Quantitative magnetic resonance imaging (qMRI) is a versatile, non-destructive and non-invasive tool in life, material, and medical sciences. When multiple components contribute to the signal in a single pixel, however, it is difficult to quantify their individual contributions and characteristic parameters. Here we introduce the concept of phasor representation to qMRI to disentangle the signals from multiple components in imaging data. Plotting the phasors allowed for decomposition, unmixing, segmentation and quantification of our in vivo data from a plant stem, a human and mouse brain and a human prostate. In human brain images, we could identify 3 main T 2 components and 3 apparent diffusion coefficients; in human prostate 5 main contributing spectral shapes were distinguished. The presented phasor analysis is model-free, fast and accurate. Moreover, we also show that it works for undersampled data.Magnetic resonance imaging (MRI), like all other imaging modalities, thrive on our brains' ability to interpret images in a very efficient way. This, in combination with experimentally encoding the magnetic resonance signal as a function of a wide range of material or tissue properties, explains the success of MRI in many disciplines of science and medicine, since its invention in the seventies 1, 2 .A major benefit of MRI compared to other imaging modalities is that it provides excellent soft-tissue contrast over large anatomical areas, and additionally provides quantitative information on a number of magnetic resonance (MR) related parameters [3][4][5][6] . In quantitative MRI (qMRI), signals are not only encoded for space to construct an image, but also non-spatially to derive these quantitative parameters. The non-spatial information can consist of signal attenuation as a function of (i) inversion or saturation recovery time for longitudinal relaxation time T 1 , (ii) spin-echo time for transverse relaxation time T 2 , (iii) the b-value for diffusion mapping, or (iv) chemical shift information of different metabolites in an NMR spectrum 7 . These parameters depend on the local environment of the observed nucleus and enable for example the use of water as an intrinsic probe molecule.In MRI, the signal from each data pixel can consist of an unknown number of different components. There is an increasing demand to retrieve quantitative information about the sub-pixel composition. In practice, however, this is often challenging because for in vivo studies on small animals or tissues at high spatial resolution the signal-to-noise ratio (SNR) is typically low, while clinical applications on humans at 1.5 and 3 Tesla are limited by total examination time and the maximum allowed deposition of radiofrequency power with the MR pulse sequence (the specific absorption rate limit, SAR). Common approaches to extract the quantitative parameters from the images are e.g. to fit multi-exponential decays or perform principle component analysis on spectra. It is often questionable whether there is sufficient SNR available to perfo...
Some of the most striking features of Rhizophoraceae mangrove saplings are their voluminous cylinder-shaped hypocotyls and thickened leaves. The hypocotyls are known to serve as floats during seed dispersal (hydrochory) and store nutrients that allow the seedling to root and settle. In this study we investigate to what degree the hypocotyls and leaves can serve as water reservoirs once seedlings have settled, helping the plant to buffer the rapid water potential changes that are typical for the mangrove environment. We exposed saplings of two Rhizophoraceae species to three levels of salinity (15, 30, and 0–5‰, in that sequence) while non-invasively monitoring changes in hypocotyl and leaf water content by means of mobile NMR sensors. As a proxy for water content, changes in hypocotyl diameter and leaf thickness were monitored by means of dendrometers. Hypocotyl diameter variations were also monitored in the field on a Rhizophora species. The saplings were able to buffer rapid rhizosphere salinity changes using water stored in hypocotyls and leaves, but the largest water storage capacity was found in the leaves. We conclude that in Rhizophora and Bruguiera the hypocotyl offers the bulk of water buffering capacity during the dispersal phase and directly after settlement when only few leaves are present. As saplings develop more leaves, the significance of the leaves as a water storage organ becomes larger than that of the hypocotyl.
Controlling self-assembly processes is of great interest in various fields where multifunctional and tunable materials are designed. We here present the versatility of lanthanide-complex-based micelles (Ln-C3Ms) with tunable coordination structures and corresponding functions (e.g. luminescence and magnetic relaxation enhancement). Micelles are prepared by charge-driven self-assembly of a polycationic-neutral diblock copolymer and anionic coordination complexes formed by Ln(III) ions and the bis-ligand L2EO4, which contains two dipicolinic acid (DPA) ligand groups (L) connected by a tetra-ethylene oxide spacer (EO4). By varying the DPA/Ln ratio, micelles are obtained with similar size but with different stability, different aggregation numbers and different oligomeric and polymeric lanthanide(III) coordination structures in the core. Electron microscopy, light scattering, luminescence spectroscopy and magnetic resonance relaxation experiments provide an unprecedented detailed insight into the core structures of such micelles. Concomitantly, the self-assembly is controlled such that tunable luminescence or magnetic relaxation with Eu-C3Ms, respectively, Gd-C3Ms is achieved, showing potential for applications, e.g. as contrast agents in (pre)clinical imaging. Considering the various lanthanide(III) ions have unique electron configurations with specific physical chemical properties, yet very similar coordination chemistry, the generality of the current coordination-structure based micellar design shows great promise for development of new materials such as, e.g., hypermodal agents.
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