Segmentation of Myocardial Boundaries in Tagged Cardiac MRI Using Active Contours: A Gradient-Based Approach Integrating Texture Analysis

The noninvasive assessment of cardiac function is of first importance for the diagnosis of cardiovascular diseases. Among all medical scanners only a few enables radiologists to evaluate the local cardiac motion. Tagged cardiac MRI is one of them. This protocol generates on Short-Axis (SA) sequences a dark grid which is deformed in accordance with the cardiac motion. Tracking the grid allows specialists a local estimation of cardiac geometrical parameters within myocardium. The work described in this paper aims to automate the myocardial contours detection in order to optimize the detection and the tracking of the grid of tags within myocardium. The method we have developed for endocardial and epicardial contours detection is based on the use of texture analysis and active contours models. Texture analysis allows us to define energy maps more efficient than those usually used in active contours methods where attractor is often based on gradient and which were useless in our case of study, for quality of tagged cardiac MRI is very poor

Temporal tracking of 3D coronary arteries in projection angiograms

International audienceA method for 3D temporal tracking of a 3D coronary tree model through a sequence of biplane cineangiography images has been developed. A registration framework is formulated in which the coronary tree centerline model deforms in an external potential ¯eld de¯ned by a multiscale analysis response map computed from the angiogram images. To constrain the procedure and to improve convergence, a set of three motion models is hierarchically used: a 3D rigid-body transformation, a 3D a±ne transformation, and a 3D B-spline deformation ¯eld. This 3D motion tracking approach has signi¯cant advantages over 2D methods: (1) coherent deformation of a single 3D coronary reconstruction preserves the topology of the arterial tree; (2) constraints on arterial length and regularity, which lack meaning in 2D projection space, are directly applicable in 3D; and (3) tracking arterial segments through occlusions and crossings in the projection images is simpli¯ed with knowledge of the 3D relationship of the arteries. The method has been applied to patient data and results are presented

Hierarchical template matching for 3D myocardial tracking and cardiac strain estimation

Myocardial tracking and strain estimation can non-invasively assess cardiac functioning using subject-specific MRI. As the left-ventricle does not have a uniform shape and functioning from base to apex, the development of 3D MRI has provided opportunities for simultaneous 3D tracking, and 3D strain estimation. We have extended a Local Weighted Mean (LWM) transformation function for 3D, and incorporated in a Hierarchical Template Matching model to solve 3D myocardial tracking and strain estimation problem. The LWM does not need to solve a large system of equations, provides smooth displacement of myocardial points, and adapt local geometric differences in images. Hence, 3D myocardial tracking can be performed with 1.49 mm median error, and without large error outliers. The maximum error of tracking is up to 24% reduced compared to benchmark methods. Moreover, the estimated strain can be insightful to improve 3D imaging protocols, and the computer code of LWM could also be useful for geo-spatial and manufacturing image analysis researchers

Spatio-Temporal Nonrigid Registration for Ultrasound Cardiac Motion Estimation

We propose a new spatio-temporal elastic registration algorithm for motion reconstruction from a series of images. The specific application is to estimate displacement fields from two-dimensional ultrasound sequences of the heart. The basic idea is to find a spatio-temporal deformation field that effectively compensates for the motion by minimizing a difference with respect to a reference frame. The key feature of our method is the use of a semi-local spatio-temporal parametric model for the deformation using splines, and the reformulation of the registration task as a global optimization problem. The scale of the spline model controls the smoothness of the displacement field. Our algorithm uses a multiresolution optimization strategy to obtain a higher speed and robustness. We evaluated the accuracy of our algorithm using a synthetic sequence generated with an ultrasound simulation package, together with a realistic cardiac motion model. We compared our new global multiframe approach with a previous method based on pairwise registration of consecutive frames to demonstrate the benefits of introducing temporal consistency. Finally, we applied the algorithm to the regional analysis of the left ventricle. Displacement and strain parameters were evaluated showing significant differences between the normal and pathological segments, thereby illustrating the clinical applicability of our method

Processing and quantitative analysis of tagged cardiac MRI sequences

The noninvasive evaluation of the cardiac function presents a great interest for the diagnosis of cardiovascular diseases. Cardiac tagged MRI allows the measurement of anatomical and functional myocardial parameters. This protocol generates a dark grid which is deformed with the myocardium. As a consequence, the tracking of the grid allows the displacement estimation in the myocardium. The work described in this paper aims to automate the myocardial contours detection and the following of the grids of tags on Short-Axis time sequences, in order to firstly optimize the 2D+T study of the parietal contractions and secondly make possible its clinical use. The method we have developed for endocardial and epicardial contours detection is based on the use of texture analysis and active contours models. Texture analysis allows us to define energy maps more efficient than those usually used in active contours methods where attractor is often based on gradient and which were useless in our case of study. The follow-up of the grid of tags that we have implemented is based on a grid of active contours (B-snakes) which part of the energy is issued from a particular selective diffusion process which leading equation is based on the recent work of [8]. The results obtained with our method is fully automatic and correct on Short-Axis sequences, when previous works on cardiac tagged MR images analysis always used manual contours detection.L'évaluation non invasive de la fonction cardiaque présente un intérêt majeur pour le diagnostic et le suivi de pathologies cardio-vasculaires. L'IRM cardiaque marquée permet de mesurer des paramètres anatomiques et fonctionnels du myocarde. Ce protocole fait apparaître sur les images des séquences temporelles cardiaques Petit-Axe (PA) une grille se déformant avec le myocarde. Le suivi de cette grille permet ainsi d'estimer le déplacement intramyocardique. L'objectif de notre étude est de rendre robuste le suivi automatique de la grille de tags sur les séquences PA afin de mener une analyse quantitative 2D+T de la fonction contractile du Ventricule Gauche (VG). La méthode que nous avons développée dans ce but, utilise un modèle de contour actif sous forme de grille dont l'énergie image se construit grâce à une diffusion sélective permettant la sauvegarde de l'information de tag au détriment du reste sur chacune des images PA extraites des séquences IRM cardiaques marquées. Cette approche, couplée à une détection automatique des contours du VG sur ces mêmes images, permet l'obtention de résultats quantitatifs (paramètres cliniques) satisfaisants à la fois en terme de précision, de robustesse, de reproductibilité et de rapidité

Reconstruction and analysis of 4D heart motion from tagged MR images.

Luo Guo.Thesis (M.Phil.)--Chinese University of Hong Kong, 2003.Includes bibliographical references (leaves 97-109).Abstracts in English and Chinese.Abstract --- p.iAcknowledgement --- p.iiiChapter 1 --- Introduction --- p.1Chapter 1.1 --- Motivation --- p.2Chapter 1.2 --- Basics --- p.3Chapter 1.2.1 --- Anatomy of Human Heart --- p.3Chapter 1.2.2 --- The Philosophy of MRI --- p.5Chapter 1.2.3 --- MRI in Practice --- p.7Chapter 1.3 --- Cardiac MR Images Analysis --- p.7Chapter 1.3.1 --- Heart Boundary Segmentation --- p.7Chapter 1.3.2 --- Motion Reconstruction --- p.13Chapter 1.4 --- Summary and Thesis Overview --- p.17Chapter 2 --- Tracking Tags in SPAMM Images --- p.21Chapter 2.1 --- Introduction --- p.21Chapter 2.2 --- The Snake Model --- p.28Chapter 2.3 --- The Improved Snake Model: Tracking Tags Using Snakes --- p.30Chapter 2.3.1 --- Imaging Protocol --- p.30Chapter 2.3.2 --- Model Formulation --- p.31Chapter 2.3.3 --- Numerical Solution --- p.39Chapter 2.4 --- Experimental Results --- p.44Chapter 3 --- B-Spline Based LV Motion Reconstruction --- p.52Chapter 3.1 --- Introduction --- p.52Chapter 3.2 --- LV Shape: Generalized Deformable Ellipsoid --- p.56Chapter 3.3 --- The New Geometric Model: Generalized Prolate Spheroid --- p.58Chapter 3.3.1 --- Generalized Prolate Spheroid --- p.58Chapter 3.3.2 --- Initial Geometric Fitting --- p.59Chapter 3.4 --- Fast Motion Reconstruction: The Enhanced Hi- erarchical Motion Decomposition --- p.65Chapter 3.4.1 --- Hierarchical Motion Decomposition --- p.65Chapter 3.4.2 --- Motion Reconstruction --- p.68Chapter 3.4.3 --- Implementation --- p.76Chapter 3.4.4 --- Time Smoothing --- p.77Chapter 3.5 --- Experimental Results --- p.79Chapter 3.5.1 --- Geometric Fitting --- p.79Chapter 3.5.2 --- Motion Reconstruction --- p.79Chapter 4 --- Conclusion --- p.93Bibliography --- p.10

3-D lung deformation and function from respiratory-gated 4-D x-ray CT images : application to radiation treatment planning.

Many lung diseases or injuries can cause biomechanical or material property changes that can alter lung function. While the mechanical changes associated with the change of the material properties originate at a regional level, they remain largely asymptomatic and are invisible to global measures of lung function until they have advanced significantly and have aggregated. In the realm of external beam radiation therapy of patients suffering from lung cancer, determination of patterns of pre- and post-treatment motion, and measures of regional and global lung elasticity and function are clinically relevant. In this dissertation, we demonstrate that 4-D CT derived ventilation images, including mechanical strain, provide an accurate and physiologically relevant assessment of regional pulmonary function which may be incorporated into the treatment planning process. Our contributions are as follows: (i) A new volumetric deformable image registration technique based on 3-D optical flow (MOFID) has been designed and implemented which permits the possibility of enforcing physical constraints on the numerical solutions for computing motion field from respiratory-gated 4-D CT thoracic images. The proposed optical flow framework is an accurate motion model for the thoracic CT registration problem. (ii) A large displacement landmark-base elastic registration method has been devised for thoracic CT volumetric image sets containing large deformations or changes, as encountered for example in registration of pre-treatment and post-treatment images or multi-modality registration. (iii) Based on deformation maps from MOFIO, a novel framework for regional quantification of mechanical strain as an index of lung functionality has been formulated for measurement of regional pulmonary function. (iv) In a cohort consisting of seven patients with non-small cell lung cancer, validation of physiologic accuracy of the 4-0 CT derived quantitative images including Jacobian metric of ventilation, Vjac, and principal strains, (V?1, V?2, V?3, has been performed through correlation of the derived measures with SPECT ventilation and perfusion scans. The statistical correlations with SPECT have shown that the maximum principal strain pulmonary function map derived from MOFIO, outperforms all previously established ventilation metrics from 40-CT. It is hypothesized that use of CT -derived ventilation images in the treatment planning process will help predict and prevent pulmonary toxicity due to radiation treatment. It is also hypothesized that measures of regional and global lung elasticity and function obtained during the course of treatment may be used to adapt radiation treatment. Having objective methods with which to assess pre-treatment global and regional lung function and biomechanical properties, the radiation treatment dose can potentially be escalated to improve tumor response and local control

MR imaging of left-ventricular function : novel image acquisition and analysis techniques.

Many cardiac diseases, such as myocardial ischemia, secondary to coronary artery disease, may be identified and localized through the analysis of cardiac deformations. Early efforts for quantifying ventricular wall motion used surgical implantation and tracking of radiopaque markers with X-ray imaging in canine hearts [1]. Such techniques are invasive and affect the regional motion pattern of the ventricular wall during the marker tracking process and, clearly are not feasible clinically. Noninvasive imaging techniques are vital and have been widely applied to the clinic. MRI is a noninvasive imaging technique with the capability to monitor and assess the progression of cardiovascular diseases (CVD) so that effective procedures for the care and treatment of patients can be developed by physicians and researchers. It is capable of providing 3D analysis of global and regional cardiac function with great accuracy and reproducibility. In the past few years, numerous efforts have been devoted to cardiac motion recovery and deformation analysis from MR imaging sequences. In order to assess cardiac function, there are two categories of indices that are used: global and regional indices. Global indices include ejection fraction, cavity volume, and myocardial mass [2]. They are important indices for cardiac disease diagnosis. However, these global indices are not specific for regional analysis. A quantitative assessment of regional parameters may prove beneficial for the diagnosis of disease and evaluation of severity and the quantification of treatment [3]. Local measures, such as wall deformation and strain in all regions of the heart, can provide objective regional quantification of ventricular wall function and relate to the location and extent of ischemic injury. This dissertation is concerned with the development of novel MR imaging techniques and image postprocessing algorithms to analyze left ventricular deformations. A novel pulse sequence, termed Orthogonal CSPAMM (OCSPAMM), has been proposed which results in the same acquisition time as SPAMM for 2D deformation estimation while keeping the main advantages of CSPAMM [4,5]: i.e., maintaining tag contrast through-out the ECG cycle. Different from CSPAMM, in OCSPAMM the second tagging pulse orientation is rotated 90 degrees relative to the first one so that motion information can be obtained simultaneously in two directions. This reduces the acquisition time by a factor of two as compared to the traditional CSPAMM, in which two separate imaging sequences are applied per acquisition. With the application of OCSPAMM, the effect of tag fading encountered in SPAMM tagging due to Tl relaxation is mitigated and tag deformations can be visualized for the entire cardiac cycle, including diastolic phases. A multilevel B-spline fitting method (MBS) has been proposed which incorporates phase-based displacement information for accurate calculation of 2D motion and strain from tagged MRI [6, 7]. The proposed method combines the advantages of continuity and smoothness of MBS, and makes use of phase information derived from tagged MR images. Compared to previous 2D B-spline-based deformation analysis methods, MBS has the following advantages: 1) It can simultaneously achieve a smooth deformation while accurately approximating the given data set; 2) Computationally, it is very fast; and 3) It can produce more accurate deformation results. Since the tag intersections (intersections between two tag lines) can be extracted accurately and are more or less distributed evenly over the myocardium, MBS has proven effective for 2D cardiac motion tracking. To derive phase-based displacements, 2D HARP and SinMod analysis techniques [8,9] were employed. By producing virtual tags from HARP /SinMod and calculating intersections of virtual tag lines, more data points are obtained. In the reference frame, virtual tag lines are the isoparametric curves of an undeformed 2D B-spline model. In subsequent frames, the locations of intersections of virtual tag lines over the myocardium are updated with phase-based displacement. The advantage of the technique is that in acquiring denser myocardial displacements, it uses both real and virtual tag line intersections. It is fast and more accurate than 2D HARP and SinMod tracking. A novel 3D sine wave modeling (3D SinMod) approach for automatic analysis of 3D cardiac deformations has been proposed [10]. An accelerated 3D complementary spatial modulation of magnetization (CSPAMM) tagging technique [11] was used to acquire complete 3D+t tagged MR data sets of the whole heart (3 dynamic CSPAMM tagged MRI volume with tags in different orientations), in-vivo, in 54 heart beats and within 3 breath-holds. In 3D SinMod, the intensity distribution around each pixel is modeled as a cosine wave front. The principle behind 3D SinMod tracking is that both phase and frequency for each voxel are determined directly from the frequency analysis and the displacement is calculated from the quotient of phase difference and local frequency. The deformation fields clearly demonstrate longitudinal shortening during systole. The contraction of the LV base towards the apex as well as the torsional motion between basal and apical slices is clearly observable from the displacements. 3D SinMod can automatically process the image data to derive measures of motion, deformations, and strains between consecutive pair of tagged volumes in 17 seconds. Therefore, comprehensive 4D imaging and postprocessing for determination of ventricular function is now possible in under 10 minutes. For validation of 3D SinMod, 7 3D+t CSPAMM data sets of healthy subjects have been processed. Comparison of mid-wall contour deformations and circumferential shortening results by 3D SinMod showed good agreement with those by 3D HARP. Tag lines tracked by the proposed technique were also compared with manually delineated ones. The average errors calculated for the systolic phase of the cardiac cycles were in the sub-pixel range

Ensembles de niveaux robustes au speckle et recalage B-spline: application à la segmentation et l'analyse du mouvement cardiaque par des images ultrasons

L'analyse du mouvement local des parois du cœur dans des images ultrasonores est souvent utilisée pour diagnostiquer certaines malformations cardiaques. Malheureusement, cette modalité produit des images caractérisées par un niveau élevé de speckle, rendant difficile la détection des cavités. La thèse présente une méthode d'estimation du mouvement des cavités dans des images 2D. Nous proposons un nouveau modèle de level sets pour segmenter l'image. Ce modèle s'appuie sur une fonction d'arrêt adaptée au speckle. Celle-ci se démarque des fonctions habituelles en remplaçant le gradient par le coefficient de variation, une statistique robuste aux bruits multiplicatifs. De plus, nous renforçant cette fonction par un classificateur perceptron multicouche rendant plus fiable la détection de contours. Les résultats obtenus montrent un apport significatif en précision. L'estimation du mouvement se fait par un processus de recalage adaptatif qui calcule une B-spline hiérarchique. Cette méthode prend en entrée les courbes produites par la segmentation et estime la déformation en appliquant successivement l'algorithme ICP, une optimisation aux moindres carrés, et un raffinage hiérarchique. L'expérimentation montre que ce modèle aboutit à une approximation précise des déformations 2D des parois du cœu