list of images: poor performances

Hi,
in a mobile app I need to display a list of 200 images. On the list I
use a tileLayout with virtualLayout=true and a custom itemRenderer that
only contains a Spark Image. On the set value method of the itemrenderer
I change the source of the image with the path to the new bitmap.
It works, but performances are poor and the list doesn't scroll well. On
iPad it's almost acceptable, but on Android I have to scroll row by row
and wait until every image of the row is loaded.
Any suggestions to improve the situation?
Thanks

Gabriele