Imperius is likely out right winning late game. His auto attack damage is nuts once stacks are not removed on attack and Artanis has little to counter it. Artanis can stall him a significant time though, as both ultimates are very effective.
Best chances would be with high AS swap build. Imperius might have issues coping with the auto attack damage and scaling and the swap might interrupt his combos. Purifier beam can also be used to force Imperius to reposition or even disenguage as he is unlikely to do well tanking its full damage. The high attack speed helps with Artanis’s own sustain due to faster trait cds.
One of the biggest factors at play would be levels. 1-2 level advantage, especially with a talent tier, could swing the results either way.
In theory if Artanis stacked tier 1 quest enough he could easily solo Imperius due to the near infinite damage scaling. In practice this might just push him into the high auto attack damage territory unless a match really lasts a long time or the enemy is tank heavy and allowed Artanis to stack near constantly.