| 1. |
- Görke, U, et al.
(författare)
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Visualization of anisotropic pulsations in extraembryonic compartments of incubated quail eggs by NMR microimaging.
- 1996
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Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 14:9, s. 1079-84
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Tidskriftsartikel (refereegranskat)abstract
- Multi-plane tagging time-of-flight and bipolar gradient phase-encoding and amplitude-weighting NMR microimaging techniques have been employed to study transport in extraembryonic compartments of fertilized quail eggs during the first seven days of incubation. After the fourth day coherent and incoherent motions became visible in certain regions, in particular in the upper part of the albumen. Coherent motions as visualized by deformations of multiplane tagging grids were specified by local velocities less than 1 mm/s at most. On the other hand, incoherent motions led to much more pronounced phenomena. The multiplane tagging grid completely faded in a region comprising the upper third of the albumen after 4.5 incubation days. Images weighted by signal attenuation owing to incoherent displacements indicate motions in the same region. The fact that a reproducible localization of the motions is only possible when signals from different transients are averaged indicates that the incoherence at least partly is temporal in nature. The signal intensity of a volume selected in the incoherent-motion region consequently fluctuates with time. The Fourier analysis of these fluctuations revealed a distinct pulsation with a frequency of 0.4 Hz.
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| 2. |
- Müller, H P, et al.
(författare)
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Six-dimensional spin density/velocity NMR microscopy of percolation clusters.
- 1996
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Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 14:7-8, s. 955-8
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Tidskriftsartikel (refereegranskat)abstract
- Using computer-simulated random-site percolation networks as templates, three-dimensional percolation cluster objects were fabricated. The pore space was filled with water and experimentally investigated with the aid of NMR microimaging. A pulse sequence for six-dimensional spin density/velocity NMR imaging was employed for the combined record of the three-dimensional spin-density distribution and the three-dimensional velocity vector field of water percolating through the pore space. An evaluation procedure for the NMR image data was established that reliably renders the characteristic parameters (fractal dimensionality, fractal dimensionality of the backbone, correlation length).
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| 3. |
- Weis, Jan, et al.
(författare)
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NMR imaging of thermal convection patterns
- 1996
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Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 14:3, s. 319-327
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Tidskriftsartikel (refereegranskat)abstract
- Two special magnetic resonance imaging techniques were applied to the Rayleigh/Bénard problem of thermal convection for the first time. The methods were tested using a water cell with horizontal bottom and top covers kept at different temperatures with a downward gradient. Using Fourier encoding velocity imaging (FEVI) a five-dimensional image data set was recorded referring to two space dimensions of slice-selective images and all three components of the local velocity vector. On this basis, the fields of the velocity components or of the velocity magnitude were evaluated quantitatively and rendered as gray shade images. Furthermore the convection rolls were visualized with the aid of two- or three-dimensional multistripe/multiplane tagging imaging pulse sequences based on two or three DANTE combs for the space directions to be probed. Movies illustrating the fluid motions by convection in all three space dimensions were produced. It is demonstrated that the full spatial information of the convection rolls is accessible with microscopic resolution of typically 100 x 100 x 100 microns3. This resolution is effectively limited by flow displacements in the echo time, which should be well within the voxel dimension. The main perspective of this work is that the combined application of FEVI and multistripe/multiplane tagging imaging permits quantitative examinations of thermal convection for arbitrary boundary conditions and with imposed through-flow apart from the direct visualization of convective flow in the form of movies.
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| 4. |
- Weis, J, et al.
(författare)
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Susceptibility, field inhomogeneity, and chemical shift-corrected NMR microscopy : application to the human finger in vivo
- 1996
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Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 14:10, s. 1165-1175
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Tidskriftsartikel (refereegranskat)abstract
- Spectroscopic proton image data recorded with the aid of a gradient-echo spectroscopic imaging pulse sequence are reported. A postdetection processing method is suggested which permits correction of artifacts due to inhomogeneity, susceptibility, and chemical-shift resonance offsets. That is, apart from the spectral information available in this way, better spatial resolutions can be achieved. The method is demonstrated by resonance-offset corrected images of the human finger in vivo. Moreover, resonance-line selective and spectroscopically resolved diffusion-weighted images and diffusivity maps rendered with the aid of the same postdetection procedure are shown.
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