Model-Based Shape and Motion Analysis: Left Ventricle of a Heart

The accurate and clinically useful estimation of the shape, motion, and deformation of the left ventricle of a heart (LV) is an important yet open research problem. Recently, computer vision techniques for reconstructing the 3-D shape and motion of the LV have been developed. The main drawback of these techniques, however, is that their models are formulated in terms of either too many local parameters that require non-trivial processing to be useful for close to real time diagnosis, or too few parameters to offer an adequate approximation to the LV motion. To address the problem, we present a new class of volumetric primitives for a compact and accurate LV shape representation in which model parameters are functions. Lagrangian dynamics are employed to convert geometric models into dynamic models that can deform according to the forces manifested in the data points. It is thus possible to make a precise estimation of the deformation of the LV shape endocardial, epicardial and anywhere in between with a small number of intuitive parameter functions. We believe that the proposed technique has a wide range of potential applications. In this thesis, we demonstrate the possibility by applying it to the 3-D LV shape and motion characterization from magnetic tagging data (MRI-SPAMM). We show that the results of our experiments with normal and abnormal heart data enable us to quantitatively verify the physicians\u27 qualitative conception of the left ventricular wall motion

A non-rigid registration approach for quantifying myocardial contraction in tagged MRI using generalized information measures.

International audienceWe address the problem of quantitatively assessing myocardial function from tagged MRI sequences. We develop a two-step method comprising (i) a motion estimation step using a novel variational non-rigid registration technique based on generalized information measures, and (ii) a measurement step, yielding local and segmental deformation parameters over the whole myocardium. Experiments on healthy and pathological data demonstrate that this method delivers, within a reasonable computation time and in a fully unsupervised way, reliable measurements for normal subjects and quantitative pathology-specific information. Beyond cardiac MRI, this work redefines the foundations of variational non-rigid registration for information-theoretic similarity criteria with potential interest in multimodal medical imaging

Relation between torsion and cross-sectional area change in the human left ventricle

During the ejection phase, motion of the left ventricular (LV) wall is such that all myocardial fibers shorten to the same extent. In a mathematical model of LV mechanisms it was found that this condition could be satisfied only if torsion around the long axis followed a unique function of the ratio of cavity volume to wall volume. When fiber shortening becomes non-uniform due to cardiac pathology, this pathology may be reflected in aberration of the torsional motion pattern. In the present study we investigated whether the predicted regular motion pattern could be found in nine healthy volunteers, using Magnetic Resonance Tagging. In two parallel short-axis cross-sections, displacement, rotation, and area ejection were derived from the motion of tags, attached non-invasively to the myocardium. Information from both sections was combined to determine area ejection, quantified as the change in the logarithm of the ratio of cavity area to wall area, and torsion, represented by the shear angle on the epicardium. Linear regression was applied to torsion as a function of area ejection. The slope thus found (-0.173 +/- 0.024 rad, mean +/- S.D.) was similar to the slope as predicted by the model of LV mechanics (-0.194 +/- 0.026 rad). In conclusion, the relation between area ejection and torsion could be assessed noninvasively in humans. In healthy volunteers, the relation was close to what was predicted by a mathematical model of LV mechanics, and also close to what was found earlier in experiments on animals. [Journal Article; In English; United States

Analysis of myocardial motion using generalized spline models and tagged magnetic resonance images

Heart wall motion abnormalities are the very sensitive indicators of common heart diseases, such as myocardial infarction and ischemia. Regional strain analysis is especially important in diagnosing local abnormalities and mechanical changes in the myocardium. In this work, we present a complete method for the analysis of cardiac motion and the evaluation of regional strain in the left ventricular wall. The method is based on the generalized spline models and tagged magnetic resonance images (MRI) of the left ventricle. The whole method combines dynamical tracking of tag deformation, simulating cardiac movement and accurately computing the regional strain distribution. More specifically, the analysis of cardiac motion is performed in three stages. Firstly, material points within the myocardium are tracked over time using a semi-automated snake-based tag tracking algorithm developed for this purpose. This procedure is repeated in three orthogonal axes so as to generate a set of one-dimensional sample measurements of the displacement field. The 3D-displacement field is then reconstructed from this sample set by using a generalized vector spline model. The spline reconstruction of the displacement field is explicitly expressed as a linear combination of a spline kernel function associated with each sample point and a polynomial term. Finally, the strain tensor (linear or nonlinear) with three direct components and three shear components is calculated by applying a differential operator directly to the displacement function. The proposed method is computationally effective and easy to perform on tagged MR images. The preliminary study has shown potential advantages of using this method for the analysis of myocardial motion and the quantification of regional strain

A Left Ventricular Motion Phantom for Cardiac Magnetic Resonance Imaging

The mammalian left ventricle (LV) has two distinct motion patterns: wall thickening and rotation. The purpose of this study was to design and build a low-cost, non-ferromagnetic LV motion phantom, for use with cardiac magnetic resonance imaging (MRI), that is able to produce physiologically realistic LV wall thickening and rotation. Cardiac MRI is continuously expanding its range of techniques with new pulse sequences, including new tissue tagging techniques which allow intra-myocardial deformation to be visualized. An essential step in the development of new cardiac MRI techniques is validating their performance in the presence of motion. MRI-compatible dynamic motion phantoms are of substantial benefit in the development of cardiac specific-magnetic resonance imaging techniques. These phantoms enable the investigation of motion effects images by mimicking the three dimensional motion of the heart. To date, no single study has succeeded in duplicating both LV motion patterns, in an MRI-compatible cardiac motion phantom. In addition, a phantom that is 100 MRI-compatible with low cost to build would be desirable to researchers. We have built two MRI-compatible phantoms, housed within a common enclosure and each filled with MRI-visible dielectric gel (as a surrogate to myocardium),which model the wall thickening and rotation motions of the left ventricle independently. The wall motion phantom is pneumatic, driven by a custom non-ferromagnetic pump which cyclically fills and empties a latex balloon within the phantom. The rotation phantom is manually driven by a plastic actuator which rotates the phantom through a specified angular rotation. Each phantom also generates a TTL pulse for triggering the MRI scanner. Although this circuitry contains ferromagnetic materials, it can be located outside the scanner bore. The wall thickening motion phantom has been tested using segmented cine, real time cine and grid tagged MRI acquisition sequences. Results were significant with 4 average variability and physiologically

Motion tracking tMRI datasets to quantify abnormal left ventricle motion using finite element modelling

According to `The Atlas of Heart Disease and Stroke'[MMMG04] published by the World Health Organization, heart disease accounts for nearly half the deaths in both the developed and developing countries and is the world's single biggest killer. However, early detection of a diseased heart condition can prevent many of these fatalities. Regional wall motion abnormalities of the heart precede both ECG abnormalities and chest pain as an indicator of myocardial ischaemia and are an excellent indicator of coronary stenosis [GZM97]. These motion abnormalities of the heart muscle are difficult to observe and track, because the heart is a relatively smooth organ with few landmarks and non-rigid motion with a twisting motion or tangential component. The MRI tissue-tagging technique gives researchers the first glimpse into how the heart actually beats. This research uses the tagged MRI images of the heart to create a three dimensional model of a beating heart indicating the stress of a region. Tagged MRI techniques are still developing and vary vastly, meaning that there needs to be a methodology that can adapt to these changes rapidly and effectively, to meet the needs of the evolving technology. The focus of this research is to develop and test such a methodology by the means of a Strain Estimation Pipeline along with an effective way of validating any changes made to the individual processes that it comprises of

A Left Ventricular Motion Phantom for Cardiac Magnetic Resonance Imaging

The mammalian left ventricle (LV) has two distinct motion patterns: wall thickening and rotation. The purpose of this study was to design and build a low-cost, non-ferromagnetic LV motion phantom, for use with cardiac magnetic resonance imaging (MRI), that is able to produce physiologically realistic LV wall thickening and rotation. Cardiac MRI is continuously expanding its range of techniques with new pulse sequences, including new tissue tagging techniques which allow intra-myocardial deformation to be visualized. An essential step in the development of new cardiac MRI techniques is validating their performance in the presence of motion. MRI-compatible dynamic motion phantoms are of substantial benefit in the development of cardiac specific-magnetic resonance imaging techniques. These phantoms enable the investigation of motion effects images by mimicking the three dimensional motion of the heart. To date, no single study has succeeded in duplicating both LV motion patterns, in an MRI-compatible cardiac motion phantom. In addition, a phantom that is 100 MRI-compatible with low cost to build would be desirable to researchers. We have built two MRI-compatible phantoms, housed within a common enclosure and each filled with MRI-visible dielectric gel (as a surrogate to myocardium),which model the wall thickening and rotation motions of the left ventricle independently. The wall motion phantom is pneumatic, driven by a custom non-ferromagnetic pump which cyclically fills and empties a latex balloon within the phantom. The rotation phantom is manually driven by a plastic actuator which rotates the phantom through a specified angular rotation. Each phantom also generates a TTL pulse for triggering the MRI scanner. Although this circuitry contains ferromagnetic materials, it can be located outside the scanner bore. The wall thickening motion phantom has been tested using segmented cine, real time cine and grid tagged MRI acquisition sequences. Results were significant with 4 average variability and physiologically

A Left Ventricular Motion Phantom for Cardiac Magnetic Resonance Imaging

The mammalian left ventricle (LV) has two distinct motion patterns: wall thickening and rotation. The purpose of this study was to design and build a low-cost, non-ferromagnetic LV motion phantom, for use with cardiac magnetic resonance imaging (MRI), that is able to produce physiologically realistic LV wall thickening and rotation. Cardiac MRI is continuously expanding its range of techniques with new pulse sequences, including new tissue tagging techniques which allow intra-myocardial deformation to be visualized. An essential step in the development of new cardiac MRI techniques is validating their performance in the presence of motion. MRI-compatible dynamic motion phantoms are of substantial benefit in the development of cardiac specific-magnetic resonance imaging techniques. These phantoms enable the investigation of motion effects images by mimicking the three dimensional motion of the heart. To date, no single study has succeeded in duplicating both LV motion patterns, in an MRI-compatible cardiac motion phantom. In addition, a phantom that is 100 MRI-compatible with low cost to build would be desirable to researchers. We have built two MRI-compatible phantoms, housed within a common enclosure and each filled with MRI-visible dielectric gel (as a surrogate to myocardium),which model the wall thickening and rotation motions of the left ventricle independently. The wall motion phantom is pneumatic, driven by a custom non-ferromagnetic pump which cyclically fills and empties a latex balloon within the phantom. The rotation phantom is manually driven by a plastic actuator which rotates the phantom through a specified angular rotation. Each phantom also generates a TTL pulse for triggering the MRI scanner. Although this circuitry contains ferromagnetic materials, it can be located outside the scanner bore. The wall thickening motion phantom has been tested using segmented cine, real time cine and grid tagged MRI acquisition sequences. Results were significant with 4 average variability and physiologically

Analysis of cardiac motion using MRI and nonrigid image registration

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