A question about training sets and metrics

[ginvermouth]

There are some irrelevant images (without liver region) in the CT volumes. Do I need to remove these images or send all of them to the network as a training set?
For metrics, I didn't get any prediction for small image with very small liver region. So some of the metrics cannot be calculated (Infinite). Do you get a predicted result for every single image, and compared with the ground-truth of foreground?