Photon-Counting Detector Computed Tomography Angiography to assess intracranial stents and flow diverters: in vivo study comprising ultra-high resolution spectral reconstructions.

BACKGROUND AND PURPOSE Neuroimaging of intracranial vessels with implanted stents (ICS) and flowdiverters (FD) is limited by artifacts. Photon-Counting-Detector-Computed Tomography (PCD-CT) is characterized by a higher resolution. The purpose of this study was to assess the image quality of ultra-high-resolution (UHR) PCD-CT-Angiography (PCD-CTA) and spectral reconstructions to define the best imaging parameters for the evaluation of vessel visibility in ICS and FD. MATERIALS AND METHODS Retrospective analysis of consecutive patients with implanted ICS or FD, who received a PCD-CTA between April 2023 and March 2024. Polyenergetic (PE), virtual monoenergetic imaging (VMI), pure lumen (PL) and iodine (I) reconstructions with different kiloelectron volt (keV) levels (keV 40, 60 and 80) and reconstruction kernels (Body vascular kernel (Bv) 48, Bv56, Bv64, Bv72, Bv76) were acquired to evaluate image quality and assessed by 2 independent radiologists using a 5-point Likert scale and regions of interest (ROI). The different kernels, keV and the optimized spectral reconstructions were compared in descriptive analysis. RESULTS In total, 12 patients with 9 FDs and 6 ICSs were analyzed. In terms of quantitative image quality, sharper kernels as Bv64 and Bv72 yielded increased image noise, and decreased signal to noise (SNR) and contrast to noise ratio (CNR) compared to the smoothest kernel Bv48, (p<0.01). Among the different keV levels and kernels, readers selected the 40 keV level (p<0.01) and sharper kernels (in the majority of cases Bv72) as the best to visualize the in-stent vessel lumen. Assessing the different spectral reconstructions virtual monoenergetic and iodine reconstructions proved to be best to evaluate in-stent vessel lumen (p<0.01). CONCLUSIONS Our preliminary study suggests that PCD-CTA and spectral reconstructions with sharper reconstruction kernels and a low keV level of 40 seem to be beneficial to achieve optimal image quality for the evaluation of ICS and FD. Iodine and virtual monoenergetic reconstructions were superior to pure lumen and polyenergetic reconstructions to evaluate in-stent vessel lumen