Abstract
The further development and demonstration of a unique, transportable magnetic resonance imaging system, the Tree Hugger, [1, 2] is presented. The work is divided into four sections. The first is the commissioning of the magnet for use in-situ in a forest environment. Technical improvements, including the replacement of the receiver multiplexer A/4 cable by a passive circuit; an active shim of the magnet; and the design and build of new gradient amplifiers, lead to increased portability of the system, improved homogeneity of the magnet and overall to a doubling of the signal to noise ratio of measured signals. Second, the feasibility of imaging living trees in the forest using the Tree Hugger is demonstrated. The first extended in-situ magnetic resonance imaging study of a living tree over a growing season is reported. Correlations are drawn between nuclear magnetic resonance measurements and other indicators such as relative humidity, soil moisture and net solar radiation. The third part of the work is a study of water self-diffusion in a living tree in-situ and in felled timber made using the Tree Hugger. Analysis of the acquired echo attenuation data reveal mean cell radii of 12.4 μm in the horizontal orientation in a living tree and 11.9 μm and 12.2 μm in the tangential and radial directions in felled timber respectively. Finally, an investigation into the drying of felled sitka spruce is presented. A probe is developed to make measurements at elevated temperatures inside the magnet. Analysis of ID nuclear magnetic resonance profiles of the timber during drying yield temperature dependent effective diffusion coefficients for the water in wood along the three orthogonal axes. Activation energies for water diffusion of 33.4 (±0.9) kJ/mol, 58.6 (±3.5) kJ/mol and 44.7 (±1.5) were calculated for the longitudinal, radial and tangential orientations in felled timber respectively.