Feasibility of improving vascular imaging in the presence of metallic stents using spectral photon counting CT and K-edge imaging

International audience; correct visualization of the vascular lumen is impaired in standard computed tomography (ct) because of blooming artifacts, increase of apparent size, induced by metallic stents and vascular calcifications. Recently, due to the introduction of photon-counting detectors in the X-ray imaging field, a new prototype spectral photon-counting CT (SPCCT) based on a modified clinical CT system has been tested in a feasibility study for improving vascular lumen delineation and visualization of coronary stent architecture. Coronary stents of different metal composition were deployed inside plastic tubes containing hydroxyapatite spheres to simulate vascular calcifications and in the abdominal aorta of one New Zealand White (NZW) rabbit. Imaging was performed with an SPCCT prototype, a dual-energy CT system, and a conventional 64-channel CT system (B64). We found the apparent widths of the stents significantly smaller on SPCCT than on the other two systems in vitro (p < 0.01), thus closer to the true size. Consequently, the intra-stent lumen was significantly larger on SPCCT (p < 0.01). In conclusion, owing to the increased spatial resolution of SPCCT, improved lumen visualization and delineation of stent metallic mesh is possible compared to dual-energy and conventional CT. Coronary artery stenting has become the most important nonsurgical coronary revascularization procedure 1. Coronary angiography using computed tomography (CT) is limited in regards to a correct assessment of in-stent restenosis and its impact on coronary circulation, one of the major complications following the stenting procedure. Indeed, blooming artifacts impair a correct visualization of the vascular lumen. Blooming artifacts result in an apparent increase in the size of strongly attenuating objects, such as the stent's metallic struts and vascular cal-cifications, leading to an apparent reduction in size of the vascular lumen. Metal strut induced blooming artifacts are more significant in stents of diameter 3 mm or less, reducing intra-stent lumen interpretability to nearly 51% compared to 81% for larger stents 2. Furthermore, severe calcifications also induce blooming artifacts and their presence at a stent location may impair the detection of the stent itself. The recent development of a clinically based small field-of-view (FOV) spectral photon counting CT (SPCCT) prototype achieves higher spatial resolutions than standard CT at similar energies, owing to an important reduction in detector size 3. The higher spatial resolution is possible owing to the direct conversion pho-ton counting detectors, which convert single x-rays to electrical pulses. Ultra-high resolution mode resulting in a 0.25 × 0.25 mm pixel size at iso-center was demonstrated recently for a photon-counting CT system 4. This increase in spatial resolution is expected to strongly reduce blooming artifacts, potentially improving restenosis detection and interpretation 5. Reduction in blooming artifacts should allow morphological assessment of the mesh of the stent which is expected to improve detection of stent deployment problems and stent integrity degradation 6. Furthermore, owing to the spectral separation capabilities of photon counting, specific K-edge images