Complex sentence: Based on the pioneering work of Stejskal and Tanner in the 1960's he thought that specific magnetic gradient pulses should be used for diffusion encoding, but the problem was to mix such pulses with those used in the MRI sequence for spatial encoding.
Split into simpler sentences: Based on the pioneering work of Stejskal and Tanner in the 1960's he suspected that diffusion encoding could be accomplished using specific magnetic gradient pulses. However this required mixing of such pulses with those used in the MRI sequence for spatial encoding.