Use of static and dynamic NMR microscopy to investigate the origins of contrast in images of biological tissues.

NMR imaging experiments have been carried out on a fruit (Actinidia deliciosa) and plant stem (Stachys sylvatica) using a wide range of image contrasts. These included T1, T2, T2*, diffusion, flow and chemical shift selection. In the case of fruit imaging we calculated relaxation time and diffusion maps and established that the imaged parameters varied significantly with fruit ripening. These changes we attribute to changes in water dynamics resulting from elevated sugar concentrations. For the plant stem, water flow has been observed in the xylem vessels with a maximum velocity of 70 microns s-1. The role of image artifacts is considered and, in the case of transverse relaxation, we have demonstrated that it is necessary to use a precursor Carr-Purcell-Meiboom-Gill pulse train if additional diffusive attenuation is to be avoided.