Spatially resolved NMR

In a factory environment NMR instrumentation needs to be robust and possibly mobile for quality and process control at different stages of product development, fabrication, 

The NMR-MOUSE is a portable NMR sensor which works in highly inhomogeneous magnetic fields. Because of field inhomogeneity NMR spectroscopy of the chemical shift is not readily possible, but relaxation times and parameters of translational motion can be measured by echo techniques. These are the most important NMR parameters which are exploited for contrast in imaging. Unless fluids are investigated field inhomogeneities are essentially no obstacle for relaxation analysis [80], because molecular motion by translational diffusion is absent. 

In elastomer samples with macroscopic segmental orientation, the residual dipolar couplings are oriented as well, so that also the transverse relaxation decay depends on orientation. Therefore, the relaxation rate 1/T2 of a strained rubber band exhibits an orientation dependence, which is characteristic of the orientational distribution function of the residual dipolar interactions in the network. For perfect order the orientation dependence is determined by the square of the second Legendre polynomial [14]. Nearly perfect molecular order has been observed in porcine tendon by the orientation dependence of 1/T2 [77]. It can be concluded, that the NMR-MOUSE appears suitable to discriminate effects of macroscopic molecular order from effects of temperature and cross-link density by the orientation dependence of T2. 

The sensitive volume, which can be investigated by a circular surface coil in a homogeneous polarizing field, is approximately given by a half sphere with the coil radius. As the coil radius is typically small compared to the largest dimension of the object, the use of surface-coil techniques is restricted to volume elements near the sample surface. 

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The slice selection procedure can be combined with a number of pulse sequences to spatially resolve NMR parameters or to contrast the profiles with a variety of filters. The most commonly used acquisition schemes implemented to sample echo train decays are the CPMG [(jt/2)0—(Jt)90] or a multi-solid echo sequence [(jt/ 2)0-(jt/2)9o]. In these instances, the complete echo train can be fitted to determine... 

Fig. 5.4.7 (a-c, e) Spatially resolved NMR spectra detected during AMS hydrogenation in a catalyst bed of 1-mm beads. Each spectrum corresponds to a voxel size of 2 x 0.17 x 0.33 mm3. Spectra in (a-c) correspond to the same radial position within the operating reactor and are detected in the top, middle and bottom parts of the reactor, respectively. Three spectra in (b, e) correspond to the same vertical position in the operating reactor, with the two spectra in (e) corresponding to voxels shifted by 1.3 mm to ether side of the voxel of the spectrum in (b). The two spectra in (e) are shifted vertically relative to each other for better presentation. The lower traces with narrow lines in (d, f) are experimental spectra detected for bulk neat AMS (d) and cumene (f), the upper traces in (d, f) were obtained by mathematically broadening the lines to 300 Hz. 

ANTIFERROMAGNETIC VORTEX CORE IN HTSC STUDIED BY SPATIALLY-RESOLVED NMR... 

Abstract Spatially-resolved NMR is used to probe antiferromagnetism in the vortex state of nearly optimally doped high-rc cuprate H2Ba2CuC>6+a (Tc = 85 K). The broadened 205Tl-spectra below 20 K and the temperature dependence of the enhanced nuclear spin-lattice relaxation rate 205 Tfl at the vortex core region indicate clear evidences of the antiferromagnetic order inside the vortex core ofTl2Ba2Cu06+J. 

Antiferromagnetic Vortex Core in HTSC Studied by Spatially-Resolved NMR 63... 

Surface coils (cf. Section 9.2) Ackl, Bosl J are applied to the object from one side so that the associated B field is inhomogeneous within the sensitive volume. Apart from symmetry, semitoroidal coils offer particular advantages in spatially resolved NMR. A semitoroidal coil is a solenoid which is bent into a semicircular arc, and the rf field... 

Sucrose is a key carbohydrate in plant metaholism. The concentration of. sucrose in space and time is an important parameter in plant growth and morphogenesis, which can be determined by spatially resolved NMR [Metl, TselJ. The sucrose distribution, for example, has been examined quantitatively in Ricinus communis seedlings Metl ]. Until now, information on the sucrose concentration in the phloem has been obtained only by several destructive methods. They all require the opening of the sieve tubes, which in turn may modify the water flow in the plant, so that it cannot be knowm whether or not... 

Spatially resolved NMR is concerned with unraveling the spatial distribution of Mo(x, y, z) and measuring associated NMR parameters at individual volume cells , or voxels at space coordinates r = (x, y, z) - If many contingent voxels are investigated on a plane, or if a projection is investigated, one refers to NMR imaging-, if individual voxels are investigated one refers to volume-selective NMR. 

Neither solution nor solid-state NMR techniques give spatial information on a sample. Basic principles and theory of spatially resolved NMR, called MR imaging or tomography, can be found in [1], [2], [3], [4], [5], we will give here only brief comments on measurement methods. 

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