Stent Lumen Visibility in Single-energy CT Angiography: Does Tube Potential Matter?

Rationale and Objectives: There has been a trend toward lowering tube potential in computed tomography angiography (CTA) examinations to reduce radiation dose or contrast medium dose. The aim of this study was to evaluate the influence of tube potential on peripheral artery in-stent lumen visibility in CTA examinations. Materials and Methods: Nine different peripheral artery stents were placed in a vessel phantom (inner diameter: 5 mm, surrounded by water) and scanned consecutively using a 128-row CT scanner with 70, 80, 100, 120, and 140 kV and two different concentrations of contrast medium to simulate contrast enhanced blood. Medium-smooth and ultra-sharp reconstruction kernels with filtered back projection (B30f, B46f) and iterative reconstruction technique (130f, 146f) were used. Visible in-stent lumen diameter and artifact width were evaluated using a semiautomatic software tool. All stents were scanned with digital angiography, which was regarded as the reference standard. Results: Averaged over all stents, visible in-stent lumen diameter ranged from 1.30 +/- 0.21 mm (CM2/70 kV/I30f) to 3.13 +/- 0.32 mm (CM1/120 kV/146f). In-stent lumen diameters were significantly higher for 120 and 140 kV compared to 70 kV (2.39 +/- 0.73 and 2.39 +/- 0.66 mm vs 1.99 +/- 0.69 mm; P = 0.01 and P = 0.005). Ultra-sharp reconstruction kernels lead to significantly better in-stent lumen visibility than smooth reconstruction kernels (B46f: 2.74 +/- 0.34 mm vs B30f: 1.57 +/- 0.36 mm; P < 0.001, respectively). Furthermore, in-stent lumen visibility was improved for iterative reconstructions compared to filtered back projection (146f: 2.93 +/- 0.30 mm vs B46f: 2.74 +/- 0.34 mm; P < 0.001). Contrast medium concentration did not influence in-stent lumen visibility. Conclusions: Despite all known benefits of low kV CTA protocols, the use of a very low tube potential may hamper in-stent lumen visibility. A sharp kernel may be of value when evaluating the inner lumen of vascular stents.