Quantitative 1H-NMR imaging of water in white button mushrooms ( Agaricus bisporus)

Abstract

MRI represents a valuable tool for studying the amount and physical status of water in plants and agricultural products, for example, mushrooms ( Agaricus bisporus). Contrast in NMR images originates from the mixed influence of the fundamental NMR parameters, amongst others, spin-density, T 2- and T 1 relaxation processes. Maps of these parameters contain valuable anatomical and physiological information. They can, however, be severely distorted, depending on the combination of parameter settings and anatomy of the object under study. The influence of the tissue structure of mushrooms, for example, tissue density (susceptibility inhomogeneity) and cell shape on the amplitude, T 2, and T 1 images is analyzed. This is achieved by vacuum infiltration of the cavities in the mushroom's spongy structure with Gd-DTPA solutions and acquiring Saturation Recovery-Multispin Echo images. It is demonstrated that the intrinsic long T 2 values in the cap and outer stipe tissue strongly relate to the size and geometry of the highly vacuolated cells in these spongy tissues. All observed T 2 values are strongly affected by susceptibility effects. The T 2 of gill tissue is shorter than T 2 of the cap and outer stipe, probably because these cells are less vacuolized and smaller in size. The calculated amplitude images are not directly influenced by susceptibility inhomogeneities as long as the observed relaxation times remained sufficient long. They reflect the water distribution in mushrooms best if short echo times are applied in a multispin echo imaging sequence at low magnetic field strength.