Why does the shape of the image change?

Hi, I read a MRI series image by Simpleitk and the shape of it is (168L, 640L, 640L).
However, when i use the 3D slicer to read the same image, the shape of the image is changed to (24L, 640L, 640L), meanwhile, I find that the image read by the Simpleitk just have many same slices (7 times repeated for each slice ).
I don’t know whether the 3D slicer does some pre-processing to merge the repeated slices to one or some else operations, so can anyone give any advice?

Slicer’s DICOM reader uses the same reader as ITK (SimpleITK) at the lowest level, but it does a lot of additional pre-processing (determine how to group and order slices) and post-processing (apply necessary warping to correct any geometrical issues).