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

Myocardial tagging by Cardiovascular Magnetic Resonance: evolution of techniques--pulse sequences, analysis algorithms, and applications

Cardiovascular magnetic resonance (CMR) tagging has been established as an essential technique for measuring regional myocardial function. It allows quantification of local intramyocardial motion measures, e.g. strain and strain rate. The invention of CMR tagging came in the late eighties, where the technique allowed for the first time for visualizing transmural myocardial movement without having to implant physical markers. This new idea opened the door for a series of developments and improvements that continue up to the present time. Different tagging techniques are currently available that are more extensive, improved, and sophisticated than they were twenty years ago. Each of these techniques has different versions for improved resolution, signal-to-noise ratio (SNR), scan time, anatomical coverage, three-dimensional capability, and image quality. The tagging techniques covered in this article can be broadly divided into two main categories: 1) Basic techniques, which include magnetization saturation, spatial modulation of magnetization (SPAMM), delay alternating with nutations for tailored excitation (DANTE), and complementary SPAMM (CSPAMM); and 2) Advanced techniques, which include harmonic phase (HARP), displacement encoding with stimulated echoes (DENSE), and strain encoding (SENC). Although most of these techniques were developed by separate groups and evolved from different backgrounds, they are in fact closely related to each other, and they can be interpreted from more than one perspective. Some of these techniques even followed parallel paths of developments, as illustrated in the article. As each technique has its own advantages, some efforts have been made to combine different techniques together for improved image quality or composite information acquisition. In this review, different developments in pulse sequences and related image processing techniques are described along with the necessities that led to their invention, which makes this article easy to read and the covered techniques easy to follow. Major studies that applied CMR tagging for studying myocardial mechanics are also summarized. Finally, the current article includes a plethora of ideas and techniques with over 300 references that motivate the reader to think about the future of CMR tagging

Rotation and torsion of the left ventricle with cardiovascular magnetic resonance tagging : comparison of two analysis methods

Background Left ventricle rotation and torsion are fundamental components of myocardial function, and several software packages have been developed for analysis of these components. The purpose of this study was to compare the suitability of two software packages with different technical principles for analysis of rotation and torsion of the left ventricle during systole. Methods A group of hypertrophic cardiomyopathy (HCM) patients (N = 14, age 43 +/- 11 years), mutation carriers without hypertrophy (N = 10, age 34 +/- 13 years), and healthy relatives (N = 12, age 43 +/- 17 years) underwent a cardiovascular magnetic resonance examination, including spatial modulation of magnetization tagging sequences in basal and apical planes of the left ventricle. The tagging images were analyzed offline using a harmonic phase image analysis method with Gabor filtering and a non-rigid registration-based free-form deformation technique. Left-ventricle rotation and torsion scores were obtained from end-diastole to end-systole with both software. Results Analysis was successful in all cases with both software applications. End-systolic torsion values between the study groups were not statistically different with either software. End-systolic apical rotation, end-systolic basal rotation, and end-systolic torsion were consistently higher when analyzed with non-rigid registration than with harmonic phase-based analysis (p <0.0001). End-systolic rotation and torsion values had significant correlations between the two software (p <0.0001), most significant in the apical plane. Conclusions When comparing absolute values of rotation and torsion between different individuals, software-specific reference values are required. Harmonic phase flow with Gabor filtering and non-rigid registration-based methods can both be used reliably in the analysis of systolic rotation and torsion patterns of the left ventricle.Peer reviewe

Rotation and torsion of the left ventricle with cardiovascular magnetic resonance tagging : comparison of two analysis methods

Background Left ventricle rotation and torsion are fundamental components of myocardial function, and several software packages have been developed for analysis of these components. The purpose of this study was to compare the suitability of two software packages with different technical principles for analysis of rotation and torsion of the left ventricle during systole. Methods A group of hypertrophic cardiomyopathy (HCM) patients (N = 14, age 43 +/- 11 years), mutation carriers without hypertrophy (N = 10, age 34 +/- 13 years), and healthy relatives (N = 12, age 43 +/- 17 years) underwent a cardiovascular magnetic resonance examination, including spatial modulation of magnetization tagging sequences in basal and apical planes of the left ventricle. The tagging images were analyzed offline using a harmonic phase image analysis method with Gabor filtering and a non-rigid registration-based free-form deformation technique. Left-ventricle rotation and torsion scores were obtained from end-diastole to end-systole with both software. Results Analysis was successful in all cases with both software applications. End-systolic torsion values between the study groups were not statistically different with either software. End-systolic apical rotation, end-systolic basal rotation, and end-systolic torsion were consistently higher when analyzed with non-rigid registration than with harmonic phase-based analysis (p <0.0001). End-systolic rotation and torsion values had significant correlations between the two software (p <0.0001), most significant in the apical plane. Conclusions When comparing absolute values of rotation and torsion between different individuals, software-specific reference values are required. Harmonic phase flow with Gabor filtering and non-rigid registration-based methods can both be used reliably in the analysis of systolic rotation and torsion patterns of the left ventricle.Peer reviewe

Joint Strain Analysis in cardia MRI

Master'sMASTER OF ENGINEERIN

Quantification of MRI-derived myocardial motion in specified cardiac disorders

Several cardiac diseases affect myocardial function, with local myocardial deformation receiving much attention over the past few years. This work aimed to examine whether globally and locally analyzed quantitative cardiovascular magnetic resonance imaging-derived strain, rotation, and torsion of the heart would bring additional value and deeper understanding to myocardial mechanics in specified cardiovascular disorders. Patients with rheumatoid arthritis, tetralogy of Fallot, hereditary gelsolin amyloidosis, and hypertrophic cardiomyopathy, together with healthy controls, were investigated. A non-rigid registration-based software solution for myocardial tagging and feature tracking analysis was used for the quantification of left ventricular and right ventricular global and regional strain in different directions. Quantitative motion analysis showed that early treatment of rheumatoid arthritis was useful in retaining the diastolic function of the left ventricle. In adolescents with tetralogy of Fallot, right ventricular circumferential strain was increased relative to healthy controls. Tetralogy of Fallot subjects with increased pulmonary regurgitation had higher right ventricular longitudinal strain than subjects with less pulmonary regurgitation; this has been considered a compensation mechanism. Hereditary gelsolin amyloidosis showed local myocardial changes focused on the basal plane of the left ventricle and differing from the more common light-chain cardiac amyloidosis. The non-rigid registration-based technique was compared with the harmonic phase-based method with Gabor filtering in the analysis of myocardial tagging-derived rotation and torsion in subjects with hypertrophic cardiomyopathy. The absolute values obtained with the two software methods were significantly different, however, neither software showed significant differences in patients with hypertrophic cardiomyopathy relative to healthy controls. Motion parameters of both ventricles were associated with other quantitative cardiac magnetic resonance imaging parameters, such as volumetric measurements and T1 relaxation times, in the studies of this thesis. Tagging and feature tracking-derived motion parameters showed significant findings in local myocardial motion in rheumatoid arthritis, tetralogy of Fallot,and hereditary gelsolin amyloidosis. Software-based reference values are required when comparing motion parameters between study subjects. Currently, no standardization for measuring different deformation parameters, such as strain, rotation, or torsion exists, and several software solutions are available for analyzing these parameters. Variability between different software solutions and individual observers should be recognized.Useat sydänsairaudet vaikuttavat sydänlihaksen paikalliseen liikkeeseen, jonka vuoksi sydänlihaksen liikkeen tutkiminen on herättänyt paljon mielenkiintoa muutaman viime vuoden aikana. Tämän työn tavoitteena oli tutkia magneettikuvauksessa määritettyjä sydänlihaksen globaaleja ja paikallisia kvantitatiivisia liikeparametrejä eri sydänsairauksissa. Väitöskirjan osatöissä tutkittiin nivelreumapotilaita, Fallotin tetralogia -potilaita, Meretojantautipotilaita ja hypertrofisen kardiomyopatian omaavia potilaita, yhdessä terveiden verrokkien kanssa. Elastisen kuvarekisteröinnin omaavaa ohelmistoratkaisua käytettiin sydänlihaksen kvantitatiivisen venymän mittaamiseen eri suunnissa sydämen vasenta ja oikeaa kammiota. Kvantitatiivinen liikeanalyysi osoitti, että varhaisen nivelreuman lääkehoito kannattaa, jotta sydämen vasemman kammion diastolinen funktio saadaan ylläpidettyä. Teini-ikäisillä Fallotin tetralogia -potilailla oikean kammion kehän suuntainen venymä oli selvästi voimakkaampaa kuin terveillä verrokeilla. Lisäksi Fallotin tetralogia -potilailla, joilla oli suuri pulmonaaliläpän vuoto, oli voimakkaampi oikean kammion pitkittäissuuntainen venymä, kuin potilailla, joilla vuoto oli pienempää; tämän ajateltiin olevan sydänlihaksen kompensaatiomekanismi. Meretojantautipotilailla havaittiin paikallisia sydänlihaksen liikkeen ja kudoskoostumuksen muutoksia erityisesti sydämen vasemman kammion basaalitasossa. Elastisen kuvarekisteröinnin menetelmää verrattiin harmoniseen Gabor -suodatettuun menetelmään sydänlihaksen vasemman kammion kiertymän ja väännön analysoinnissa. Näillä kahdella menetelmällä määritetyt absoluuttiset kiertymän ja väännön arvot erosivat merkittävästi toisistaan, mutta kummallakaan menetelmällä määritetyt kiertymän ja väännön arvot eivät eronneet merkittävästi hypertrofisen kardiomyopatian omaavien potilaiden ja terveiden verrokkien välillä. Sydämen vasemman ja oikean kammion liikeparametrejä verrattiin muihin kvantitatiivisiin sydämen magneettikuvauksen parametreihin, kuten kammioiden volumetrisiin mittauksiin ja sydänlihaksen T1 relaksaatioaikoihin, väitöskirjan eri osatöissä. Sydämen magneettikuvauksessa määritetyt kvantitatiivisen liikeanalyysin eri parametrit osoittivat merkittäviä löydöksiä sydänlihaksen toiminnassa nivelreumassa, Fallotin tetralogiassa ja Meretojantaudissa. Ohjelmistokohtaiset referenssiarvot ovat tarpeen, kun absoluuttisia liikeparametriarvoja vertaillaan eri yksilöiden välillä. Tällä hetkellä ei ole olemassa standardeja eri liikekomponenttien mittaamiselle ja eri ohjelmistoratkaisuja on useita erilaisia. Vaihteluväli erilaisia ohjelmistoratkaisuja käytettäessä, ja eri tarkkailijoiden välinen vaihtelu, on syytä tiedostaa

An image segmentation and registration approach to cardiac function analysis using MRI

Cardiovascular diseases (CVDs) are one of the major causes of death in the world. In recent years, significant progress has been made in the care and treatment of patients with such diseases. A crucial factor for this progress has been the development of magnetic resonance (MR) imaging which makes it possible to diagnose and assess the cardiovascular function of the patient. The ability to obtain high-resolution, cine volume images easily and safely has made it the preferred method for diagnosis of CVDs. MRI is also unique in its ability to introduce noninvasive markers directly into the tissue being imaged(MR tagging) during the image acquisition process. With the development of advanced MR imaging acquisition technologies, 3D MR imaging is more and more clinically feasible. This recent development has allowed new potentially 3D image analysis technologies to be deployed. However, quantitative analysis of cardiovascular system from the images remains a challenging topic. The work presented in this thesis describes the development of segmentation and motion analysis techniques for the study of the cardiac anatomy and function in cardiac magnetic resonance (CMR) images. The first main contribution of the thesis is the development of a fully automatic cardiac segmentation technique that integrates and combines a series of state-of-the-art techniques. The proposed segmentation technique is capable of generating an accurate 3D segmentation from multiple image sequences. The proposed segmentation technique is robust even in the presence of pathological changes, large anatomical shape variations and locally varying contrast in the images. Another main contribution of this thesis is the development of motion tracking techniques that can integrate motion information from different sources. For example, the radial motion of the myocardium can be tracked easily in untagged MR imaging since the epi- and endocardial surfaces are clearly visible. On the other hand, tagged MR imaging allows easy tracking of both longitudinal and circumferential motion. We propose a novel technique based on non-rigid image registration for the myocardial motion estimation using both untagged and 3D tagged MR images. The novel aspect of our technique is its simultaneous use of complementary information from both untagged and 3D tagged MR imaging. The similarity measure is spatially weighted to maximise the utility of information from both images. The thesis also proposes a sparse representation for free-form deformations (FFDs) using the principles of compressed sensing. The sparse free-form deformation (SFFD) model can capture fine local details such as motion discontinuities without sacrificing robustness. We demonstrate the capabilities of the proposed framework to accurately estimate smooth as well as discontinuous deformations in 2D and 3D CMR image sequences. Compared to the standard FFD approach, a significant increase in registration accuracy can be observed in datasets with discontinuous motion patterns. Both the segmentation and motion tracking techniques presented in this thesis have been applied to clinical studies. We focus on two important clinical applications that can be addressed by the techniques proposed in this thesis. The first clinical application aims at measuring longitudinal changes in cardiac morphology and function during the cardiac remodelling process. The second clinical application aims at selecting patients that positively respond to cardiac resynchronization therapy (CRT). The final chapter of this thesis summarises the main conclusions that can be drawn from the work presented here and also discusses possible avenues for future research

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

QUANTITATIVE ELASTICITY IMAGING AND SOFT TISSUE CHARACTERIZATION USING TAGGED MAGNETIC RESONANCE IMAGING

Ph.DDOCTOR OF PHILOSOPH

Filter Design and Consistency Evaluation for 3D Tongue Motion Estimation using Harmonic Phase Analysis Method

Understanding patterns of tongue motion in speech using 3D motion estimation is challenging. Harmonic phase analysis has been used to perform noninvasive tongue motion and strain estimation using tagged magnetic resonance imaging (MRI). Two main contributions have been made in this thesis. First, the filtering process, which is used to produce harmonic phase images used for tissue tracking, influences the estimation accuracy. For this work, we evaluated different filtering approaches, and propose a novel high-pass filter for volumes tagged in individual directions. Testing was done using an open benchmarking dataset and synthetic images obtained using a mechanical model. Second, the datasets with inconsistent motion need to be excluded to yield meaningful motion estimation. For this work, we used a tracking-based method to evaluate the motion consistency between datasets and gave a strategy to identify the inconsistent dataset. Experiments including 2 normal subjects were done to validate our method. In all, the first work about 3D filter design improves the motion estimation accuracy and the second work about motion consistency test ensures the meaningfulness of the estimation results