Abstract： Objective:To investigate the optimal monoenergetic level of spectral reconstructions and contrast agent concentration for the structure and lumen of isolated coronary stents on a dual-layer spectral detector CT (DLCT).Methods:Eighteen scaffolds of different materials were implanted into the artificial simulated coronary artery, and were filled with conventional and low concentration contrast agents (1/2 of the conventional dose). Spectral CT scan was performed, and 50-100 keV (interval 10 keV) and 120 keV single-level reconstruction were performed at the conventional concentration and low concentration, which were recorded as A 50-100, 120 keV group and B 50-100, 120 keV group respectively; Another group of conventional concentration data was reconstructed with conventional iDose 4, which was recorded as conv group. The image was evaluated subjectively, including stent structure score (Likert 5-score) and stent lumen score (Likert 4-score); objective evaluation, including background noise, contrast noise ratio (CNR) and stent inner diameter difference (AlN). The differences of subjective and objective evaluation indexes were analyzed. Results:The stent structure scores of A 80, 90 keV group [(3.56±0.64), (4.11±0.58) points] and B 90 keV group [(3.61±0.50) points] were significantly better than those of other groups ( P<0.01), and the A 90 keV group had the highest score. The scores of stent lumen in A 70 keV group [(3.61±0.50) points] and B 70 keV group [(3.47±0.63) points] were significantly better than other groups ( P<0.01), and the score of A 70 keV group was the highest. There was no significant difference in noise, CNR and AlN ( F=1.67, 0.15, 1.16, P>0.05). The main effect analysis was energy level, there were significant differences in noise, CNR and AlN between groups a, B and conv ( F=83.74, 23.95, 24.63, P<0.01). A 70, 80, 90 keV group [(11.43±0.48), (11.81±0.34), (12.01±0.33) HU] and B 70, 80, 90 keV group [(11.50±0.31), (11.58±0.18), (12.13±0.30) HU], image background noise was significantly lower than other groups ( P<0.01). There was no significant difference between the six groups ( P>0.05). The noise of A 70 keV group was the least. The CNR in stent lumen of A 50, 60, 70 keV groups (26.85±5.19, 26.03±4.29, 24.46±5.40) and B 50, 60, 70 keV groups (25.88±5.67, 24.18±5.46, 24.91±7.67) was significantly higher than that of other groups ( P<0.01). The highest CNR value was found in A 50 keV group. The AlN value of A 90, 100, 120 keVgroup [(32.22±6.16) %, (30.79±5.55) %, (27.05±4.47)%] was higher than that of conv group [(41.76±6.00)%], the difference was statistically significant ( P<0.01). The AlN values of A 90, 100, 120 keV group and B 90, 100, 120 keV group [(34.34±5.73)%, (33.95±5.46)%, (33.92±5.45)%] were lower than those of other subgroups, and the differences were statistically significant ( P<0.01). There was no statistically significant difference between the six groups ( P>0.05). The AlN of A 120 keV group was the lowest. Conclusions:Regarding stent phantom imaging, DLCT monoenergetic imaging was better than conventional mixed energy imaging. When DLCT scanning was performed, 90 keV (structure) and 70 keV (lumen) combined reconstruction could not reduce the imaging quality when the concentration was halved.