Mixed coronary plaque phantom analysis by photon-counting CT: impact of calcium and iodine on low-attenuation plaque detection

Szilveszter, Bálint and Kolossváry, Márton and Kubovje, Anikó and Marques, Hugo and Vattay, Borbála and Jokkel, Zsófia and Sipos, Barbara and Vecsey-Nagy, Milán and Boussoussou, Melinda and Maurovich-Horváth, Pál and Newlander, Shawn and Wesbey, George and McVeigh, Elliot (2026) Mixed coronary plaque phantom analysis by photon-counting CT: impact of calcium and iodine on low-attenuation plaque detection. EUROPEAN HEART JOURNAL. IMAGING METHODS AND PRACTICE, 4 (3). No. qyag119. ISSN 2755-9637

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Abstract

To test whether photon-counting detector CT (PCD-CT) improves low-attenuation plaque (LAP) detection compared with energy-integrating detector CT (EID-CT) using a mixed-plaque phantom and full-rotation helical images as high-resolution reference. We imaged a custom phantom housing three different sized mixed-plaque inserts (LAP5.5mm, LAP4mm, and LAP7mm) combining iodinated lumen (600/1000 HU), calcified arcs (200/800 mg/cc), and a narrow LAP central strip (1–1.5 mm, 75 HU), embedded in a fat-equivalent ring (−60 HU). Polychromatic and virtual monoenergetic images (40/70/100/130 keV) were reconstructed with soft (Qr40) and sharp (Qr72) kernels and quantum iterative reconstruction (QIR) levels. Findings were compared with a clinically used EID-CT protocol. HU line profiles and edge-width-at-half-maximum (EWHM) at the iodine–phantom interface were measured. Reference EWHM was 0.125 mm. Cardiac half-rotation Qr40 reconstructions yielded EWHM 0.68–0.75 mm, whereas Qr72 approached reference values (0.18–0.23 mm). In LAP5.5mm, the 1-mm LAP layer was detectable on standard and UHR images with sharp kernels and higher QIR, with best attenuation fidelity using Qr72. For the smallest LAP4mm, only Qr72/QIR2 resolved the 1-mm LAP component, although measured attenuation remained elevated because of blooming from adjacent iodine and calcium. In LAP7mm, Qr72/QIR4 most closely reproduced the nominal LAP attenuation. Lower-keV images (40–70) increased LAP masking from iodine. EID-CT did not clearly depict LAP4mm. PCD-CT provides superior spatial resolution and HU fidelity for detecting LAP, particularly when using UHR images combined with sharp kernels (Qr72) and higher iterative strength (QIR 2–4). LAP detection improved at 130 keV vs. lower energies. Low-attenuation plaque is a potentially dangerous type of coronary plaque, but it can be hard to detect on computed tomography because calcium and contrast dye may hide it. In this laboratory phantom study, we showed that photon-counting computed tomography can detect these plaque features more accurately than conventional computed tomography, especially when ultra-high-resolution images and sharper reconstruction settings are used. Higher-energy reconstructions also helped reduce the masking effect of contrast dye. These results may help improve coronary computed tomography protocols for identifying high-risk plaque more reliably.

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