Quantitative ultrasonic imaging: tissue characterization and instantaneous quantification of cardiac function

Current and evolving echocardiographic techniques for the quantitative evaluation of cardiac mechanics: ASE/EAE consensus statement on methodology and indications endorsed by the Japanese Society of Echocardiography

Echocardiographic imaging is ideally suited for the evaluation of cardiac mechanics because of its intrinsically dynamic nature. Because for decades, echocardiography has been the only imaging modality that allows dynamic imaging of the heart, it is only natural that new, increasingly automated techniques for sophisticated analysis of cardiac mechanics have been driven by researchers and manufacturers of ultrasound imaging equipment. Several such techniques have emerged over the past decades to address the issue of reader's experience and inter-measurement variability in interpretation. Some were widely embraced by echocardiographers around the world and became part of the clinical routine, whereas others remained limited to research and exploration of new clinical applications. Two such techniques have dominated the research arena of echocardiography: (1) Doppler-based tissue velocity measurements, frequently referred to as tissue Doppler or myocardial Doppler, and (2) speckle tracking on the basis of displacement measurements. Both types of measurements lend themselves to the derivation of multiple parameters of myocardial function. The goal of this document is to focus on the currently available techniques that allow quantitative assessment of myocardial function via image-based analysis of local myocardial dynamics, including Doppler tissue imaging and speckle-tracking echocardiography, as well as integrated back- scatter analysis. This document describes the current and potential clinical applications of these techniques and their strengths and weaknesses, briefly surveys a selection of the relevant published literature while highlighting normal and abnormal findings in the context of different cardiovascular pathologies, and summarizes the unresolved issues, future research priorities, and recommended indications for clinical use.

Current and evolving echocardiographic techniques for the quantitative evaluation of cardiac mechanics: ASE/EAE consensus statement on methodology and indications endorsed by the Japanese Society of Echocardiography

Echocardiographic imaging is ideally suited for the evaluation of cardiac mechanics because of its intrinsically dynamic nature. Because for decades, echocardiography has been the only imaging modality that allows dynamic imaging of the heart, it is only natural that new, increasingly automated techniques for sophisticated analysis of cardiac mechanics have been driven by researchers and manufacturers of ultrasound imaging equipment.Several such technique shave emerged over the past decades to address the issue of reader's experience and inter measurement variability in interpretation.Some were widely embraced by echocardiographers around the world and became part of the clinical routine,whereas others remained limited to research and exploration of new clinical applications.Two such techniques have dominated the research arena of echocardiography: (1) Doppler based tissue velocity measurements,frequently referred to as tissue Doppler or myocardial Doppler, and (2) speckle tracking on the basis of displacement measurements.Both types of measurements lend themselves to the derivation of multiple parameters of myocardial function. The goal of this document is to focus on the currently available techniques that allow quantitative assessment of myocardial function via image-based analysis of local myocardial dynamics, including Doppler tissue imaging and speckle-tracking echocardiography, as well as integrated backscatter analysis. This document describes the current and potential clinical applications of these techniques and their strengths and weaknesses,briefly surveys a selection of the relevant published literature while highlighting normal and abnormal findings in the context of different cardiovascular pathologies, and summarizes the unresolved issues, future research priorities, and recommended indications for clinical use.

Sensitivity and specificity of left ventricular ejection fraction by echocardiographic automated border detection: comparison with radionuclide ventriculography

BACKGROUND

Echocardiographic automated border detection (ABD) provides on-line, beat-to-beat estimation of left ventricular (LV) ejection fraction (EF). Sensitivity and specificity of using ABD-EF for diagnosing LV dysfunction in routine clinical situations have not been previously studied.

HYPOTHESIS

Analysis of ABD-EF data based on receiver operating characteristic (ROC) should provide useful information about sensitivity and specificity for clinical diagnosis of LV function based on ABD-EF.

METHODS

The study group included 50 consecutive patients with EF measured by both ABD and radionuclide ventriculography (RVG). ABD-EF was recorded for 25 consecutive heart beats in the apical four-chamber view. Data were analyzed statistically by linear regression, Bland-Altman plot, and ROC. In ROC analysis, abnormal LV function was defined RVG-EF < or = 40%.

RESULTS

ABD and RVG showed a moderate correlation in the EF measurements: slope = 0.93, intercept = 17%, r = 0.79 (n = 50). Interbeat variability in ABD was diminished by averaging consecutive beats; standard error of estimate (SEE) decreased from 15.6% without averaging to 12.5% with 25-beat averaging. Bland-Altman analysis indicated that ABD-EF compared unfavorably with RVG-EF, with limits of agreement from -11% to 39%. ABD-EF showed a systematic overestimation (p < 0.005), which was compensated by increasing the threshold for abnormal ABD-EF to 56%. With the optimized threshold, ABD-EF provided 89% sensitivity and 89% specificity (85% overall diagnostic accuracy) for diagnosing abnormal LV function.

CONCLUSION

This study explored the limitations of on-line echocardiographic measurement of EF in a clinical setting and provided useful data for assessing interbeat variability, sensitivity, and specificity.

Effect of preload reduction on sonographic myocardial integrated backscatter

PURPOSE

Sonographic myocardial tissue characterization with integrated backscatter (IBS) is affected by both structural and functional properties of the myocardium. The aim of the present study was to investigate the effect of preload reduction by hemodialysis (HD) on IBS measurements.

METHODS

Fifty-two patients on maintenance HD underwent echocardiography before and after a routine HD session. Measurements included the variation of IBS during the cardiac cycle (CV-IBS) and calibrated IBS (cal-IBS).

RESULTS

After HD, there were significant reductions in left ventricular end-diastolic and end-systolic dimensions and left atrial diameter. There was a reduction in stroke volume and LV ejection fraction consistent with a reduction in preload. Furthermore, CV-IBS was significantly lower after HD (7.9 +/- 2.2 versus 6.9 +/- 1.8 dB, 7.0 +/- 2.1 versus 6.2 +/- 1.9 dB, and 9.0 +/- 2.6 versus 8.1 +/- 2.0 dB [p < 0.01], respectively, in the left anterior, lateral, and inferior wall of the ventricle). Cal-IBS remained unchanged after dialysis compared with baseline. CV-IBS and ultrafiltration volume were significantly correlated.

CONCLUSION

HD leads to a decrease in CV-IBS that appears to be preload-dependent. This finding is in concordance with diminished left ventricular performance during HD.

Effects of acute myocardial ischemia on intramyocardial contraction heterogeneity: A study performed with ultrasound integrated backscatter during transesophageal atrial pacing

BACKGROUND

[corrected] Subendocardial thickening is greater than subepicardial thickening and acute myocardial ischemia mainly impairs the former. Integrated backscatter cyclic variations (IBScv) reflect regional myocardial contractility and are blunted during myocardial ischemia. We hypothesized that stress-induced myocardial ischemia mainly affects subendocardial IBScv.

METHODS AND RESULTS

Multiplane transesophageal echocardiography and simultaneous atrial pacing were performed in 12 patients without coronary artery disease (CAD) and in 25 with significant CAD. In a transgastric 2-chamber view, we calculated IBScv in subendocardium and subepicardium and a heterogeneity index, both at rest and at peak-pacing. In 27 myocardial segments of patients with normal coronary arteries, and in 16 myocardial segments supplied by coronary artery without significant stenosis in patients with CAD, there was a transmural gradient of IBScv at rest and the heterogeneity index did not change during all the protocol steps. In the 53 myocardial segments related to a significantly narrowed coronary artery, the transmural gradient of IBScv, present at rest, significantly decreased at peak-pacing because of subendocardial blunting, but promptly recovered 5 seconds after pacing interruption. Moreover, the myocardial thickening at rest and peak pacing correlated with the subendocardial IBScv behavior and not with the subepicardial one.

CONCLUSIONS

IBScv are greater in the subendocardium than in the subepicardium. Atrial pacing stress test does not affect IBScv in segments supplied by nonstenotic coronary arteries, whereas it affects segments supplied by diseased coronary arteries, blunting exclusively subendocardial IBScv. Heterogeneity of IBScv intramyocardial changes caused by stress-induced ischemia must be taken into account when using IBScv for investigating myocardial ischemia.

Alterations in ultrasonic backscatter during intra-aortic balloon counterpulsation support in patients with acute myocardial infarction

Alterations of ultrasonic backscatter parameters have been evident in humans with myocardial infarction or ischemia. The backscatter variability could be restored in ischemic or stunned myocardium after reperfusion. The aims of this study were to determinate changes in regional myocardial ultrasonic backscatter during intra-aortic balloon counterpulsation (IABP) support in patients with acute myocardial infarction (AMI), and to evaluate whether backscatter imaging could be a functional guide of IABP support. A total of 9 patients with AMI were investigated during IABP support with a two-dimensional (2-D) ultrasonic backscatter imaging approach for parasternal short-axis view. Coronary angiography was performed in 6 of the 9 patients. A total of 21 vessel territories were studied in different modes of IABP support: 1:1, 1:2 and standby. Restoration of cyclic variation of backscatter after IABP support was demonstrated in 10 vessel territories. Failure of restoration of cyclic variation of backscatter after IABP support was noted in 6 vessel territories with severe coronary lesions (total or nearly total occlusion) or scar tissue. No changes of the ultrasonic backscatter were found in nonischemic vessel territories with patent coronary arteries or TIMI III coronary flow. In addition, the wall motion score did not change significantly with different IABP support. These results suggest that IABP could restore the cyclic variation of backscatter in ischemic myocardium. Myocardial anisotropy may play an influential role in the alterations of ultrasonic backscatter. We propose that ultrasonic backscatter could be a noninvasively functional guide of IABP use in patients with AMI.

Normal Values in Children for Myocardial Ultrasonic Tissue Characterization by Integrated Backscatter

Normal values in adults for ultrasonic tissue characterization by integrated backscatter have been reported previously and subsequently applied to patients with specific diseases. Factors influencing integrated backscatter values in a pediatric population are not clearly defined. To obtain normal values for myocardial ultrasonic integrated backscatter in a pediatric population, we studied 72 children with normal cardiac anatomy using an ultrasonic integrated backscatter imaging system. The parameters measured were at peak, nadir, and end-diastole in eight different regions with two different settings: fixed and variable. We subsequently calculated cyclic variation, the ratios of cyclic variation to end-diastole and to peak. Age ranged from 1 day to 17.4 years (median 4.4 years). More than 90% of data curves from the two regions in the left ventricular posterior wall in long-axis view had normal patterns, whereas more than 50% of curves for the other regions had abnormal patterns. Comparing the two posterior wall positions, there were no differences in cyclic variation between the two regions, with little effect of setting. Less effect of regions and settings was noted for the ratios of cyclic variation to end-diastole or peak. There was no relation between backscatter variables and age, gender, or height, and some variables correlated weakly with body surface area. The assessment of integrated backscatter in children is optimal with interrogation of the left ventricular posterior wall imaged in the long-axis view. More stable estimates are obtained when the cyclic variation is related to the peak or end-diastolic value.

Abnormal Ultrasonic Tissue Characterization of the Myocardium in Children Receiving Doxorubicin for Cancer Therapy

Ultrasonic tissue characterization by integrated backscatter is a sensitive tool to detect myocardial changes related to specific diseases. Cardiotoxicity related to doxorubicin use is well known and remains a major concern. To determine if ultrasonic tissue characterization of the myocardium is abnormal in patients receiving doxorubicin, we studied the myocardium of pediatric patients receiving doxorubicin by a real-time integrated backscatter (IB) imaging system. Three values of IB parameters were averaged from the left ventricular posterior wall at the level of the tip of the mitral valve. In addition to standard echo parameters, we obtained the following IB parameters: peak, nadir, cyclic variation (CV), end-diastole, heart-rate corrected delay of nadir (Delay(c)), and the ratio of CV over end-diastole. IB parameters were normalized as Z scores from multiple linear regression equations including echo wall thickness and functional indices from a normal control group of 72 children. We evaluated 27 patients at a median age of 11.6 years (1.6 years to 20.3 years) and median time of 1.7 m (2 days to 7.2 years) after a mean cumulative dose of doxorubicin of 188 +/- 120 mg/m(2) for treatment of neoplasm. Mean (+/-SD) Z scores for IB variables were as follows: zPeak 0.15 +/- 1.07, P = 0.47; zNadir 0.41 +/- 1.16, P = 0.08; zCV -0.49 +/- 0.95, P = 0.01; zEnd-diastole 0.17 +/- 0.94, P = 0.38; zDelay(c) 0.33 +/- 0.80, P = 0.06, and zCV/Peak -0.59 +/- 1.06, P = 0.009. This study shows that ultrasonic IB of the myocardium of children receiving doxorubicin is abnormal and is independent of the cumulative dosage of doxorubicin or the amount of time since the last dose.

Color Doppler imaging of the myocardium: current status and potential clinical applications

Doppler myocardial imaging (DMI) is a new technique with potential clinical and research applications. It applies traditional pulsed and color Doppler techniques to the analysis of myocardial contractile velocity. A major area of focus is in the quantitation of regional and global myocardial function and evaluation of myocardial perfusion in conjunction with myocardial contrast studies. DMI may also provide a direct, relatively load-independent assessment of diastolic function. Further work is required to identify its role in clinical and research studies.

Cyclic variation of integrated ultrasound backscatter: normal and abnormal myocardial patterns in children

Cyclic variation of integrated backscatter (CVIBS) is altered in adults with myocardial infarction, allograft rejection, and cardiomyopathy. Its utility in children has not been tested. We studied 99 normal subjects: 16 fetuses, 13 newborns, 47 children, and 23 teenagers. Fifteen children with cardiomyopathy (13 dilated and two infiltrative) were studied to define abnormal CVIBS. CVIBS was measured in the anterior septum and the left ventricular posterior wall from a two-dimensional ultrasound image with an acoustic densitometry software package. CVIBS was similar in the anterior septum (3.7 +/- 1.9 dB) and the posterior wall (4.1 +/- 2.4 dB) of all children after birth. CVIBS was significantly lower in the fetus (septum: 2.8 +/- 1.6 dB) and in children with cardiomyopathy (septum: 0.6 +/- 1.6 dB, dilated; -1.2 +/- 4.2 dB, infiltrative; p < 0.01). Four children, studied after recovery from cardiomyopathy, had diminished CVIBS despite the return of normal systolic function. The pattern and extent of CVIBS in children is similar to that of adults. CVIBS is diminished in children with cardiomyopathy.

Beat-to-beat variability of left ventricular indexes measured by acoustic quantification: influence of heart rate and respiration--correlation with M-mode echocardiography

Influence of heart rate and respiration on beat-to-beat variability of left ventricular indexes measured by acoustic quantification was examined. These indexes were correlated with their counterparts measured by M-mode echocardiography. Parameters of left ventricular performance were recorded for 1 full minute in 43 children with a mean age of 5.9 +/- 3.9 years. Beat-to-beat variability was documented. The effect of respiration on such variability was examined in another 10 subjects. A wide range of heart rates and respiration did not show significant influence on the degree of variance among these parameters. The indexes measured correlated well with their counterparts measured by M-mode echocardiography. Acoustic quantification separated those with normal from those with abnormal left ventricular function with the same statistical significance as did M-mode echocardiography. A moderate degree of beat-to-beat variability occurs in acoustic quantification-derived left ventricular indexes. Heart rate variability and respiration do not influence the beat-to-beat variance of parameters of left ventricular performance measured with the acoustic quantification. Excellent correlation was documented between this technique and M-mode echocardiography.

Measurement of left ventricular ejection fraction by acoustic quantification and comparison with radionuclide angiography

Left ventricular (LV) ejection fraction (EF) is an important measure of systolic function, with radionuclide angiography being the accepted standard for its determination. Echocardiography is ideal for repeated measurements of EF, but most methods are either subject to error in the presence of regional wall abnormalities or require cumbersome off-line analysis. Acoustic quantification is a recently introduced method that allows for the continuous on-line display of LV cavity dimensions, but the on-line algorithm for the measurement of EF has not been validated against an independent standard in the clinical setting. This study attempted to validate acoustic quantification in the determination of EF by comparison with off-line echocardiographic analysis and radionuclide angiography in 54 patients referred for this latter procedure. Acoustic quantification correlated well with off-line analysis in both the apical 4-chamber (r = 0.89, n = 43) and 2-chamber (r = 0.86, n = 26) views. Similarly, it also correlated well with radionuclide angiography in the 4-chamber (r = 0.81, n = 44) and 2-chamber (r = 0.83, n = 26) views. The correlation between the 2 methods was further improved when only the last 30 patients were assessed (r = 0.91, n = 25 for 4-chamber views; r = 0.86, n = 16 for 2-chamber views). The correlation was worse in patients with regional asynergy (r = 0.69, n = 17 for 4-chamber views; r = 0.76, n = 10 for 2-chamber views). Moreover, acoustic quantification tended to underestimate EF when compared with radionuclide angiography.(ABSTRACT TRUNCATED AT 250 WORDS)