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At least 253 records · Page 14Linked to original sources
PubMed1997

Patient specific color texture mapping of CT-based anatomical surface models utilizing cryosection data.

In traditional medical imaging modalities, color and texture information can add considerable information for diagnostics. Presently, multimodal images of a patient are unregistered and referenced independent of each other, or registered and fused into a single hybrid volume. Doctors and other medical professionals need to be able to visualize and interrogate, on a per-patient basis, a wide variety of 2D and 3D data representations that can be created from non-invasive imaging modalities, such as MRI and CT. In addition, any colorization that may be applied to the image data is strictly based on tissue density, radiation emission, or magnetic signature, and not on any physiological foundation. In order for "true-to-life" color information to be incorporated with non-invasive imaging techniques, and for it to be of consistent quality across the entire body, a single whole-body cryosection specimen with associated medical image data is needed. The National Library of Medicine's Visible Human Project offers just such a specimen. Using the full-body medical image data along with the cryosection images of the Visible Human subject, a set of color lookup tables for all visually well defined structures and organs can be created. As a result, patient-specific colorization based on real tissue color and characteristics can be incorporated into traditional intensity-based imaging modalities. The primary goal of this work has been to create CT color lookup tables for all visually well-defined structures in the Visible Human male cryosection data set. The subsequent goal has been to develop a method for stripping textures from a volumetric data set for polygonal models and non-uniform rational B-spline (NURBS) models, also generated from the volumetric data.

Color↗
PubMed1991

The effect of dead space on inhaled particle deposition.

Mathematical models which have been developed to predict the deposition of particles in the conducting airways of the lung require simplified anatomical models of the dimensions and geometry of the bronchial airways. In order to produce valid deposition predictions, the computed volumes of the conducting airways must be realistic in comparison to anatomical dead space. This requirement must be met even as the developing lung grows to maturity and then undergoes aging. The effect of these age-related changes on predicted particle deposition efficiencies has not been well studied. Numerous authors have suggested that differences in lung volumes (total lung capacity, functional residual capacity, dead space and tidal volume) may account for significant variations between predicted or observed particle deposition but no general age-specific relationship has been proposed. New models are proposed to describe changes in dead space as functions of age and body size, and methods to adjust existing anatomical models to various dead space predictions are given. Also, the effect of these modifications to anatomical models on particle deposition efficiencies are simulated for a variety of breathing patterns for models scaled to represent young children, adults, and aged persons.

Age Factors↗
PubMed2006

[The trapezio-metacarpal joint: the strain of the ligaments as a function of the thumb position. Study on an enlarged model].

INTRODUCTION: The aim of this paper was to develop an enlarged anatomical model of the trapezio-metacarpal joint in order to measure the strains on the ligaments when this joint was passively moved in several directions under constant loading. MATERIAL AND METHOD: A model of the two first rays of the hand was made in polystyrene, at a X3 enlargement, and the ligaments substituted by rubber bands with well characterized mechanical properties so as to reproduce the actual ratio of stiffness (approximately = 10) of the different tissues (bones and ligaments) found in real life. The first metacarpal was moved in 6 directions as described by Ebskov (1970) and Pieron (1973, 1980) using a small spring exerting a constant force (1.5 N) tilted at 30 degrees with respect to the transverse plane. The strain was measured between two white marks for each model ligament and each direction respectively, and the percentage of lengthening was calculated. A statistical study was performed using the non-parametrical Test of Wilcoxon in order to compare the ligament strains obtained in the different directions of loading. RESULTS: The largest strains were observed in the intermetacarpal ligament and in the anterior oblique ligament reaching 26 to 39% in direction J (posteromedial) and in direction L (posterolateral). Deformations of the two parts of the dorsoradial ligament and of the posterior oblique ligament were equal or inferior to 12% and were observed in the other 4 directions: D, F, K, I (Anterolateral, maximal anteposition, anteromedial, medial) and their combinations. CONCLUSION: . These data may be useful for helping the understanding of the biomechanics of the basal joint of the thumb. Nevertheless, we are dealing here with a simplified model, which must be considered with caution if the results are to be applied to the living joint.

Carpometacarpal Joints↗
PubMed2001

Parametric dependence of SAR on permittivity values in a man model.

The development and widespread use of advanced three-dimensional digital anatomical models to calculate specific absorption rate (SAR) values in biological material has resulted in the need to understand how model parameters (e.g., permittivity value) affect the predicted whole-body and localized SAR values. The application of the man dosimetry model requires that permittivity values (dielectric value and conductivity) be allocated to the various tissues at all the frequencies to which the model will be exposed. In the 3-mm-resolution man model, the permittivity values for all 39 tissue-types were altered simultaneously for each orientation and applied frequency. In addition, permittivity values for muscle, fat, skin, and bone marrow were manipulated independently. The finite-difference time-domain code was used to predict localized and whole-body normalized SAR values. The model was processed in the far-field conditions at the resonant frequency (70 MHz) and above (200, 400, 918, and 2060 MHz) for E orientation. In addition, other orientations (K, H) of the model to the incident fields were used where no substantial resonant frequency exists. Variability in permittivity values did not substantially influence whole-body SAR values, while localized SAR values for individual tissues were substantially affected by these changes. Changes in permittivity had greatest effect on localized SAR values when they were low compare to the whole-body SAR value or when errors involved tissues that represent a substantial proportion of the body mass (i.e., muscle). Furthermore, we establish the partial derivative of whole-body and localized SAR values with respect to the dielectric value and conductivity for muscle independently. It was shown that uncertainties in dielectric value or conductivity do not substantially influence normalized whole-body SAR. Detailed investigation on localized SAR ratios showed that conductivity presents a more substantial factor in absorption of energy in tissues than dielectric value for almost all applied exposure conditions.

Absorption↗
PubMed1998

Accuracy of single-dipole inverse solution when localising ventricular pre-excitation sites: simulation study.

Different factors are investigated that may affect the accuracy of an inverse solution that uses a single-dipole equivalent generator, in a standardised inhomogeneous torso model, when localising the pre-excitation sites. An anatomical model of the human ventricular myocardium is used to simulate body surface potential maps (BSPMs) and magnetic field maps (MFMs) for 35 pre-excitation sites positioned on the epicardial surface along the atrioventricular ring. The sites of pre-excitation activity are estimated by the single-dipole method, and the measure for the accuracy of the localisation is the localisation error, defined as the distance between the location of the best-fitting single dipole and the actual site of pre-excitation in the ventricular model. The findings indicate that, when the electrical properties of the volume conductor and lead positions are precisely known and the 'measurement' noise is added to the simulated BSPMs and MFMs, the single-dipole method optimally localises the pre-excitation activity 20 ms after the onset of pre-excitation, within 0.71 +/- 0.28 cm and 0.65 +/- 0.30 cm using BSPMs and MFMs, respectively. When the standard torso model is used to localise the sites of onset of the pre-excitation sequence initiated in four individualised torso models, the maximum errors are as high as 2.6-3.0 cm (even though the average error, for both the BSPM and MFM localisations, remains within the 1.0-1.5 cm range). In spite of these shortcomings, it is thought that single-dipole localisations can be useful for non-invasive pre-interventional planning.

Body Surface Potential Mapping↗
PubMed1994

An anatomical and physiological model of the renal parenchyma--model development and parametric identification.

Renal function is often characterized by the activity/time curves obtained by imaging the aorta and kidney. Non-parametric deconvolution of the activity/time curves is clinically useful as a diagnostic tool in determining renal transit times. Typically non-parametric deconvolution is performed using a technique that does not require a priori information, e.g. matrix-based and Fourier-transform methods. Using data filtering and conservation of mass constraints, non-parametric deconvolution continues to exhibit noise in the deconvolved curves. This noise hampers the identification of renal transit times. Given the shortcomings of non-parametric deconvolution, a parametric model of the renal response has been developed. Our model is shown to be anatomically and physiologically plausible. In this paper, the parametric model structure is used, in conjunction with experimental data, to estimate renal physiological parameters. These parameters include the filtration fraction, renal blood transit time and urine transit times. The model parameters are then related to the minimum transit time (MinTT), mean transit time (MTT), glomerular filtration rate (GFR) and parenchymal transit time index (PTTI). As deconvolution techniques often produce negative artifacts, Fine et al developed a technique to determine an aorta background to minimize this effect. In this paper this work is extended to determine a reasonable renal background from aorta activity/time curves. Non-parametric deconvolution is used to provide initial estimates of model parameters. The model is then fitted to twelve healthy background-corrected kidneys by an iterative parameter-estimation technique. The normal values correspond to those reported in the literature. These normal values are then used to identify renal arterial stenosis in two renal hypertensive patients. The results suggest that parametric identification, based on a renal-retention-function model, may provide additional anatomical and physiological information that is not provided by conventional non-parametric methods.

Aging↗
PubMed1998

Computer-generated patient models for reconstruction of cranial and facial deformities.

The use of three-dimensional, computer-generated anatomic models can be used in the diagnosis and reconstruction of a variety of craniofacial problems. They are readily manufactured from computed tomography scans at a reasonable cost with only several weeks of preparation and delivery time. Their contemporary value is in the preoperative treatment planning, intraoperative implant fashioning, and preoperative implant fabrication in appropriately selected patients.

Adolescent↗
PubMed2006

Cardiac function estimation from MRI using a heart model and data assimilation: advances and difficulties.

In this paper, we present a framework to estimate local ventricular myocardium contractility using clinical MRI, a heart model and data assimilation. First, we build a generic anatomical model of the ventricles including muscle fibre orientations and anatomical subdivisions. Then, this model is deformed to fit a clinical MRI, using a semi-automatic fuzzy segmentation, an affine registration method and a local deformable biomechanical model. An electromechanical model of the heart is then presented and simulated. Finally, a data assimilation procedure is described, and applied to this model. Data assimilation makes it possible to estimate local contractility from given displacements. Presented results on fitting to patient-specific anatomy and assimilation with simulated data are very promising. Current work on model calibration and estimation of patient parameters opens up possibilities to apply this framework in a clinical environment.

Adult↗
PubMed2001

Specific absorbed fractions from the image-based VIP-Man body model and EGS4-VLSI Monte Carlo code: internal electron emitters.

VIP-Man is a whole-body anatomical model newly developed at Rensselaer from the high-resolution colour images of the National Library of Medicine's Visible Human Project. This paper summarizes the use of VIP-Man and the Monte Carlo method to calculate specific absorbed fractions from internal electron emitters. A specially designed EGS4 user code, named EGS4-VLSI, was developed to use the extremely large number of image data contained in the VIP-Man. Monoenergetic and isotropic electron emitters with energies from 100 keV to 4 MeV are considered to be uniformly distributed in 26 organs. This paper presents, for the first time, results of internal electron exposures based on a realistic whole-body tomographic model. Because VIP-Man has many organs and tissues that were previously not well defined (or not available) in other models, the efforts at Rensselaer and elsewhere bring an unprecedented opportunity to significantly improve the internal dosimetry.

Bone Marrow↗
PubMed2003

Modelling dependencies between relations to ensure consistency of a cerebral cortex anatomy knowledge base.

A symbolic model of anatomy that could be used in various contexts is a key feature. However, explicitly representing anatomy requires managing many specialisation, part-whole and topological relationships. Furthermore, we notice dependencies between some of them. These dependencies have to be taken into account in order to insure both intrinsic and incremental consistency of the model. Our approach is composed of three steps. First, we define the relationships between anatomical concepts by relationships between the space region they take up or the portion of matter they are made of. Second, we use these definitions and properties of spatial and matter relationships to infer dependencies between anatomical relationships. Eventually, we apply these dependencies to the set of independent anatomical relationships to automatically generate all the dependent relationships. This method was used to maintain an anatomical model of the frontal, temporal, parietal and occipital regions of the cerebral cortex. For 113 concepts, 221 of the 370 relationships could be automatically generated. The more the number of concepts increase, the more pertinent the method appears.

Artificial Intelligence↗
PubMedDate not supplied

Knowledge-based multi-modality three-dimensional image analysis of the brain.

With the recent advances in medical imaging, three-dimensional anatomical and metabolic images of the brain are now available through MR/CT and PET/SPECT imaging modalities. Computerized multi-modality three-dimensional brain image registration and analysis can provide important correlated information for improving diagnosis and studying the pathology of disease. Such analysis may also provide help in planning brain surgery. Further, an anatomical model based quantification and analysis of internal structure can be used to develop a computerized anatomical atlas. Conventional anatomical atlases provide rigid spatial distribution of internal structures extracted from a single subject. The proposed computerized anatomical atlas provides probabilistic spatial distributions which can be easily updated to incorporate the variability of brain structures of subjects selected from pre-defined groups. This paper first presents a review of the current trends in knowledge-based segmentation, labeling, and analysis of MR brain images and then describes the Principal Axes Transformation based registration of three-dimensional MR brain images to develop composite models of selected internal brain structures. The composite models can be used as a computerized anatomical atlas in model-based segmentation and labeling of MR brain images. Three-dimensional labeled MR images of the brain can also be registered and correlated with PET images for analyzing the metabolic activity in the anatomically selected volume of interest. On the other hand, a volume of interest can be selected using the metabolic information and then analyzed for correlated anatomical information using the registered MR-PET images.

Algorithms↗
PubMed1992

Specific absorption rates and induced current distributions in an anatomically based human model for plane-wave exposures.

We have previously reported local, layer-averaged, and whole-body-averaged specific absorption rates and induced currents for a 5,628-cell anatomically based model of a human for plane-wave exposures 20-100 MHz (Chen and Gandhi 1989). Using a higher resolution, 45,024-cell model of the human body, calculations have now been extended to 915 MHz using the finite-difference time-domain method. Because of the higher resolution of the model, it has been possible to calculate specific absorption rates for various organs (brain, eyes, heart, lungs, liver, kidneys, and intestines) and for various parts of the body (head, neck, torso, legs, and arms) as a function of frequency in the band 100-915 MHz. Consistent with some of the experimental data in the literature, the highest part-body-averaged specific absorption rate for the head and neck region (as well as for the eyes and brain) occurs at 200 MHz for the isolated condition and at 150 MHz for the grounded condition of the model. Also observed is an increasing specific absorption rate for the eyes for frequencies above 350 MHz due to the superficial nature of power deposition at increasing frequencies.

Algorithms↗
PubMed2003

An approach to the three-dimensional display of left ventricular function and viability using MRI.

Cardiac MRI was performed in human volunteers to determine the magnitude of the misregistration (MSR) of cardiac landmarks due to variability in the diaphragm position for repeated breath-holds. Seven normal volunteers underwent MR imaging of the left ventricle (LV) to evaluate the magnitude of the endocardial centroid MSR. The MSR for a mid-ventricle short-axis image was 3.01 +/- 1.68 mm through-plane and 4.16 +/- 1.62 mm in-plane. A second order polynomial fit through the LV centroid coordinates minimized the in-plane component of the MSR error. Short-axis cine images, corrected for MSR, provided high-resolution 2D data from which an accurate anatomical model of the LV was generated. Anatomical landmarks were used to register parametric maps of myocardial perfusion and viability to the three-dimensional (3D) model, with the corresponding parameters displayed as color-encoded values on the endo- and epicardial surfaces of the LV. Registration of regional wall motion, perfusion and viability to the 3D model was performed for three patients with a history of cardiovascular disease. The proposed 3D reconstruction technique allows visualization in 3D of the LV anatomy, in combination with parametric mapping of its functional status.

Cardiomyopathies↗
PubMed2006

Applicability of the single equivalent moving dipole model in an infinite homogeneous medium to identify cardiac electrical sources: a computer simulation study in a realistic anatomic geometry torso model.

We have previously proposed an inverse algorithm for fitting potentials due to an arbitrary bio-electrical source to a single equivalent moving dipole (SEMD) model. The algorithm achieves fast identification of the SEMD parameters by employing a SEMD model embedded in an infinite homogeneous volume conductor. However, this may lead to systematic error in the identification of the SEMD parameters. In this paper, we investigate the accuracy of the algorithm in a realistic anatomic geometry torso model (forward problem). Specifically, we investigate the effect of measurement noise, dipole position and electrode configuration in the accuracy of the algorithm. The boundary element method was used to calculate the forward potential distribution at multiple electrode positions on the body surface due to a point dipole in the heart. We have found that the position and not the number of electrodes as well as the site of the origin of the arrhythmia in the heart have a significant effect on the accuracy of the inverse algorithm, while the measurement noise does not. Finally, we have shown that the inverse algorithm preserves the topology of the source distribution in the heart, thus potentially allowing the cardiac electrophysiologist to efficiently and accurately guide the tip of the catheter to the ablation site.

Action Potentials↗