Endoleak detection with photon-counting detector CT at various radiation doses after endovascular aneurysm repair: a phantom study.

After endovascular aneurysm repair, patients require lifelong CT follow-ups. Photon-counting detector CT (PCD-CT) may improve detection of tiny iodinated structures at low radiation dose. The aim of this experimental study was to find the lowest dose which still provides high detectability of small endoleaks using PCD-CT with 55 keV and 50 keV virtual monoenergetic images (VMIs). An abdominal aneurysm phantom mimicking medium and large patients was scanned at 100%, 50%, 25%, and 12.5% radiation dose using PCD-CT. Besides standard 55 keV images, 50 keV VMI were reconstructed at 25% and 12.5% dose. The ninety-six CT series containing 1728 endoleaks of 2-6 mm were read by three independent observers. Areas under the alternative free-response operational characteristic curve (A1) were analysed with the jackknife-method. In the medium phantom, A1 for 6 mm endoleaks was similar at 100% and 50% doses (0.93 vs. 0.86; p = 0.23), but performance at 50% dose decreased in 4-6 mm endoleaks (A1, 0.81 vs. 0.68; p = 0.02). In the large phantom, A1 decreased at 50% dose both for 6 mm (0.72 vs. 0.42; p = 0.003) and for 4-6 mm (0.49 vs. 0.29; p = 0.02) endoleaks. Compared with standard reconstruction, 50 keV VMIs did not change A1 at 25% dose (0.56 vs. 0.52; p = 0.38) and led to worse performance at 12.5% dose (0.30 vs. 0.19; p = 0.01). In summary, diagnostic performance for 6 mm endoleaks remained high with 50%-dose reduction using PCD-CT in simulated medium but not in large patients. 50 keV VMIs at 12.5% and 25% dose did not improve endoleak detection.