  In porous material research, one main interest of nuclear magnetic resonance
diffusion (NMR) experiments is the determination of the shape of pores. While
it has been a longstanding question if this is in principle achievable, it has
been shown recently that it is indeed possible to perform NMR-based diffusion
pore imaging. In this work we present a generalization of these previous
results. We show that the specific temporal gradient profiles that were used so
far are not unique as more general temporal diffusion gradient profiles may be
used. These temporal gradient profiles may consist of any number of 'short'
gradient pulses, which fulfil the short-gradient approximation. Additionally,
'long' gradient pulses of small amplitude may be present, which can be used to
fulfil the rephasing condition for the complete profile. Some exceptions exist.
For example, classical q-space gradients consisting of two short gradient
pulses of opposite sign cannot be used as the phase information is lost due to
the temporal antisymmetry of this profile.
