A deformable finite element model of the breast for predicting mechanical deformations under external perturbations.

RATIONALE AND OBJECTIVES: Live guidance during needle breast procedures is not currently possible with high-field-strength (1.5-T), superconducting magnetic resonance (MR) imaging. The physician can calculate only the approximate location and extent of a tumor in the compressed patient breast before inserting the needle, and the tissue specimen removed at biopsy may not actually belong to the lesion of interest. The authors developed a virtual reality system for guiding breast biopsy with MR imaging, which uses a deformable finite element model of the breast. MATERIALS AND METHODS: The geometry of the model is constructed from MR data, and its mechanical properties are modeled by using a nonlinear material model. This method allows the breast to be imaged with or without mild compression before the procedure. The breast is then compressed, and the finite element model is used to predict the position of the tumor during the procedure. Three breasts of patients with cancer were imaged with and without compression. Deformable models of these breasts were built, virtually compressed, and used to predict tumor positions in the real compressed breasts. The models were also used to register MR data sets of the same patient breast imaged with different amounts of compression. RESULTS: The model is shown to predict reasonably well the displacement by plate compression of breast lesions 5 mm or larger. CONCLUSION: A deformable model of the breast based on finite elements with nonlinear material properties can help in modeling and predicting breast deformation. The entire procedure lasts less than half an hour, making it clinically practical.

Three-dimensional motion reconstruction and analysis of the right ventricle using tagged MRI.

Right ventricular (RV) dysfunction can serve as an indicator of heart and lung disease and can adversely affect the left ventricle. However, normal RV function must be characterized before abnormal states can be detected. We describe a method for reconstructing the 3D motion of the RV by fitting a deformable model to tag and contour data extracted from multiview tagged magnetic resonance images. The deformable model is a biventricular finite element mesh built directly from segmented contours. Our approach accommodates the geometrically complex RV by using the entire lengths of the tags, localized degrees of freedom, and finite elements for geometric modeling. Also, we outline methods for converting the 3D motion reconstruction results into potentially useful motion variables, such as strains and displacements. The technique was applied to synthetic data, two normal hearts, and two hearts with right ventricular hypertrophy (RVH). Noticeable differences were found between the motion variables calculated for normal volunteers and RVH patients.

Cascaded MRI-SPAMM for LV motion analysis during a whole cardiac cycle.

We present a new paradigm which incorporates multiple sets of tagged MRI data (MRI-SPAMM) acquired in a cascaded fashion in order to estimate the full 3-D motion of the left ventricle (LV) during its entire cardiac cycle. Our technique is based on an extension of our volumetric physics-based deformable models, whose parameters are functions. Using these parameters, we can characterize the local shape variation of an object with a small number of intuitive parameters. By integrating a cascaded sequence of SPAMM data sets into our modeling technique, we have extended the capability of the MRI-SPAMM technique and have provided an accurate representation of the LV motion during the full cardiac cycle (from end-diastole to end-diastole) to better understand cardiac mechanics.

Efficient dynamic constraints for animating articulated figures.

This paper presents an efficient dynamics-based computer animation system for simulating and controlling the motion of articulated figures. A non-trivial extension of Featherstone's O(n) recursive forward dynamics algorithm is derived which allows enforcing one or more constraints on the animated figures. We demonstrate how the constraint force evaluation algorithm we have developed makes it possible to simulate collisions between articulated figures, to compute the results of impulsive forces, to enforce joint limits, to model closed kinematic loops, and to robustly control motion at interactive rates. Particular care has been taken to make the algorithm not only fast, but also easy to implement and use. To better illustrate how the constraint force evaluation algorithm works, we provide pseudocode for its major components. Additionally, we analyze its computational complexity and finally we present examples demonstrating how our system has been used to generate interactive, physically correct complex motion with small user effort.

A three-dimensional virtual environment for modeling mechanical cardiopulmonary interactions.

We have developed a real-time computer system for modeling mechanical physiological behavior in an interactive, 3-D virtual environment. Such an environment can be used to facilitate exploration of cardiopulmonary physiology, particularly in situations that are difficult to reproduce clinically. We integrate 3-D deformable body dynamics with new, formal models of (scalar) cardiorespiratory physiology, associating the scalar physiological variables and parameters with the corresponding 3-D anatomy. Our framework enables us to drive a high-dimensional system (the 3-D anatomical models) from one with fewer parameters (the scalar physiological models) because of the nature of the domain and our intended application. Our approach is amenable to modeling patient-specific circumstances in two ways. First, using CT scan data, we apply semi-automatic methods for extracting and reconstructing the anatomy to use in our simulations. Second, our scalar physiological models are defined in terms of clinically measurable, patient-specific parameters. This paper describes our approach, problems we have encountered and a sample of results showing normal breathing and acute effects of pneumothoraces.

Complete left ventricular wall motion estimation from cascaded MRI-SPAMM data.

We present a new paradigm which incorporates multiple sets of tagged MRI data (MRI-SPAMM) acquired in a cascaded fashion in order to estimate the full 3-D motion of the left ventricle (LV) during its entire cardiac cycle. Our technique is based on the extension of the volumetric physics-based deformable models, whose parameters are functions, which can capture the local shape variation of an object with a small number of intuitive parameters. By integrating a cascaded sequence of SPAMM data sets into our modeling technique, we have extended the capability of MRI-SPAMM and have provided an accurate representation of the LV motion from end-diastole to end-diastole to better understand cardiac mechanics.

Analysis of left ventricular wall motion based on volumetric deformable models and MRI-SPAMM.

We present a new approach for the analysis of the left ventricular shape and motion based on the development of a new class of volumetric deformable models. We estimate the deformation and complex motion of the left ventricle (LV) in terms of a few parameters that are functions and whose values vary locally across the LV. These parameters capture the radial and longitudinal contraction, the axial twisting, and the long-axis deformation. Using Lagrangian dynamics and finite-element theory, we convert these volumetric primitives into dynamic models that deform due to forces exerted by the datapoints. We present experiments where we used magnetic tagging (MRI-SPAMM) to acquire datapoints from the LV during systole. By applying our method to MRI-SPAMM datapoints, we were able to characterize the 3-D shape and motion of the LV both locally and globally, in a clinically useful way. In addition, based on the model parameters we were able to extract quantitative differences between normal and abnormal hearts and visualize them in a way that is useful to physicians.

Deformable models with parameter functions for cardiac motion analysis from tagged MRI data.

The authors present a new method for analyzing the motion of the heart's left ventricle (LV) from tagged magnetic resonance imaging (MRI) data. Their technique is based on the development of a new class of physics-based deformable models whose parameters are functions. They allow the definition of new parameterized primitives and parameterized deformations which can capture the local shape variation of a complex object. Furthermore, these parameters are intuitive and require no complex post-processing in order to be used by a physician. Using a physics-based approach, the authors convert the geometric models into dynamic models that deform due to forces exerted from the datapoints and conform to the given dataset. The authors present experiments involving the extraction of the shape and motion of the LV's mid-wall during systole from tagged MRI data based on a few parameter functions. Furthermore, by plotting the variations over time of the extracted LV model parameters from normal and abnormal heart data along the long axis, the authors are able to quantitatively characterize their differences.

Linking anatomy and physiology in modeling respiratory mechanics.

We present an integrated 3D virtual environment for the quantitative modeling of the anatomy and the physiology of the pulmonary system. Our approach formally integrates 3D deformable object modeling with conventional models of respiratory mechanics. We demonstrate quantitatively, aspects of the behavior of the respiratory system qualitatively known to clinicians, such as normal quiet breathing and an open sucking chest wound. Our methodology is general and can be used to model both the anatomy and the physiology at many levels of detail. Another important aspect of our approach is that based on our previously developed computer vision techniques we can make such a simulation patient specific. The usefulness of such a system is manifold. Medical education, surgical planning, disease diagnosis are some of the many areas such a system can be applied.

Modeling respiratory anatomy and physiology in VR.

In trauma, many injuries impact anatomical structures, which may in turn affect physiological processes--not only those processes within the structures, but ones occurring in physical proximity to them as well. Our goal is to endow a 3D anatomical model with physiological mechanisms to demonstrate such effects. Our approach couples deformable object simulation for organs with physiological modeling, in a way that supports three-dimensional animated simulation. We demonstrate our approach through our current model of respiratory mechanics in a virtual 3D environment. Anatomical models that can capture physiological and pathophysiological changes can serve as an infrastructure for more detailed modeling, as well as benefiting surgical planning, surgical training, and general medical education.

Anatomical and physiological simulation for respiratory mechanics.

Injuries in trauma affect anatomical structures, indirectly affecting physiological systems through mechanical behavior and physical proximity. This paper describes the theory for and preliminary results from our approach to couple a three-dimensional (3-D) anatomical model of the chest with a physiological model of respiratory mechanics. In particular, we investigated behavior in quiet, normal breathing and in an open, sucking chest wound. We envision that our integrated simulation of respiratory anatomy and respiratory mechanics could assist students in visualizing and predicting relationships between structural-anatomical and functional-physiological changes in an interactive, 3-D environment.

Climatic fluctuation of temperature and air circulation in the Mediterranean

global warming is tested in the mediterranean area during the last 45 year using SST and 1000/500 mb thickness data, in order to avoid urban effects. The area is divided in two parts vis. The west and the east mediterranean. Since wrming is not apparent in the east mediterranean but only during the last year, the time series of surface pressure and relative geostrophic vorticity were examined for possible explanations. It is found that there exists a continuous and considerable increase of the mean vorticity in the extreme east mediterranean, meaning increased frequency and/or strength of N. winds there, causing a delay of the warming. The opposite phenomenon appeared in the extreme West Mediterranean where increased S. winds may contribute to the warming there (AU)