Nmr Imaging Of Roots - Methods For Reducing The Soil Signal And For Obtaining A 3-Dimensional Description Of The Roots

Studies of root morphology or root architecture are limited by the problems of observing roots in soil. NMR imaging can preferentially detect the water in roots rather than soil and can therefore produce a map Of the distribution of the water in roots, even though there is much more water in the soil than in the roots. The gradient echo imaging technique was shown to detect less signal from water in soil than the more usual spin-echo technique, probably because the signal loss due to magnetic field inhomogeneities was not refocused in the gradient echo experiments. The gradient echo sequence produced images of a water-filled capillary tube in soil and of the main roots of a 31-day-old oat plant, images which had better contrast than those from the spin-echo sequence. The improvement was particularly noticeable in the wetter soils. The finer roots could only be observed in the driest of soil and with the spin-echo sequence. Magnetic field inhomogeneities have a greater effect on thinner roots than on thicker ones, and because the initial signal from thin roots was so small, the additional signal loss due to magnetic field inhomogeneities made the fine roots undetectable with the gradient echo sequence. The problem of loss of perspective associated with projection images was overcome by taking a number of images with different projection planes. By comparing images, a set of (x, y, z) coordinates was obtained for the 4 main roots of a 31-day-old oat plant. Computer graphics methods made it possible to compare the digitised root coordinate data set with the original images, thereby confirming the accuracy of the digitised data.