Quantitative T2 imaging of plant tissues by means of multi-echo MRI microscopy.

A method for quantitative T2 imaging is presented which covers the large range of T2 values in plants (5 to 2000 ms) simultaneously. The transverse relaxation is characterized by phase-sensitive measurement of many echo images in a multi-echo magnetic resonance imaging sequence. Up to 1000 signal-containing echo images can be measured with an inter-echo time of 2.5 ms at 0.47 T. Separate images of water density and of T2 are obtained. Results on test samples, on the cherry tomato and on the stem of giant hogweed are presented. The effects of field strength, spatial resolution and echo time on the observed T2 values is discussed. The combination of a relatively low magnetic field strength, short echo time and medium pixel resolution results in excellent T2 contrast and in images hardly affected by susceptibility artifacts. The characterization of transverse relaxation by multi-echo image acquisition opens a new route for studies of water balance in plants.