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 he terogeneous systems by means of MRI and deuterium oxide (D2O)/water (H2O) c ontrast. In this demonstration a piece of a pine tree was used. In pine xyl em, water flows in tube-like dead cells, that is, tracheids, which are abou t 10-40 mum in diameter and 1-4 mm in length. Water how in tracheids of a p iece of a pine branch was studied by means of D2O-H2O contrast obtained wit h MRI at 1.5 T. D2O flowing through the object caused reduction of signal w hen H-1 detection was used. Observed how velocity in the compression wood w as 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 cr oss section was reduced to its minimum, the experiment was renewed with dis tilled H2O. Flow of the H2O and hence replacement of D2O through the wood r esulted 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 dy namics within heterogeneous systems. (C) 2001 Academic Press.