Photon-Counting Computed Tomography for Coronary Stent Imaging: In Vitro Evaluation of 28 Coronary Stents

Abstract

Objectives: The aim of this study was to assess in-stent lumen visibility and quantitative image characteristics of different coronary stents using a novel photon-counting detector (PCD) computed tomography (CT) system in comparison to a state-of-the-art energy-integrating detector (EID) CT scanner.

Materials and methods: In this in vitro phantom study, 28 different coronary stents ranging from 2.25 to 4.5 mm lumen diameter were expanded into plastic tubes filled with contrast agent. Stent-containing plastic tubes were positioned in a custom-made emulsion-filled phantom, which was inserted into an anthropomorphic phantom simulating a medium-sized patient. Computed tomography scans were acquired parallel to the scanners' z axis using a novel cadmium telluride-based PCD CT system (SOMATOM CountPlus; Siemens Healthcare GmbH, Forchheim Germany), operating in 2 different modes (standard-resolution mode [SR] and ultra-high-resolution [UHR] mode), and a latest generation dual-source EID CT system (SOMATOM Force; Siemens Healthcare GmbH, Forchheim). CTDIvol-matched images were reconstructed with comparable convolution kernels and using the same reconstruction parameters. In-stent lumen visibility (in %), increase in in-stent attenuation (expressed as Δ in-stent CT attenuation), and image noise (in Hounsfield unit) were manually measured. Parts of the image analysis (in-stent lumen visibility) were additionally performed in an automated way. Differences were tested using Wilcoxon signed rank test.

Results: The best in-stent lumen visibility was achieved with the PCD-UHR mode and the lowest noise levels with the PCD-SR mode. The median in-stent lumen visibility was significantly higher (P < 0.001) with PCD (SR, 66.7%; interquartile range [IQR], 63.3-72.3; UHR, 68.9%; IQR, 64.4-74.4) compared with EID (65.4%; IQR, 62.2-70.4). The Δ in-stent CT attenuation was significantly lower for PCD in both SR (78 HU; IQR, 46-108; P = 0.024) and UHR (85 HU; IQR, 59-113; P = 0.006) compared with EID (108 HU; IQR, 85-126). Image noise was significantly lower (P < 0.001) for PCD-SR (21 HU; IQR, 21-21) compared with EID images (25 HU; IQR, 24-25.0).

Conclusions: The PCD provides superior in-stent lumen visibility and quantitative image characteristics when compared with conventional EID.