Myocardial velocity gradients detected by Doppler imaging

High-Spatiotemporal-Resolution Visualization of Myocardial Strains Through Vector Doppler Estimation: A Small-Animal Study

High-frequency ultrasound (HFUS) imaging is extensively used for cardiac diseases in small animals due to its high spatial resolution. However, there is a lack of a system that can provide a 2-D high-spatiotemporal dynamic visualization of mouse myocardial strains. In this article, a dynamic HFUS (40 MHz) high-resolution strain imaging was developed through the vector Doppler imaging. Following in vitro tests using a rubber balloon phantom, in vivo experiments were performed on wild-type (WT) and myocardial infarction (MI) mice. High-resolution dynamic images of myocardial strains were obtained in the longitudinal, radial, and circumferential directions at a frame rate of 1 kHz. Global peak strain values for WT mice were -19.3% ± 1.3% (longitudinal), 31.4% ± 1.7% (radial in the long axis), -19.9% ±.8% (circumferential), and 34.4% ± 1.9% (radial in the short axis); those for the MI mice were -16.1% ±.9% (longitudinal), 26.8% ± 2.9% (radial in the long axis), -15.2% ± 2.7% (circumferential), and 21.6% ± 4.8% (radial in the short axis). These results indicate that the strains for MI mice are significantly lower than those for WT mice. Regional longitudinal strain curves in the epicardial, midcardial, and endocardial layers were measured and the peak strain values for WT mice were -22.% and -16.8% in the endocardial and epicardial layers, respectively. However, no significant difference in the layer-based values was noted for the MI mice. Regional analysis results revealed obvious myocardial strain variation in the apical anterior region in the MI mice. The experimental results demonstrate that the proposed dynamic cardiac strain imaging can be useful in high-performance imaging of small-animal cardiac diseases.

3D angle-independent Doppler and speckle tracking for the myocardium and blood flow

A technology based on velocity ratio indices is described for application in the myocardium. Angle-independent Doppler indices, such as the pulsatility index, which employ velocity ratios, can be measured even if the ultrasound beam vector at the moving target and the motion vector are not in a known plane. The unknown plane situation is often encountered when an ultrasound beam interrogates sites in the myocardium. The velocities employed in an index calculation must be close to the same or opposite directions. The Doppler velocity ratio indices are independent of angle in 3D space as are ratio indices based on 1D strain and 1D speckle tracking. Angle-independent results with spectral Doppler methods are discussed. Possible future imaging techniques based on velocity ratios are presented. By using indices that involve ratios, several other sources of error cancel in addition to that of angular dependence for example errors due to less than optimum gain settings and beam distortion. This makes the indices reliable as research or clinical tools. Ratio techniques can be readily implemented with current commercial blood flow pulsed wave duplex Doppler equipment or with pulsed wave tissue Doppler equipment. In 70 patients where the quality of the real-time B-mode looked suitable for the Doppler velocity ratio technique, there was only one case where clear spectra could not be obtained for both the LV wall and the septum. A reproducibility study of spectra from the septum of the heart shows a 12% difference in velocity ratios in the repeat measurements.

Improvement in left ventricular function assessed by tissue Doppler imaging after aortic valve replacement for severe aortic stenosis

INTRODUCTION

The effects of reduction of left ventricular (LV) systemic afterload following aortic valve replacement (AVR) for severe aortic valve stenosis (AS) were investigated, using echocardiography and tissue Doppler imaging (TDI).

METHODS

We compared the preoperative and postoperative echocardiographic assessments of 23 patients with severe AS who had undergone isolated AVR (n = 13) or concomitant AVR with coronary artery bypass grafting (CABG) (n = 10). Conventional echocardiographic evaluations and TDI at the lateral mitral annulus were performed.

RESULTS

Echocardiography was performed at a median of 120 (interquartile range: 66-141) days after AVR. There was significant reduction in aortic transvalvular mean pressure gradient after AVR. Although LV dimensions, mass and ejection fraction remained unchanged, LV diastolic and systolic functions improved (as observed on TDI). Early diastolic (E'), late diastolic (A') and systolic (S') mitral annular velocities increased significantly (p < 0.05). There was significant improvement in TDI-derived parameters among the patients who had isolated AVR, while among the patients who had concomitant AVR with CABG, only S' had significant improvement (p = 0.028).

CONCLUSION

TDI was able to detect improvements in LV systolic and diastolic function after AVR for severe AS. There was less improvement in the TDI-derived diastolic parameters among patients who underwent concomitant AVR with CABG than among patients who underwent isolated AVR.

Normal values for longitudinal tissue velocity and strain rate imaging in individual segments of the left and right ventricles of healthy adult hearts

OBJECTIVES

To quantify the normal peak mean systolic velocities and strain rate parameters in the left ventricle (LV) and right ventricle (RV) and define their regional differences in normal adult hearts.

METHODS

Sixty-nine healthy volunteers (42% male; mean age ± SD, 30.03 ± 5.35 years) underwent color tissue Doppler and strain rate imaging. The first and second peak mean systolic velocities, peak strain, and strain rate in the systolic ejection phase were determined for 16 LV segments, the apex (17th segment), and 3 RV free wall segments.

RESULTS

The first peak mean systolic velocity was measurable in less than 50% of segments in the inferior and septal (-posterior) walls and RV free wall and in greater than 70% of segments of the other LV walls. The first and second peak mean systolic velocities of all LV walls and the RV free wall decreased significantly from the basal to apical region (P < .001).The strain and strain rate in the lateral and anterior walls decreased significantly from base to apex, whereas the anteroseptal and posterior walls were homogeneous. The strain rate in the inferior wall increased remarkably from base to apex, whereas it decreased significantly from the mid level to the apex. The strain in the RV was homogeneous, whereas the strain rate decreased significantly from the mid level to the apex. The apex (17th segment) showed the lowest value for each of the study parameters.

CONCLUSIONS

Longitudinal velocities decreased from base to apex, whereas deformation measurements did not show uniform patterns in LV walls and the RV free wall. In most cases, there are 1 peak systolic velocity in the inferior and septal (-posterior) walls and 2 peak systolic velocities in the other 4 LV walls.

In vivo functional imaging of blood flow and wall strain rate in outflow tract of embryonic chick heart using ultrafast spectral domain optical coherence tomography

During cardiac development, the cardiac wall and flowing blood are two important cardiac tissues that constantly interact with each other. This dynamic interaction defines appropriate biomechanical environment to which the embryonic heart is exposed. Quantitative assessment of the dynamic parameters of wall tissues and blood flow is required to further our understanding of cardiac development. We report the use of an ultrafast 1310-nm dual-camera spectral domain optical coherence tomography (SDOCT) system to characterize/image, in parallel, the dynamic radial strain rate of the myocardial wall and the Doppler velocity of the underlying flowing blood within an in vivo beating chick embryo. The OCT system operates at 184-kHz line scan rate, providing the flexibility of imaging the fast blood flow and the slow tissue deformation within one scan. The ability to simultaneously characterize tissue motion and blood flow provides a useful approach to better understand cardiac dynamics during early developmental stages.

Assessment of strain and strain rate in embryonic chick heart in vivo using tissue Doppler optical coherence tomography

We present a method to assess the in vivo radial strain and strain rate of the myocardial wall, which is of great importance to understand the biomechanics of cardiac development, using tissue Doppler optical coherence tomography (tissue-DOCT). Combining the structure and velocity information acquired from tissue-DOCT, the velocity distribution in the myocardial wall is plotted, from which the radial strain and strain rate are evaluated. The results demonstrate that tissue-DOCT can be used as a useful tool to describe tissue deformation, especially, the biomechanical characteristics of the embryonic heart.

Measurement of strain and strain rate in embryonic chick heart in vivo using spectral domain optical coherence tomography

The ability to measure in vivo strain and strain rate in embryonic chick heart is one of the key requirements for understanding the mechanisms of cardiac development. Due to its high temporal and spatial resolution as well as its fast imaging capability, optical coherence tomography (OCT) has the potential to reveal the complex myocardial activity in the living chick heart. We describe a method to evaluate the in vivo strain and strain rate of the myocardium through analyzing the periodic variation of the myocardial wall thickness calculated from real time serial OCT images. The results demonstrate that OCT can be a useful tool to describe the biomechanical characteristics of the embryonic heart.

Transthoracic coronary Doppler vibrometry in the evaluation of normal volunteers and patients with coronary artery stenosis

Coronary artery vibrometry is a new transthoracic Doppler ultrasound method for the detection of coronary artery stenosis. It detects audio-frequency vibrations generated by coronary artery luminal diameter reduction. We studied 31 patients with known or suspected stenosis using coronary artery vibrometry and quantitative coronary angiography and 83 normal volunteers. A tissue vibration difference index (TVDI) was calculated from the left anterior descending, circumflex, left main and right coronary arteries. Accuracy for coronary artery stenosis detection using TVDI was assessed. Sensitivity for detecting coronary stenosis equal or greater than 25% diameter reduction was 89% in the left anterior descending coronary artery (16/18, 95% confidence interval [CI] = 64%-98%), 87% in the right coronary artery (13/15, 95% CI = 58%-98%), 83% in the circumflex coronary artery (5/6, 95% CI = 36%-99%) and 100% in the left main artery (3/3, 95% CI = 31%-100%). The median TVDI increased with severity of stenosis, suggesting that this measure might be used to track progression/regression of coronary artery stenosis.

Comparison of 2-D speckle tracking and tissue Doppler imaging in an isolated rabbit heart model

Ultrasound strain imaging has been proposed to quantitatively assess myocardial contractility. Cross-correlation-based 2-D speckle tracking (ST) and auto-correlation-based tissue Doppler imaging (TDI) [often called Doppler tissue imaging (DTI)] are competitive ultrasound techniques for this application. Compared with 2-D ST, TDI, as a 1-D method, is sensitive to beam angle and suffers from low strain signal-to-noise ratio because a high pulse repetition frequency is required to avoid aliasing in velocity estimation. In addition, ST and TDI are fundamentally different in the way that physical parameters such as the mechanical strain are derived, resulting in different estimation accuracy and interpretation. In this study, we directly compared the accuracy of TDI and 2-D ST estimates of instantaneous axial normal strain and accumulated axial normal strain using a simulated heart. We then used an isolated rabbit heart model of acute ischemia produced by left descending anterior artery ligation to evaluate the performance of the two methods in detecting abnormal motion. Results showed that instantaneous axial normal strains derived using TDI (0.36% error) were less accurate with larger variance than those derived from 2-D ST (0.08% error) given the same spatial resolution. In addition to poorer accuracy, accumulated axial normal strain estimates derived using TDI suffered from bias, because the accumulation method for TDI cannot trace along the actual tissue displacement path. Finally, we demonstrated the advantage 2-D ST has over TDI to reduce dependency on beam angle for lesion detection by estimating strains based on the principal stretches and their corresponding principal axes.

Noninvasive evaluation of left ventricular noncompaction: what's new in 2009?

Significant interest in clinical practice as well as the medical literature exists regarding the presentation and outcome of children and adults with left-ventricular noncompaction (LVNC). The mainstay in the diagnosis of LVNC has been the anatomic definition of the ventricular myocardium by two-dimensional echocardiographic imaging. Although helpful, this approach lacks diagnostic precision and fails to evaluate the functional impact of this abnormal myocardial architecture on global and regional myocardial performance. This review will focus on the use of novel echocardiographic modalities of tissue Doppler, strain, and strain rate imaging to identify and characterize abnormalities of regional myocardial function in patients with LVNC.

Phase rotation methods in filtering correlation coefficients for ultrasound speckle tracking

In speckle-tracking-based myocardial strain imaging, large interframe/volume peak-systolic strains cause peak hopping artifacts separating the highest correlation coefficient peak from the true peak. A correlation coefficient filter was previously designed to minimize peak hopping artifacts. For large strains, however, the correlation coefficient filter must follow the strain distribution to remove peak hopping effectively. This processing usually means interpolation and high computational load. To reduce the computational burden, a narrow band approximation using phase rotation is developed in this paper to facilitate correlation coefficient filtering. Correlation coefficients are first phase rotated to increase coherence, then filtered. Rotated phase angles are determined by the local strain and spatial position. This form of correlation coefficient filtering enhances true correlation coefficient peaks in large strain applications if decorrelation due to deformation does not completely destroy the coherence among neighboring correlation coefficients. The assumed strain used in the filter can also deviate from the true strain and still be effective. Further improvement in displacement estimation can be expected by combining correlation coefficient filtering with a new Viterbi-based displacement estimator.

Strain and strain rate imaging by echocardiography - basic concepts and clinical applicability

Echocardiographic strain and strain-rate imaging (deformation imaging) is a new non-invasive method for assessment of myocardial function. Due to its ability to differentiate between active and passive movement of myocardial segments, to quantify intraventricular dyssynchrony and to evaluate components of myocardial function, such as longitudinal myocardial shortening, that are not visually assessable, it allows comprehensive assessment of myocardial function and the spectrum of potential clinical applications is very wide. The high sensitivity of both tissue Doppler imaging (TDI) derived and two dimensional (2D) speckle tracking derived myocardial deformation (strain and strain rate) data for the early detection of myocardial dysfunction recommend these new non-invasive diagnostic methods for extensive clinical use. In addition to early detection and quantification of myocardial dysfunction of different etiologies, assessment of myocardial viability, detection of acute allograft rejection and early detection of allograft vasculopathy after heart transplantation, strain and strain rate data are helpful for therapeutic decisions and also useful for follow-up evaluations of therapeutic results in cardiology and cardiac surgery. Strain and strain rate data also provide valuable prognostic information, especially prediction of future reverse remodelling after left ventricular restoration surgery or after cardiac resynchronization therapy and prediction of short and median-term outcome without transplantation or ventricular assist device implantation of patients referred for heart transplantation.The Review explains the fundamental concepts of deformation imaging, describes in a comparative manner the two major deformation imaging methods (TDI-derived and speckle tracking 2D-strain derived) and discusses the clinical applicability of these new echocardiographic tools, which recently have become a subject of great interest for clinicians.

Ultrasound frame rate requirements for cardiac elastography: experimental and in vivo results

Cardiac elastography using radiofrequency echo signals can provide improved 2D strain information compared to B-mode image data, provided data are acquired at sufficient frame rates. In this paper, we evaluate ultrasound frame rate requirements for unbiased and robust estimation of tissue displacements and strain. Both tissue-mimicking phantoms under cyclic compressions at rates that mimic the contractions of the heart and in vivo results are presented. Sinusoidal compressions were applied to the phantom at frequencies ranging from 0.5 to 3.5 cycles/sec, with a maximum deformation of 5% of the phantom height. Local displacements and strains were estimated using both a two-step one-dimensional and hybrid two-dimensional cross-correlation method. Accuracy and repeatability of local strains were assessed as a function of the ultrasound frame rate based on signal-to-noise ratio values. The maximum signal-to-noise ratio obtained in a uniformly elastic phantom is 20 dB for both a 1.26 Hz and a 2 Hz compression frequency when the radiofrequency echo acquisition is at least 12 Hz and 20 Hz respectively. However, for compression frequencies of 2.8 Hz and 4 Hz the maximum signal-to-noise ratio obtained is around 16 dB even for a 40 Hz frame rate. Our results indicate that unbiased estimation of displacements and strain require ultrasound frame rates greater than ten times the compression frequency, although a frame rate of about two times the compression frequency is sufficient to estimate the compression frequency imparted to the tissue-mimicking phantom. In vivo results derived from short-axis views of the heart acquired from normal human volunteers also demonstrate this frame rate requirement for elastography.

High frequency ultrasound imaging detects cardiac dyssynchrony in noninfarcted regions of the murine left ventricle late after reperfused myocardial infarction

Cardiac dyssynchrony in the left ventricles of murine hearts late (> or =28 d) after reperfused myocardial infarction (post-MI) was assessed using high frequency 30 MHz B-mode ultrasound imaging. Nine post-MI and six normal C57Bl/6 mice were studied in both short- and long-axis views. Regional time to peak displacement (T(peak_d)) and time to peak strain (T(peak_s)) were calculated in 36 sectors along the myocardial circumference; then their standard deviations (SD_T(peak_d) and SD_T(peak_s)) were computed among noninfarcted myocardial regions for each mouse and were compared between the normal and post-MI mouse groups with Student's t-test. The comparison revealed that SD_T(peak_d) and SD_T(peak_s) were significantly larger in the post-MI hearts than in the normal hearts. The displacement uniformity ratio was determined to be 0.97 +/- 0.01 and 0.85 +/- 0.07 for radial and circumferential displacements in the normal hearts, respectively; and 0.59 +/- 0.17 and 0.64 +/- 0.24 in the post-MI hearts. In conclusion, this high resolution ultrasound image tracking method provides for the detection of cardiac dyssynchrony in the noninfarcted regions in the murine left ventricles late after MI by identifying the temporal and spatial disparity of regional myocardial contraction.

Assessment of Early Changes in the Segmental Functions of the Left and the Right Ventricles After Biventricular Pacing in Heart Failure: A Study With Tissue Doppler Imaging

Tissue Doppler imaging allows assessment of systolic and diastolic regional ventricular function. The aim of this study was to assess early changes in regional systolic and diastolic functions and differences in transition time to contraction between the ventricles after cardiac resynchronization therapy. Fourteen patients were included, who underwent echocardiography before and 1 month after resynchronization. The difference between transition time to contraction of left and right ventricles decreased to 24.4 ± 10.7 milliseconds from 65.3 ± 18.2 milliseconds after resynchronization therapy ( P = .001). There was a significant relation between the decrease in difference between transition time and increase in ejection fraction (r = 0.80, P = .002). Early or late diastolic myocardial motion increased in 7 segments of left and 2 segments of right ventricles. Systolic myocardial motion increased in 7 segments of left and in all segments of right ventricles. Resynchronization therapy improved systolic and diastolic functions in both ventricles. The difference between transition time to contraction of ventricles might be helpful in estimating optimal resynchronization.

Strain and strain rate deformation parameters: from tissue Doppler to 2D speckle tracking

Strain and strain rate deformation parameters based on Color Doppler Myocardial Imaging, and more recently on two-dimensional (2D) gray scale images, have evolved as important methods for the quantification of myocardial function. Although these parameters are already applicable in the research field, their acquisition and analysis involve a number of technical challenges and complexities. Accurate knowledge of the basic principles of those techniques, as presented in this article, will further enhance their applicability to clinical practice.

Detection of myocardial dysfunction in the presence of normal ejection fraction

Detection of subclinical myocardial involvement is of utmost importance in risk stratification and prognosis; the role of ejection fraction in the detection of subclinical disease may be unhelpful. Our aim was to evaluate the methodology and importance of early detection of myocardial involvement in the presence of normal ejection fraction. Most of the pertinent English and non-English articles published from 1980 to 2006 in Medline, Scopus, and EBSCO Host research databases have been reviewed. Serial assessment of systolic function with different techniques should be avoided, since imaging modalities and ejection fraction measurements are not interchangeable. Additional non-invasive tools still are needed for the identification of subclinical left ventricular dysfunction in certain diseases. The recognition of subclinical involvement will prompt initiation of specific therapy to prevent the development of overt left ventricular dysfunction. This also is needed for determining the best timing for intervention in asymptomatic patients with metabolic and valvular disorders.

Radial versus longitudinal myocardial deformation from gray-scale echocardiography

The objectives of this work are to evaluate a novel non-Doppler-based echocardiographic method that makes it possible to simultaneously obtain the radial and longitudinal components of myocardial velocity (V) and strain (S), and to assess whether left ventricular fiber architecture affects the net function of the myocardium. Previous reports state that differences in the estimation of regional function between septum and lateral walls can be related to the anatomic disposition of myocardial fibers. In this work we measure and compare in 21 healthy volunteers longitudinal and radial peak systolic velocity V (V(long), V(rad): cm/s), peak systolic strain S (S(long), S(rad): %) and time-to-peak S and V (T-Smax, T-V(max): ms) at the midsegments of the septal and lateral walls. Results show that V was higher, both in the radial and longitudinal components, in the lateral wall than in the septum (V(rad): 4.77 +/- 0.26 cm/s vs. 3.77 +/- 0.20 cm/s, p = 0.007; V(long): 5.60 +/- 0.48 cm/s vs. 4.13 +/- 0.11 cm/s, p = 0.01). Radial strain was higher in the septum (S(rad): 28.63 +/- 2.25% vs. 22.54 +/- 1.5%, p = 0.015), and longitudinal strain, in the lateral wall (S(long): -25.89 +/- 1.43% vs. -22.20 +/- 0.87%, p = 0.02). There was a significant delay in longitudinal T-Smax between the lateral and septal medial segments (mean: 14.5 ms; CI 95%: 0.3-28.6 ms; p = 0.04), with no difference in radial T-Smax (277.1 +/- 8.6 ms vs. 277.2 +/- 12.4 ms, p = 0.93). The assessment of regional myocardial function by this new method enables the simultaneous analysis of its radial and longitudinal components. These measurements correlate well with previous anatomical knowledge of the architecture of myocardial fibers, emphasizing its functional significance in regional myocardial function analysis.

Feasibility and reliability of strain and strain rate measurement in neonates by optimizing the analysis parameters settings

The optimal combination of region-of-interest (ROI) size and strain length (SL) allowing two-segment strain and strain rate analyses in term neonates was investigated. The impact of different ROI sizes and SLs on the strain and strain rate beat-to-beat variation (BBV) was assessed in 80 good-quality tissue velocity images. Both BBVs decreased with increased ROI length and with increased SL (p < 0.05). There were no significant differences in the BBVs for ROI width 2, 3 and 4 mm (p > 0.05). Among the combinations eligible for two segment analysis, the lowest BBVs were found using SL 10 mm, ROI length 1 mm and ROI width 3 mm. Using this combination, the mean difference between the single-cycle value and two-cycle compound value for peak systolic strain rate was 6.2%, peak systolic strain was 2.9% and end systolic strain was 3.2% of the two-cycle compound mean values. Hence, strain and strain rate measurement in tissue velocity images in neonates is feasible and reliable.

Potential clinical perspectives of Doppler myocardial imaging and strain rate imaging during stress echocardiography

Stress echocardiography has become a common non-invasive test in patients with chest pain and known or suspected coronary artery disease, but, as with exercise electrocardiography, it shows several major limitations. Analysis of gray-scale images based on subjective visual interpretation of wall motion and thickening has considerable variability even among experts. Doppler myocardial imaging and strain rate imaging echocardiography provides additional information in comparison with conventional echocardiography. These techniques provide quantification of regional wall motion at rest and during stress. Quantification of both systolic and diastolic myocardial function by either Doppler myocardial imaging or strain rate imaging mapping during dobutamine stress test has been shown to be a feasible, accurate, non-invasive tool that should be considered to be a sensitive alternative to the present echocardiographic and scintigraphic imaging techniques for stress tests. Time consuming off-line analysis of color images is required in the present state of technology. However, these non-invasive techniques are rapidly evolving and expanding. Further refinements in signal processing and quantitative analysis are likely in the near future.

Grading of myocardial dysfunction by tissue Doppler echocardiography: a comparison between velocity, displacement, and strain imaging in acute ischemia

OBJECTIVES

The aim of the study was to compare the ability of the tissue Doppler echocardiographic imaging (TDI) modalities velocity, strain, and displacement to quantify systolic myocardial function.

BACKGROUND

Several TDI modalities may be used to quantify regional myocardial function, but it is not clear how the different modalities should be applied.

METHODS

In 10 anesthetized dogs we measured left ventricular pressure, longitudinal myocardial velocity, strain, and displacement by TDI at baseline and during left anterior descending coronary artery (LAD) stenosis and occlusion. Reference methods were segmental shortening by sonomicrometry and segmental work. In 10 patients with acute anterior wall infarction (LAD occlusion) and 15 control subjects, velocity, strain, and displacement measurements were performed.

RESULTS

In the animal study, systolic strain correlated well with segmental shortening (r = 0.96, p < 0.01) and work (r = 0.90, p < 0.01), and differentiated well between non-ischemic (-13.5 +/- 3.2% [mean +/- SD]), moderately ischemic (-6.5 +/- 2.8%), and severely ischemic myocardium (7.1 +/- 13.2%). The ratio post-systolic strain/total strain also differentiated well between levels of ischemia. Displacement and ejection velocity had weaker correlations with segmental shortening (r = 0.92 and r = 0.74, respectively) and regional work (r = 0.85 and r = 0.69), and there was marked overlap between values at baseline and at different levels of ischemia. In the human study, systolic strain differentiated well between infarcted and normal myocardium (1.0 +/- 5.0% vs. -17.8 +/- 3.8%), whereas systolic displacement (-0.3 +/- 1.3 mm vs. -2.3 +/- 0.6 mm) and ejection velocity (0.9 +/- 0.6 cm/s vs. 2.2 +/- 0.6 cm/s) showed overlap. In the infarction group, strain was reduced in segments with infarcted tissue, while systolic velocity and displacement were reduced in all segments and did not reflect the extension of the infarct.

CONCLUSIONS

Strain was superior to velocity and displacement for quantification of regional myocardial function. Provided technical limitations can be solved, strain Doppler is the preferred TDI modality for assessing function in ischemic myocardium.

Strain estimation in abdominal aortic aneurysms from 2-D ultrasound

The rupture risk of abdominal aortic aneurysms (AAAs) is routinely inferred from the maximum diameter of the AAA. However, clinical experience indicates that this criterion has poor accuracy and that noninvasive assessment of the elastic properties of the vessel might give better correspondence with the rupture risk. We have developed a method for analysis of circumferential strain in AAAs from sequences of cross-sectional ultrasound B-mode images. The algorithm is fast, semiautomatic and well-suited for real-time applications. The method was developed and evaluated using data from 10 AAA patients. The preliminary results demonstrate that the method is sufficiently accurate and robust for clinically acquired data. An important finding is that local strain values may exceed the circumferential average strain significantly. Furthermore, the calculated strain shows no apparent covariation with the diagnosed diameter. This implies that the method may give new and essential information on the clinical condition of the AAA.

Effects of Ultrasound Contrast During Tissue Velocity Imaging on Regional Left Ventricular Velocity, Strain, and Strain Rate Measurements

BACKGROUND

Strain (epsilon) rate (SR) imaging and left ventricular (LV) opacification with intravenous (IV) contrast both potentially decrease operator dependency in interpretation of stress echocardiography. The aim of this study was to evaluate whether contrast present during tissue velocity imaging (TVI) significantly affected measurements of velocity, epsilon, and SR. Secondly, we sought to evaluate whether increased scan line density improved feasibility of simultaneous TVI and contrast echocardiography.

METHODS

The 4-chamber LV view in 15 healthy volunteers and 25 patients was acquired at rest before and after IV injections of contrast using: (1) conventional TVI; (2) LV opacification with standard TVI added; and (3) modified LV opacification with doubled TVI line density. Velocity, SR, and epsilon curves, along with peak systolic velocity, peak systolic SR, and end-systolic epsilon, were assessed from midwall segments.

RESULTS

IV contrast significantly reduced feasibility of TVI with standard settings, giving noisy data for SR and epsilon, particularly in the septum. Absolute values of peak systolic SR and end-systolic epsilon from adequately shaped curves were significantly higher with contrast compared with baseline. However, increased TVI line density significantly improved feasibility of velocity traces with contrast and decreased the level of noise in SR and epsilon. Furthermore, higher line density improved agreement between peak systolic velocity, peak systolic SR, and end-systolic epsilon measured with contrast, and corresponding precontrast values from the conventional TVI setting.

CONCLUSIONS

SR imaging was not feasible performed with IV contrast during conventional TVI settings, and we do not recommend the clinical use of this combination. Increased TVI line density made velocity curves with contrast feasible and resulted in less noisy SR and epsilon curves, but variability in SR and epsilon measurements with contrast is still too high for clinical use.

Propagation of spontaneously actuated pulsive vibration in human heart wall and in vivo viscoelasticity estimation

Though myocardial viscoelasticity is essential in the evaluation of heart diastolic properties, it has never been noninvasively measured in vivo. By the ultrasonic measurement of the myocardial motion, we have already found that some pulsive waves are spontaneously excited by aortic-valve closure (AVC) at end-systole (T0). These waves may serve as an ideal source of the intrinsic heart sound caused by AVC. In this study, using a sparse sector scan, in which the beam directions are restricted to about 16, the pulsive waves were measured almost simultaneously at about 160 points set along the heart wall at a sufficiently high frame rate. The consecutive spatial phase distributions, obtained by the Fourier transform of the measured waves, clearly revealed wave propagation along the heart wall for the first time. The propagation time of the wave along the heart wall is very small (namely, several milliseconds) and cannot be measured by conventional equipment. Based on this phenomenon, we developed a means to measure the myocardial viscoelasticity in vivo. In this measurement, the phase velocity of the wave is determined for each frequency component. By comparing the dispersion of the phase velocity with the theoretical one of the Lamb wave (the plate flexural wave), which propagates along the viscoelastic plate (heart wall) immersed in blood, the instantaneous viscoelasticity is determined noninvasively. This is the first report of such noninvasive determination. In in vivo experiments applied to five healthy subjects, propagation of the pulsive wave was clearly visible in all subjects. For the 60-Hz component, the typical propagation speed rapidly decreased from 5 m/s just before the time of AVC (t = T0 - 8 ms) to 3 m/s at t = T0 + 10 ms. In the experiments, it was possible to determine the viscosity more precisely than the elasticity. The typical value of elasticity was about 24-30 kPa and did not change around the time of AVC. The typical transient values of viscosity decreased rapidly from 400 Pa x s at t = T0 - 8 ms to 70 Pa x s at t = T0 + 10 ms. The measured shear elasticity and viscosity in this study are comparable to those obtained for the human tissues using audio frequency in in vitro experiments reported in the literature.

New aspects of the ventricular septum and its function: an echocardiographic study

OBJECTIVES

To examine whether the line dividing the septum into two layers is found consistently by conventional echocardiography and to evaluate functional differences in the right and left side of the septum in terms of wall thickening, strain rate, and strain imaging.

DESIGN

In a systematic study in 30 normal subjects, M mode and Doppler myocardial imaging data from the interventricular septum (IVS) were recorded. Velocity curves, regional strain rate, and strain profiles were obtained. Systolic deformation (wall thickening, radial and longitudinal strain rate, and strain) of both sides were assessed. Furthermore, three patients with one sided abnormalities were studied.

RESULTS

A bright echo consistently segmented the IVS into a left and right part. In this normal population radial deformation was different for the left and right side of the septum (mean (SD) wall thickening on the left, 49 (46)%, and on the right, 17 (38)%; strain rate on the left, 3.8 (0.6) 1/s, and on the right, 2.1 (1.9) 1/s; strain on the left, 41 (17)%, and on the right, 22 (14)%), whereas longitudinal deformation was found to be similar (strain rate on the left, -2.2 (0.7) 1/s, and on the right, -2.0 (0.6) 1/s; strain on the left, -28 (12)%, and on the right, -25 (12)%). The presented clinical examples show that abnormalities can be strictly limited to one layer.

CONCLUSIONS

Differential radial deformation and knowledge of fibre architecture showing an abrupt change in the middle of the septum, together with the clinical cases, suggest the septum to be a morphologically and functionally bilayered structure potentially supplied by different coronary arteries.

Multiscale motion mapping: a novel computer vision technique for quantitative, objective echocardiographic motion measurement independent of Doppler: first clinical description and validation

BACKGROUND

Objective, quantitative, segmental noninvasive/bedside measurement of cardiac motion is highly desirable in cardiovascular medicine, but current technology suffers from significant drawbacks, such as subjectivity of conventional echocardiographic reading, angle dependence of tissue Doppler measurements, radiation exposure by computer tomography, and infrastructure requirements in MRI. We hypothesized that computer vision technology could represent a powerful new paradigm for quantification in echocardiography.

METHODS AND RESULTS

We present multiscale motion mapping, a novel computer vision technology that is based on mathematical image processing and that exploits echocardiographic information in a fashion similar to the human visual system. It allows Doppler- and border-independent determination of motion and deformation in echocardiograms at arbitrary locations. Correctness of the measurements was documented in synthetic echocardiograms and phantom experiments. Exploratory case studies demonstrated its usefulness in a series of complex motion analyses that included abnormal septal motion and analysis of myocardial twisting. Clinical applicability was shown in a consecutive series of echocardiograms, in which good feasibility, good correlation with expert rating, and good intraobserver and interobserver concordance were documented. Separate assessment of 2D displacement and deformation at the same location was successfully applied to elucidate paradoxical septal motion, a common clinical problem.

CONCLUSIONS

This is the first clinical report of multiscale motion mapping, a novel approach to echocardiographic motion quantification. For the first time, full 2D echocardiographic assessment of both motion and deformation is shown to be feasible. Overcoming current limitations, this computer vision-based technique opens a new door to objective analysis of complex heart motion.

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.

Tissue Doppler, strain, and strain rate echocardiography for the assessment of left and right systolic ventricular function

Tissue Doppler (TDE), strain, and strain rate echocardiography are emerging real time ultrasound techniques that provide a measure of wall motion. They offer an objective means to quantify global and regional left and right ventricular function and to improve the accuracy and reproducibility of conventional echocardiography studies. Radial and longitudinal ventricular function can be assessed by the analysis of myocardial wall velocity and displacement indices, or by the analysis of wall deformation using the rate of deformation of a myocardial segment (strain rate) and its deformation over time (strain). A quick and easy assessment of left ventricular ejection fraction is obtained by mitral annular velocity measurement during a routine study, especially in patients with poor endocardial definition or abnormal septal motion. Strain rate and strain are less affected by passive myocardial motion and tend to be uniform throughout the left ventricle in normal subjects. This paper reviews the underlying principles of TDE, strain, and strain rate echocardiography and discusses currently available quantification tools and clinical applications.

Clinical applications of strain rate imaging

Myocardial strain (epsilon) is a dimensionless index of change in myocardial length in response to an applied force. epsilon Rate (SR) is the rate of change of length and is usually obtained as the time derivative of the epsilon signal. In echocardiography, SR is calculated as the difference between 2 velocities normalized to the distance between the 2 velocities. SR imaging (SRI) has a theoretic advantage over Doppler tissue imaging in that SRI is relatively immune to cardiac translational motion and tethering. Therefore, SRI may be superior to Doppler tissue imaging in quantitative assessment of regional myocardial function and may find clinical application in the interrogation of coronary artery disease. The high frame rates of SRI have also renewed interest in timings of global and regional mechanical events, and their potential clinical applications. The high temporal resolution allows SRI to depict regional systolic and diastolic asynchrony. Ongoing clinical trials will determine the sensitivity, specificity, and accuracy of SRI parameters for a variety of clinical conditions. Potential clinical applications include investigation of ischemia (at rest and with stress), myocardial viability, and altered global and regional systolic and diastolic function in cardiomyopathies. Suboptimal signal quality remains a major limitation of strain imaging, and advances in data acquisition and postprocessing capabilities will help determine its future incorporation into standard regional myocardial assessment.

Application of ultrasound-based velocity estimate statistics to strain-rate estimation

Quantification of the relative myocardial deformation rate, or strain rate, is an emerging capability to aid a cardiologist in assessing myocardial function. Ultrasound Doppler techniques can be used to compute tissue motion relative to a transducer. The myocardial strain rate can be computed as the localized spatial derivative of the tissue velocity. Such a strain-rate estimate is typically numerically noisy. We present the relevant speckle statistics to faciliate the computation of the strain rate based on a weighted least squares regression, with statistically appropriate weights.

New Techniques for the Assessment of Regional Left Ventricular Wall Motion

The assessment of regional left ventricular (LV) function has been an important yet unresolved problem since the introduction of echocardiography as a diagnostic tool. Abnormal regional LV wall motion is an early finding in multiple cardiac pathologies and its diagnosis is of critical importance. In the last few years diagnostic procedures based on combined use of existing echocardiographic technologies were geared toward improving the accuracy of detection of baseline and/or induced regional wall motion abnormalities. One of the assumptions is that the combination of reduced LV wall thickening and reduced myocardial velocities can be used to accurately diagnose regional myocardial dysfunction. In this article we will discuss several new techniques for the quantification of regional LV function using Doppler echocardiography.

Myocardial velocity gradient as a noninvasively determined index of left ventricular diastolic dysfunction in patients with hypertrophic cardiomyopathy

OBJECTIVES

We investigated the utility of the peak negative myocardial velocity gradient (MVG) derived from tissue Doppler imaging (TDI) for evaluation of diastolic dysfunction in patients with hypertrophic cardiomyopathy (HCM).

BACKGROUND

Hypertrophic cardiomyopathy is characterized by impaired diastolic function with abnormal stiffness and prolonged relaxation. However, it remains difficult to evaluate these defects noninvasively.

METHODS

Both TDI and conventional echocardiography were performed in 36 patients with HCM and in 47 control subjects. Left ventricular (LV) pressure was measured simultaneously in all HCM patients and in 26 controls.

RESULTS

The peak negative MVG occurred soon after the isovolumic relaxation period during the initial phase of rapid filling (auxotonic relaxation). It was significantly smaller in HCM patients than in control subjects (2.32 +/- 0.52/s vs. 4.82 +/- 1.15/s, p < 0.0001); the cutoff value for differentiation between all HCM patients and 47 normal individuals was determined as 3.2/s. Both the left ventricular end-diastolic pressure (LVEDP) (19.6 +/- 6.1 mm Hg vs. 6.5 +/- 1.7 mm Hg, p < 0.0001) and the time constant of LV pressure decay during isovolumic diastole (tau) (44.0 +/- 6.7 ms vs. 32.1 +/- 5.5 ms, p < 0.0001) were increased in HCM patients compared with controls. The peak negative MVG was negatively correlated with both LVEDP (r = -0.75, p < 0.0001) and tau (r = -0.58, p < 0.0001).

CONCLUSIONS

A reduced peak negative MVG reflects both prolonged relaxation and elevated LVEDP. The peak negative MVG might thus provide a noninvasive index of diastolic function, yielding unique information about auxotonic relaxation in patients with HCM.

Tissue Doppler analysis is hindered in abnormal wall motion and changes in afterload

BACKGROUND

Tissue Doppler (TD) analysis is used to estimate contractility. However, interference with hemodynamics has not been investigated.

OBJECTIVE

To evaluate the effect of hemodynamic conditions and wall motion abnormalities on TD indices.

METHODS

TD indices were obtained in 16 dogs and correlated with hemodynamics and wall thickening.

RESULTS

An inverse relation between TD indices and systemic vascular resistance was observed when afterload-related parameters were included in the analysis (early systolic subendocardial velocity: r((multiple regression))=0.82, P<0.0001 vs. r((simple regression))=0.57, P=0.0002). Early systolic TD data were more closely related to hemodynamics than those derived from the entire systole. TD data did not correspond to the hyperkinesia of the contralateral wall in myocardial infarction, whereas the increase of gradient parameters reflected hypercontractility (P<0.05).

CONCLUSION

TD indices are directly related to contractility and inversely to afterload. They do not reflect wall motion of those segments not involved in regional ischemia.

Peak mean myocardial velocities and velocity gradients measured by color M-mode tissue Doppler imaging in healthy cats

We sought to assess the feasibility of recording the myocardial velocity gradients (MVGs) and mean myocardial velocities (MMVs) measured by color M-mode tissue Doppler imaging (TDI) in the free wall of unsedated normal cats (n = 18) with a 7.4-MHz probe equipped to record TDI images. The peak MVG and MMV values during the different phases of the cardiac cycle corresponded to certain color velocity patterns occurring in the left ventricular free wall (LVFW). Biphasic shifts were recorded in the tracings of both the MVG and MMV during early diastole (E1 and E2) as well as during the isovolumic relaxation (IVR) and isovolumic contraction (IVC) phases. Stepwise regression analysis showed that age was the only significant predictor for the peak MVG values during the 2nd phase of early diastole (E2) (r = -0.79, r2 = 0.63, and P < .001). The peak late diastolic MVG values were associated positively with age (r = 0.50, r2 = 0.25, and P < .05). The peak MMV values showed a negative association with age during E2 (r = -0.71, r2 = 0.50, and P < .001) as well as during early systole (Se) (r = -0.55, r2 = 0.30, and P < .05) and late systole (SI) (r = -0.62, r2 = 0.39, and P < .01). A positive association was found between age and the peak MMV values during late diastole (r = 0.54, r2 =- 0.29, and P < .05). The MVG values showed cyclic variations consistent with wall thickness changes. The accuracy of velocity determination and the spatial resolution of the system used were validated with a phantom. To our knowledge, this study is the 1st report of the application of this technique to the myocardium of cats,providing insights into the physiology of myocardial motion. It provides reference ranges of the peak MVG and MMV values for future studies of feline myocardial diseases.

Novel approach to the quantitation of regional left ventricular systolic and diastolic function using tissue Doppler imaging to create a myocardial velocity profile and gradient

The myocardial velocity profile (MVP) and gradient (MVG) between the endocardium and epicardium of the left ventricular (LV) wall measured by color-coded tissue Doppler imaging (TDI) are new indices for evaluating regional LV myocardial function. However, accurate recording and measurement of the MVP is difficult using conventional methodology because of the stochastic nature of the ultrasound signal; that is, the effect of speckled noise. The aim of this study was to validate the accuracy and establish the validity of a newly developed method for measuring the MVP and MVG using 10 clinically normal controls and 10 patients with a hypertensive hypertrophied LV posterior wall. A non-isotropic, averaging algorithm was developed that was capable of obtaining a stable MVP (averaged MVP). Averaged MVP was recorded using parasternal, LV short-axis, color-coded TDI, placing regions of interest along the LV posterior wall with the reference point for angle-correction being at the center of LV contraction. The velocity from epicardium to endocardium within the region of interest was automatically angle-corrected to calculate the velocity component radially relative to the LV cavity and was spatially averaged along the circumference within the region of interest. Inter- and intraobserber variabilities of measurements were lower in the averaged MVP and MVG than in the conventional MVP and MVG. The correlation coefficients of the linear regression lines of systolic and early diastolic MVPs in the LV posterior wall were higher in all controls and hypertensive patients with the averaged method than with the conventional TDI procedures. The mean peak systolic and early diastolic MVGs were lower in the hypertensive group than in the controls. In conclusion, the newly developed averaged MVP provides a stable and reproducible index for the quantitative assessment of regional LV myocardial function.

Myocardial velocity gradient reflects the severity of myocardial damage regardless of the presence or absence of mitral regurgitation

Complicating mitral regurgitation (MR) apparently enhances left ventricular ejection fraction, thereby leading to the underestimation of myocardial damage by routine echocardiography. We sought to assess the significance of myocardial velocity gradient (MVG) derived from Doppler tissue imaging as an indicator of the severity of myocardial damage in the presence or absence of MR. Peak systolic and diastolic MVG was obtained from 39 participants: 12 healthy participants, 10 patients with dilated cardiomyopathy complicating moderate to severe MR [MR (+) group], and 17 patients with dilated cardiomyopathy without significant MR [MR (-) group]. MVG was compared with standard echocardiographic and Doppler transmitral flow velocity indices. Plasma brain natriuretic peptide levels were measured in all patients. Left ventricular dimension and fractional shortening was similar between MR (+) and MR (-) groups. Plasma brain natriuretic peptide levels were significantly increased in MR (+) group (440 +/- 417 pg/mL) as compared with MR (-) group (122 +/- 107 pg/mL, P <.05). Peak systolic MVG was significantly attenuated in dilated cardiomyopathy group with or without MR [MR (+) group = 1.3 +/- 0.5 seconds(-1), MR (-) group = 2.1 +/- 0.5 seconds(-1), where normal = 4.0 +/- 0.9 seconds(-1), P <.01, respectively]. Peak systolic MVG was further attenuated in MR (+) group than in MR (-) group (P <.01). Plasma brain natriuretic peptide levels were negatively correlated with peak systolic MVG (r = -0.66, P <.0005). Peak diastolic MVG was attenuated in MR (+) and also in MR (-) groups [MR (+) group = -4.5 +/- 2.0 seconds(-1), MR (-) group = -4.4 +/- 1.1 seconds(-1), where normal = -8.7 +/- 2.4 seconds(-1), P <.01, respectively], whereas transmitral flow indices failed to distinguish MR (+) group from normal as a result of pseudonormalization. MVG may reflect the severity of myocardial damage regardless of the presence or absence of complicating MR.

Ultrasonic imaging of myocardial strain using cardiac elastography

Clinical assessment of myocardial ischemia based on visually-assessed wall motion scoring from echocardiography is semiquantitative, operator dependent, and heavily weighted by operator experience and expertise. Cardiac motion estimation methods such as tissue Doppler imaging, used to assess myocardial muscle velocity, provides quantitative parameters such as the strain-rate and strain derived from Doppler velocity. However, tissue Doppler imaging does not differentiate between active contraction and simple rotation or translation of the heart wall, nor does it differentiate tethering (passively following) tissue from active contraction. In this paper, we present a strain imaging modality called cardiac elastography that provides two-dimensional strain information. A method for obtaining and displaying both directional and magnitude cardiac elastograms and displaying strain over the entire cross-section of the heart is described. Elastograms from a patient with coronary artery disease are compared with those from a healthy volunteer. Though observational, the differences suggest that cardiac elastography may be a useful tool for assessment of myocardial function. The method is two-dimensional, real time and avoids the disadvantage of observer-dependent judgment of myocardial contraction and relaxation estimated from conventional echocardiography.