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 ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive any funding. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Ethics Committee of the Aachen Medical Faculty had no ethical or professional objections to the research project. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors