In microscopic MRI (≈ 10 Am resolution), diffusion boundaries impermeable to water on a millisecond time scale distort the lineshape function of the observed frequency spectra from the transverse magnetization in a manner similar to motional narrowing in MR spectroscopy. Reconstruction techniques developed for macroscopic imaging interpret these distortions as spatial deformations of objects. This distortion of frequency spectra is demonstrated for geometrically simple objects, and it is shown how in such cases the reconstructed images should be interpreted and how diffusion-induced distortions in frequency space may actually be exploited to enhance image contrast around compartmental boundaries. The distortions are properly described by Kubo's lineshape function, for which suitable numerical algorithms are provided. A parameter is introduced that provides an estimation of the extent of diffusion-induced distortions which can vary from an enhancement of image intensity near boundaries to, for extreme motional narrowing, a focusing of image intensity around compartment centers.