A low-field Magnetic Resonance Imaging (MRI) technique was used for noninvasive studies of the internal structure of three types of wood, using water and He-3 gas as contrast agents. In the conditions of steady state water flow through the sample, the fluid flow pathways were found to be mainly located in the late wood. A substantial increase in sensitivity, or equivalently, a decrease in experiment time was demonstrated, when the hyperpolarized He-3 gas was used. The method opens new opportunities of studying a wide range of similar biologically permeable materials in a nondestructive way. (C) 2015 Elsevier Ltd. All rights reserved.