Visualization of tensor fields using superquadric glyphs (original) (raw)
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Journal of Cardiovascular Magnetic Resonance, 2015
Background: Cardiovascular magnetic resonance (CMR) can through the two methods 3D FLASH and diffusion tensor imaging (DTI) give complementary information on the local orientations of cardiomyocytes and their laminar arrays. Methods: Eight explanted rat hearts were perfused with Gd-DTPA contrast agent and fixative and imaged in a 9.4T magnet by two types of acquisition: 3D fast low angle shot (FLASH) imaging, voxels 50 × 50 × 50 μm, and 3D spin echo DTI with monopolar diffusion gradients of 3.6 ms duration at 11.5 ms separation, voxels 200 × 200 × 200 μm. The sensitivity of each approach to imaging parameters was explored. Results: The FLASH data showed laminar alignments of voxels with high signal, in keeping with the presumed predominance of contrast in the interstices between sheetlets. It was analysed, using structure-tensor (ST) analysis, to determine the most (v 1 ST
Ultrasound elastic tensor imaging: comparison with MR diffusion tensor imaging in the myocardium
Physics in Medicine and Biology, 2012
We have previously proven the feasibility of ultrasound-based shear wave imaging (SWI) to non-invasively characterize myocardial fiber orientation in both in vitro porcine and in vivo ovine hearts. The SWI-estimated results were in good correlation with histology. In this study, we proposed a new and robust fiber angle estimation method through a tensor-based approach for SWI, coined together as elastic tensor imaging (ETI), and compared it with magnetic resonance diffusion tensor imaging (DTI), a current gold standard and extensively reported non-invasive imaging technique for mapping fiber architecture. Fresh porcine (n = 5) and ovine (n = 5) myocardial samples (20 × 20 × 30 mm 3 ) were studied. ETI was firstly performed to generate shear waves and to acquire the wave events at ultrafast frame rate (8000 fps). A 2.8 MHz phased array probe (pitch = 0.28 mm), connected to a prototype ultrasound scanner, was mounted on a customized MRI-compatible rotation device, which allowed both the rotation of the probe from −90 • to 90 • at 5 • increments and co-registration between two imaging modalities. Transmural shear wave speed at all propagation directions realized was firstly estimated. The fiber angles were determined from the shear wave speed map using the least-squares method and eigen decomposition. The test myocardial sample together with the rotation device was then placed inside a 7T MRI scanner. Diffusion was encoded in six directions. A total of 270 diffusion-weighted images (b = 1000 s mm −2 , FOV = 30 mm, matrix size = 60 × 64, TR = 6 s, TE = 19 ms, 24 averages) and 45 B 0 images were acquired in 14 h 30 min. The fiber structure was analyzed by the fiber-tracking module in software, MedINRIA. The fiber orientation in the overlapped myocardial region which both ETI and DTI accessed was therefore compared, thanks to the co-registered imaging system. Results from all ten samples showed good correlation 4
Ex vivo 3D diffusion tensor imaging and quantification of cardiac laminar structure
Magnetic Resonance in Medicine, 2005
A three-dimensional (3D) diffusion-weighted imaging (DWI) method for measuring cardiac fiber structure at high spatial resolution is presented. The method was applied to the ex vivo reconstruction of the fiber architecture of seven canine hearts. A novel hypothesis-testing method was developed and used to show that distinct populations of secondary and tertiary eigenvalues may be distinguished at reasonable confidence levels (P ≤ 0.01) within the canine ventricle. Fiber inclination and sheet angles are reported as a function of transmural depth through the anterior, lateral, and posterior left ventricle (LV) free wall. Within anisotropic regions, two consistent and dominant orientations were identified, supporting published results from histological studies and providing strong evidence that the tertiary eigenvector of the diffusion tensor (DT) defines the sheet normal.
IEEE Transactions on Medical Imaging, 2000
We propose a unified computational framework to build a statistical atlas of the cardiac fiber architecture from diffusion tensor magnetic resonance images (DT-MRIs). We apply this framework to a small database of nine ex vivo canine hearts. An average cardiac fiber architecture and a measure of its variability are computed based on most recent advances in diffusion tensor statistics. This statistical analysis confirms the already established good stability of the fiber orientations and a higher variability of the laminar sheet orientations within a given species. The statistical comparison between the canine atlas and a standard human cardiac DT-MRI shows a better stability of the fiber orientations than their laminar sheet orientations between the two species. The proposed computational framework can be applied to larger databases of cardiac DT-MRIs from various species to better establish intra-and inter-species statistics on the anatomical structure of cardiac fibers. This information will be useful to guide the adjustment of average fiber models onto specific patients from in vivo anatomical imaging modalities.
Journal of cardiovascular magnetic resonance : official journal of the Society for Cardiovascular Magnetic Resonance, 2014
The complex cardiac fiber structural organization and spatial arrangement of cardiomyocytes in laminar sheetlets contributes greatly to cardiac functional and contractile ejection patterns. This study presents the first comprehensive, ultra-high resolution, fully quantitative statistical tensor map of the fixed murine heart at isotropic resolution of 43 μm using diffusion tensor (DT) cardiovascular magnetic resonance (CMR). Imaging was completed in approximately 12 hours using a six-directional encoding scheme, in five ex vivo healthy C57BL/6 mouse hearts. The tensor map constructed from this data provides an average description of the murine fiber architecture visualized with fiber tractography, and its population variability, using the latest advances in image tensor analysis and statistics. Results show that non-normalized cardiac tensor maps are associated with mean fractional anisotropy of 0.25 ± 0.07 and mean diffusivity of 8.9 ± 1.6 × 10-4 mm2/s. Moreover, average mid-ventric...
Mohr diagram representation of anisotropic diffusion tensor in MRI
Magnetic Resonance in Medicine, 2002
With current approaches, it is difficult to visually comprehend the complete information contained in a diffusion tensor (DT) measured from a microscopically heterogeneous biological tissue. Therefore, in this work the Mohr diagram is introduced to graphically display the key aspects of DTs and to interpret the underlying anisotropy, both qualitatively and quantitatively. Specifically, the mathematical basis for the construction of the Mohr diagram from the elements of DTs is described, the merits of the approach are illustrated with examples of DTs reported for various biological tissues, and the results are discussed in the context of relating the diffusion anisotropy to the tissue structures. Magn Reson Med 47:823–827, 2002. © 2002 Wiley-Liss, Inc.
NMR in Biomedicine, 2019
Diffusion tensor imaging has been used for assessing the orientation of cardiac myocytes for decades. Striking methodological differences exist between studies when quantifying these orientations. This limits the comparability between studies, and impedes collaboration and the drawing of appropriate physiological conclusions. We have sought to elucidate these differences, permitting us to propose a standardised “tool set” that might better establish consensus in future studies.We fixed hearts from seven 25 kg pigs in formalin, and scanned them using diffusion tensor imaging. Using various angle definitions as found in literature, we assessed the orientations of cardiomyocytes, comparing them in terms of helical and intrusion angles, along with the orientation of their aggregations. The difference between assessment of the helical angle with and without relation to the epicardial curvature was 25.2° (SD: 7.9) at the base, 5.8° (1.9) at the equatorial level, and 28.0° (7.0) at the ape...
Towards a High-quality Visualization of Higher-order Reynold’s Glyphs for Diffusion Tensor Imaging
Mathematics and Visualization, 2012
Recent developments in magnetic resonance imaging (MRI) have shown that displaying second-order tensor information reconstructed from diffusion-weighted MRI does not display the full structure information acquired by the scanner. Therefore, higher-order methods have been developed. Besides the visualization of derived structures such as fiber tracts or tractography (directly related to stream lines in fluid flow data sets), an extension of Reynold's glyph for second-order tensor fields is widely used to display local information. At the same time, fourth-order data becomes increasingly important in engineering as novel models focus on the change in materials under repeated application of stresses. Due to the complex structure of the glyph, a proper discrete geometrical approximation, e.g., a tessellation using triangles or quadrilaterals, requires the generation of many such primitives and, therefore, is not suitable for interactive exploration. It has previously been shown that those glyphs defined in spherical harmonic coordinates can be rendered using hardware acceleration. We show how tensor data can be rendered efficiently using a similar algorithm and demonstrate and discuss the use of alternative high-accuracy rendering algorithms.
Progress in Biophysics and Molecular Biology, 2014
Diffusion tensor magnetic resonance imaging (MRI) reveals valuable insights into tissue histo-anatomy and microstructure, and has steadily gained traction in the cardiac community. Its wider use in small animal cardiac imaging in vivo has been constrained by its extreme sensitivity to motion, exaggerated by the high heart rates usually seen in rodents. Imaging of the isolated heart eliminates respiratory motion and, if conducted on arrested hearts, cardiac pulsation. This serves as an important intermediate step for basic and translational studies. However, investigating the micro-structural basis of cardiac deformation in the same heart requires observations in different deformation states.