Does the train and validation set contain the same intensity values?
Out of 20 3D subject images(172x220x156), I have split the train-valid-test as 16-2-2. So the train and validation sets are not from the same subject.
Also, do the training inputs contain a lot of air (-1000HU), while the validation data contain more organs?
The train and validation patches are taken in a similar pattern, so it should not be dissimilar drastically.
Could you be a little specific about the normalization?
Shall I normalize both input and output from [-1,1] and train the network?