Conventional Speckle Research Articles

Fully automated measurements of echocardiographic mechanical dispersion using deep learning: enhanced prediction of ventricular arrhythmias in a large heart failure cohort

Abstract Background Assessment of left ventricular (LV) myocardial deformation by strain echocardiography has shown improved prognostic value over LV ejection fraction (LVEF). Mechanical dispersion (MD) by strain reflects deformation heterogeneity. Also, MD is a marker of ventricular arrhythmia (VA) that improves risk prediction independently of LVEF in patients with heart failure. However, to analyze MD is time consuming and operator-dependent, and clinical use remains limited. Purpose We aimed to investigate the performance of a novel deep learning (DL) based method for fully automated measurements of MD and evaluate its prognostic utility in patients with heart failure compared to a conventional speckle tracking application. Methods In this prospective multicenter follow up study, the IMPROVE study, we consecutively included patients with recently diagnosed heart failure of all cause with LVEF ≤ 40%. Echocardiograms, ECG, blood samples and clinical data were acquired during index hospitalization. All patients were treated according to contemporary guidelines with optimal medical therapy and revascularization if necessary. Two experienced cardiologists recorded all echocardiograms using Vivid E9 or E95 scanners. We obtained data regarding sudden cardiac death, ventricular arrhythmia and appropriate shock from the ICD from medical records and ICD recordings. The primary endpoint was sudden cardiac death or ventricular arrhythmia (SCD/VA) during follow-up. The prognostic value of DL-based and reference MD measurements was assessed through survival statistics. Results We included 492 patients (mean ± SD 73 ± 13 years old, 32% females). Follow-up time was median (IQR) 5 (3) years. The incidence of SCD/VA was 9% (n=45). Patients with MD ≥70ms had increased risk of SCD/VA both by DL-based and reference measurements (both p <0.001). Furthermore, automated MD measurements using DL had higher prognostic value (HR 4.3) compared to manual reference measurements (HR 3.1) (p <0.001). Conclusion Fully automated measurements of MD using a novel DL method was fast, feasible, and improved prediction of SCD/VA in patients with heart failure and reduced LVEF. The integration of DL measurements may facilitate the clinical implementation of MD assessment and improve risk prediction in echocardiography.

High-visibility calculating ghost imaging with self-reconstruction capability and extendible depth-of-field.

We customized light speckle fields with both super-bunching and non-diffracting properties, accordingly named as the super-bunching, non-diffracting (SP-ND) speckle fields, by introducing pupil function of a ring aperture with azimuthally correlated phases in the vertically opposite angles. Calculating ghost imaging based on the SP-ND speckle fields was demonstrated to be of higher visibility, higher spatial resolution and larger depth of field than that based on the conventional speckle fields such as pseudo-thermal fields. Interestingly, the SP-ND speckles are also of self-healing capability in respect of not only the speckle intensity distribution but also the high-order coherence properties. Therefore, even when the SP-ND speckle fields are seriously disturbed, for example, blocked partially by an opaque obstacle, ghost images are able to be reconstructed once the object is placed in the self-healed speckle fields.

High frame rate speckle tracking echocardiography to assess diastolic function

Abstract Background Left ventricular (LV) strain rate (SR) during isovolumic relaxation (SRIVR) and early diastolic filling (SRe) has previously been shown to correlate with the invasive gold standard for LV diastolic function (i.e. the time constant of LV pressure decay tau). However, the translation of these biomarkers to the clinic has been hampered by technical limitations. Indeed, conventional speckle tracking (STE) is limited by its temporal resolution, whereas tissue Doppler imaging (TDI) is angle-dependent, labor-intensive and thus rarely used clinically nowadays. Purpose The aim of this study was to show that these limitations could be overcome by using a recently proposed STE algorithm operating on high frame rate (HFR) imaging data. Methods 37 subjects (age: 64±12, 81% male) were included in the study; 16 had cardiac amyloidosis, 12 were undergoing clinically indicated left and/or right heart cardiac catheterization and 9 were healthy volunteers. Since the sequence of left ventricular activation and thus the repolarization process (i.e. relaxation) starts at mid septum, we measured SRIVR and SRe in the mid septal segment in an apical 4 chamber view using a commercially available clinical system with: (1) TDI (frame rate (FR) ∼142 Hz); (2) STE (FR ∼65 Hz). Moreover, subjects were scanned with HD-PULSE, an experimental high frame ultrasound scanner (FR ∼915 Hz) and then a manually placed contour was tracked during the cardiac cycle by a custom-made 2D HFR STE algorithm, to compute and extract SRIVR and SRe from the mid septum. Since TDI is considered the reference method to assess SR, conventional as well as HFR STE values were correlated against the TDI SR values. Results In 3 subjects, SRIVR could not be reliably assessed with the clinical STE approach, which we attributed to the relatively low temporal resolution of the images; all other measurements could be made in all subjects. For both biomarkers, HFR STE values correlated better with the TDI reference measurements than the clinical STE estimates (Fig.1). The latter estimates showed a systematic underestimation (bias −0.19 1/s (p<0.01) and −0.46 1/s (p<0.01) for SRIVR and SRe respectively) while no significant bias was observed for the HFR STE values. Similarly, the limits of agreement of the HFR STE values were narrower (−0.45 to +0.54 1/s and −0.94 to +0.86 1/s) than those of the clinical STE measurements (−0.85 to +0.48 1/s and −1.32 to +0.41 1/s). Conclusions These results show that HFR STE offers a reliable way to assess novel biomarkers of diastolic function in a user-friendly manner and can therefore facilitate their incorporation to the clinical practice. Funding Acknowledgement Type of funding sources: None.

Role of Speckle Tracking in the Evaluation of Left Ventricular Remodeling After Streptokinase Infusion in Patients with Acute Anterior Myocardial Infarction

Background. Left ventricular (LV) remodeling is an adverse consequence after acute myocardial infarction.Aim. To assess the role of speckle tracking in the evaluation of LV remodeling after streptokinase infusion in patients with acute anterior ST-segment elevation myocardial infarction (STEMI).Material and methods. A total of 200 patients with first acute anterior STEMI received streptokinase as a reperfusion therapy were included. Conventional echocardiography and speckle tracking were performed within 3 days of admission and 3 months later. According to the development of LV remodeling, patients were classified into two groups. Group (I) patients with LV remodeling (60 patients) and group (II) patients without remodeling (140 patients).Results. Patients with LV remodeling had lower global longitudinal (GLS) and circumferential (GCS) strain values (-13.19±4.57 vs. -18.90±4.23 % and -13.16±4.27 vs. -17.16±3.3 %, respectively, p<0.001). GLS cutoff value of >-13.5 was shown to have the best diagnostic accuracy (sensitivity =60.0% & specificity =87.1%) in predicting LV remodeling (AUC 0.816, 95% confidence interval [CI] 0.754-0.877, p<0.001). GCS cutoff value of >-16.21 was shown to have the best diagnostic accuracy (sensitivity =75.0% & specificity =71.4%) in predicting LV remodeling (AUC 0.785, 95%CI 0.719-0.85, p<0.001).Conclusion. Speckle tracking echocardiography either longitudinal or circumferential strain has good sensitivity and specificity in predicting LV remodeling after acute myocardial infarction.

The Effect of Anti-TNF Therapy on Cardiac Function in Rheumatoid Arthritis: An Observational Study.

Congestive heart failure (CHF) is the second most prevalent cause of death in rheumatoid arthritis (RA). The systemic inflammatory state in RA patients is deemed responsible for this finding. Anti-inflammatory treatment with anti-tumor necrosis factor (anti-TNF) therapy decreases CV risk and subsequently might improve the cardiac function by lowering the overall inflammatory state. This study investigated the effect of anti-TNF on the cardiac function in RA patients. Fifty one RA patients were included, of which thirty three completed follow-up. Included patients were >18 years, had moderate–high disease activity and no history of cardiac disease. Patients were assessed at baseline and after six months of anti-TNF treatment. Patients underwent conventional Speckle tracking and tissue Doppler echocardiography in combination with clinical and laboratory assessments at baseline and follow-up. The left ventricular ejection fraction (LVEF) and global longitudinal strain (GLS) showed no changes during follow-up, LVEF 63% (±9) to 62% (±8) p = 0.097 and GLS −20 (±4) to −20 (±3) p = 0.79, respectively. Furthermore, E/e’ nor E/A changed significantly between baseline and follow-up, respectively 8 (7–9) and 8 (7–9) p = 0.17 and 1.1 (±0.4) and 1.1 (±0.4) p = 0.94. Follow-up NT-proBNP decreased with 23%, from 89 ng/L (47–142) to 69 ng/L (42–155), p = 0.10. Regression analysis revealed no association between change in inflammatory variables and cardiac function. Echocardiography showed no effect of anti-TNF treatment on the cardiac function in RA patients with low prevalence of cardiac dysfunction. Moreover, NT-proBNP decreased, possibly indicating (subtle) improvement of the cardiac function.

SPECKLE REDUCTION IN SAR IMAGES USING A BAYESIAN MULTISCALE APPROACH

Abstract. Synthetic aperture radar (SAR) images are corrupted by speckles, which influence the interpretation of the images. Therefore, to reduce speckles and obtain reliable information from images, researchers studied different methods. This study proposes a Bayesian multiscale method, to reduce speckles in SAR images. First, it was shown that Laplacian probability density function can capture the characteristics of noise-free curvelet coefficients, and then, a maximum a posteriori (MAP) estimator was designed for estimating them. Comparison of the results obtained with those obtained from conventional speckle filters, such as Lee, Kuan, Frost, and Gamma filters, and also curvelet non-Bayesian despeckling, shows better achievement of the proposed algorithm. For instance, the improvement in different parameters is as follows: ‘noise mean value’ (NMV) 0.24 times, ‘noise standard deviation’ (NSD) 0.34 times, ‘mean square difference’ (MSD) 2.6 times and ‘equivalent number of looks’ (ENL) 0.61 times.

Insulin resistance linked to subtle myocardial dysfunction in normotensive Turner syndrome young patients without structural heart diseases.

Background Turner syndrome (TS) patients have increased cardiovascular risk. This cardiovascular risk is famously attributed to structural abnormalities of the left side of the heart such as aortic stenosis and aortic coarctation. However, due to insulin resistance and subsequent pathogenic mechanisms, normotensive TS patients without structural abnormalities may develop varying degrees of myocardial dysfunction. The aim of this research was to examine the role of speckle tracking echocardiography in early detection of Turner cardiomyopathy and to correlate this myocardial dysfunction with measures of insulin resistance. Methods This cross-sectional case control study included 30 children with TS and 30 age-matched healthy controls. TS patients were excluded if: hypertensive, with major structural abnormalities of the heart or other systemic diseases that may affect myocardial function. Conventional speckle tracking echocardiography and glucose-insulin ratio were performed for all study subjects. Results Routine echocardiographic parameters of left ventricular systolic function were similar in cases and controls while global longitudinal and circumferential strain (GLS and GCS) were lower in patients with TS than controls: (-13.2±1.1 vs. -18.3±2.4, p-value<0.000) and (-11.3±1.1 vs. -16.3±2.1, p-value<0.000), respectively. Fasting glucose:insulin ratio (FGIR) proved to be the best predictor of myocardial dysfunction in TS patients by multivariate analysis. Conclusions This study points towards the potential role of two-dimensional (2D) speckle tracking echocardiography in early detection of subtle systolic myocardial dysfunction in TS patients. It also points towards the implication of insulin resistance in precipitation of the observed dysfunction in TS patients.

A Nonlinear Beamformer Based on p-th Root Compression—Application to Plane Wave Ultrasound Imaging

Ultrafast medical ultrasound imaging is necessary for 3D and 4D ultrasound imaging, and it can also achieve high temporal resolution (thousands of frames per second) for monitoring of transient biological phenomena. However, reaching such frame rates involves reduction of image quality compared with that obtained with conventional ultrasound imaging, since the latter requires each image line to be reconstructed separately with a thin ultrasonic focused beam. There are many techniques to simultaneously acquire several image lines, although at the expense of resolution and contrast, due to interference from echoes from the whole medium. In this paper, a nonlinear beamformer is applied to plane wave imaging to improve resolution and contrast of ultrasound images. The method consists of the introduction of nonlinear operations in the conventional delay-and-sum (DAS) beamforming algorithm. To recover the value of each pixel, the raw radiofrequency signals are first dynamically focused and summed on the plane wave dimension. Then, their amplitudes are compressed using the signed p t h root. After summing on the element dimension, the signed p-power is applied to restore the original dimensionality in volts. Finally, a band-pass filter is used to remove artificial harmonics introduced by these nonlinear operations. The proposed method is referred to as p-DAS, and it has been tested here on numerical and experimental data from the open access platform of the Plane wave Imaging Challenge in Medical UltraSound (PICMUS). This study demonstrates that p-DAS achieves better resolution and artifact rejection than the conventional DAS (for p = 2 with eleven plane wave imaging on experimental phantoms, the lateral resolution is improved by 21 % , and contrast ratio (CR) by 59 % ). However, like many coherence-based beamformers, it tends to distort the conventional speckle structure (contrast-to-noise-ratio (CNR) decreased by 45 % ). It is demonstrated that p-DAS, for p = 2 , is very similar to the nonlinear filtered-delay-multiply-and-sum (FDMAS) beamforming, but also that its impact on image quality can be tuned changing the value of p.

Surface topography measurement of plasma-facing materials by dual-wavelength phase-shifting speckle interferometry technique

A dual-wavelength phase-shifting speckle interferometry approach has been proposed to diagnose the topography of plasma-facing materials (PFMs) in tokamak. The conventional speckle interferometric surface measurement, which uses single-wavelength, can offer excellent vertical resolution, but limitation in measuring large height step and phase ambiguity would occur during their application. To solve the problem, a dual-wavelength method was developed. Experiments were conducted on molybdenum (Mo) sample, which is related to PFMs of experimental advanced superconducting tokamak (EAST), and a laser ablation method was adopted to simulate the erosion happed on PFMs. The laser ablation craters were measured by both single-wavelength and dual-wavelength phase-shifting speckle interferometry, and a multistep phase-shifting method has been investigated for their effectiveness on reducing noise in calculating the phase map. This work demonstrates the superiority of the dual-wavelength speckle interferometry and the feasibility of applying the measurement system in topographic measurement of PFMs in EAST.

Super-thermal light for imaging applications

AbstractWe report on a new classical light source useful for ghost-imaging applications. The light is obtained by frequency doubling a conventional speckle pattern having an overall multi-mode thermal distribution. The frequency-doubled light acquires a super-thermal distribution, which induces higher correlations at a beam splitter and, as a consequence, a higher visibility in ghost-imaging protocols.

Cardiac structure and function in elite Native Hawaiian and Pacific Islander Rugby Football League athletes: an exploratory study

The aim of this exploratory study was to define the Athletes Heart (AH) phenotype in Native Hawaiian & Pacific Islander (NH&PI) Rugby Football League (RFL) athletes. Specifically, (1) to describe conventional echocardiographic indices of left ventricle (LV) and right ventricle (RV) structure and function in NH&PI RFL players and matched RFL Caucasian controls (CC) and (2) to demonstrate LV and RV mechanics in these populations. Ethnicity is a contributory factor to the phenotypical expression of the AH. There are no data describing the cardiac phenotype in NH&PI athletes. Twenty-one male elite NH&PI RFL athletes were evaluated using conventional echocardiography and myocardial speckle tracking, allowing the assessment of global longitudinal strain (ε) and strain rate (SR); and basal, mid and global radial and circumferential ε and SR. Basal and apical rotation and twist were also assessed. Results were compared with age-matched Caucasian counterparts (CC; n = 21). LV mass [42 ± 9 versus 37 ± 4 g/(m2.7)], mean LV wall thickness (MWT: 9.5 ± 0.7 and 8.7 ± 0.4 mm), relative wall thickness (RWT: 0.35 ± 0.04 and 0.31 ± 0.03) and RV wall thickness (5 ± 1 and 4 ± 1 mm, all p < 0.05) were greater in NH&PI compared with CC. LV and RV cavity dimensions and standard indices of LV and RV systolic and diastolic function were similar between groups. NH&PI demonstrated reduced peak LV mid circumferential ε and early diastolic SR, as well as reduced global radial ε. There was reduced basal rotation at 25–35% systole, reduced apical rotation at 25–40% and 60–100% systole and reduced twist at 85–95% systole in NH&PI athletes. There were no differences between the two groups in RV wall mechanics. When compared to Caucasian controls, NH&PI rugby players have a greater LV mass, MWT and RWT with concomitant reductions in circumferential and twist mechanics. This data acts to prompt further research in NH&PI athletes.

Developing a bio-inspired multi-gene genetic programming based intelligent estimator to reduce speckle noise from ultrasound images

The speckle noise commonly occurs in ultrasound imaging based applications. Due to the multiplicative nature, speckle noise deteriorates the visual quality of ultrasound images. This affects the performance of radiologists and practitioners for disease diagnosis and/or patient treatment. The current study proposes a bio-inspired multi-gene genetic programming (MGGP) based intelligent estimator to reduce the speckle noise from ultrasound images. The proposed MGGP approach is based on the parallel framework of multiple genes and has effectively utilized the evolutionary learning capabilities to develop an intelligent estimator, by exploiting the useful statistical features extracted from local neighboring pixels. The performance of the proposed novel approach is evaluated on ultrasound images of common carotid artery corrupted with different noise levels. Further, the robust performance was validated on several diverse types of ultrasound images of Breast Cyst, Kidney Cancer, Liver, Liver Cyst, and Fetal Head. The proposed bio-inspired approach showed superior denoising performance over existing approaches. The proposed intelligent estimator is capable of removing speckle noise effectively while preserving the fine lines and edges. During evolution, the MGGP framework automatically selects the useful statistical features and primitive functions from a wider solution space to develop the intelligent estimator. Further, the proposed approach does not require image-dependent optimal threshold values, as conventional speckle denoising approaches required.

Problems of Bad Contrast in Conventional Microscopy Solution and Speckle Elimination with a Laser Fourier Holographic Microscope

The problem of bad contrast in conventional microscopy is well-known and was solved in part by colouring the samples. It is shown theoretically that a laser Fourier holographic microscope produces images undisturbed by speckle-noise. A laser holographic microscope (LHM) is investigated experimentally. The instrument uses visible radiation of λ = 0.514 µm, Mach – Zehnder scheme optical setup, and CCD detector of the hologram. Images are reconstructed digitally. The standard slide of Parascaris Univalens Iarva (ascaris) is studied without any drying as for electron microscope. Comparison of the pictures of the same ascaris cell, observed by the LHM and high-quality Nikon conventional optical microscope with immersion oil and green filter indicates dramatically different contrast. The ultrahigh contrast of the LHM gives much more micromorphological information.

Non-diffractive computational ghost imaging.

Computational ghost imaging (CGI) enables an image to be recorded using a single-pixel detector. The image can be reconstructed from correlations between the scene and a series of known projected intensity patterns. In this work we investigate the performance of CGI using pseudo non-diffracting (ND) speckle patterns. We demonstrate an extended depth-of-field that is ∼ 2-3 times greater than that achievable with conventional speckle, when only computing each intensity pattern to a single depth. In addition, the average speckle grain size of ND speckle is reduced by a factor of ∼ 1.5 relative to conventional speckle, which enhances the lateral Rayleigh-limit resolving power of our reconstructed images. However, the point-spread function (PSF) of our imaging system takes the form of a Bessel beam, which manifests itself as long-range correlations between speckle grains in the projected patterns. We discuss the trade-off between enhancement of the depth-of-field and the lateral resolution when using ND speckle, at the expense of a reduction in image contrast. Our work demonstrates that the tailoring of lateral and axial correlations in projected intensity patterns permits PSF engineering in CGI.

Investigation on sensitivity enhancement for optical fiber speckle sensors.

We present a detailed theoretical and experimental study on the sensitivity enhancement for multimode fiber (MMF) speckle sensor. Using mode coupling theory, we derive an expression showing that the sensitivity of the MMF speckle sensor depends on the intensity profile of the MMF modes. Particularly, we use our theory to study the influence of the spatial filtering window on the sensitivity, and the experimental results have found a good agreement with the theory. Our results suggest that the sensitivity of an MMF speckle sensor can be greatly enhanced by adjusting the size and location of the spatial filtering window. An 80-fold improvement on sensitivity was achieved in our experiment, as compared with the conventional MMF speckle sensor with the filtering window placed at the center of the speckle field.

Comparison of phase recovery methods in spiral speckle pattern interferometry correlation fringes

Spiral interferometry can be used as a solution to the problem of sign ambiguity presented in the conventional speckle pattern interferometric technique when the optical phase needs to be reconstructed from a single closed fringe system. Depressions and elevations of the topography corresponding to the object deformation are distinguished by the direction of rotation of the local spiral fringe pattern. In this work, we implement and compare several methods for optical phase reconstruction by analyzing a single image composed of spiral speckle pattern interferometry correlation fringes. The implemented methods are based on contour line demodulation, center line demodulation, Spiral Phase Quadrature Transform and the 2D Riesz transform with multivector structure. Contour line and center line demodulation approaches are exclusively dedicated to images containing a fringe system with spiral structure. The others are based on the 2D Riesz transform, these being well known approaches in conventional interferometry. We examine simulated experiments and analyze some of the emerging drawbacks for solving the phase reconstruction problem by using different mean values of speckle size and background noise levels. We also discuss several numerical procedures that may well improve the efficiency and robustness of the presented numerical implementations. The performance of the implemented demodulation methods is evaluated by using a universal image quality index and therefore a quantitative comparison is also presented.

Abstract 12217: A Hierarchical Model for Stage B Heart Failure Screening- Results of a Classification and Regression-Based Decision Tree

Purpose: In pts with stage A heart failure (SAHF), the identification of stage B HF relies on echo, but application of this to community based screening is limited by access and cost. We sought to use clinical characteristics and functional capacity to select at risk subjects for echo. Methods: 308 asymptomatic subjects ≥65 years with the presence of ≥ 1 HF risk factor (hypertension, type 2 diabetes, obesity, previous chemotherapy, family history of heart failure and history of cardiac disease but not in HF) were recruited from the local community. All subjects underwent baseline risk quantification using ARIC risk score, functional assessment by 6 minute-walk test (6MW) and a comprehensive echocardiogram including conventional diastology and speckle tracking analysis for global longitudinal strain (GLS) and diastolic strain (DS). New HF was assessed at 14±4 m, based on 3 independent cardiologists using Framingham criteria. A classification and regression-based decision tree (CART) was built using baseline characteristics as independent variables. Results: In the CART model, a 3-level decision tree model was chosen to predict 19 pts (6%) who developed new HF at 1 year. The best predictor was 6MW followed by ARIC risk score (Figure). Using this model, 190 individuals (6MW≤330, or ARIC score&gt;4.75%) were classified as high risk (9.5% events) and 118 (38%) were classified as low risk (0.8% events). GLS, DS and conventional diastolic measures (e’, E/e’) were significantly impaired in the high risk group (Figure). The AUC of the combined CART model with GLS was 0.72 (95% CI: 0.62-0.82, p=0.001) for new HF. Conclusion: Pts with SAHF with low HF risk and preserved exercise capacity have preserved LV function and a low event rate. GLS assessment in SAHF may be considered in pts with &gt;4.75% 4 year risk, or 6MW≤330m.

Abstract P635: Improvement of Cardiovascular Outcomes in Diabetic Rats by a Novel Angiotensin II Receptor Peptide Agonist

Diabetes Mellitus (DM) is an independent predictor of cardiovascular disease (CVD). Recent reports show that Angiotensin II type 2 receptor (AT2R) promotes cardiac repair after myocardial infarction. Therefore, we hypothesized that activation of AT2R would improve cardiac function in diabetic rats. Male Zucker obese (ZO) rats are leptin receptor–deficient and exhibit hyperphagia, obesity, insulin resistance and hyperlipidemia. They are a widely used rodent model for early stage Type 2 DM (T2DM). We and others have reported that male ZO rats exhibit diastolic and systolic dysfunction. Therefore we investigated whether a two week treatment with an AT2R agonist could improve cardiac functions of young male ZO rats. Thirteen-week old male ZO rats were subjected to daily intraperitoneal injections (0.9mg/kg/day) with a novel peptide AT2R agonist, NP-6A4 (from Novopyxis, Inc.) dissolved in saline (n=7) or saline only (n=6) for two weeks. Conventional echocardiography and speckle tracking strain analysis were performed using a Vevo 2100 (visualsonics) small animal ultrasound system. Fasting (6 hours) plasma analysis showed that triglycerides (mg/dL) were significantly reduced in response to treatment (ZO+ Saline=1229±164; ZO+NP-6A4= 610±109; p&lt;0.015). Importantly, NP-6A4 treatment improved E/E’ ratio (ZO+Saline= 32.3±2.06; ZO+NP-6A4= 26±2.1; p&lt;0.005), which indicates a significant improvement in diastolic dysfunction. A unit rise in the E/E' ratio is associated with a 17% increment in risk of a cardiac event. Moreover, myocardial performance index of NP-6A4 treated rats was also reduced (ZO+ Saline= 0.516±0.03; ZO+ NP-6A4= 0.389±0.02; p&lt;0.006). Finally, circumferential strain (deg/sec) of endocardium (short axis view) was also significantly improved in response to treatment, while no significant changes were observed in radial or longitudinal strains (ZO+ Saline= -20.56±1.65; ZO+ NP-6A4= -26.11±2.47; p&lt;0.024). Collectively, these data suggest that activation of the AT2R by NP-6A4 had significant lipid lowering effect and improved diastolic and systolic functions in diabetic rats.

A maximum likelihood approach to diffeomorphic speckle tracking for 3D strain estimation in echocardiography.

The strain and strain-rate measures are commonly used for the analysis and assessment of regional myocardial function. In echocardiography (EC), the strain analysis became possible using Tissue Doppler Imaging (TDI). Unfortunately, this modality shows an important limitation: the angle between the myocardial movement and the ultrasound beam should be small to provide reliable measures. This constraint makes it difficult to provide strain measures of the entire myocardium. Alternative non-Doppler techniques such as Speckle Tracking (ST) can provide strain measures without angle constraints. However, the spatial resolution and the noisy appearance of speckle still make the strain estimation a challenging task in EC. Several maximum likelihood approaches have been proposed to statistically characterize the behavior of speckle, which results in a better performance of speckle tracking. However, those models do not consider common transformations to achieve the final B-mode image (e.g. interpolation). This paper proposes a new maximum likelihood approach for speckle tracking which effectively characterizes speckle of the final B-mode image. Its formulation provides a diffeomorphic scheme than can be efficiently optimized with a second-order method. The novelty of the method is threefold: First, the statistical characterization of speckle generalizes conventional speckle models (Rayleigh, Nakagami and Gamma) to a more versatile model for real data. Second, the formulation includes local correlation to increase the efficiency of frame-to-frame speckle tracking. Third, a probabilistic myocardial tissue characterization is used to automatically identify more reliable myocardial motions. The accuracy and agreement assessment was evaluated on a set of 16 synthetic image sequences for three different scenarios: normal, acute ischemia and acute dyssynchrony. The proposed method was compared to six speckle tracking methods. Results revealed that the proposed method is the most accurate method to measure the motion and strain with an average median motion error of 0.42 mm and a median strain error of 2.0 ± 0.9%, 2.1 ± 1.3% and 7.1 ± 4.9% for circumferential, longitudinal and radial strain respectively. It also showed its capability to identify abnormal segments with reduced cardiac function and timing differences for the dyssynchrony cases. These results indicate that the proposed diffeomorphic speckle tracking method provides robust and accurate motion and strain estimation.

Temporal averaging of two-dimensional correlation functions for velocity vector imaging of cardiac blood flow.

Ultrasonic imaging of blood flow in the cardiac lumen is a very useful tool to evaluate the pumping function of the human heart. The speckle tracking technique makes it possible to estimate the blood velocity vector. However, a stable estimation of the velocity vector of blood flow is difficult because signal-to-noise ratios of echoes from tiny blood particles are low. In this study, the speckle tracking technique with averaging of multiple two-dimensional correlation functions was employed for stable estimation of the blood velocity vector. Multiple two-dimensional correlation functions can be averaged during a very short period by using the echo data acquired by high-frame-rate echocardiography with diverging beam transmission. A steady flow experiment using blood-mimicking fluid (mean fluid velocity 0.2 m/s, flow angle 56° from the transducer surface) was implemented to investigate the effect of the averaging of two-dimensional correlation functions at a frame rate of 6024 Hz. First, to examine the averaging duration required for stable estimation of the flow velocity vector, the accuracies of vector estimates were evaluated at different durations for averaging of two-dimensional correlation functions in the steady flow measurement. It was found that the proposed averaging process with an averaging duration of over 8 frames could reduce the directional error in vector estimation to almost half that of the conventional speckle tracking technique. In subsequent experiments, the averaging duration was set at 12 frames corresponding to 2 ms. Measurements of steady flow at higher velocities were further implemented. The steady flow measurements with higher flow velocities of 0.4 and 0.6 m/s were simulated by changing the frame interval of the echo data at a flow velocity of 0.2 m/s. Although the averaging duration was a mere 2 ms, directional errors at mean flow velocities of 0.2, 0.4, and 0.6 m/s were reduced significantly. In an in vivo experiment of the healthy human heart, to produce a fine B-mode image, the diverging wave transmissions with different steered angles for compounding were interleaved in the transmission sequence. From the in vivo experimental result, the blood velocity vector of the left ventricular cavity showed the flow getting into/out of the cavity in ejection and early diastolic phases. Furthermore, estimated flow directions revealed rotating flow in the cavity in mid-diastole. Our proposed method has the feasibility to visualize the vortex flow by velocity vector mapping without a contrast agent.