| 1. |
- Hänni, Mari, et al.
(författare)
-
Quantitation of atherosclerosis by magnetic resonance imaging and 3-D morphology operators
- 1999
-
Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 17:4, s. 585-591
-
Tidskriftsartikel (refereegranskat)abstract
- The objective was to ascertain whether MRI and image processing can be used to quantify atherosclerosis by measuring wall thickness in rabbit aorta. The abdominal aortas of 2 healthy and 5 atherosclerotic rabbits were examined with a gradient-echo inflow angiography sequence (2DI) and a proton density weighted turbo-spin-echo sequence (PDW). Using thresholding by four observers and 3D morphology operators, segmentation of the artery and vein lumina was performed from the 2DI sequence, and of surrounding fat and muscle from the PDW sequence. Remaining voxels adjacent to the aortic lumen were classified as vessel wall. By measuring the vessel wall volume and the lumen volume, the wall percentage was calculated. The values were significantly higher for the diseased animals than for unaffected individuals (p < 0.01). It is concluded that aortic wall thickening in atherosclerotic rabbits can be measured quantitatively by using MRI combined with 3D morphology image processing operators.
|
|
| 2. |
- Weis, Jan, et al.
(författare)
-
Characterization of human head vasculature by percolation parameters
- 1999
-
Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 17:3, s. 411-415
-
Tidskriftsartikel (refereegranskat)abstract
- A data reduction procedure, originally proposed for characterization of fractals and random percolation clusters, has been used to evaluate the vascular system of the human head. The motivation behind this study arose from the wish to study empirically transport properties of vascular systems and to find a suitable formalism for their description. MR angiographic data acquired by a standard 3D inflow method were used. The evaluated parameters refer to the backbone fractal dimensionality and the correlation length. The fractal dimensionality of the backbone was found to be 1.71 for the human head vasculature. This value fits the theoretical range of random percolation networks. It is concluded that concepts of percolation theory might have some value for characterizing the structure and transport properties of the vascular system.
|
|
| 3. |
- Weis, J, et al.
(författare)
-
Susceptibility, field inhomogeneity, and chemical shift-corrected NMR microscopy : application to the human finger in vivo
- 1996
-
Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 14:10, s. 1165-1175
-
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.
|
|
| 4. |
|
|
| 5. |
- Görke, U, et al.
(författare)
-
Visualization of anisotropic pulsations in extraembryonic compartments of incubated quail eggs by NMR microimaging.
- 1996
-
Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 14:9, s. 1079-84
-
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.
|
|
| 6. |
|
|
| 7. |
- Müller, H P, et al.
(författare)
-
Six-dimensional spin density/velocity NMR microscopy of percolation clusters.
- 1996
-
Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 14:7-8, s. 955-8
-
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).
|
|
| 8. |
|
|
| 9. |
- Weis, J, et al.
(författare)
-
Characterization of human head vasculature byprelocation parameters
- 1999
-
Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 17:3, s. 411-415
-
Tidskriftsartikel (refereegranskat)abstract
- A data reduction procedure, originally proposed for characterization of fractals and random percolation clusters, has been used to evaluate the vascular system of the human head. The motivation behind this study arose from the wish to study empirically transport properties of vascular systems and to find a suitable formalism for their description. MR angiographic data acquired by a standard 3D inflow method were used. The evaluated parameters refer to the backbone fractal dimensionality and the correlation length. The fractal dimensionality of the backbone was found to be 1.71 for the human head vasculature. This value fits the theoretical range of random percolation networks. It is concluded that concepts of percolation theory might have some value for characterizing the structure and transport properties of the vascular system.
|
|
| 10. |
- Weis, J, et al.
(författare)
-
Chemical shift artifact-free imaging : a new option in MRI?
- 1998
-
Ingår i: Magnetic Resonance Imaging. - 0730-725X .- 1873-5894. ; 16:7, s. 839-44
-
Tidskriftsartikel (refereegranskat)abstract
- A high-speed proton spectroscopic imaging method with high spatial resolution was used for obtaining water, fat, and chemical shift artifact-free images on a 1.5 T MR scanner. The technique is based on a fast radiofrequency (RF) spoiled gradient-echo sequence. The chemical shift information is encoded by incrementing the echo time in a series of image records. Suppression of water or fat signals is not used. The technique does not require a highly homogeneous magnetic field. Spectroscopic images of a human volunteer were compared with corresponding conventional images obtained using the short inversion time inversion recovery (STIR) and the selective partial inversion recovery (SPIR) methods. The results demonstrate that it is possible to produce images entirely free from chemical shift artifacts using only a few chemical shift encoding steps. The technique also produces pure water and fat images which are significantly better than those produced by using the conventional methods STIR and selective partial inversion recovery. The described method appears to be promising for routine clinical applications because it can be fully automated.
|
|
