I just spent an hour saving an original vector graphic in a variety of formats trying to retain the crispness of the original image. Finally managed to arrive at one that was head and shoulders above the rest (even though once pasted into Storyline, I'm sure it was converted to raster.) Out of Adobe Illustrator (CC) I selected: Export\Export As... then .png file format. When you click "Export" again, it brings up a dialog box where you can set your resolution to High Resolution 300 dpi, Anti-aliasing: None. Transparent background.
Bring this into Storyline as a normal .png image. This will give you a larger file size, but the image quality is FAR greater than anything else I have tried.
Hope this helps someone.