Abstract Body (Do not enter title and authors here): Background
In 2021, the Food and Drug Administration approved the first Photon Counting Computed Tomography (PCCT) system, marking an extraordinary milestone in medical imaging. This advanced technology offers significant advantages in cardiac imaging, particularly in detecting severe calcification lesions and in-stent restenosis (ISR). Subsequently, in October 2023, our hospital became the first to implement a PCCT system. Leveraging the benefits of PCCT, we conducted a study to investigate ISR in patients who had undergone stenting over the course of a year.

Methods
From October 2023 to January 2024, all high-risk stented patients, including those with multiple stents, bifurcation lesions, chronic total occlusions, and severe calcification lesions, were included in the study. The PCCT system (tube voltage 120 kV, collimation 120 x 0.2 mm, 50-70 ml Iohexol 300 mg/ml) was utilized to detect ISR. Intra-stent lesions with more than 50% narrowing were classified as ISR. Additionally, the quality of the PCCT images was assessed by two radiology experts using a five-point scale, where 1 indicated excellent quality (absence of artifacts) and 5 indicated non-diagnostic quality (severe artifacts).

Results
Eighty patients (77.5% male) met the inclusion criteria, with a mean age of 64.7 ± 10.9 years. Among these patients, 56 had stents in the Left Anterior Descending (LAD) artery, while 27 and 34 had stents in the Left Circumflex Artery (LCx) and Right Coronary Artery (RCA), respectively. In total, 25 patients (31.2%) were identified with ISR. Specifically, ISR was most prevalent in the LCx at 25.9% (7/27), followed by the LAD at 21.4% (12/56), and the RCA at 17.7% (6/34). Nine patients underwent repeat percutaneous coronary intervention (PCI). The overall image quality was rated as excellent, with a median score of 1.5 [IQR, 1-2]. Additionally, 40 patients (50%) had a calcium score over 400.

Conclusion
These findings represent the first results obtained using PCCT at our hospital. The results indicated a relatively high rate of ISR, particularly among high-risk patients. Given the excellent image quality, PCCT is a promising technique for the follow-up of patients post-PCI.