDIvol 20 mGy; B, D) with axial and sagittal reconstructions of a FRED 4,5 × 20 × 13 mm flow diverter. Note the pronounced metal artifacts at the flow diverter ends and the limited assessability of the lumen in both modalities. Window settings were manually optimized for contrast: A, B) W: 700 HU, L: 2000 HU; C, D) W: 250 HU, L: 700 HU.