Color coding of digitized echocardiograms: description of a new technique and application in detecting and correcting for cardiac translation

Detection of left ventricular systolic and diastolic abnormalities in patients with coronary artery disease by color kinesis

BACKGROUND

Color kinesis (CK) is a recently developed echocardiographic technique based on acoustic quantification that automatically tracks and displays endocardial motion in real time and has been used in initial studies to improve the evaluation of global and regional wall motion.

HYPOTHESIS

For further validation of the use of CK for analysis of segmental ventricular dysfunction, we assessed its sensitivity and specificity for detection of regional systolic and diastolic wall motion abnormalities in patients with coronary artery disease (CAD).

METHODS

Two-dimensional (2-D) echocardiography and CK were used to study 15 normal subjects and 63 patients with technically good quality echocardiographic tracings, who underwent coronary arteriography within 1 month of echocardiography. Significant (> 70% luminal diameter stenosis) CAD was present in 50 patients (79%).

RESULTS

Color kinesis tracked endocardial motion accurately in 93% of left ventricular segments. Wall motion score, systolic segmental endocardial motion (SEM), and the time of systolic SEM (tSEM) and diastolic (tDEM) segmental endocardial motion were calculated. Intra- and interobserver variability were within narrow limits. SEM and tSEM were significantly lower and tDEM was significantly higher in the patient population than in the control group (p < 0.001). Comparison between CK and 2-D echocardiography showed a correlation coefficient of 0.81 between the two techniques. The score was identically graded in 74% of segments, with concordance of 82% in diagnosing segments as abnormal. Interobserver concordance was 86% for CK (r = 0.85) and 81% for 2-D echocardiography (r = 0.80). The sensitivity and specificity of systolic and diastolic CK parameters for the detection of CAD were 88 and 92% and 77 and 85%, respectively. The positive predictive values were 93 and 96%, respectively, the negative predictive values were 63 and 73%, respectively, and the overall accuracy was 86 and 91%, respectively.

CONCLUSIONS

Our data suggest that CK is a feasible and sensitive technique for identifying regional systolic as well as diastolic wall motion abnormalities in patients with CAD.

Color encoding of endocardial motion improves the interpretation of contrast-enhanced echocardiographic stress tests by less-experienced readers

BACKGROUND

We hypothesized that color encoding of endocardial motion could aid less-experienced readers in detection of wall-motion abnormalities at rest and stress in patients with poor acoustic windows.

METHODS

Color-encoded images (color kinesis) were obtained at rest and peak dobutamine stress in 4 standard views during intravenous infusion of contrast agent in 117 patients with poorly visualized endocardium. In 101 of 117 patients (86%), in whom contrast enhancement allowed endocardial tracking, images were reviewed by two expert readers without color overlays. Each reader graded regional wall motion as normal, abnormal, or uninterpretable, and their consensus grades served as a gold standard. The same images were then reviewed and graded with and without color overlays by 3 cardiology fellows. The accuracy of the interpretation was calculated against the gold standard separately for the 3 vascular territories (left anterior descending, left circumflex, and right coronary arteries) and averaged for the 3 fellows.

RESULTS

With the addition of color encoding: (1) the number of uninterpretable segments decreased by 55% at rest and 61% at peak stress; and (2) all 3 fellows reached higher levels of accuracy in all 3 vascular territories both at rest (6%-82% average) and at stress (73%-80%).

CONCLUSION

The addition of color encoding of wall motion to contrast-enhanced images obtained in patients with poor acoustic windows during stress tests improves the interpretation of regional left ventricular function by less-experienced readers.

Improvement in echocardiographic evaluation of left ventricular wall motion using still-frame parametric imaging

BACKGROUND

Conventional echocardiographic assessment of left ventricular wall motion is based on visual interpretation of dynamic images, which depends on readers' experience. We tested the feasibility of evaluating endocardial motion using still-frame parametric images.

METHODS AND RESULTS

In protocol 1, integrated backscatter images were obtained in 8 anesthetized pigs at baseline, 5, and 60 seconds after left anterior descending coronary occlusion and during reperfusion. Images from 1 cardiac cycle were analyzed offline to create a parametric image of local video intensity oscillations. Ischemia-induced changes were quantified by segmenting the parametric images and calculating regional pixel-intensity profiles. In protocol 2, parametric images were obtained from contrast-enhanced echocardiograms in 30 patients (18 with wall-motion abnormalities; 12 control subjects). "Gold standard" for wall motion was determined from independent interpretations of dynamic images made by 3 experienced reviewers. Dynamic images were independently classified by 3 inexperienced and 3 intermediate-level readers. Interpretation was then repeated in combination with parametric images. Parametric images showed a bright band in the area spanned by endocardial motion, which gradually decreased in brightness and thickness in the left anterior descending territory during coronary occlusion in all animals. In patients, the agreement with the gold standard correlated with the readers' experience (68% inexperienced, 87% intermediate) and significantly improved by adding parametric images (83% and 91%, respectively).

CONCLUSION

Parametric imaging provides a still-frame display of regional endocardial motion, sensitive to track ischemia-induced abnormalities. When combined with dynamic images, this technique improves the accuracy of the interpretation of wall motion, especially by less experienced echocardiographers.

Objective assessment of left ventricular wall motion from contrast-enhanced power modulation images

There is no method to objectively evaluate left ventricular (LV) function from contrast-enhanced images. We tested the feasibility of evaluating regional LV function by using power modulation imaging. In protocol 1, 9 anesthetized closed-chest pigs were studied. Images were obtained during contrast infusion at baseline, during LAD occlusion and reperfusion. In protocol 2, images were obtained in 20 patients (14 wall-motion abnormalities; 6 controls) during contrast enhancement. Off-line, frame-by-frame, semiautomated endocardial border detection was followed by color encoding of endocardial motion, followed by segmentation and calculation of regional fractional area changes. In all animals, coronary occlusions resulted in hypokinesis and decreased fractional area changes in LAD-related segments only, which were reversed during reperfusion. In patients, wall-motion analysis was in agreement with an expert reader of dynamic images in 92.5% segments, with interobserver variability of 12.5%. Color encoding of endocardial motion from contrast-enhanced power modulation images allows accurate quantitative assessment of regional LV function.

New method of on-line quantification of regional wall motion with automated segmental motion analysis

We have recently developed an automated segmental motion analysis (A-SMA) system, based on an automatic "blood-tissue interface" detection technique, to provide real-time and on-line objective echocardiographic segmental wall motion analysis. To assess the feasibility of A-SMA in detecting regional left ventricular (LV) wall motion abnormalities, we performed 2-dimensional echocardiography with A-SMA in 13 healthy subjects, 22 patients with prior myocardial infarction (MI), and 9 with dilated cardiomyopathy (DCM). Midpapillary parasternal short-axis and apical 2- and 4-chamber views were obtained to clearly trace the blood-tissue interface. The LV cavity was then divided into 6 wedge-shaped segments by A-SMA. The area of each segment was calculated automatically throughout a cardiac cycle, and the area changes of each segment were displayed as bar graphs or time-area curves. The systolic fractional area change (FAC), peak ejection rate (PER), and filling rate (PFR) were also calculated with the use of A-SMA. In the control group, a uniform FAC was observed in real time among 6 segments in the short-axis view (60% +/- 10% to 78% +/- 9%), or among 5 segments in either the 2-chamber (59% +/- 12% to 75% +/- 16%) or 4-chamber view (58% +/- 13% to 72% +/- 12%). The variations of FAC, PER, and PFR were obviously decreased in infarct-related regions in the MI group and were globally decreased in the DCM group. We conclude that A-SMA is an objective and time-saving method for assessing regional wall motion abnormalities in real time. This method is a reliable new tool that provides on-line quantification of regional wall motion.

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.

Atrioventricular plane motion during dobutamine-atropine stress echocardiography: the biphasic response in healthy subjects revisited

This study was undertaken to establish normal values for the systolic atrioventricular plane motion (AVPM) from base to apex during dobutamine-atropine stress echocardiography (DASE) and to compare them with those of patients with coronary artery disease. The AVPM was measured at baseline, low dose and peak dobutamine-atropine infusion in 20 patients referred for coronary angiography and in 20 control subjects. Atrioventricular plane motion was measured at the posterior, anterior, septal, and lateral positions of the mitral annulus in the apical 2- and 4-chamber views by an observer blinded to clinical and angiographic data. In healthy subjects undergoing DASE, AVPM initially increased but subsequently decreased to below baseline values at peak stress. Atrioventricular plane motion at any stage and the changes therein during DASE were within the normal reference interval in the majority of patients. In conclusion, AVPM decreased during DASE in healthy subjects and was not a sensitive marker of coronary artery disease.

Comparison of methods of fractional area change for detection of regional left ventricular dysfunction

Three methods for assessment of fractional area change (FAC) and conventional versus cross-sectional segmentation were compared under conditions known to occur frequently during stress echocardiography. Quantitative analysis of 80 echocardiograms obtained from healthy subjects, patients with left ventricular (LV) dysfunction and after coronary artery bypass grafting included segmental and cross-sectional FACs by the centroid method with fixed and floating reference and a method with floating external reference. All segmental and cross-sectional FACs were equally sensitive to LV dysfunction, and segmental FACs failed to accurately predict the location of coronary lesions. The centroid method with floating reference and cross-sectional FACs were the least affected by surgery induced intrathoracic heart motion. In moderate to severe LV dysfunction FAC by the centroid method with floating reference and cross sections were rarely within normal limits. Cross-sectional FACs may prove to be useful in stress echocardiography. For viability studies segmental FAC by fixed reference appears to be the method of choice.

Assessment of nonuniformity of transmural myocardial velocities by color-coded tissue Doppler imaging: characterization of normal, ischemic, and stunned myocardium

BACKGROUND

Transmural myocardial contractile performance is nonuniform across the different layers of the left ventricular wall. We evaluated the accuracy of color M-mode tissue Doppler imaging (TDI) to assess the transmural distribution of myocardial velocities and to quantify the severity of dysfunction induced by acute ischemia and reperfusion in the inner and outer myocardial layers.

METHODS AND RESULTS

Thirteen open-chest dogs underwent 15 minutes of left anterior descending coronary artery occlusion followed by 120 minutes of reperfusion. M-mode TDI was obtained from an epicardial short-axis view. Systolic velocities were calculated within endocardium and epicardium of the anterior and posterior walls. Regional myocardial blood flow was assessed by radioactive microspheres. Segment shortening was measured by sonomicrometry in endocardium and epicardium of both the anterior and posterior walls. At baseline, endocardial velocities were higher than epicardial velocities, resulting in an inner/outer myocardial velocity gradient. Ischemia caused a significant and comparable reduction in endocardial and epicardial systolic velocities in the anterior wall with the disappearance of the velocity gradient. Systolic velocities significantly correlated with segment shortening in both endocardium and epicardium during ischemia and reperfusion. In the first minutes after reflow, endocardial velocities showed a greater improvement than epicardial velocities, and the velocity gradient resumed although to a limited extent, indicative of stunning.

CONCLUSIONS

TDI is an accurate method to assess the nonuniformity of transmural velocities and may be a promising new tool for quantifying ischemia-induced regional myocardial dysfunction.

Mean myocardial velocity mapping in quantifying regional myocardial contractile reserve in patients with impaired left ventricular systolic function: Doppler myocardial imaging study

The aim of this study was to use Doppler myocardial imaging-derived mean myocardial velocity (MMV) at baseline and during low-dose dobutamine stress echocardiography (DSE) to quantify regional contractile reserve of the left ventricle (LV). Sixteen patients (mean age 59 +/- 7 years) with coronary artery disease and regional left ventricular wall motion abnormalities were studied. During each increment of Dobutamine infusion, 6 2-dimensional transthoracic apical images were acquired in standard gray-scale and Doppler myocardial imaging modes at 30 degrees steps over 180 degrees. For the analysis, the LV was divided into 18 segments. For each segment, both wall motion score and MMV obtained in systole and both early and late diastole were measured at baseline and at each stage of DSE. In viable segments by wall motion score, MMV increased during DSE in systole and in early and late diastole. In contrast, in nonviable segments, MMV did not change during DSE. Mean myocardial velocity mapping is a promising new approach to quantify regional myocardial contractile reserve of the LV.

Echocardiographic quantification of regional left ventricular wall motion with color kinesis

Echocardiographic assessment of regional systolic left ventricular function is usually performed qualitatively and depends on investigator experience. In this study, we investigated a new method for quantifying regional systolic wall motion based on color kinesis. In this study, regional systolic wall motion velocity (Vsys) was determined by dividing end-systolic color width by systolic time. High regional wall motion velocity (Vhigh) was determined by dividing the width of the widest color by its duration of 40 ms. First, in vitro measurements with an acrylic glass model were obtained; these demonstrated a high correlation between echocardiographically determined and real "wall motion velocities" (R = 0.99, p<0.001, R2 = 0.99). Then, 17 healthy, young persons were examined, and normal values for each left ventricular wall segment (16-segment model) were determined. The mean Vsys and Vhigh of all 272 wall segments were 2.3+/-0.6 and 7.4+/-1.8 cm/s, respectively. Finally, in 12 patients with coronary artery disease and prior myocardial infarction, Vsys and Vhigh of each left ventricular wall segment were determined and compared with conventional echocardiographic wall motion analysis using the usual 4-grade score system. Analysis of data showed that quantitative color kinesis measurements demonstrated significantly lower velocity values in pathologic than in normal wall segments (Mann-Whitney U test, p<0.05). Measurements discriminated between pathologic and normal wall motion, with an accuracy of 89% for Vsys and 83% for Vhigh (chi-square test, p<0.05). To summarize, in this first study, measurements of regional wall motion velocities with color kinesis demonstrated reliable results for the quantification of regional left ventricular systolic function.

Advances in Exercise Echocardiography Can This Technique Still Thrive in the Era of Pharmacologic Stress Testing?

In the current literature, pharmacologic stress techniques are the focus of interest and excitement regarding new technologies and new indications such as the diagnosis of viable myocardium. In contrast, exercise echocardiography has evolved less and is less amenable to the introduction of new technologies. This article reviews the indications for exercise echocardiography (especially in contrast to pharmacologic stress), its accuracy relative to other testing, and application to clinical decision making. Exercise echocardiography remains to be well accepted as a diagnostic and risk-assessment technique, and in some clinical situations it provides valuable data that are not available during pharmacologic stress testing.

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.

Regional mean systolic myocardial velocity estimation by real-time color Doppler myocardial imaging: a new technique for quantifying regional systolic function

A new color Doppler myocardial imaging (CDMI) system with high spatial and temporal resolution and novel postprocessing modalities has been developed that could allow quantifiable stress echocardiography. The purpose of this study was to determine whether regional myocardial systolic velocities could be accurately and reproducibly measured both at rest and during bicycle ergometry by using CDMI. Thirty normal subjects were examined with CDMI at rest, and peak mean systolic myocardial velocities (MSV) were measured for 34 predetermined left ventricular myocardial segments. Interobserver variability and intraobserver variability were established for all segments. Submaximal bicycle ergometry was performed in 20 normal subjects by using standardized weight-related increases in workload. MSV were measured at each step of exercise for 16 left ventricular stress echo segments. At rest, a base-apex gradient in regional MSV was recorded with highest longitudinal shortening velocities at the base. A similar pattern was noted for circumferential shortening MSV. Measurements were predictable and highly reproducible with low interobserver and intraobserver variability for 26 of 34 segments. Reproducibility was poor for basal anteroseptal segments in all views and mid anterior, anteroseptal, and septal segments in the short-axis views. During exercise, mid and basal segments of all walls showed a significant increase of MSV between each workload step and for apical segments between alternate steps. The resting base-apex velocity gradient observed at rest remained in all walls throughout ergometry. Thus a CDMI system with improved spatial and temporal resolution and postprocessing analysis modalities provided reproducible and accurate quantification of segmental left ventricular circumferential and longitudinal contraction both at rest and during exercise.

Segmental analysis of color kinesis images: new method for quantification of the magnitude and timing of endocardial motion during left ventricular systole and diastole

BACKGROUND

We describe a method for objective assessment of left ventricular (LV) endocardial wall motion based on Color Kinesis, a new echocardiographic technique that color-encodes pixel transitions between blood and myocardial tissue.

METHODS AND RESULTS

We developed a software that analyzes Color Kinesis images and provides quantitative indices of magnitude and timing of regional endocardial motion. Images obtained in 12 normal subjects were used to evaluate the variability in each index. Esmolol, dobutamine, and atropine were used to track variations in LV function in 14 subjects. Objective evaluation of wall motion was tested in 20 patients undergoing dobutamine stress testing. Regional fractional area change, displacement, and radial shortening were displayed as histograms and time curves. Global function was assessed by calculating magnitude and timing of peak ejection or filling rates and mean time of ejection or filling. Patterns of endocardial motion were consistent between normal subjects. Fractional area change and peak ejection rate decreased with esmolol and increased with dobutamine. Time to peak ejection and mean time of contraction were prolonged with esmolol and shortened with dobutamine. Using atropine, we proved that our findings with dobutamine were not secondary to its chronotropic effects. Dobutamine induced regional wall motion abnormalities in 10 patients in 38 segments diagnosed conventionally. Segmental analysis detected abnormalities in 36 of these 38 segments and in an additional 5 of 322 segments.

CONCLUSIONS

Analysis of Color Kinesis images allows fast, objective, and automated evaluation of regional wall motion sensitively enough to evaluate clinical dobutamine stress data. This method has significant potential in the diagnosis of myocardial ischemia.

Echocardiographic quantification of regional left ventricular wall motion with color kinesis

BACKGROUND

Color kinesis is a new technology for the echocardiographic assessment of left ventricular wall motion based on acoustic quantification. This technique automatically detects endocardial motion in real time by using integrated backscatter data to identify pixel transitions from blood to tissue during systole on a frame-by-frame basis. In this study, we evaluated the feasibility and accuracy of quantitative segmental analysis of color kinesis images to provide objective evaluation of regional systolic endocardial motion.

METHODS AND RESULTS

Two-dimensional echocardiograms were obtained in the short-axis and apical four-chamber views in 20 normal subjects and 40 patients with regional wall motion abnormalities. End-systolic color overlays superimposed on the gray scale images were obtained with color kinesis to color encode left ventricular endocardial motion throughout systole on a frame-by-frame basis. These color-encoded images were divided into segments by use of custom software. In each segment, pixels of different colors were counted and displayed as stacked histograms reflecting the magnitude and timing of regional endocardial excursion. In normal subjects, histograms were found to be highly consistent and reproducible. The patterns of contraction obtained in normal subjects were used as a reference for the objective automated interpretation of regional wall motion abnormalities, defined as deviations from this pattern. The variability in the echocardiographic interpretation of wall motion between two experienced readers was similar to the diagnostic variability between the consensus of the two readers and the automated interpretation.

CONCLUSIONS

Color kinesis is a promising new tool that may be used clinically to improve the qualitative and quantitative evaluation of spatial and temporal aspects of global and regional wall motion. In this initial study, segmental analysis of color kinesis images provided accurate, automated, and quantitative diagnosis of regional wall motion abnormalities.

Doppler tissue imaging: myocardial wall motion velocities in normal subjects

With a scanner modified for Doppler tissue imaging, mean myocardial velocities (MMV) across the myocardium were measured. The aim of this study was to determine the normal range of the maximum MMV in six standardized phases of the cardiac cycle. The MMV was defined as the average value of the myocardial velocity measured along each M-mode scan line throughout the thickness of the myocardium. The maximum MMV was defined as the maximum value of the MMV during the particular cardiac phase. Simultaneous gray-scale and Doppler tissue imaging M-mode images were taken of the interventricular septum and the left ventricular posterior wall from the parasternal long-axis and short-axis views in 15 normal volunteers (aged 21 to 47 years; mean 32 +/- 6 years). Each cardiac cycle was divided into six phases: atrial contraction, isovolumetric contraction, ventricular ejection, isovolumetric relaxation, rapid ventricular filling, and diastasis. Isovolumetric contraction, isovolumetric relaxation, and diastasis were subdivided into two parts a and b because of changes in the direction of the myocardial movement. For each volunteer, the mean and standard deviation of the maximum MMV were measured for each cardiac phase averaged from 12 cardiac cycles from both long-axis and short-axis views. Finally, the mean and standard deviation were taken for each cardiac phase from 180 cardiac cycles from 15 volunteers. We have found that specific cardiac phases show significant differences in the maximum MMV between the adjoining cardiac phases and significant differences also occur between the maximum MMV measured in the interventricular septum and the left ventricular posterior wall during the same cardiac phases. These normal values provide a standard against which future Doppler tissue imaging M-mode studies of abnormal left ventricular function might be compared.