Improved quantification of left ventricular mass based on endocardial and epicardial surface detection with real time three dimensional echocardiography.

OBJECTIVE: To develop a technique for volumetric analysis of real time three dimensional echocardiography (RT3DE) data aimed at quantifying left ventricular (LV) mass and to validate the technique against magnetic resonance (MR) assumed as the reference standard. DESIGN: RT3DE, which has recently become widely available, provides dynamic pyramidal data structures that encompass the entire heart and allows four dimensional assessment of cardiac anatomy and function. However, analysis techniques for the quantification of LV mass from RT3DE data are fundamentally two dimensional, rely on geometric modelling, and do not fully exploit the volumetric information contained in RT3DE datasets. Twenty one patients underwent two dimensional echocardiography (2DE), RT3DE, and cardiac MR. LV mass was measured from 2DE and MR images by conventional techniques. RT3DE data were analysed to semiautomatically detect endocardial and epicardial LV surfaces by the level set approach. From the detected surfaces, LV mass was computed directly in the three dimensional space as voxel counts. RESULTS: RT3DE measurement was feasible in 19 of 21 patients and resulted in higher correlation with MR (r = 0.96) than did 2DE (r = 0.79). RT3DE measurements also had a significantly smaller bias (-2.1 g) and tighter limits of agreement (2SD = +/-23 g) with MR than did the 2DE values (bias (2SD) -34.9 (50) g). Additionally, interobserver variability of RT3DE (12.5%) was significantly lower than that of 2DE (24.1%). CONCLUSIONS: Direct three dimensional model independent LV mass measurement from RT3DE images is feasible in the clinical setting and provides fast and accurate assessment of LV mass, superior to the two dimensional analysis techniques.

Combined assessment of myocardial perfusion and regional left ventricular function by analysis of contrast-enhanced power modulation images.

BACKGROUND: Echocardiographic contrast media have been used to assess myocardial perfusion and to enhance endocardial definition for improved assessment of left ventricular (LV) function. These methodologies, however, have been qualitative or have required extensive offline image analysis. Power modulation is a recently developed imaging technique that provides selective enhancement of microbubble-generated reflections. Our goal was to test the feasibility of using power modulation for combined quantitative assessment of myocardial perfusion and regional LV function in an animal model of acute ischemia. METHODS AND RESULTS: Coronary balloon occlusions were performed in 18 anesthetized pigs. Transthoracic power modulation images (Agilent 5500) were obtained during continuous intravenous infusion of the contrast agent Definity (DuPont) at baseline and during brief coronary occlusion and reperfusion and were analyzed with custom software. At each phase, myocardial perfusion was assessed by calculation, in 6 myocardial regions of interest, of mean pixel intensity and the rate of contrast replenishment after high-power ultrasound impulses. LV function was assessed by calculation of regional fractional area change from semiautomatically detected endocardial borders. All ischemic episodes caused detectable and reversible changes in perfusion and function. Perfusion defects, validated with fluorescent microspheres, were visualized in real time and confirmed by a significant decrease in pixel intensity in the left anterior descending coronary artery territory after balloon inflation and reduced rate of contrast replenishment. Fractional area change decreased significantly in ischemic segments and was restored with reperfusion. CONCLUSIONS: Power modulation allows simultaneous online assessment of myocardial perfusion and regional LV wall motion, which may improve the echocardiographic diagnosis of myocardial ischemia.

Recent advances in echocardiographic evaluation of left ventricular anatomy, perfusion, and function.

This article provides a brief overview of several recently developed, emerging technologies and discusses their potential uses on clinical grounds. These new technologies include three-dimensional imaging, objective automated evaluation of ventricular function with acoustic quantification, assessment of regional ventricular performance using color kinesis and tissue Doppler imaging, harmonic imaging, and power Doppler imaging. Our hope is that readers will gain a better understanding of the principles underlying these technological advances, which will help them to integrate these new techniques efficiently into their clinical practices.

Detection of regional temporal abnormalities in left ventricular function during acute myocardial ischemia.

Echocardiographic diagnosis of myocardial ischemia is based on visualizing hypokinesis, which occurs late in the ischemic cascade. We hypothesized that temporal changes in endocardial motion may constitute sensitive early markers of ischemia. Two protocols were performed in 19 anesthetized pigs. Protocol 1 included 54 intracoronary balloon occlusions. Transthoracic images were acquired at baseline and every 15 s during 5 min of occlusion and reperfusion. In protocol 2, ischemia was induced in 12 animals by use of graded dobutamine infusion, after creating significant partial occlusions without a resting wall motion abnormality. Systolic and diastolic endocardial motion was color encoded using color kinesis and analyzed using custom software. All ischemic episodes caused detectable and reversible changes. The earliest sign of ischemia was tardokinesis in 31/54 occlusions, whereas hypokinesis appeared first in 23/54 cases. Dobutamine-induced ischemia caused tardokinesis first in 9/12 and hypokinesis in 3/12 animals. Reversible ischemic changes in regional left ventricular performance can be objectively detected using analysis of echocardiographic images and will likely improve the early noninvasive diagnosis of acute ischemia.

Effects of aging on left atrial reservoir, conduit, and booster pump function: a multi-institution acoustic quantification study.

OBJECTIVE: To assess the feasibility of measuring left atrial (LA) function with acoustic quantification (AQ) and then assess the effects of age and sex on LA reservoir, conduit, and booster pump function. PATIENTS AND SETTING: 165 subjects without cardiovascular disease, 3-79 years old, were enrolled by six tertiary hospital centres. INTERVENTIONS: Continuous LA AQ area data were acquired and signal averaged to form composite waveforms which were analysed off-line. MAIN OUTCOME MEASURES: Parameters of LA performance according to age and sex. RESULTS: Signal averaged LA waveforms were sufficiently stable and detailed to allow automated analysis in all cases. An age related increase in LA area was noted. LA reservoir function did not vary with age or sex. All parameters of LA passive and active emptying revealed a significant age dependency. Overall, the passive emptying phase accounted for 66% of total LA emptying ranging from 76% in the youngest to 44% in the oldest decade. LA contraction accounted for 34% of atrial emptying in all subjects combined with the older subjects being more dependent on atrial booster pump function. When adjusted for atrial size, there were no sex related differences in LA function. CONCLUSIONS: LA reservoir, conduit, and booster pump function can be assessed with automated analysis of signal averaged LA area waveforms. As LA performance varies with age, establishment of normal values should enhance the evaluation of pathologic states in which LA function is important.

Electronic transmission of digital echocardiographic studies: effects of MPEG compression.

The acquisition, storage and retrieval of digital echocardiographic studies greatly facilitates image review and quantitation and permits the transmission of studies electronically. However, the considerable size of digital echocardiographic data files makes transmission over existing networks slow and impractical. Reduction in the size of these data files can be accomplished with digital image compression. We sought to evaluate the effects of MPEG-1 compression on the transfer time of digital echocardiographic studies over currently available network connections. Ninety consecutive routine clinical echocardiographic studies were randomly compressed at one of three compression ratios 60:1, 80:1, or 120:1 and sent to a receiving terminal using simulated transmission rates. Compression of digital echocardiographic studies at these ratios which, have been shown to maintain diagnostic image quality, reduced the size of digital echocardiographic studies to less than 1% of their original sizes which allowed transmission of echocardiographic studies over networks using 3ISDN or T1 lines with minimal waiting time.

Normal values of regional left ventricular endocardial motion: multicenter color kinesis study.

Our goal was to establish normal values for quantitative color kinesis indexes of left ventricular (LV) wall motion over a wide range of ages, which are required for objective diagnosis of regional systolic and diastolic dysfunction. Color-encoded images were obtained in 194 normal subjects (95 males, 99 females, age 2 mo to 79 yr) in four standard views. Quantitative indexes of magnitude and timing of systolic and diastolic function were studied for age- and gender-related differences. Normal limits of all ejection and filling indexes were in a narrow range (< or =25% of the mean), with no major gender-related differences. Despite invariable ejection fractions, both peak filling and ejection rates decreased with age (30 and 20%, correspondingly) with a concomitant increase in mean filling and ejection times, resulting in five- and twofold increases in the late to early filling and ejection ratios, correspondingly. Diastolic asynchrony increased with age (from 4.7 +/- 2.0 to 6.4 +/- 3.2 from the 2nd to 7th decade). The normal values of color kinesis indexes should allow objective detection of regional LV systolic and diastolic dysfunction.

Power Doppler imaging as a basis for automated endocardial border detection during left ventricular contrast enhancement.

Echocardiographic evaluation of left ventricular (LV) systolic function relies on endocardial visualization, which can be improved when necessary using contrast enhancement. However, there is no method to automatically detect the endocardial boundary from contrast-enhanced images. We hypothesized that this could be achieved using harmonic power Doppler imaging. Twenty-two patients were studied in two protocols: (1) 11 patients with poorly visualized endocardium (> 3 contiguous segments not visualized) and (2) 11 consecutive patients referred for dobutamine stress echocardiography who were studied at rest and at peak dobutamine infusion. Patients were imaged in the apical four-chamber view using harmonic power Doppler mode (HP SONOS 5500) during LV contrast enhancement (Optison or Definity DMP115). Digital images were analyzed using custom software designed to automatically extract the endocardial boundary from power Doppler color overlays. LV cavity area was automatically measured frame-by-frame throughout the cardiac cycle, and fractional area change calculated and compared with those obtained by manually tracing the endocardial boundary in end-systolic and end-diastolic gray scale images. Successful border detection and tracking throughout the cardiac cycle was possible in 9 of 11 patients with poor endocardial definition and in 10 of 11 unselected patients undergoing dobutamine stress testing. Fractional area change obtained from power Doppler images correlated well with manually traced area changes (r = 0.82 and r = 0.97, in protocols 1 and 2, respectively). Harmonic power Doppler imaging with contrast may provide a simple method for semi-automated border detection and thus facilitate the objective evaluation of LV function both at rest and under conditions of stress testing. This methodology may prove to be particularly useful in patients with poorly visualized endocardium.

Spectral analysis of left ventricular area variability as a tool to improve the understanding of cardiac autonomic control.

Spectral analysis of the fluctuations in heart rate (HR) or blood pressure (BP) has been extensively used as a tool for the noninvasive assessment of autonomic control of the heart. The recently developed echocardiographic acoustic quantification allows noninvasive continuous measurement of the left ventricular cross-sectional area (LVA) signal. In this study, we investigated whether the LVA signal, and more specifically its fluctuations, can be reliably subjected to spectral analysis, and whether the results of such analysis may improve the understanding of the cardiovascular control mechanisms. Our results show that the general pattern of power spectra of LVA fluctuations, as well as their reproducibility, is similar to the power spectra of HR and BP fluctuations. Analysis of LVA signals obtained in normal subjects at rest as well as under vagal blockade and under held respiration, and in patients with known autonomic dysfunction, showed significant differences between groups and states. The effects of age, related to the reduction in parasympathetic activity, were not evident in the spectral content of the LVA and BP signals. The high frequency LVA fluctuations are mainly of mechanical origin, since they were eliminated by breath-holding. We observed an increase in the high frequency LVA fluctuations under vagal blockade, indicating that under normal (control) conditions, these high frequency fluctuations are attenuated by parasympathetic activity. The enhancement in high frequency fluctuations in LVA observed in diabetic patients can thus be attributed to reduced parasympathetic activity. The analysis of LVA variability may be used as a tool for basic research and, possibly, as a quantitative clinical measure for specific disease states.

Effects of inotropic stimulation on segmental left ventricular relaxation quantified by color kinesis.

Although myocardial ischemia impairs left ventricular (LV) relaxation before contractile function, regional LV diastolic dysfunction is difficult to evaluate by conventional echocardiography. Because beta-adrenergic stimulation enhances myocardial relaxation, we sought to characterize segmental LV diastolic function (by color kinesis) during dobutamine stress echocardiography and compare it with independently assessed segmental systolic function. We studied 22 patients with suspected coronary artery disease with color kinesis by acquiring digital images with endocardial motion display throughout diastole. Quantification of LV segmental diastolic peak filling rate (SPFR, normalized to segmental end-diastolic area/s) was obtained at rest, low-dose, and peak dobutamine infusion in myocardial segments visualized from the short-axis and/or apical 4-chamber views. In patients with resting normal LV systolic function and a dobutamine-induced hypercontractile response (group I, n = 13 patients; 102 segments), progressive increases in SPFR (p <0.001) were seen in all segments. However, in LV segments with resting systolic wall motion abnormalities (group II, n = 9 patients; 74 segments) SPFR measured at rest was significantly lower than that in group I (p <0.005) and did not increase significantly in response to dobutamine. In both groups of patients, LV myocardial segments (n = 528; rest and after dobutamine)-systolic and quantitative diastolic function-were concordant in 84% and 77% as viewed from short-axis and apical views, respectively. Thus, segmental LV diastolic function can be measured with color kinesis at rest and after inotropic stimulation, allowing comparison with segmental systolic function during pharmacologic stress testing.

The role of echocardiographic harmonic imaging and contrast enhancement for improvement of endocardial border delineation.

Despite advances in imaging technology, many myocardial segments remain poorly visualized with echocardiography; however, both contrast enhancement and harmonic imaging have shown promise for improving endocardial definition. Fifty subjects with technically limited echocardiograms were studied with fundamental and harmonic imaging as well as during echocardiographic contrast injection. Overall endocardial visualization scores improved with both techniques compared with fundamental imaging. Harmonic imaging improved endocardial visualization in 43% of all segments and in 57% of segments nonvisualized with fundamental imaging. The benefit of harmonic imaging was seen in all segments. Contrast echocardiography had similar overall improvements in visualization (42% of all segments, 67% of segments nonvisualized with fundamental imaging) but was not helpful in all regions. Harmonic imaging outperformed contrast in 9 of 22 segments, whereas contrast was superior in 4 of 22. In a subgroup of patients with very poor images, contrast enhancement was superior, with a greater increase in overall score and a higher salvage rate than harmonic (68% vs 40%).

Effects of MPEG compression on the quality and diagnostic accuracy of digital echocardiography studies.

The advantages of digital echocardiography studies include ease of retrieval, review, comparison, duplication, and quantitation as well as the potential for moving studies over networks. However, the large amounts of data associated with digital echocardiography studies have posed new problems. Reduction of the amount of data can be accomplished with image compression, in particular MPEG-1 (Moving Pictures Expert Group), which is designed for dynamic image sequences. However the effects of different levels of compression on the quality and diagnostic content of echocardiographic images need to be established. Digital sequences of single cardiac cycles were acquired in 40 consecutive patients, MPEG-1-compressed at different effective ratios (60:1, 80:1, 120:1, 200:1, 300:1, 370:1, 500:1), reviewed, and scored for endocardial visualization. The overall visualization scores and percentages of nonvisualized segments in the compressed images were not different from the uncompressed images up to a compression ratio of 200:1. Differential effects of compression were noted on a segmental basis and also varied with baseline image quality. The ability to correctly identify regional wall motion abnormalities did not decrease until compression ratios of 1:200 or higher were used. Digital echocardiography loops, MPEG-1-compressed at an effective ratio of 200:1, demonstrate no degradation in endocardial visualization quality or diagnostic content. Compression at this ratio has the potential to reduce the storage size of digital echocardiography studies to less than 1% of their current size.

Three-dimensional echocardiography in adult patients: comparison between transthoracic and transesophageal reconstructions.

BACKGROUND: Three-dimensional (3D) echocardiography is a relatively new technique typically implemented with transesophageal imaging with multiplane transducers. OBJECTIVES: The goals of this study were (1) to test the feasibility of 3D reconstruction with a new transthoracic multiplane transducer in adult subjects with excellent quality of 2-dimensional images and (2) to compare these reconstructions with those obtained in the same patients with the transesophageal approach. METHODS: Transthoracic multiplane image acquisition was performed in 37 patients who were selected on the basis of the quality of their 2-dimensional images. In addition, transesophageal acquisition was also performed in 19 of 37 patients. Three-dimensional reconstruction of mitral and aortic valves was performed. Three-dimensional images were reviewed, and the visualization of various anatomic features was graded. RESULTS: The reconstruction of 25 mitral valves and 16 aortic valves, normal and pathologic, was feasible and resulted in visualization of anatomic detail. Score indexes of all valvular characteristics studied were not significantly different when transthoracic and transesophageal reconstructions were compared. CONCLUSIONS: Transthoracic 3D echocardiography with a multiplane transducer in adult patients with good acoustic windows is feasible. This technique will allow easy noninvasive serial assessment of valvular pathophysiologic characteristics.

Identification of cardiac masses and abnormal blood flow patterns with harmonic power Doppler contrast echocardiography.

Power Doppler is an ultrasound technique that color-encodes the change in amplitude of the ultrasound signal, which reflects changes in the position of scatterers between ultrasound pulses. Power Doppler can be used with echocardiographic contrast agents in a harmonic imaging mode to opacify a cardiac chamber. The opacification of a cardiac chamber can aid in visualizing the silhouette of intracardiac masses and displaying blood flow patterns. Four cases are presented that demonstrate the use of harmonic power Doppler to aid in the identification of a left ventricular apical thrombus, a left atrial thrombus, and a left ventricular pseudoaneurysm.

Objective evaluation of regional left ventricular wall motion during dobutamine stress echocardiographic studies using segmental analysis of color kinesis images.

OBJECTIVES: To test the feasibility of objective and automated evaluation of echocardiographic stress tests, we studied the ability of segmental analysis of color kinesis (CK) images to detect dobutamine-induced wall motion abnormalities and compared this technique with inexperienced reviewers of conventional gray-scale images. BACKGROUND: Conventional interpretation of stress echocardiographic studies is subjective and experience dependent. METHODS: CK images were obtained in 89 of 104 consecutive patients undergoing clinical dobutamine stress studies and were analyzed using custom software to calculate regional fractional area change in 22 segments in four standard views. Each patient's data obtained at rest was used as a control for automated detection of dobutamine-induced wall motion abnormalities. Independently, studies were reviewed without CK overlays by two inexperienced readers who classified each segment's response to dobutamine. A consensus reading of two experienced reviewers was used as the gold standard for comparisons. In a subgroup of 16 patients, these consensus readings and CK detection of wall motion abnormalities were compared with coronary angiography. RESULTS: The consensus reading detected ischemic response to dobutamine in 43 of 1958 segments in 23 of 89 patients. Automated detection of stress-induced wall motion abnormalities correlated more closely with the standard technique than the inexperienced reviewers (sensitivity 0.76 vs. 0.55, specificity 0.98 vs. 0.94 and accuracy 0.97 vs. 0.92). When compared with coronary angiography in a subgroup of patients, analysis of CK images differentiated between normal and abnormal wall motion more accurately than expert readers of gray-scale images (accuracy of 0.93 vs. 0.82). CONCLUSIONS: Analysis of CK images allows fast, objective and automated evaluation of regional wall motion, sensitive enough for clinical dobutamine stress data and more accurate than inexperienced readers. This method may result in a valuable adjunct to conventional visual interpretation of dobutamine stress echocardiography.

Quantitative assessment of regional right ventricular function with color kinesis.

We used color kinesis, a recent echocardiographic technique that provides regional information on the magnitude and timing of endocardial wall motion, to quantitatively assess regional right ventricular (RV) systolic and diastolic properties in 76 subjects who were divided into five groups, as follows: normal (n = 20), heart failure (n = 15), pressure/volume overload (n = 14), pressure overload (n = 12), and RV hypertrophy (n = 15). Quantitative segmental analysis of color kinesis images was used to obtain regional fractional area change (RFAC), which was displayed in the form of stacked histograms to determine patterns of endocardial wall motion. Time curves of integrated RFAC were used to objectively identify asynchrony of diastolic endocardial motion. When compared with normal subjects, patients with pressure overload or heart failure exhibited significantly decreased endocardial motion along the RV free wall. In the presence of mixed pressure/volume overload, the markedly increased ventricular septal motion compensated for decreased RV free wall motion. Diastolic endocardial wall motion was delayed in 17 of 72 segments (24%) in patients with RV pressure overload, and in 31 of 90 segments (34%) in patients with RV hypertrophy. Asynchrony of diastolic endocardial wall motion was greater in the latter group than in normal subjects (16% versus 10%: p < 0.01). Segmental analysis of color kinesis images allows quantitative assessment of regional RV systolic and diastolic properties.

Quantitative evaluation of left ventricular function in a TransgenicMouse model of dilated cardiomyopathy with 2-dimensional contrast echocardiography.

The study of transgenic mouse models of human cardiovascular disease has been limited by the small size and high heart rate of the mouse heart. Advances in digital echocardiographic imaging equipment have provided the high spatial and temporal resolution necessary for 2-dimensional (2D) in vivo imaging of the mouse heart. The goal of this study was to test the use of contrast-enhanced 2D echocardiography to quantitatively assess left ventricular (LV) size and function in normal and transgenic mice with dilated cardiomyopathy. Images were obtained with a 12-MHz broadband transducer in the parasternal short-axis view in 8 control mice and 8 transgenic mice with dilated cardiomyopathy resulting from expression of a dominant-negative CREB transcription factor in the heart. LV opacification was achieved with injections of human albumin microspheres, injectable suspension (Optison) (15 to 30 microliter bolus). LV area was measured throughout the cardiac cycle with manual frame-by-frame tracing of the endocardial boundary. End-systolic and end-diastolic areas (ESA and EDA) were measured and fractional area change (FAC) calculated in both groups at baseline and during administration of dobutamine (40 microgram/kg/min intravenously). High-quality 2D images, which yielded LV area over time waveforms, were obtained in all mice. Under baseline conditions, ESA was significantly higher and FAC lower in the transgenic mice compared with their controls. During administration of dobutamine, normal mice had significantly smaller ESA and significantly larger FAC compared with baseline conditions, whereas this trend did not reach significance in the transgenic mice. In summary, quantitative assessment of LV size and function may be achieved with contrast-enhanced 2D echocardiographic imaging. This technique promises to facilitate studies of pathophysiology in murine models of human cardiovascular disease.

Age dependency of left atrial and left ventricular acoustic quantification waveforms for the evaluation of diastolic performance in left ventricular hypertrophy.

We evaluated diastolic performance in 50 normal subjects and 50 patients with concentric left ventricular (LV) hypertrophy. Age-dependent normal values were determined for LV and left atrial (LA) acoustic quantification parameters. Pulsed wave Doppler echocardiography was also performed on all subjects. Patients with LV hypertrophy had higher peak velocities of atrial contraction and atrial contributions to filling. The acoustic quantification waveforms revealed lower rapid filling percentage of total filling and lower peak rapid filling rates. The LA acoustic quantification analysis confirmed the dependence on active atrial emptying in the patients with LV hypertrophy. There were significant correlations with age for most of the LV and LA acoustic quantification parameters. Acoustic quantification provided confirmatory results in subjects with an abnormal relaxation or restrictive Doppler pattern. In subjects with a normal Doppler pattern, the acoustic quantification was of added diagnostic value, identifying abnormalities in 77% to 80% of the patients.