A beech (Fagus sylvatica L.) branch with two small dead branches (knots) was cut from a tree and coated with air and water impermeable coating to prevent it form drying. The sample was imaged by the 3D spin-echo technique and processed by ImageJ (NIH Image) image processing software for volume rendering. Cross-sectional planar images of intact tissue revealed high moisture in pith, in radially oriented xylem rays, in water conducting early wood and in wood producing a cambial zone. In xylem growth rings we could distinguish late (autumn) wood from early (spring) wood. The cross-section image of a dead branch (left image) clearly revealed a position of the protection zone delimiting sound wood from the branch cavity. This zone is protecting living wood against dehydration and against ingression of atmospheric oxygen and pathogenic microorganisms.
Volume rendered images (right images) clearly displayed anatomical structures of the branch. On the surface can be seen cavities at the position of two shed branches and increased increment of wood trying to close these two wounds. The images also enabled insight into spatial distribution of the moisture content. Surprisingly, the images showed that a part of the pith of dead branches still contained high moisture content. Our research demonstrated that structural response is associated with passive water distribution in mechanically injured tree tissues [1,2].
Another study done in our laboratory was focused on testing effects of different wood impregnation methods on wood protection against surface water. Samples of different wood spices (fir, spruce, larch, chestnut) in a shape of 12 mm cube were vacuum impregnated with oil or surface treated with vax or left unprotected. Then each of the samples was immersed for half an hour in water and then inserted in our 400 MHz MRI scanner and started scanning. The samples were scanned dynamically in 1D in three different interchanging directions with respect to the wood growing rings (axial, radial and tangential direction). The 1D scanning was interrupted after 1, 2.3, 18.6, 35 and 68 hours for acquisition of high-resolution 3D images using 3D gradient-echo imaging methods. While sequences of 1D profiles in different directions have good temporal resolution and provide deficient spatial information, 3D images have excellent spatial resolution for the price of poor temporal resolution. However, combination of both methods, 1D profiles and 3D images, provides all needed information. For demonstration of the method, two images of fir wood are shown below. In the first one it is shown by a sequence of 1D profiles in radial, tangential and axial directions how dynamics of sample drying is different in each of the three directions. It can also be seen that the amount water that migrated into the sample after the soaking period is quite substantial for the nonimpregnated sample of which mass has after the soaking increased by 40%.
