Dear @josedolz, My errors as following, please help me fix this error.  My the preparing the data:  And in each Training and Validation folder has : GT, T1, T1_IR, T2_FLAIR, and in each of these folders has GT.nii, T1.nii, T1_IR. nii, T2_FLAIR.nii.   Thank you, @josedolz very much.