MRI-based D2O/H2O-contrast method to study water flow and distribution in heterogeneous systems: Demonstration in wood xylem

We demonstrate a method for examining water flow and distribution within heterogeneous systems by means of MRI and deuterium oxide (D₂O)/water (H₂O) contrast. In this demonstration a piece of a pine tree was used. In pine xylem, water flows in tube-like dead cells, that is, tracheids, which are about 10-40 μm in diameter and 1-4 mm in length. Water flow in tracheids of a piece of a pine branch was studied by means of D₂O/H₂O contrast obtained with MRI at 1.5 T. D₂O flowing through the object caused reduction of signal when ₁H detection was used. Observed flow velocity in the compression wood was about one-third of that in the tension wood, the former having a smaller average cell lumen size than the latter. After the signal in the entire cross section was reduced to its minimum, the experiment was renewed with distilled H₂O. Flow of the H₂O and hence replacement of D₂O through the wood resulted in the return of the signal. This study demonstrates the dependence of the flow velocity on the cell lumen size. The results suggest that D₂O/H₂O contrast obtained with MRI is an effective tool for studies of water dynamics within heterogeneous systems. © 2001 Academic Press.