Ultra-High-Resolution Photon-Counting CT Angiography for Noninvasive Detection of Neurovascular In-Stent Restenosis

BACKGROUND: Noninvasive detection of neurovascular in-stent restenosis (ISR) remains challenging because of blooming artifacts and limited spatial resolution on conventional computed tomography angiography (CTA). Ultra-high-resolution (UHR) photon-counting detector CTA (PCD-CTA) may offer an improved approach for accurate ISR detection, potentially overcoming these challenges. METHODS: In this prospective study, consecutive patients who had undergone neurovascular stent implantation were enrolled at The First Affiliated Hospital of Nanjing Medical University between July and November 2025. All participants underwent UHR PCD-CTA. Simulated energy-integrating detector CTA data sets were reconstructed from the same raw data to approximate conventional CTA for comparison. Two blinded radiologists independently assessed subjective image quality, diagnostic confidence for ISR, and visualization of in-stent intimal hyperplasia and low-attenuation plaque in stents without restenosis. Diagnostic performance for ISR detection was evaluated on a stent-based level, using digital subtraction angiography as the reference standard when available. RESULTS: Forty-three participants (mean age, 63.1 years ± 9.5; 8 women) with 51 stents were included. ISR was present in 14 stents and absent in 37; digital subtraction angiography was available for 26 stents, including all stents with ISR. Compared with simulated energy-integrating detector CTA, UHR PCD-CTA demonstrated significantly higher subjective image quality ( P =0.004) and diagnostic confidence for ISR ( P <0.001), and markedly reduced blooming artifacts ( P <0.001). UHR PCD-CTA achieved excellent diagnostic performance for ISR detection, with a sensitivity of 100.0%, specificity of 97.3%, and overall accuracy of 98.0%. In stents without restenosis, visualization of in-stent intimal hyperplasia and low-attenuation plaque was significantly improved with UHR PCD-CTA compared with simulated energy-integrating detector CTA ( P <0.001). CONCLUSIONS: UHR PCD-CTA demonstrates high diagnostic performance for noninvasive detection of neurovascular ISR and may serve as a promising tool for poststent surveillance.