2004
An epitope variable-reservoir model for HIV-1 infection
Horacio Ortega, Miguel Martín-Landrove
Acta Científica Venezolana, 55: 247-263, 2004
A model of HIV-1 infection based on immunodominance concepts is presented. The model considers not only mutating virions and T-CD4 cells, but also viral reservoirs, such as macrophages and follicular dendritic cells. It also considers strong cytotoxic attack against reservoirs and extra cellular attack on virions, which are both coordinated by T-CD4 cells. As a first case, only one viral variant is dealt with, and approximations were used to obtain a manageable model. A stability criterion was found that marks the transition between progression and regression of the viral infection. This criterion was proven valid for the model without any approximation, i.e., two randomly mutant viral epitopes with two variants each. Data suggest that a) the role played by the reservoirs in the maintenance of the viral infection is a very important one, b) maintaining CTL attack on infected cells facilitates the control of HIV-1 infection, and c) therapy considerations should be addressed to these points.
Brain tumor segmentation with diffusion tensor anisotropy
Martín-Landrove M., Bautista I.
American Society of Neuroradiology, 2004
The present work exploits diffusion tensor anisotropy differences between neoplastic tissue and white matter fibers to separate the active portion of the tumor and necrotic tissue from unaffected tissue. Previous work had demonstrated that the segmentation of the tumor is possible by integration of in vivo spectroscopy information with relaxation data, but in some cases the discrimination between the peripheral edematuous region and the tumor itself is rather difficult to perform. On the other hand, diffusion tensor anisotropy is not as modified in the edematous tissue as it is in the tumoral or necrotic tissue, and in consequence it can be used as a good discrimination parameter which combined to other information related to the diffusion tensor such as its trace could give relevant parameters for a suitable segmentation of the tumor image
Assessment of the unilateral pulmonary function by means of electrical impedance tomography using a reduced electrode set
Roberto E Serrano, Pere J Riu, Bruno de Lema, Pere Casan
Physiol. Meas. 25 (2004) 803–813
The usefulness of electrical impedance tomography (EIT) to assess ventilationrelated phenomena in the thorax has already been demonstrated, especially in controlled environments. We focus on our developments in the assessment of the unilateral pulmonary function (UPF) in real clinical environments. The impact of the reduction of the number of electrodes used is analysed theoretically and experimentally with different approaches. Sixteen-electrode EIT measurements were performed on a group of lung cancer patients (19 M, 2 F, ages 25–77 years). Results are compared with those obtained from ventilation scintigraphy. Eight-electrode measurements were synthesized from the 16-electrode ones. The Bland and Altman analysis indicates an agreement of about ±1 percent points in the estimation of UPF. On five of these patients real 8-electrode measurements were performed, obtaining differences from 0.2 percent to 6 percent points. It is concluded that reducing the number of electrodes does not adversely affect the assessment of UPF, but there is a reproducibility issue affecting all the techniques which needs further study.
T-snakes y triangulación de Delaunay como método de generación de mallados de estructuras anatómicas para la aplicación del método de elementos finitos [T-snakes and Delaunay triangulation as a method in anatomical structures meshing for finite element method application]
E. Coto, O. Rodríguez
Proceedings del VI Congreso Internacional de Métodos Numéricos en Ingeniería y Ciencias Aplicadas, pp TC 11-18. Abril, 2004.
The segmentation of anatomic structures from medical images and the reconstruction of analytical compact representations of these structures is a challenging problem. This work uses the T-Snakes technique to detect the contour of an anatomicstructure on one slice of a Computer Tomography (CT) image dataset, and then propagates the detected contour through the rest of the slices in order to build the surface of theanatomic structure. The interior of the surface is built out of tetrahedrons obtained from a3D variant of the Constrained Delaunay Triangulation, verifying that the tetrahedrons havethe proper conditions for a subsequent Finite Elements Analysis of the structure. Weconclude the paper with an example of this approach using a CT image dataset.
Dynamic response of cancer under the influence of immunological activity and therapy
Harold P. de Vladar, Jorge A. González
Journal of Theoretical Biology 227 (2004) 335 - 348
The dynamical basis of tumoral growth has been controversial. Many models have been proposed to explain cancer development. The descriptions employ exponential, potential, logistic or Gompertzian growth laws. Some of these models are concerned with the interaction between cancer andthe immunological system. Among other properties, these models are concernedwith the microscopic behavior of tumors and the emergence of cancer. We propose a modification of a previous model by Stepanova, which describes the specific immunological response against cancer. The modification consists of the substitution of a Gompertian law for the exponential rate usedfor tumoral growth. This modification is motivatedby the numerous works confirming that Gompertz’s equation correctly describes solid tumor growth. The modified model predicts that near zero, tumors always tend to grow. Immunological contraposition never suffices to induce a complete regression of the tumor. Instead, a stable microscopic equilibrium between cancer and immunological activity can be attained. In other words, our model predicts that the theory of immune surveillance is plausible. A macroscopic equilibrium in which the system develops cancer is also possible. In this case, immunological activity is depleted. This is consistent with the phenomena of cancer tolerance. Both equilibrium points can coexist or can exist without the other. In all cases the fixedpoint at zero tumor size is unstable. Since immunity cannot induce a complete tumor regression, a therapy is required. We include constant-dose therapies and show that they are insufficient. Final levels of immunocompetent cells andtumoral cells are finite, thus post-treatment regrowth of the tumor is certain. We also evaluate lateintensification
therapies which are successful. They induce an asymptotic regression to zero tumor size. Immune response is also suppressedby the therapy, andthus plays a negligible role in the remission. We conclude that treatment evaluation should be successful without taking into account immunological effects
Geometric Methods for Vessel Visualization and Quantification - A Survey
Katja Bühler, Petr Felkel, Alexandra La Cruz
Geometric Modelling for Scientific Visualization, G. Brunnett et al. (eds.) (2004) 399-419
Visualization and quantitative analysis of vessel data is an important preprocessing step in diagnosis of vascular diseases, monitoring, surgery planning, blood flow simulation, education and training of surgeons. This paper surveys several geometrie methods to solve basie visualization and quantification problems like centerline computation, boundary detection, projection teehniques, and geometrie model generation.
The VesselGlyph: Focus & Context Visualization in CT- Angiography
Matús Straka, Michal Cervenansky, Alexandra La Cruz, Arnold Köchl, Milos Srámek, Eduard Gröller, Dominik Fleischmann
VIS '04 Proceedings of the conference on Visualization '04 (2004) 385-392
Accurate and reliable visualization of blood vessels is still a challenging problem, notably in the presence of morphologic changes resulting from atherosclerotic diseases. In this paper we take advantage of partially segmented data with approximately identified vessel centerlines to comprehensively visualize the diseased peripheral arterial tree.
We introduce the VesselGlyph as an abstract notation for novel focus & context visualization techniques of tubular structures such as contrast-medium enhanced arteries in CT-Angiography (CTA). The proposed techniques combine direct volume rendering (DVR) and curved planar reformation (CPR) within a single image. The VesselGlyph consists of several regions where different rendering methods are used. The region type, the used visualization method and the region parameters depend on the distance from the vessel centerline and on viewing parameters as well. By selecting proper rendering techniques for different regions, vessels are depicted in a naturally looking and undistorted anatomic context. This may facilitate the diagnosis and treatment planning of patients with peripheral arterial occlusive disease.
In this paper we furthermore present a way how to implement the proposed techniques in software and by means of modern 3D graphics accelerators
Non-linear Model Fitting to Parameterize Diseased Blood Vessels
Alexandra La Cruz, Matús Straka, Arnold Köchl, Milos Srámek, Eduard Gröller, Dominik Fleischmann
VIS '04 Proceedings of the conference on Visualization '04 (2004) 393-400
Accurate estimation of vessel parameters is a prerequisite for automated visualization and analysis of healthy and diseased blood vessels. The objective of this research is to estimate the dimensions of lower extremity arteries, imaged by computed tomography (CT). These parameters are required to get a good quality visualization of healthy as well as diseased arteries using a visualization technique such as curved planar reformation (CPR). The vessel is modeled using an elliptical or cylindrical structure with specific dimensions, orientation and blood vessel mean density. The model separates two homogeneous regions: Its inner side represents a region of density for vessels, and its outer side a region for background. Taking into account the point spread function (PSF) of a CT scanner, a function is modeled with a Gaussian kernel, in order to smooth the vessel boundary in the model. A new strategy for vessel parameter estimation is presented. It stems from vessel model and model parameter optimization by a nonlinear optimization procedure, i.e., the Levenberg-Marquardt technique. The method provides center location, diameter and orientation of the vessel as well as blood and background mean density values. The method is tested on synthetic data and real patient data with encouraging results.
