Dear Prof. Rorden,

thank you very much for your immediate reply. 
I take form your answer that SPM12 correctly reads the converted images as the images are displayed correctly (despite the fact that the header looks differently compared to the SPM Dicom import).
Is my conclusion correct that SPM12 reads all images correctly independent of the conversion method (dcm2nii, dcm2niix, Dicom import function in SPM12) and that these images can be further processed in SPM12 without worrying about any coordinate transformations?

Kind regards,
Julia Binder