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| Hauptseite > Publikationsdatenbank > Engineering for mobility and ease of use: small-scale devices for NMR sensing and NMR imaging of plants in the field |
| Hauptseite > Publikationsdatenbank > Engineering for mobility and ease of use: small-scale devices for NMR sensing and NMR imaging of plants in the field |
| Conference Presentation (After Call) | FZJ-2024-06307 |
2024
Abstract: In this contribution we present the development of mobile NMR sensors and MR imagers for measuring plants in the field. A prerequisite for the systems whas that they be based on permanent magnets, to minimize power consumption, and that the air gap should be wide and freely accessible. This should allow measurements of branches and stems of field grown plants, but also allow objects such as leaves and cereal spikes to be illuminated inside the magnet. An open C-shaped magnet design was chosen, a type of magnet that can be both affordable and easy to build. To permit operation under variable environmental conditions, both temperature stable and temperature stabilized versions were constructed. In order to maximize space for plants, pole gap width of the magnet and resilience against handling were prioritized over homogeneity and field strength. For the imagers, to overcome the adverse effects of short T2* that may result from these design choices, multi-spin echo imaging strategies were employed with short echo times and high spectral widths [1]. To achieve microscopic resolution under these constraints requires fast switching field gradients, driven by strong and fast gradient amplifiers. While small-scale spectrometers and RF amplifiers are readily available, appropriate small-scale gradient amplifiers or designs thereof currently are not. We therefore constructed a small, 3-channel gradient amplifier on the basis of a conventional current-controlled AB amplifier design. Tailored to small low-impedance gradient coils the amplifiers could remain small, suitable for battery driven operation and still meet our requirements regarding switching speed, power and duty cycle. The finished gradient amplifier weighed 5 kg and was capable of delivering 40 A gradient pulses of up to 6 ms in duration, sufficient for micro imaging and flow mapping. With all components built onto an aluminum hand trolley, the entire imaging setup weighed 45 kg and was small enough to fit into a car [2]. For an MR imager such a system already is small, mobile and relatively low in complexity. However, without imaging and tailored for use as a time domain NMR (TD-NMR) relaxometer, such systems can become simpler, smaller and more affordable still. The limiting factor then becomes the design of the TD-NMR experiment and the subsequent data analysis. Key is to tailor the method for a single, well-defined application: this way TD-NMR can become simple and fast, and suitable for non-expert operators with minimal training. An example of this approach is the Solid-Fat Content determination, currently the gold standard method to determine the ratio between liquid oil and solid fat in mixtures, or to measure moisture or lipid contents in dry seeds [3]. For living plant tissues we developed a similarly simplified TD-NMR method, to estimate total proton density (linearly correlated to fresh weight) and solid proton density (linearly correlated to solid matter content) in samples with a moisture content of between 15 and 100% [4]. For further details on this method also see Woertche et al, this abstract book. Mobile relaxometry, in this manner, becomes a valuable tool to non-invasively monitor plant water content as a function of drought, or to characterize dry matter accumulation (yield development) in grain crops.
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