Quantitative validation of optical flow based myocardial strain measures using sonomicrometry

Dynamic cardiac metrics, including myocardial strains and displacements, provide a quantitative approach to evaluate cardiac function. However, in current clinical diagnosis, largely 2D strain measures are used despite that cardiac motions are complex 3D volumes over time. Recent advances in 4D ultrasound enable the capability to capture such complex motion in a single image data set. In our previous work, a 4D optical flow based motion tracking algorithm was developed to extract full 4D dynamic cardiac metrics from such 4D ultrasound data. In order to quantitatively evaluate this tracking method, in-vivo coronary artery occlusion experiments at various locations were performed on three canine hearts. Each dog was screened with 4D ultrasound and sonomicrometry data was acquired during each occlusion study. The 4D ultrasound data from these experiments was then analyzed with the tracking method and estimated principal strain measures were directly compared to those recorded by sonomicrometry. Strong agreement was observed independently for the three canine hearts. This is the first validation study of optical flow based strain estimation for 4D ultrasound with a direct comparison with sonomicrometry using in-vivo data

Analysis of strain in the human left ventricle using real-time 3D echocardiography and optical flow

Cardiovascular disease (CVD) consistently ranks among the leading causes of death in the United States. The most common subtype of CVD, ischemic heart disease, is a frequent precursor of myocardial infarction and heart failure, most commonly affecting the left ventricle (LV). Today, echocardiography is regarded as the gold standard in screening, diagnosis, and monitoring of LV dysfunction. But while global assessment of LV function tends to be quantitative, cardiologists with specific expertise still perform many regional evaluations subjectively. However, a more objective and quantitative measure of regional function – myocardial strain – has been developed and widely studied using 2D echocardiography. With recent developments in real-time 3D echocardiography (RT3DE), it has become possible to measure strain in its native 3D orientation as well. Our laboratory’s earlier work introduced the Optical Flow (OF) method of strain analysis, which was validated on simulated echocardiograms as well as through animal studies. The principal goal of this thesis is to translate this OF-based method of strain estimation from the research setting to the patient’s bedside. We have performed a series of studies to evaluate the feasibility, accuracy, and reproducibility of OF-based myocardial strain estimation in a routine clinical setting. The first investigation focused on the optimization of RT3DE acquisition and the OF processing pipeline for use in human subjects. Subsequently, we evaluated the capacity of this technique to distinguish abnormal strain patterns in patients with CVD and varying degrees of LV dysfunction. Our analysis revealed that segmental strain measures obtained by OF may have better sensitivity and specificity than the more commonly used global LV strains. Our third validation study examined the reproducibility of these strain measures in both healthy and diseased populations. We established that OF-based strain measures demonstrate repeatability comparable to that achieved by the latest commercial software commonly used in clinical research to estimate 2D or 3D strain. These studies were driven in large part by the absence of a ground truth or accepted gold standard of 3D strain measurements in the human LV. However, cardiac magnetic resonance imaging has had considerable success in measuring some forms of strain in the human LV. We therefore began to develop an image-processing pipeline to derive strain estimates from a new pulse sequence called 3D-DENSE. We further sought to improve the OF pipeline by automating the process of tracking the LV border. To this end, we developed a level-set based technique which tracks the LV endocardium. Our evaluation of its performance on RT3DE data confirmed that this method performs within the limits of inter-observer variability. Overall, our pilot studies of OF-based strain estimation demonstrate that the technique possesses several promising features for improving cardiologists’ ability to quantify and interpret the complex three-dimensional deformations of the human LV

A new 2D-based method for myocardial velocity strain and strain rate quantification in a normal adult and paediatric population: assessment of reference values

<p>Abstract</p> <p>Background</p> <p>Recent advances in technology have provided the opportunity for off-line analysis of digital video-clips of two-dimensional (2-D) echocardiographic images.</p> <p>Commercially available software that follows the motion of cardiac structures during cardiac cycle computes both regional and global velocity, strain, and strain rate (SR).</p> <p>The present study aims to evaluate the clinical applicability of the software based on the tracking algorithm feature (studied for cardiology purposes) and to derive the reference values for longitudinal and circumferential strain and SR of the left ventricle in a normal population of children and young adults.</p> <p>Methods</p> <p>45 healthy volunteers (30 adults: 19 male, 11 female, mean age 37 ± 6 years; 15 children: 8 male, 7 female, mean age 8 ± 2 years) underwent transthoracic echocardiographic examination; 2D cine-loops recordings of apical 4-four 4-chamber (4C) and 2-chamber (2C) views and short axis views were stored for off-line analysis.</p> <p>Computer analyses were performed using specific software relying on the algorithm of optical flow analysis, specifically designed to track the endocardial border, installed on a Windows™ based computer workstation. Inter and intra-observer variability was assessed.</p> <p>Results</p> <p>The feasibility of measurements obtained with tissue tracking system was higher in apical view (100% for systolic events; 64% for diastolic events) than in short axis view (70% for systolic events; 52% for diastolic events). Longitudinal systolic velocity decreased from base to apex in all subjects (5.22 ± 1.01 vs. 1.20 ± 0.88; p < 0.0001). Longitudinal strain and SR significantly increased from base to apex in all subjects (-12.95 ± 6.79 vs. -14.87 ± 6.78; p = 0.002; -0.72 ± 0.39 vs. -0.94 ± 0.48, p = 0.0001, respectively). Similarly, circumferential strain and SR increased from base to apex (-21.32 ± 5.15 vs. -27.02 ± 5.88, p = 0.002; -1.51 ± 0.37 vs. -1.95 ± 0.57, p = 0.003, respectively).</p> <p>Values of global systolic SR, both longitudinal and circumferential, were significantly higher in children than in adults (-1.3 ± 0.2, vs. -1.11 ± 0.2, p = 0.006; -1.9 ± 0.6 vs. -1.6 ± 0.5, p = 0.0265, respectively). No significant differences in longitudinal and circumferential systolic velocities were identified for any segment when comparing adults with children.</p> <p>Conclusion</p> <p>This 2D based tissue tracking system used for computation is reliable and applicable in adults and children particularly for systolic events. Measured with this technology, we have established reference values for myocardial velocity, Strain and SR for both young adults and children.</p

Measurement of left ventricular deformation using 3D echocardiography

Bakgrunn: 3D speckle tracking ekkokardiografi (STE) er en hjerteultralydmetode som gir mulighet for måling av deformasjonsparametere, som strain, rotasjon, tvist og torsjon. Den største begrensningen for 3D STE er lav tids- og romlig oppløsning. Økes den ene oppløsingen vil den andre bli redusert. I tillegg vil andre faktorer som antall flettede bilder, sektorstørrelse og dybde påvirke begge oppløsningene. Denne avhandlingen har hatt som mål å finne tilstander og opptaksinnstillinger for å optimalisere nøyaktigheten til 3D STE-parametere i et kontrollert miljø. Videre har det vært som mål å finne regional deformasjon fra 3D STE i en klinisk studie på pasienter med aortaklaffestenose (AS) ved bruk av optimaliserte innstillinger. Materiale og metode: Studie 1 og 2 utforsket nøyaktigheten til 3D STE ved bruk av et in vitro-oppsett med et fantom av venstre ventrikkel. Studie 1 sammenlignet 3D STE strain mot sonomikromertri som gullstandard i longitudinell, sirkumferensiell og radiell retning. Ved å bruke et annet fantom i studie 2 ble 3D STE tvist sammenlignet mot sonomikrometri tvist for å finne nøyaktigheten til 3D STE tvistmålinger. Studie 3 inkluderte 85 pasienter med variabel grad av AS i en tverrsnittstudie. 3D ekkokardiografi ble utført og 3D STE-parametere ble sammenlignet mellom grupper av pasienter med mild, moderat og alvorlig AS. Resultater: Studie 1 fant godt samsvar mellom 3D STE og sonomikrometri med optimalt volum rate på 36,6 volumer per sekund (VPS) ved bruk av 6 sammenflettede bilder. I studie 2 hadde 3D STE godt samsvar ved bruk av både 4 og 6 sammenflettede bilder med volum rater på henholdsvis 20,3 og 17,1 VPS. Studie 3 fant lavere global longitudinal strain i pasienter med alvorlig AS sammenlignet med mild AS. Basal og midtre longitudinal strain var også lavere i alvorlig sammenlignet med mild AS. Apikal-basal ratio var høyere for moderat i forhold til mild AS. Maks apikal-basal tvist var høyere hos pasienter med alvorlig sammenlignet med mild og moderat AS. Konklusjon: Måling av venstre ventrikkelfunksjon med 3D STE er mest nøyaktig med volum rater < 40 VPS. Høy romlig oppløsning virker å være mer viktig enn tidsoppløsning. Pasienter med alvorlig AS har lavere global, basal og midtre longitudinal strain enn pasienter med mild AS, ved bruk av 3D STE. De har også høyere tvist enn mild og moderat AS. Områder som involverer apeks, har høyere spredning av data og har antagelig lavere nøyaktighet ved bruk av 3D STE.Background: 3D speckle tracking echocardiography (STE) enables measurement of multiple parameters of deformation, such as strain, rotation, twist and torsion. The main limitation of 3D STE is low temporal and spatial resolution. Increasing resolution in time will decrease resolution in space, and vice versa. In addition, other factors such as number of stitched images, sector size and depth, influence the resolution. This thesis aimed to find conditions and acquisition settings to optimize accuracy for 3D STE parameters in a controlled in vitro environment. Secondly, it aimed to evaluate regional deformation by 3D STE in a clinical study on patients with aortic valve stenosis (AS) using optimized settings. Materials and methods: Study 1 and 2 explored the accuracy of 3D STE using an in vitro setup with a left ventricle (LV) phantom. Study 1 compared 3D STE strain to strain by sonomicrometry as the gold standard. Measurements were compared in both longitudinal, circumferential and radial direction. Using a different twisting phantom in study 2, 3D STE twist was compared to twist by sonomicrometry to evaluate the accuracy of 3D STE twist. Study 3 was a cross-sectional analysis of 85 patients with variable degree of AS in a cross-sectional study. 3D echocardiography was done, and 3D STE parameters were compared between groups of patients with mild, moderate and severe AS. Results: Study 1 found 3D STE strain to have good agreement with sonomicrometry. Optimal acquisition settings were found to be volume rate 36.6 volumes per second (VPS) obtained by 6 stitched images. Study 2 found 3D STE twist to have good agreement with sonomicrometry when using both 4 and 6 stitched images with volume rates 20.3 and 17.1 VPS, respectively. Study 3 found global longitudinal strain to be lower in patients with severe AS compared to those with mild AS. Basal and mid longitudinal strains were also lower in severe AS than in mild AS. Apical basal ratio was higher for moderate than mild AS. Peak apical-basal twist was higher in patients with severe AS than in those with mild and moderate AS. Conclusion: Assessment of LV function by 3D STE is most accurate at volume rates < 40 VPS. High spatial resolution seems to be more important than temporal resolution. Patients with severe AS have lower global, as well as lower regional basal and mid longitudinal strain compared to patients with mild AS, assessed with 3D STE. They also have higher twist than mild and moderate AS. Segments involving the apex have high dispersion and probably lower accuracy in 3D STE.Doktorgradsavhandlin

Oscillatory wall strain reduction precedes arterial intimal hyperplasia in a murine model

Cardiovascular diseases (CVD) remain the most common cause of death in the United States. Additionally, peripheral artery disease affects thousands of people each year. A major underlying cause of these diseases is the occlusion of the coronary or peripheral arteries due to arteriosclerosis. To overcome this, a number of vascular interventions have been developed including angioplasty, stenting, endarterectomies and bypass grafts. Although all of these methods are capable of restoring blood flow to the distal organ after occlusion, they are all plagued by unacceptably high restenosis rates. While the biological reactions that occur as a result of each of these methods differ, the initiating factor of both the primary atherosclerosis and subsequent failure of vascular interventions appears to be intimal hyperplasia (IH). Intimal hyperplasia is most simply defined as the expansion of multiple layers of cells internally to the internal elastic lamina of the blood vessel. This excessive cellular growth leads to arterial stenosis, plaque formation and inflammatory reactions. Despite extensive research the underlying factors that cause IH remain unclear. A quantity of research to date has implicated endothelial cell mechanosensation as the mechanism by which IH is initiated with evidence positively correlating wall shear stress with IH. Others, however, have demonstrated that changes in the stresses applied to the wall in vitro can modulate IH independent of hemodynamic shear stress. Thus, relations between wall tensile stress and IH in vivo may shed light on the underlying mechanisms of IH. Since noninvasive measurement of wall tensile stress in vivo is difficult, it is most feasible to measure oscillatory wall strain which is intimately related to wall tensile stress through the mechanical properties of the arterial wall. In this dissertation, we hypothesize that reductions in oscillatory wall strain precede the formation of intimal hyperplasia in a murine model. To test our hypothesis, we first developed a novel, high spatial and temporal resolution method to measure oscillatory wall strains in the murine common carotid artery. We validated this method both in vitro using an arterial phantom and in vivo using a murine model of abdominal aortic aneurysms. To assess relationships between strain and IH, we applied our strain measurement technique to a recently developed mouse model of IH. In this model, a suture is used to create a focal stenosis and reduce flow through the common carotid artery by 85%; resulting in proximal IH formation. Using this approach, we identified a relationship between oscillatory strain reductions and IH. Subsequent analysis demonstrated that early reductions in mechanical strain just 4 days after focal stenosis creation correlate with IH formation nearly 1 month later. Since IH is not expected to form by day 4 in this model, we went on to assess changes in gross vascular morphology at day 4. We discovered that, although strains are significantly reduced by day 4, no significant IH can be observed, suggesting that changes in wall structure are resulting in strain reductions. At day 4 post-op, we observed cellular proliferation and leukocyte recruitment to the wall without intimal hyperplasia. These studies suggest that early reductions in mechanical strain may be an important predictor of IH formation. Clinically, this relation could be important for the development of novel techniques for predicting IH formation before it becomes hemodynamically significant

Principles of cardiovascular magnetic resonance feature tracking and echocardiographic speckle tracking for informed clinical use

Tissue tracking technology of routinely acquired cardiovascular magnetic resonance (CMR) cine acquisitions has increased the apparent ease and availability of non-invasive assessments of myocardial deformation in clinical research and practice. Its widespread availability thanks to the fact that this technology can in principle be applied on images that are part of every CMR or echocardiographic protocol. However, the two modalities are based on very different methods of image acquisition and reconstruction, each with their respective strengths and limitations. The image tracking methods applied are not necessarily directly comparable between the modalities, or with those based on dedicated CMR acquisitions for strain measurement such as tagging or displacement encoding. Here we describe the principles underlying the image tracking methods for CMR and echocardiography, and the translation of the resulting tracking estimates into parameters suited to describe myocardial mechanics. Technical limitations are presented with the objective of suggesting potential solutions that may allow informed and appropriate use in clinical applications

Load-Independent And Regional Measures Of Cardiac Function Via Real-Time Mri

LOAD-INDEPENDENT AND REGIONAL MEASURES OF CARDIAC FUNCTION VIA REAL-TIME MRI Francisco Jose Contijoch Robert C Gorman, MD Expansion of infarcted tissue during left ventricular (LV) remodeling after a myocardial infarction is associated with poor long-term prognosis. Several interventions have been developed to limit infarct expansion by modifying the material properties of the infarcted or surrounding borderzone tissue. Measures of myocardial function and material properties can be obtained non-invasively via imaging. However, these measures are sensitive to variations in loading conditions and acquisition of load-independent measures have been limited by surgically invasive procedures and limited spatial resolution. In this dissertation, a real-time magnetic resonance imaging (MRI) technique was validated in clinical patients and instrumented animals, several technical improvements in MRI acquisition and reconstruction were presented for improved imaging resolution, load-independent measures were obtained in animal studies via non-invasive imaging, and regional variations in function were measured in both na�ve and post-infarction animals. Specifically, a golden-angle radial MRI acquisition with non-Cartesian SENSE-based reconstruction with an exposure time less than 95 ms and a frame rate above 89 fps allows for accurate estimation of LV slice volume in clinical patients and instrumented animals. Two technical developments were pursued to improve image quality and spatial resolution. First, the slice volume obtained can be used as a self-navigator signal to generate retrospectively-gated, high-resolution datasets of multiple beat morphologies. Second, cross-correlation of the ECG with previously observed values resulted in accurate interpretation of cardiac phase in patients with arrhythmias and allowed for multi-shot imaging of dynamic scenarios. Synchronizing the measured LV slice volume with an LV pressure signal allowed for pressure-volume loops and corresponding load-independent measures of function to be obtained in instrumented animals. Acquiring LV slice volume at multiple slice locations revealed regional differences in contractile function. Motion-tracking of the myocardium during real-time imaging allowed for differences in contractile function between normal, borderzone, and infarcted myocardium to be measured. Lastly, application of real-time imaging to patients with arrhythmias revealed the variable impact of ectopic beats on global hemodynamic function, depending on frequency and ectopic pattern. This work established the feasibility of obtaining load-independent measures of function via real-time MRI and illustrated regional variations in cardiac function

Model-based quantification of systolic and diastolic left ventricular mechanics

Het linker ventrikel (LV) is de meest gespierde kamer van het hart. Door het gecoördineerd samentrekken van de spiercellen in de LV-wand wordt zuurstofrijk bloed in de aorta gepompt (systolische fase). Daarna ontspannen de spiercellen zich snel waardoor het LV opnieuw met bloed wordt gevuld (diastolische fase). In de kliniek en de onderzoekswereld bestaat er een waaier van modelgebaseerde methoden en concepten om de performantie en de mechanische eigenschappen van het LV te kwantificeren. Invasief bekomen druk- en volumedata laten toe om de systolische en diastolische mechanica van het LV met grote nauwkeurigheid te kennen. In de klinische praktijk wordt echter vaker gebruik gemaakt van (Doppler-) echocardiografie, een snelle en veilige niet-invasieve beeldtechniek. In een eerste deel van dit doctoraatsonderzoek werd een originele methode voorgesteld om, op basis van echocardiografie en klassieke bloeddrukmetingen, de intrinsieke krachtontwikkeling (contractiliteit) van het LV te schatten. De methode werd toegepast bij 2524 mensen die deelnemen aan de Asklepios-studie. De onderzoeksresultaten verschaften ons nieuwe informatie over hoe de evolutie van de krachtontwikkeling verschilt tussen gezonde mannen en vrouwen. De mechanische en vloeistofdynamische fenomenen tijdens de diastole vormden het onderwerp van het tweede deel van het onderzoek. Met behulp van een hydraulisch model van het LV werd nagegaan welke factoren een belangrijke invloed uitoefenen op het gedrag van het LV tijdens de isovolumetrische ontspanningsfase. In dit deel werd eveneens een uitgebreid overzicht gegeven van de meest recente echocardiografische methoden om de diastolische LV-mechanica te begroten. Daarbij werden de bloedstroming, de wandbeweging en de interactie tussen beiden gedetailleerd behandeld

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