Imaging spin-density

Once the job is completed, the UniChem GUI can be used to visualize results. It can be used to visualize common three-dimensional properties, such as electron density, orbital densities, electrostatic potentials, and spin density. It supports both the visualization of three-dimensional surfaces and colorized or contoured two-dimensional planes. There is a lot of control over colors, rendering quality, and the like. The final image can be printed or saved in several file formats. 

Just as we obtain the spin density distribution q(i), and hence the projection of the investigated object, in phase encoded imaging, we can reconstruct P(R, A) by... 

Under such circumstances, spin density diffusometry turned out to be more favorable. We are not discussing solvent intrusion experiments with solid-like materials, as they are typically carried out with the aid of stray field imaging [24]. 

Fig. 3.3.8 Two-dimensional cross section through the fixed-bed reactor (upper) and radial spin-density distribution obtained from the images (lower) for (a) spherical glass beads of 2 mm in diameter and (b) cylindrical pellets with average equivalent diameter of 2.2 mm.

Fig. 4.6.3 2D spin density images (a, c) and corresponding 2D velocity maps (b, d) along the cross section of miniaturized hemodialyzer modules of the type SMC and SPAN. The applied flow rate on the SMC module is... 

A practical ramification of this rule is utilized in segregation studies. The most obvious way to study segregation by NMR/MRI is to use two different types of beads, one that is NMR-visible and the other not. However, size segregation studies can be performed by simply using two different sizes of NMR-visible particles because they have different overall spin densities, for the reason stated above. Therefore, the image intensity will depend on the relative concentration of each particle in a voxel. 

Clearly by working with typical spatial resolutions of approximately 30-50 pm, individual pores within the material are not resolved. However, a wealth of information can be obtained even at this lower resolution (53,54,55). Typical data are shown in Fig. 20, which includes images or maps of spin density, nuclear spin-lattice relaxation time (Ti), and self-diffusivity of water within a porous catalyst support pellet. In-plane spatial resolution is 45 pm x 45 pm, and the image slice thickness is 0.3 mm. The spin-density map is a quantitative measure of the amount of water present within the porous pellet (i.e., it is a spatially resolved map of void volume). Estimates of overall pellet void volume obtained from the MR data agree to within 5% with those obtained by gravimetric analysis. 

Fig. 20. Spin density, and water diffusion images for a 2.2-inm-diameter, spherical silica catalyst support pellet. In-plane pixel resolution was 45 pm x 45 pm image slice thickness was 0.3 mm. (a) Spin-density map lighter shades indicate higher liquid content, (b) map (150 00 ms) lighter shades indicate longer values of Ti. (c) Diffusivity map ((0-1.5) x 10 m s ) lighter shades indicate higher values of water diffusivity within the pellet.

In an investigation of the spin-density (voidage) and spin-lattice relaxation time maps of many pellets, it was found that it was the heterogeneity in pore size, as characterized by the fractal dimension of the Ti map, that was consistent between images of pellets drawn from the same batch 58). The fractal dimensional of these images identifies a constant perimeter-area relationship for clusters of pixels of... 

---