1,721,039 research outputs found
A model of ultrasound backscatter for the assessment of myocardial tissue structure and architecture
No full textA statistical parametric model of returning echoes from myocardium is theorized in order to investigate the relationship between normal myocardium structure and spectral signatures with the use of ultrasonic tissue characterization. It is hypothesized, that in a clinical setting the normal myofiber architecture in the left ventricular wall is structured as a matrix of cylinder scatterers whose orientation and spatial distribution vary according to two different statistical distribution laws: 1) a Gaussian law to approximate parametric angular myofiber variability at each site within the myocardial wall; 2) a gamma distribution law to describe parametric regularity in scatterer interdistance. In the model, the effect of the angle of insonification with respect to the alignment of myofibers on ultrasound backscatter was considered. The slope of the power spectral density (PSD) evaluated within the echocardiographic transducer bandwidth has been used as a ultrasonic tissue characterization parameter. The model has been tested by computer simulation and in vitro measurements on myocardial pig tissue specimens. The concordance between experimental and simulated results confirms that the model accounts for the process underlying the echo formation from normal myocardium. Moreover, it provides a simple method of simulation which can be easily implemented and used for the assessment of pathologic alterations
Combining high-performance computing and networking for advanced 3-D cardiac imaging RID A-6953-2008
No full textThis paper deals with the integration of a powerful parallel computer-based image analysis and visualization system for cardiology into a hospital information system. Further services are remote access to the hospital Web server through an internet network. The visualization system includes dynamic three-dimensional representation of two types of medical images (e.g,, magnetic resonance and nuclear medicine) as well as two images in the same modality (e.g., basal versus stress images). A series of software tools for quantitative image analysis developed for supporting diagnosis of cardiac disease are also available, including automated image segmentation and quantitative time evaluation of left ventricular volumes and related indices during cardiac cycle, myocardial mass, and myocardial perfusion indices. The system has been tested both at a specialized cardiologic center and for remote consultation in diagnosis of cardiac disease by using anatomical and perfusion magnetic resonance images
A REGRESSION-MODEL OF ULTRASOUND REFLECTIVITY FROM NORMAL MYOCARDIUM
No full textIn this paper the potentialities of back-scattered ultrasound to detect changes in transmural myocardial wall structure have been assessed by using a second order regression model of integrated back-scatter. The model was tested through simulation studies and experimental measurements. The experimental results prove the proposed model attractive to detect physiological transmural changes in myofibre orientation from epicardial to endocardial left ventricular wall
Can Imaging Techniques Identify Smoking-Related Cardiovascular Disease?
No full textThis article reviews the current techniques employed to assess endothelial dysfunction in different categories of smokers. Simple but effective methods to assess regional and local properties of large arteries for epidemiologic studies are firstly discussed. After, more complex but accurate image-based methods are described. In particular, the role of high resolution magnetic resonance to quantify, in a single examination, vascular function at different sites of peripheral and central arteries is summarized. Finally, the role of positron emission tomography and magnetic resonance flow mapping is described to assess myocardial microcirculation at rest and under external stressors
Non-linear prediction for oesophageal voice analysis RID A-6953-2008
No full textHerein, non-linear prediction methods are applied to oesophageal voice analysis, The research aims to investigate normal and pathological subjects, in order to improve knowledge of the oesophageal voice behaviour. Analysis is performed in the reconstructed phase space, using both non-linear prediction with local linear approximation and the S-Map method. Preliminary results seem to confirm that in normal subjects a non-linear stable deterministic behaviour takes place, while in pathological subjects the non-linear contribution reduces while the time series becomes unstable. (C) 2002 Published by Elsevier Science Ltd on behalf of IPENI
Low-Field MR Coils: Comparison between Strip and Wire Conductors
No full textThis work describes how the cross-sectional shape of radio-frequency coil conductors affects coils performance. This is of particular importance at low Larmor frequencies such as those of low-field magnetic resonance imaging systems where conductor and capacitor losses are the dominant power dissipation mechanisms. We demonstrate that conductors having a circular cross section allow the coil to achieve significantly better performance than the one built using flat strips. The change in coil quality factor due to conductor geometry was verified to be due only to changes in the conductors' resistance and not their inductance. The results are not limited to low-field proton imaging but they are equally applicable to other situations where the Larmor frequency is in the megahertz range, including nuclear magnetic resonance of other nuclear species at intermediate fields
Nonlinear analysis of carotid artery echographic images RID A-6953-2008
No full textThis study deals with application of nonlinear analysis to the identification of spatial complex patterns in echographic images of normal and pathological carotid arteries. Complexity measures indices in normal and atherosclerotic plaques, related to slow space-temporal evolution of biological patterns, are evaluated. In particular, we found that the correlation dimension index lets to differentiate normal from pathological groups, allowing to infer on complex interaction mechanism responsible of plaque formation process
Regularization techniques on least squares non-uniform fast Fourier transform
No full textNon-Cartesian acquisition strategies are widely used in MRI to dramatically reduce the acquisition time while at the same time preserving the image quality. Among non-Cartesian reconstruction methods, the least squares non-uniform fast Fourier transform (LS_NUFFT) is a gridding method based on a local data interpolation kernel that minimizes the worst-case approximation error. The interpolator is chosen using a pseudoinverse matrix. As the size of the interpolation kernel increases, the inversion problem may become ill-conditioned. Regularization methods can be adopted to solve this issue. In this study, we compared three regularization methods applied to LS_NUFFT. We used truncated singular value decomposition (TSVD), Tikhonov regularization and L1-regularization. Reconstruction performance was evaluated using the direct summation method as reference on both simulated and experimental data. We also evaluated the processing time required to calculate the interpolator. First, we defined the value of the interpolator size after which regularization is needed. Above this value, TSVD obtained the best reconstruction. However, for large interpolator size, the processing time becomes an important constraint, so an appropriate compromise between processing time and reconstruction quality should be adopted
Volume rendering in medicine: The role of image coherence RID A-6953-2008
No full textIn this paper a study is described dealing with the role of image coherence on medical volume rendering algorithm performances. In particular, a simulator has been implemented in order to assess how algorithm performance can be improved by exploiting the amount of coherence for volumetric images. Moreover, typical cardiac images of different imaging modalities, were analysed in order to derive experimental coherence degree and relevant performance optimization indexes
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