The strategy for the seed selection in the reconstructions of lower resolution in the scale-space was to scale these values in proportion to the downscaling Points for Ventricular Tractography Reconstruction. Although our simplified models provide easier interpretation of global trends, they are still too complex for summarizing complex structures such as the Torrent-Guasp HVMB. For a successful tractography reconstruction, DT-MRI vector fields should be reoriented.
Output analysis of our tractographic representations showed exact correlation with low-level details of myocardial architecture, but also with the more abstract conceptualization of a continuous helical ventricular myocardial fiber nclusions. We sought to deepen this knowledge through advanced computer graphical representations of the myocardial fiber architecture by diffusion tensor magnetic resonance thods. With fewer streamlines than on the previous captures, Figure 9 shows 3 populations where in this area streams coming from the apex start a noticeable ascent (fading from green to red coloration of the streams, denoting an increased slope) below the two other populations that are the beginning of the right segment at its connection with the pulmonary mplified Tractography. However, on DT-MRI data the vectors can be considered bidirectional because the water diffusion represented by this eigenvector occurs in one dimension but it does so on both possible orientations at the same time. The DT-MRI technique provides trustworthy and detailed information of myocardial tissue. The main property that clearly defines a streamline is that it is a curve tangential to the vector field at any point of such curve. My gfs roomate is thick af.org. It was also necessary to define a method that ensures a correct use of streamlining techniques to the particularities of the DT-MRI vector fields. El análisis objetivo de la arquitectura miocárdica mediante un método automatizado que incluye el miocardio completo y utiliza diferentes niveles de complejidad tridimensional revela una organización de las fibras en forma de estructura helicoidal continua que conforma ambos ventrículos. Sometimes the datasets will have a nearly organized structure, but we can also get opposed orientations (Fig.
These "summaries" are statistically complete so that the Gaussian smoothing keeps the contextual information before applying downsampling. The problem in the studies of ventricular models is that unlike skeletal muscles, myocardial tissue is locally arranged in a discrete mesh of branching myocytes. Figure 10 shows 4 tracts of simplified models reconstructed from manually picked seeds located at basal level near the pulmonary artery. There is a clear similarity between the HVMB schematic model (Fig. To minimize this artifact, our streamlining method stops integration of streams with a large Runge-Kutta estimated reconstruction error. During the last decade, a new imaging modality, diffusion tensor magnetic resonance imaging (DT-MRI), has enabled computational validation of the muscular structure of the heart. Noise on the streamline reconstruction is mainly caused by thin atrial tissue, which introduces significant clutter on the visualization. Datasets used in this study come from the public database of the Johns Hopkins University. My gfs roomate is thick af ... hp. 11, left) and reconstructed paths (Fig. Therefore, at every axial cut of the DT-MRI we reorganize vector orientations in a stream-like fashion (Fig. For studies requiring Q-ball analysis it is mandatory to use not less than 60 directions per voxel. We will extrapolate this everyday behavior to our problem. We also introduced a novel multiscale visualization technique in order to obtain a simplified tractography.
Deeper understanding of the myocardial structure linking the morphology and function of the heart would unravel crucial knowledge for medical and surgical clinical procedures and studies. In comparison with the full-scale tractography shown in Figure 2, the simplified one keeps the main geometric features of fibers. En el análisis de las tractografías de todo el espectro multiescalar, encontramos una correlación exacta en los detalles de bajo nivel, así como de la conceptualización abstracta de la disposición helicoidal continua de las fibras miocárdicas que conforman la arquitectura nclusiones. DT-MRI Vector field orientation: tractography is a graphical representation inherited from fluid mechanics, where both direction and orientation of the vector fields are a meaningful part of the represented information. 22 These datasets were obtained from 4 normal canine hearts. We want to acknowledge Drs. Comparison between helical ventricular myocardial band scheme and a simplified ventricular tractography. Researchers have proposed at least 7 conceptual models 11 in attempts to accurately describe the architecture of the heart from dissection or histological procedures. 12, 13 and the helical ventricular myocardial band (HVMB) proposed by Torrent-Guasp, 14 and Torrent-Guasp et al.
Ventricular anatomy can be described by a longitudinal axis and angular coordinates with respect to this axis on axial cuts. 31 This technique applies a Gaussian filtering and later an exponential reduction via a subsampling of the full-scale texture. Helm and Raimond L. Winslow at the Center for Cardiovascular Bioinformatics and Modeling and Dr. Elliot McVeigh at the National Institute of Health for provision of DT-MRI datasets. This may help to generate simpler visualizations, which in turn may help to better understand the detailed myocardial architecture. Data completeness: it is undisputed that the basal ring is crucial to fully understand heart anatomy and function. The long axis of the hearts was aligned with the z-axis of the scanner. This methodology retains the main geometric features of the fiber tracts, making it easier to decipher the main properties of the architectural organization of the sults. We compared such tracts to the proposed HVMB (Fig. Furthermore, a recent study reports that the DTI primary eigenvector is invariant under a large variation of acquisition device parameters and, in particular, to a low number of diffusion directions. Heart tractography is seen as a reconstruction composed of several streamlines 28 (also known as fiber tracks in this field). The only agreement is the existence of a layered structure of the myocardium through tractographic representations and visualization improvements in color coding.
Esta metodología permite mantener las principales propiedades geométricas de las fibras y descifrar las principales propiedades de la organización arquitectónica del sultados. The goal of this procedure was to provide a comprehensive reconstruction that allows interpretation at first sight by any possible observer. 1B) around the point where the coordinate axis intersects the same axial cut. To simplify the backbone myocardial fiber spatial orientation, we explored the geometry of the heart by looking for long paths that can represent connected regions on the DT-MRI tractography. 18 This entangled structure is prone to hinder or even mislead the interpretation of "tracts" that define the muscular structure of the myocardium. In order to settle this disagreement we used all the DT-MRI data without segmentation to avoid instrumentalization of the study, and demonstrated that it is possible to reconstruct the whole myocardium including some complex structures such as the basal loop, unfortunately hidden or misinterpreted by other studies. 4) keeps the main geometric features of fibers, allowing an easier identification of overall trends.
Visualization: comprehensive visualization of fiber tracts should involve a proper assignment of colors providing information about the orientation of the myocardial fibers. The use of visualizations with single tracts changes the way in which this structure can be viewed. This structure continues to the apex and most of these streams continue on the right segment. This implementation allows fast reorientation, avoiding any smoothing of the vector field. Af, aberrant fibers; Ao, aorta; AS ascending segment; DS, descending segment; if, intraseptal fibers; LS, left segment; lt, left trigone; PA, pulmonary artery; ptc, pulmonary-tricuspid cord; rf, right septal fibers; RS, right segment; rt, right trigone. This muscle wraps the left ventricle and part of the right ventricle (right and left segments), connecting to a helicoidal structure starting at the basal ring going inside the left ventricle towards the apex and returning to connect with the aorta (descending and ascending segments), with this turn wrapping the entire anatomy of the heart. 20 DT-MRI has been established as the reference imaging modality for the measurement of the whole cardiac architecture with acceptable resolution (300 μm×300 μm×1000 μm) compared to the size of myocytes (50-100 μm long and 10-20 μm thick). These tracts loop at the basal ring toward the endocardium, describing what looks like a simple folding (Fig. We computed those streamlines using a fifth-order Runge-Kutta-Fehlbert 29 integration method that is able to provide successful results using variable integration steps based on error estimation. Figure 12 shows a full-resolution tractographic reconstruction of muscle fibers obtained using our software. Indeed, DT-MRI provides a summary of the microscopic mesh enhancing the preferred pathway of the connected myocytes, which constitutes the concept of myocardial fiber. To deal with higher-level interpretations of the architectural organization of the heart we also looked for higher-level representations that can ease its interpretation and validation.
To compare tractographic results with the band model, step-by-step tractographic reconstructions were compared with the myocardial fiber tracts depicted in the Torrent-Guasp rubber-silicone mould of the HVMB 32 (Figs. The analysis of this segment is more complex due to the cluttered view of several crossings of myocyte populations. Two of the most controversial approaches are the cardiac mesh model proposed by Anderson et al. The final dataset was arranged in about 256×256×108 arrays (depending on the scanned heart) and contains two kinds of data: geometry/scalar data and diffusion tensor data. This supports the Torrent-Guasp description of the HVMB. 15 The cardiac mesh model proposes that the myocytes are arranged longitudinally and radially, changing angulations along with myocardial depth and binding this architectural disposition to a functional one. 3, 4 It is also accepted that myocardium, as well as its fibers, may undergo architectural alterations in many heart diseases, 5, 6 leading to inefficient heart function. A clear pattern is observed where the reconstructed tracts on the epicardium are oriented towards the basal ring. To achieve a valid vector field for streamlining, this axis should define a center of rotation for each axial cut. También aportamos una nueva técnica de visualización multiescalar para obtener tractografías simplificadas. We observed that the tracts define a sample-wide coherent helical structure for all canine samples.
In both models the main segments (labeled from A to G) of the helical architecture are clearly identified. The use of these downscaled images is also common in other fields such as computer vision, where this operation can be seen as a computation on the scale space. Results show an unequivocal ventricular fiber connectivity describing a continuous muscular structure consisting of the two ventricles arranged in a double helical orientation. Therefore, it allows easier identification of global morphological SULTS. We have contributed a multiresolution method for tractography using downsampling of the DT-MRI volumes to show overall features of the heart structure. This technique can be applied to the DT-MRI dataset to simplify its complexity. However, interpretation of its outcome for heart architecture validation is indirect. Schematic presentation of the ventricular myocardial band dissection. To obtain more comprehensive descriptions of global myocardial structure, we propose a multiresolution approach applied to the standard tractographic algorithms.
The coloring indicates the sign of the fiber z-component (red for positive and green for negative) and, thus, its orientation. El objetivo de nuestro estudio es analizar objetivamente la arquitectura de las fibras miocárdicas mediante métodos avanzados de procesamiento gráfico por computadora aplicados a imágenes de resonancia magnética por tensor de difusión. In order to resolve this in a computer graphic representation it is common to use multiresolution models, which attempt to build different models of the same data with different levels of detail but without a loss of fidelity. 26 since, due to its level of detail, it has been widely discussed in the literature hinting at opposite readings. The HVMB model describes a longitudinal arrangement of ventricular myocardial fibers forming a unique functional muscleband (Fig. These seeds were randomly chosen from the entire anatomy, excluding only a very small range of points related to the lowest eigenvalues that are likely to be bad starting points for the reconstruction.
In this study, tractographies will be composed of streamlines computed on the vector field of primary eigenvectors at the diffusion-tensor volumes. We performed automatic tractography reconstruction of unsegmented diffusion tensor magnetic resonance imaging datasets of canine heart from the public database of the Johns Hopkins University. There are many factors that should be taken into account in order to obtain widely acceptable reconstructions and interpretations. 25 based on the optimization of graph models that promise future developments. Usually applied to texture mapping, this technique is known as mipmapping, 30 based on the well-known pyramid representation.