  Transverse NMR relaxation in a macroscopic sample is shown to be extremely
sensitive to the structure of mesoscopic magnetic susceptibility variations.
Such a sensitivity is proposed as a novel kind of contrast in the NMR
measurements. For suspensions of arbitrary shaped paramagnetic objects, the
transverse relaxation is found in the case of a small dephasing effect of an
individual object. Strong relaxation rate dependence on the objects' shape
agrees with experiments on whole blood. Demonstrated structure sensitivity is a
generic effect that arises in NMR relaxation in porous media, biological
systems, as well as in kinetics of diffusion limited reactions.
