Undulation artifact in the Z direction

[Espin]

(I tried to post this in the artifact sub-forum but apparently I cannot post anything there)

I do not have experience with MRI and I would like to know something about an artifact or geometric distortion that remains totally unnoticed for the radiologists in my clinic because nothing strange is seen in in each slice, the problem arises if you want to do a 3D or multiplanar reconstruction, or track a structure across the different axial slices: each 3 or 4 slices you can see a "jump" in the structures, and in a sagital/coronal reconstruction it is seen as an undulation of the structures (with a "wavelength" os 3-4 slice-widths)

Examples (T2 images reconstructed from 3 mm-width axial slices, with 0.5 mm-gap in an old Philips scanner):
http://postimg.org/image/8pqn0044b/
http://postimg.org/image/tlveb1ctx/

Is it normal? May it be due to the patient breathing? Scanner issues? Incorrect acquisition settings?

(it is possible to acquire directly sagital or coronal slices, and their quality is OK, but I want to make a 3D reconstruction using axial slices) Thanks!

[AndrewBworth]

Are you trying to reconstruct a 2D acquisition as a 3D one?