In group 3 , stent evaluability was significantly higher and artifact rate was significantly lower than in group 2 ( 99 % vs. 91 % and 4 % vs. 15 % ) and group 1 ( 99 % vs. 92 % and 4 % vs. 17 % ) , respectively , mainly because of a significant lower rate of beam-hardening artifacts ( 3 cases in group 3 vs. 22 and 27 in groups 2 and 3 , respectively ) .