Purpose:

Novel photon-counting detector-CT angiography using ultra-high resolution mode (UHR-

CCTA) has been shown to be feasible for coronary imaging. However, correlation with

invasive coronary angiography has not yet been thoroughly investigated. Here, we compare

UHR-CCTA with invasive quantitative coronary angiography (QCA) as the gold standard.

Methods:
Retrospective analysis including all consecutive patients who had undergone UHR-

CCTA for the assessment of coronary artery disease with subsequent clinically indicated

coronary angiography within 30 days from CCTA at the University Medical Center Mainz

since 07/2022. Exclusion criteria were a chronic total coronary occlusion and prior coronary

intervention. In addition to a standard reconstruction with 0.6 mm slice thickness, datasets

with 0.4 mm slice thickness as well as a UHR reconstruction with 0.2 mm slice thickness were

obtained. Degree of stenosis as assessed by invasive QCA (CAAS, Pie Medical Imaging) and

quantitative CCTA (Syngo.via, Siemens Healthcare) were compared using univariate analysis

of variance with post-hoc testing and Bland-Altman plots.

Results:
A total of 23 patients were included (mean age 71.0 ± 8.6 years; 74% males; mean

BMI 29±7 kg/m 2 ; mean heart rate 66±7 bpm). CT identified 50 coronary stenoses with a

mean degree of 62.9±17.6% in the 0.6 mm datasets which declined with significantly

decreasing slice thickness (0.4 mm: 58.7±18.5%; UHR 0.2 mm: 51.9±19.9%; both p≤0.001).

When comparing with invasive measurement, the 0.6 mm reconstruction significantly

overestimated degree of stenosis with QCA (49.4±18.2%, p=0.002), but not the 0.4 and UHR

0.2 mm reconstructions (p=0.82 and p=1.0). Bland Altman analysis revealed a significant bias

between 0.6 mm (mean bias 13.6, limits of agreement 3.6.6 to 23.5, Figure 1) and 0.4 mm

(9.3, -0.6 to 19.2) reconstructions with QCA, respectively. UHR 0.2 mm reconstruction did

not show a clinically significant bias with the gold standard (2.5, -7.4 to 12.4).

Conclusions:
In this early clinical photon-counting detector-CT study, UHR-CCTA showed an

improved correlation with invasive QCA compared to a standard CT reconstruction. Larger

trials are necessary to investigate the potential for reducing unnecessary referral for follow-

up invasive imaging.