Objectives <p>To objectively and subjectively compare the detectability of pulmonary nodules on an ultra-high-resolution CT (UHR-CT) scanner equipped with energy-integrating detectors and a photon-counting CT (PCCT)&#xa0;in UHR mode.</p> Materials and methods <p>An image quality phantom and an anthropomorphic phantom were scanned on a UHR-CT and a PCCT in UHR mode at 7.5/2.5/0.4 mGy. The parameters typically used for UHR chest CT scans were selected. Noise power spectrum and task-based transfer function were computed to assess noise-magnitude, noise texture (<i>f</i>_av), and spatial resolution (<i>f</i>₅₀), respectively. Detectability indices (<i>d</i>’) were computed to model the detection of three chest nodules. Five radiologists subjectively evaluated their confidence in detecting these nodules available on the anthropomorphic phantom.</p> Results <p>For PCCT, noise magnitude increased, and <i>f</i>_av values were similar as the dose decreased. For UHR-CT, noise-magnitude decreased, and <i>f</i>_av values decreased as the dose decreased. For both inserts and CT systems, <i>f</i>₅₀ values decreased as the dose decreased. For both inserts and at all dose levels, <i>f</i>₅₀ values were higher with PCCT than with UHR-CT. <i>d</i>’ values increased as the dose increased with PCCT, and the opposite was found with UHR-CT. Confidence in nodule detection was considered clinically sufficient at all dose levels for high-contrast solid nodules at 7.5 and 2.5 mGy for subsolid nodules, and only for PCCT at 7.5 mGy for low-contrast nodules.</p> Conclusion <p>Under UHR conditions, pulmonary nodule detectability strongly depends on the dose level and reconstruction parameters. High-contrast nodule detection can be performed at all dose levels with both CT systems, but reconstruction strategies must be optimized for low-contrast nodule detection.</p> Key Points <p><UnorderedList Mark="Bullet"> <ItemContent> <p><i>Do the performance of UHR-CT and PCCT scanners improve the detectability of pulmonary nodules</i>?</p> </ItemContent> <ItemContent> <p><i>PCCT showed dose-invariant noise texture and higher effective spatial resolution, whereas UHR-CT relied on dose-dependent noise suppression, producing smoother images and reduced spatial frequency</i>.</p> </ItemContent> <ItemContent> <p><i>High-contrast nodule detection can be performed at all dose levels with both CT systems, particularly at ultra-low dose levels, but reconstruction strategies must be optimized for low-contrast nodule detection</i>.</p> </ItemContent> </UnorderedList></p> Graphical Abstract <p></p>