Semi-automatic outlining of levator hiatus.

OBJECTIVE: To create a semi-automated outlining tool for the levator hiatus, to reduce interobserver variability and and speed up analysis. METHODS: The proposed automated hiatus segmentation (AHS) algorithm takes a C-plane image, in the plane of minimal hiatal dimensions, and manually defined vertical hiatal limits as input. The AHS then creates an initial outline by fitting predefined templates on an intensity-invariant edge map, which is further refined using the B-spline explicit active surfaces framework. The AHS was tested using 91 representative C-plane images. Reference hiatal outlines were obtained manually and compared with the AHS outlines by three independent observers. The mean absolute distance (MAD), Hausdorff distance and Dice and Jaccard coefficients were used to quantify segmentation accuracy. Each of these metrics was calculated both for computer-observer differences (COD) and for interobserver differences. The Williams index was used to test the null hypothesis that the automated method would agree with the operators at least as well as the operators agreed with each other. Agreement between the two methods was assessed using the intraclass correlation coefficient (ICC) and Bland-Altman plots. RESULTS: The AHS contours matched well with the manual ones (median COD, 2.10 (interquartile range (IQR), 1.54) mm for MAD). The Williams index was greater than or close to 1 for all quality metrics, indicating that the algorithm performed at least as well as did the manual references in terms of interrater variability. The interobserver differences using each of the metrics were significantly lower, and a higher ICC was achieved (0.93), when obtaining outlines using the AHS compared with manually. The Bland-Altman plots showed negligible bias between the two methods. Using the AHS took a median time of 7.07 (IQR, 3.49) s, while manual outlining took 21.31 (IQR, 5.43) s, thus being almost three-fold faster. Using the AHS, in general, the hiatus could be outlined completely using only three points, two for initialization and one for manual adjustment. CONCLUSIONS: We present a method for tracing the levator hiatal outline with minimal user input. The AHS is fast, robust and reliable and improves interrater agreement. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

The relative value of strain and strain rate for defining intrinsic myocardial function.

It is well accepted that strain and strain rate deformation parameters are not only a measure of intrinsic myocardial contractility but are also influenced by changes in cardiac load and structure. To date, no information is available on the relative importance of these confounders. This study was designed to investigate how strain and strain rate, measured by Doppler echocardiography, relate to the individual factors that determine cardiac performance. Echocardiographic and conductance measurements were simultaneously performed in mice in which individual determinants of cardiac performance were mechanically and/or pharmacologically modulated. A multivariable analysis was performed with radial and circumferential strains and peak systolic radial and circumferential strain rates as dependent parameters and preload recruitable stroke work (PRSW), arterial elastance (E(a)), end-diastolic pressure, and left ventricular myocardial volume (LVMV) as independent factors representing myocardial contractility, afterload, preload, and myocardial volume, respectively. Radial strain was most influenced by E(a) (ß = -0.58, R(2) = 0.34), whereas circumferential strain was strongly associated with E(a) and moderately with LVMV (ß = 0.79 and -0.52, respectively, R(2) = 0.54). Radial strain rate was related to both PRSW and LVMV (ß = 0.79 and -0.62, respectively, R(2) = 0.50), whereas circumferential strain rate showed a prominent correlation only with PRSW (ß = -0.61, R(2) = 0.51). In conclusion, strain (both radial and circumferential) is not a good surrogate measure of intrinsic myocardial contractility unless the strong confounding influence of afterload is considered. Strain rate is a more robust measure of contractility that is less influenced by changes in cardiac load and structure. Thus, peak systolic strain rate is the more relevant parameter to assess myocardial contractile function noninvasively.

Echocardiographic assessment of left ventricular untwist rate: comparison of tissue Doppler and speckle tracking methodologies.

AIMS: The study was designed to test the influence of the temporal resolution, at which tissue Doppler imaging (TDI) and speckle tracking imaging (STI) operate, on the accurate assessment of left ventricular (LV) untwist rate (UR). METHODS AND RESULTS: Echo imaging and invasive LV pressure measurements were performed during right atrial (RA) pacing and dobutamine challenge in eight pigs. LV torsion and torsional rate profiles were analysed from grey scale and tissue Doppler data (apical and basal short axis) at frame rates of 82 +/- 17 and 183 +/- 14 Hz, respectively. Temporal subsampling of TDI data sets was performed at 82 +/- 6 Hz in order to mimic the mean temporal resolution of STI and the LV torsional curves were again extracted. At rest, LV UR values were comparable for both imaging techniques. However, during dobutamine stimulation, TDI estimated peak UR was predominantly higher than UR measured by STI (-112.1 +/- 64.5 degrees /s vs. -75.5 +/- 31.4 degrees /s, P < 0.05). The similarity of LV UR measurements with respect to the STI/TDI data was examined by a Bland-Altman analysis. CONCLUSION: Although both methods regarding LV UR correlated well, these methods cannot be interchanged. STI showed a bias to underestimate UR at high values.

A Framework for the Generation of Realistic Synthetic Cardiac Ultrasound and Magnetic Resonance Imaging Sequences From the Same Virtual Patients.

The use of synthetic sequences is one of the most promising tools for advanced in silico evaluation of the quantification of cardiac deformation and strain through 3-D ultrasound (US) and magnetic resonance (MR) imaging. In this paper, we propose the first simulation framework which allows the generation of realistic 3-D synthetic cardiac US and MR (both cine and tagging) image sequences from the same virtual patient. A state-of-the-art electromechanical (E/M) model was exploited for simulating groundtruth cardiac motion fields ranging from healthy to various pathological cases, including both ventricular dyssynchrony and myocardial ischemia. The E/M groundtruth along with template MR/US images and physical simulators were combined in a unified framework for generating synthetic data. We efficiently merged several warping strategies to keep the full control of myocardial deformations while preserving realistic image texture. In total, we generated 18 virtual patients, each with synthetic 3-D US, cine MR, and tagged MR sequences. The simulated images were evaluated both qualitatively by showing realistic textures and quantitatively by observing myocardial intensity distributions similar to real data. In particular, the US simulation showed a smoother myocardium/background interface than the state-of-the-art. We also assessed the mechanical properties. The pathological subjects were discriminated from the healthy ones by both global indexes (ejection fraction and the global circumferential strain) and regional strain curves. The synthetic database is comprehensive in terms of both pathology and modality, and has a level of realism sufficient for validation purposes. All the 90 sequences are made publicly available to the research community via an open-access database.

Radial strain assessment of the interventricular septum wall by a new technique in healthy subjects.

The aim of this study was to design a new approach for the acquisition of regional radial strain from the middle portion of the interventricular septum. We designed and wrote a program in Matlab (computer-assisted method) for use on a personal computer so that the septum thickness throughout the cardiac cycle could be measured instantaneously. Computer-assisted and conventional manual methods were used on the same 2D echocardiography image frames. Then, real-time 2D color Doppler myocardial imaging and conventional 2D imaging of the septum walls of 12 healthy participants at rest using apical four-chamber view were acquired. Wall thickness was measured using both the computerized program and velocity data used for tracking the segment and intensity line profile modification automatically. Then, the radial strain was estimated. Bland-Altman statistical analysis shows good agreement between the computer-assisted method and conventional manual method. The average of the peak and mean radial strains from the mid-septum of 12 healthy participants were 63.5 +/- 10.7 and 31.7 +/- 7.5%, respectively. We introduced a simple approach that is capable of radial strain estimation of the septum wall, which cannot be measured by current Doppler based methods in echocardiography systems.

Integration of Multi-Plane Tissue Doppler and B-Mode Echocardiographic Images for Left Ventricular Motion Estimation.

Although modern ultrasound acquisition systems allow recording of 3D echocardiographic images, tracking anatomical structures from them is still challenging. In addition, since these images are typically created from information obtained across several cardiac cycles, it is not yet possible to acquire high-quality 3D images from patients presenting varying heart rhythms. In this paper, we propose a method to estimate the motion field from multi-plane echocardiographic images of the left ventricle, which are acquired simultaneously during a single cardiac cycle. The method integrates tri-plane B-mode and tissue Doppler images acquired at different rotation angles around the long axis of the left ventricle. It uses a diffeomorphic continuous spatio-temporal transformation model with a spherical data representation for a better interpolation in the circumferential direction. This framework allows exploiting the spatial relation among the acquired planes. In addition, higher temporal resolution of the transformation in the beam direction is achieved by uncoupling the estimation of the different components of the velocity field. The method was validated using a realistic synthetic dataset including healthy and ischemic cases, obtaining errors of 0.14 ± 0.09 mm for displacements, 0.96 ± 1.03% for longitudinal strain and 3.94 ± 4.38% for radial strain estimation. In addition, the method was also demonstrated on a healthy volunteer and two patients with ischemia.

In-vivo validation of a new clinical tool to quantify three-dimensional myocardial strain using ultrasound.

Three-dimensional (3D) strain analysis based on real-time 3-D echocardiography (RT3DE) has emerged as a novel technique to quantify regional myocardial function. The goal of this study was to evaluate accuracy of a novel model-based 3D tracking tool (eSie Volume Mechanics, Siemens Ultrasound, Mountain View, CA, USA) using sonomicrometry as an independent measure of cardiac deformation. Thirteen sheep were instrumented with microcrystals sutured to the epi- and endocardium of the inferolateral left ventricular wall to trace myocardial deformation along its three directional axes of motion. Paired acquisitions of RT3DE and sonomicrometry were made at baseline, during inotropic modulation and during myocardial ischemia. Accuracy of 3D strain measurements was quantified and expressed as level of agreement with sonomicrometry using linear regression and Bland-Altman analysis. Correlations between 3D strain analysis and sonomicrometry were good for longitudinal and circumferential strain components (r = 0.78 and r = 0.71) but poor for radial strain (r = 0.30). Accordingly, agreement (bias ± 2SD) was -5 ± 6 % for longitudinal, -5 ± 7 % for circumferential, and 15 ± 19 % for radial strain. Intra-observer variability was low for all components (intra-class correlation coefficients (ICC) of respectively 0.89, 0.88 and 0.95) while inter-observer variability was higher, in particular for radial strain (ICC = 0.41). The present study shows that 3D strain analysis provided good estimates of circumferential and longitudinal strain, while estimates of radial strain were less accurate between observers.

A spectroscopic study of the chromatic properties of GafChromicEBT3 films.

PURPOSE: This work provides an interpretation of the chromatic properties of GafChromicEBT3 films based on the chemical nature of the polydiacetylene (PDA) molecules formed upon interaction with ionizing radiation. The EBT3 films become optically less transparent with increasing radiation dose as a result of the radiation-induced polymerization of diacetylene monomers. In contrast to empirical quantification of the chromatic properties, less attention has been given to the underlying molecular mechanism that induces the strong decrease in transparency. METHODS: Unlaminated GafChromicEBT3 films were irradiated with a 6 MV photon beam to dose levels up to 20 Gy. The optical absorption properties of the films were investigated using visible (vis) spectroscopy. The presence of PDA molecules in the active layer of the EBT3 films was investigated using Raman spectroscopy, which probes the vibrational modes of the molecules in the layer. The vibrational modes assigned to PDA's were used in a theoretical vis-absorption model to fit our experimental vis-absorption spectra. From the fit parameters, one can assess the relative contribution of different PDA conformations and the length distribution of PDA's in the film. RESULTS: Vis-spectroscopy shows that the optical density increases with dose in the full region of the visible spectrum. The Raman spectrum is dominated by two vibrational modes, most notably by the ν(C≡C) and the ν(C=C) stretching modes of the PDA backbone. By fitting the vis-absorption model to experimental spectra, it is found that the active layer contains two distinct PDA conformations with different absorption properties and reaction kinetics. Furthermore, the mean PDA conjugation length is found to be 2-3 orders of magnitude smaller than the crystals PDA's are embedded in. CONCLUSIONS: Vis- and Raman spectroscopy provided more insight into the molecular nature of the radiochromic properties of EBT3 films through the identification of the excited states of PDA and the presence of two PDA conformations. The improved knowledge on the molecular composition of EBT3's active layer provides a framework for future fundamental modeling of the dose-response.

Noninvasive quantification of the contractile reserve of stunned myocardium by ultrasonic strain rate and strain.

BACKGROUND: We sought to investigate ultrasonic strain rate and strain as new indices to quantify the contractile reserve of stunned myocardium during dobutamine infusion. METHODS AND RESULTS: Stunning of the left ventricular posterior wall was induced in 9 closed-chest pigs after 30 minutes of severe hypoperfusion followed by 60 minutes of reperfusion of the left circumflex coronary artery territory. A second group of 7 animals had no coronary occlusion and served as normal controls. An incremental dobutamine infusion protocol was used in both groups. Changes in regional radial function were monitored by use of ultrasound-derived maximal systolic radial strain rate (SR) and systolic strain (epsilon). In the control group, dobutamine induced an increase in both SR and maximal dP/dt, which correlated linearly (r=0.85). Conversely, epsilon values increased at low doses of dobutamine (2.5 to 5 microg. kg(-1). min(-1)) but decreased during higher infusion rates (10 to 20 microg. kg(-1). min(-1)). During circumflex hypoperfusion, SR and epsilon of the posterior wall decreased from 5.0+/-0.3 s(-1) and 63+/-6% to 2.9+/-0.3 s(-1) and 27+/-4%, respectively (P<0.01). After 60 minutes of reperfusion, SR and epsilon failed to fully resume because of stunning, averaging 3.6+/-0.2 s(-1) and 35+/-3%, respectively (P=0.12 versus ischemia, P<0.05 versus baseline). During dobutamine infusion, SR increased at 5 microg. kg(-1). min(-1) and exceeded baseline values at 20 microg. kg(-1). min(-1) (P<0.05), whereas epsilon increased only at high doses and remained below baseline levels (P<0.05). CONCLUSIONS: The changes in regional function of stunned myocardium during inotropic stimulation could be characterized by use of ultrasonic deformation parameters. During dobutamine infusion, strain-rate values quantified the contractile reserve better than strain values.

A Pipeline for the Generation of Realistic 3D Synthetic Echocardiographic Sequences: Methodology and Open-Access Database.

Quantification of cardiac deformation and strain with 3D ultrasound takes considerable research efforts. Nevertheless, a widespread use of these techniques in clinical practice is still held back due to the lack of a solid verification process to quantify and compare performance. In this context, the use of fully synthetic sequences has become an established tool for initial in silico evaluation. Nevertheless, the realism of existing simulation techniques is still too limited to represent reliable benchmarking data. Moreover, the fact that different centers typically make use of in-house developed simulation pipelines makes a fair comparison difficult. In this context, this paper introduces a novel pipeline for the generation of synthetic 3D cardiac ultrasound image sequences. State-of-the art solutions in the fields of electromechanical modeling and ultrasound simulation are combined within an original framework that exploits a real ultrasound recording to learn and simulate realistic speckle textures. The simulated images show typical artifacts that make motion tracking in ultrasound challenging. The ground-truth displacement field is available voxelwise and is fully controlled by the electromechanical model. By progressively modifying mechanical and ultrasound parameters, the sensitivity of 3D strain algorithms to pathology and image properties can be evaluated. The proposed pipeline is used to generate an initial library of 8 sequences including healthy and pathological cases, which is made freely accessible to the research community via our project web-page.

Quantitation of left-ventricular asynergy by cardiac ultrasound.

The clinical evaluation of regional delays in myocardial motion (myocardial asynchrony) has proved problematic, yet it remains an important functional parameter to evaluate. Prior attempts to quantify regional asynergy have met with limited success, often thwarted by the low temporal resolution of imaging-system data acquisition. If a delay in onset of motion of 30-40 msec is clinically important to measure, then data acquisition at frame rates of 50-100 per second is required. This is out of the current temporal resolution of angiographic, nuclear, or magnetic resonance studies. Only cardiac ultrasound can currently achieve the necessary frame rates. Furthermore, quantitative studies into the accuracy with which a trained observer can identify computed regional myocardial asynchrony in a left-ventricular 2-dimensional (2-D) image have shown that regional delays of < 80 msec are not normally recognized in a moving image. This may be improved to 60 msec when either training is undertaken or comparative image review is used. However, this is still out of the temporal resolution required in clinical practice. Thus, visual interpretation of asynchrony is not sufficiently accurate. Two ultrasound data sets based on either integrated backscatter or Doppler myocardial imaging data may provide the solution. Doppler myocardial imaging is a new ultrasound technique which, in either its pulsed or color Doppler format, can achieve the required temporal resolution (with temporal resolutions of 8 msec and 16 msec, respectively). In contrast, color Doppler myocardial imaging, in its curved M-mode format, can display the timing of events during the cardiac cycle for all in-plane myocardial segments. This should allow the quantitation of regional delay for all systolic and diastolic events. Potentially, asynchrony due to regional ischemia, bundle branch block, ventricular premature beats, and ventricular preexcitation could all be identified and the degree of delay quantified. This overview will aim to establish the potential role of these new ultrasound methodologies in the recognition and quantitation of left-ventricular asynergy and how they might best be introduced into clinical practice.

Abnormal postsystolic thickening in acutely ischemic myocardium during coronary angioplasty: a velocity, strain, and strain rate doppler myocardial imaging study.

We report a case in which the combination of gray scale imaging of wall thickness changes allied to color DMI regional velocity, strain, and strain rate data identified the development and regression of diastolic thickening in the acute ischemic segment during a right coronary artery percutaneous transluminal coronary angioplasty (PTCA). We also discuss the possible mechanisms and potential clinical implications of this finding.

Quantification of the spectrum of changes in regional myocardial function during acute ischemia in closed chest pigs: an ultrasonic strain rate and strain study.

The objectives of this study were to define the spectrum of regional myocardial function changes during acute ischemia in closed chest animals by using newly developed ultrasonic strain rate and strain indexes derived from regional color Doppler myocardial imaging (CDMI) velocity data. Myocardial ischemia was induced in 18 pigs either with acute total 20-second occlusions (group 1, n = 12) or graded hypoperfusion (40 to 0 mL/min, group 2, n = 6) of the circumflex coronary artery. In addition, a dobutamine challenge (5 to 10 microg/kg per minute) was performed during sustained subtotal ischemia (10 mL/min) in group 2. CDMI acquisitions with parasternal views monitored the myocardial posterior wall function. Regional radial strain rate and strain (epsilon(r)) were measured for systole, isovolumic relaxation, early diastole, and atrial filling, respectively. During total and graded ischemia, epsilon(r) profiles were consistently modified, showing a delayed onset and a decrease in regional systolic thickening as well as increased postsystolic thickening. Radial strain rate and epsilon(r) indexes decreased consistently during systole and early diastole and increased during isovolumic relaxation. End-systolic epsilon(r) could differentiate total ischemia from severe hypoperfusion (10 mL/min), decreasing from 32% +/- 8% to 16% +/- 5% (versus 60% +/- 10% at baseline). During dobutamine infusion (10 microg/kg per minute), end-systolic epsilon(r) tended to decrease from 27% +/- 5% to 18% +/- 11%, whereas postsystolic thickening increased by 2-fold (P <.05). The combined analysis of regional deformation characteristics and global cardiac event timing derived from CDMI data can identify and quantify regional function changes induced by experimental acute ischemia in closed chest pigs. This would appear to be a potentially promising new noninvasive approach to the clinical evaluation of ischemia-induced changes in segmental myocardial function.

Changes in systolic and postsystolic wall thickening during acute coronary occlusion and reperfusion in closed-chest pigs: Implications for the assessment of regional myocardial function.

The aim of the study was to characterize the impact of short-lived total coronary occlusions in closed-chest pigs on radial wall thickening within the "at-risk" myocardial segment by using gray-scale M-mode echocardiography. Twelve pigs underwent a series of 20-second total circumflex coronary artery occlusions with an angioplasty balloon. Myocardial thickening/thinning indexes were continuously monitored before ischemia, during ischemia, and on reperfusion by high-resolution M-mode recordings of the posterior wall obtained from parasternal views. The timing of regional events was compared with global systolic time intervals derived from the color Doppler myocardial imaging velocity data. Each occlusion induced a rapid decrease in end-systolic thickening (epsilon(ES)), closely paralleled by an increase in postsystolic thickening in the ischemic segment. After 20 seconds of ischemia, epsilon(ES) decreased by -86% and postsystolic thickening increased by +100%, whereas maximal thickening decreased only by -34% in comparison with preocclusion values. All wall thickening parameters returned to baseline after 15 seconds of reperfusion. During acute total ischemia in a closed-chest animal model, the changes in regional myocardial function were best characterized by the combined analysis of systolic and postsystolic thickening abnormalities and by their respective timings relative to global cardiac events markers.

Are changes in myocardial integrated backscatter restricted to the ischemic zone in acute induced ischemia? An in vivo animal study.

Integrated backscatter (IB) from a myocardial region, calculated from radiofrequency echocardiographic data, has been proposed as a useful parameter for investigating changes in myocardial tissue induced by ischemia. In 10 closed-chest dogs, 5 minutes of myocardial ischemia was induced by either a proximal occlusion of the circumflex coronary artery (CX) (5 dogs), resulting in extensive ischemia in the posterior wall, or by occluding the distal CX vessel (5 dogs) to produce a small localized ischemic zone in the posterior wall. High-resolution digital radiofrequency data from the whole left ventricular myocardium, in the imaging plane during one complete heart cycle, were acquired with a whole-image real-time acquisition approach. Regions in the septum and posterior wall (both ischemic tissue and, in the case of distal occlusions, tissue surrounding the ischemic zone) were chosen for analysis, and IB and cyclic variation (CV) of IB were calculated. Post occlusion, an increase in mean IB values was found in the ischemic segment. However, an increase in CV was also observed in the peri-ischemic zone for the distal CX occlusion and in the septum after proximal CX occlusion. These findings show that changes in CV are not restricted to the ischemic zone but may also occur in distal myocardium. This may be explained by changes in the regional contractile state and loading conditions of the "normal" myocardium, which are altered in response to the distal ischemia.

Comparison of time-domain displacement estimators for two-dimensional RF tracking.

Techniques have been described in the literature to enable multidimensional strain rate estimation. They are based on multidimensional velocity estimation. One of the problems in obtaining robust lateral strain rate estimates is the fact that lateral velocity estimates are intrinsically noisier than axial ones. The aim of this study was to find the optimal estimator for tracking of the radiofrequency patterns both in axial and lateral directions. Performances of the following estimators were investigated using simulations: cross-correlation, normalized cross-correlation, sum of absolute differences and sum of squared differences. Two-dimensional (2-D) velocity estimation was not feasible using cross-correlation. However, normalized cross-correlation, sum of absolute differences and sum of squared differences showed accurate axial and lateral results. For smaller window lengths, sum of squared differences was found to be the preferred estimator for 2-D velocity estimation using a 1-D kernel.

Quantifying myocardial deformation throughout the cardiac cycle: a comparison of ultrasound strain rate, grey-scale M-mode and magnetic resonance imaging.

Strain rate imaging (SRI) is a new ultrasound (US) approach to the quantification of regional myocardial deformation. It previously has been validated in vitro and in vivo against other imaging techniques. However, in all such studies, only peak strain values were compared, and the temporal evolution of the strain curve was not studied. Yet, it is the temporal evolution of the strain curves that contains the more important clinical information (e.g., asynchrony, viability, etc). Thus, the aim of this study was to compare the evolution of strain during the complete cardiac cycle as measured by US SRI, US grey-scale M-mode and magnetic resonance imaging (MRI). In 10 healthy volunteers and 20 patients with chronic ischaemic heart disease, radial deformation of the inferolateral segment of the left ventricle was measured by US SRI, US M-mode and MRI. The correspondence of the temporal characteristics of these strain curves were compared by defining an intraclass correlation coefficient (ICC). In healthy volunteers, an overall good agreement (mean ICC: 0.75 and 0.63 for systole and diastole) was found between the different methods. However, in patients with abnormal segmental deformation and low peak strain values, the agreement was less (mean ICC: 0.42 and 0.32), but remained within acceptable limits for clinical decision making. Myocardial deformation measurements using SRI correlated well with MRI and US M-mode measurements throughout the complete cardiac cycle.

Robustness of integrated backscatter for myocardial tissue characterization.

Integrated backscatter (IB) has been used for ultrasonic tissue characterization. To assess the potential variables in IB measurements, we performed both theoretical simulations and in vitro phantom measurements. First, we simulated data in which the scatterer position randomly was varied. IB values for the resulting images were calculated. Second, RF data from a tissue-mimicking phantom were acquired. Third, an adapted imaging approach, based on phase insensitivity, was evaluated. For both the simulations and phantom measurements, IB showed a standard deviation of +/-20%. These large deviations can be explained by variations in interference of signals and are not related to the state of the tissue. Small deviations in position of the scatterers resulted in important variations in IB. They must be taken into account and may limit the use of IB in cardiological applications. An improvement potentially can be obtained using phase insensitivity in new ultrasound processing schemes.

Can natural strain and strain rate quantify regional myocardial deformation? A study in healthy subjects.

Strain rate (SR) and strain (epsilon) have been proposed as new ultrasound (US) indices for quantifying regional wall deformation, and can be measured from color Doppler myocardial data by determining the local spatial velocity gradient. The aim of this study was to define normal regional SR/epsilon values for both radial and longitudinal myocardial deformation. SR/epsilon profiles were obtained from 40 healthy volunteers. For radial deformation, posterior left ventricular (LV) wall SR/epsilon were calculated. For longitudinal, they were determined for basal, mid- and apical segments of the 1. septum; 2. lateral, 3. posterior and 4. anterior LV walls and for the 5. right ventricular (RV) lateral wall. SR/epsilon values describing radial deformation were higher than the corresponding SR/epsilon values obtained for longitudinal deformation. Longitudinal SR/epsilon were homogeneous throughout the septum and all LV walls. This was in contrast to the normal base-apex velocity gradient. The RV segmental SR/epsilon values were higher than those obtained from the corresponding LV wall and inhomogeneous (higher in the apical segments). SR/epsilon imaging appears to be a robust technique for quantifying regional myocardial deformation.

Is there a change in myocardial nonlinearity during the cardiac cycle?

The distortion of a sound wave during propagation results in progressive transfer of the energy from fundamental to higher harmonics, and is dependent on the nonlinearity of the medium. We studied if relative changes in acoustical nonlinearity occur in healthy myocardium during the cardiac cycle. Radiofrequency data were acquired from transthoracic echocardiography (2.5 and 3.5 MHz), parasternal long axis view, from five dogs and nine healthy volunteers. Integrated backscatter was calculated after filtering for fundamental (FIB) and second harmonic frequencies (SHIB), from a region in the posterior myocardial wall. The results suggest that there is little difference between the SHIB and FIB, although there were large variations between individuals. The maximal changes in nonlinearity, as estimated by SHIB/FIB ratio, mostly occurred during systole. SHIB presented similar cyclic variation with FIB (p = NS). Further studies are necessary to separate the role of myocardial nonlinearity, attenuation, propagating distance, or acoustical properties of the blood. The results are important in further tissue characterization studies employing second harmonic data.