Myocardial contrast two-dimensional echocardiography: comparison of contrast disappearance rates in normal and underperfused myocardium

Three-Dimensional Echocardiographic Evaluation of Myocardial Perfusion

One of the most intriguing developments in ultrasound imaging of the heart was the use of contrast media to assess myocardial perfusion, which sparked tremendous interest and over the years generated a significant body of research. Although most published work has been based on the use of contrast for 2D perfusion imaging, there are a few recent studies aimed at exploring the idea of 3D assessment of myocardial perfusion, which has the potential to overcome many of the limitations of the 2D methodology. We provide a brief overview of the 2D work that provided the scientific basis for the emerging 3D methodology and discuss the unique features and promises as well as the challenges posed by this novel approach.

Clinical utility of contrast-enhanced echocardiography

Over the past three decades, echocardiography has become a major diagnostic tool in the arsenal of clinical cardiology for real-time imaging of cardiac dynamics. More and more, cardiologists' decisions are based on images created from ultrasound wave reflections. From the time ultrasound imaging technology provided the first insight into a human heart, our diagnostic capabilities have increased exponentially as a result of our growing knowledge and developing technologies. One of the most intriguing developments that brought about a decade-long combination of expectations and disappointments was the introduction of echocardiographic contrast agents. Despite repeated waves of controversy regarding the readiness of this technology for clinical use, it has overcome multiple hurdles and currently provides useful clinical information that helps cardiologists to diagnose heart disease accurately. Since the initial reports on the use of ultrasound contrast media such as agitated saline or renografin, the major advances in the field of contrast echocardiography have included (1) the development of stable perfluorocarbon-filled microbubbles, frequently referred to as second-generation contrast agents; and (2) the development of contrast-targeted nonlinear imaging modes, such as harmonic imaging, pulse inversion, and power modulation, which allow consistent real-time visualization of these agents. These contrast agents in conjunction with the new imaging technology constitute powerful tools that improve our ability to evaluate left ventricular function and myocardial perfusion, and allow differential diagnosis of thrombi and intravascular masses. In this manuscript, we briefly review some of the literature that has provided the scientific basis for the use of echocardiographic contrast agents in the context of these important variables.

Abnormal myocardial blood flow distribution in patients with angina pectoris and normal coronary arteriograms

To evaluate coronary microvascular function and its relation to the genesis of chest pain and ST-segment depression during exercise in patients with syndrome X, pacing-induced changes in transmural myocardial blood flow distribution were quantitatively assessed by 2-dimensional myocardial contrast echocardiography. Of 25 patients with a history of chest pain and normal coronary arteries with the negative ergonovine test, 11 had exercise-induced chest pain and ST-segment depression (syndrome X), and 14 did not (controls). Myocardial blood flow distribution before and after pacing stress was assessed by measuring the ratio of the endocardial to epicardial gray level (ie, endo/epi gray level ratio) in the territory of the left anterior descending coronary artery. Pacing-induced chest pain and ST-segment depression were observed in syndrome X, but not in controls. The endo/epi gray level ratio in syndrome X significantly decreased after pacing (from 0.98+/-0.10 to 0.76+/-0.17, p<0.01), but not in controls (from 0.97+/-0.08 to 0.99+/-0.08, NS). Abnormal myocardial blood flow distribution may play an important role in exercise-induced chest pain and ST-segment depression in these patients.

Contrast echocardiography: clinical utility

This article reviews the advances made by the echocardiographic contrast agents from their first appearance in the early 1970s with homemade preparations up to the new generation of transpulmonary contrast agents made of small microbubbles capable of transversing the lung's capillary bed. The great progress in contrast agent development has kept pace with the progress made by echocardiographic equipment, thus making the study of myocardial perfusion in the clinical settings a near-future reality. This article also discusses the medical need that myocardial contrast echo has the potential to satisfy.

New technology in echocardiography II: imaging techniques

Images

Myocardial transit time of the echocardiographic contrast media

The mean transit time of a tracer through a sample of tissue is a quantitative marker most closely related to regional tissue blood flow. Therefore, an accurate estimation of the mean time of transit of an ultrasonic tracer through a sample of myocardial tissue, obtained by contrast echocardiography, may provide a quantitative noninvasive estimate of myocardial perfusion. We hereby present an algorithm for the determination of the mean transit time by computerized analysis of a series of contrast-enhanced echocardiographic images. The algorithm comprises the evaluation of the echocardiographic impulse response function of a selected region of interest, using a deconvolution technique based on a fast Fourier transform and a frequency domain division of the videointensities measured in the sample, by that measured in a predetermined reference region. An extensive computer simulation study was designed to facilitate the optimization of the steps of analysis. We present the results of the evaluation study performed in order to assess the accuracy of the procedure in computer-simulated echocardiographic images. Within a wide range of parameters chosen to define these functions, the analysis is shown to be essentially independent of the rise and decay times of the impulse response function of the tissue sample as well as of the simulated intensities. The effects of random noise introduced into the simulated intensity curves and of their variable width were investigated. The mean transit time was found to be accurately evaluated within about 10% of error for the variety of widths and noise levels permitted. The reconvolution error did not correlate with the accuracy of the evaluation of the mean transit time, indicating that the reconvolution error cannot be used as an estimate of the accuracy of the procedure. The numerical methods and the results of the computer study are discussed in detail. The approach is proposed to be used as part of a more general technique for the quantitative measurement of regional myocardial tissue blood flow.

Myocardial perfusion and contrast echocardiography: review and new perspectives

Myocardial perfusion can be assessed qualitatively and quantitatively with new ultrasound contrast techniques. This article reviews progress and problems in this area, discussing intracoronary and aortic root injections in animals and humans. The technique has great potential clinical application for the identification of coronary flow reserve, and the assessment of the need for and outcome of coronary revascularization procedures. It may allow direct measurements of regional myocardial perfusion.

Reproducibility of quantitative myocardial contrast echocardiography

To determine whether myocardial contrast echocardiography is quantitatively reproducible, repeated intracoronary injections of sonicated albumin (5%) were performed in eight open chest dogs. Paired injections were performed at baseline, during ischemia produced by ligation of a coronary artery, and during hyperemia induced by intravenous infusion of 0.75 mg/kg body weight of dipyridamole. Contrast washout curves were generated for the left anterior descending coronary artery territory (ischemic area) and left circumflex coronary artery territory (nonischemic area) by beat per beat analysis of frozen end-diastolic frames of left ventricular short-axis views. Peak contrast intensity, contrast washout half-time and area under the curve were derived from these curves. A total of 75 contrast washout curves were analyzed for the study of interinjection, intraobserver and interobserver reproducibility. The correlation coefficients between measurements obtained from paired injections of the echocardiographic contrast agent (interinjection reproducibility) ranged from 0.78 for peak contrast intensity to 0.87 for area under the curve. Percent error varied between 14.7% and 24.7%. The intraobserver variability in measurements was less than the interinjection variability, with a cumulative mean percent error of 17.8% and correlation coefficients of 0.72 (peak contrast intensity), 0.95 (area under the curve) and 0.96 (washout half-time). Interobserver correlation for all indexes was high (r = 0.92 to 0.96). It is concluded that peak contrast intensity, contrast washout half-time and the area under the curve derived from myocardial contrast washout curves can be measured reproducibly from videotapes. In addition, the variability between two injections attempted under identical conditions is greater than reader variability from videotapes.

Echocardiographic contrast in two-dimensional echocardiography: new applications for an old technique?

Although Gramiak and Shah first introduced the technique of using contrast enhanced two-dimensional echocardiography in 1968, it has seen a resurgence of new and varied applications. Three of the areas of interest are in the use of microbubble enhanced contrast agents to evaluate: (1) regional myocardial blood flow; (2) regional myocardial function; and (3) myocardial ischemic areas and infarct size. Whether these new approaches will have applications and value in the clinical laboratory is still a matter of conjecture. The objective of this review is to briefly summarize the potential uses and the advantages and disadvantages of each application.

Factors affecting penetration of retrograde coronary venous injections into normal and ischemic canine myocardium: assessment by contrast echocardiography and digital angiography

Ths experimental study described myocardial echo contrast enhancement through coronary venous injections. Retrograde administration of renografin was performed in 15 closed-chest dogs. Two-dimensional echocardiography was used to study myocardial echo contrast enhancement before and after coronary artery occlusion. Digital subtraction venography was used to assess delivery, drainage and shunting of the retrograde injectate. Systolic/diastolic blood pressure in the great cardiac vein measured 7 +/- 3/1 +/- 0.6 mm Hg and increased to 29 +/- 11/5 +/- 3 after coronary sinus occlusion and to 55 +/- 2.3/15 +/- 12 mm Hg during coronary sinus contrast injection. Myocardial contrast echo appearance in a midpapillary left ventricular short axis cross-section was limited to the anteroseptal region, extending to 28.4 +/- 11.3% of the section circumference after great cardiac vein injections and 35.3 +/- 17% after coronary sinus injections (difference NS). After occlusion of the left anterior descending coronary artery, great cardiac vein contrast injections resulted in opacification of 36.6 +/- 9.7% of the section circumference (N.S. vs preocclusion control) and opacified most, but not all asynergic segments. After occlusion of the circumflex coronary artery, myocardial echo contrast uptake was restricted to the septum and the anterior wall. The ischemic and asynergic posterolateral myocardial segments were not opacified. Digital subtraction coronary venography revealed rapid drainage of retrogradely injected contrast to the right atrium, in spite of coronary sinus balloon occlusion via venovenous anastomoses. Retrograde coronary venous contrast injections may help define myocardial regions which are accessible with retrograde coronary venous interventions.

Myocardial perfusion imaging by contrast echocardiography with use of intracoronary sonicated albumin in humans

Sonicated albumin has been proposed as a near ideal echocardiographic contrast agent with little myocardial toxicity or hemodynamic effect. Its use has not yet been reported in humans, partly because of difficulties in preparation. With use of the newly modified sonication method, 10 ml of 5% albumin was sonicated for 75 s with a 5.0 ml slow infusion of air. This resulted in microbubbles with a mean diameter (+/- SD) of 5 +/- microns). Fourteen patients undergoing routine coronary angiography were studied. One patient had normal coronary arteries; the other 13 had significant coronary artery disease. In a subgroup of nine patients, sonicated albumin and sonicated diatrizoate meglumine sodium (microbubble diameter 9 +/- 3 microns) were injected several minutes apart, using the same technique. Videodensity-time curves were obtained from a region of interest in the myocardium. Corrected peak contrast intensity (baseline contrast intensity subtracted from peak contrast intensity, gray scale U/pixel) for sonicated albumin and for sonicated diatrizoate meglumine sodium was 51 +/- 26 and 52 +/- 19, respectively (p = 0.89). Washout half-time (T1/2) for the two agents was 5.5 +/- 4.5 and 16.0 +/- 12.2 s, respectively (p = 0.01). One patient with unstable angina experienced transient chest pain after repeated albumin injections. No electrocardiographic changes, blood pressure changes or wall motion abnormalities were observed. Administered by intracoronary injection, sonicated 5% albumin is a safe and effective echocardiographic contrast agent for myocardial perfusion imaging, yielding excellent myocardial contrast with physiologic washout time.

Myocardial contrast two-dimensional echocardiography: dose-myocardial effect relations of intracoronary microbubbles

It is controversial whether echocardiographic contrast agents prepared by sonication cause transient myocardial depression beyond that known to occur with contrast agents alone. In nine open chest dogs, contrast injections were made into the left anterior descending coronary artery during two-dimensional echocardiography. One hundred forty-four recordings were analyzed subsequently, by an observer who was unaware of other data, for percent depression of systolic wall thickening, duration of regional wall motion abnormalities, peak contrast enhancement and contrast washout. Two microbubble sizes were obtained by sonicating Renografin-76 (meglumine sodium diatrizoate): mean diameter 12 +/- 3 (SEE) and 20 +/- 6 micron. Four doses (range 0.5 to 3 ml) of each of four agents (12 and 20 micron bubbles in Renografin, nonsonicated Renografin and saline solution) were injected in random order. Significant relations were found between percent depression of systolic wall thickening, duration of regional wall motion abnormalities and contrast washout time versus microbubble size (p less than 0.001) and microbubble dose (p less than 0.01). Little increased contrast effect was found at larger doses or with larger microbubbles compared with the smaller doses and size studied. Injections of nonsonicated Renografin caused less depression of systolic wall thickening (p less than 0.05), faster resolution of wall motion abnormalities (p less than 0.05), less contrast (p less than 0.001) and more rapid contrast washout (p less than 0.001) than did 12 micron bubbles in Renografin. A significant correlation was found between the duration of regional wall motion abnormalities and contrast washout time (r = 0.93, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of reperfusion hyperemia with myocardial contrast echocardiography

In this study we used myocardial contrast echocardiography to evaluate reperfusion hyperemia in an open-chest canine model of temporary coronary artery occlusion. Eight dogs had coronary occluders and electromagnetic flow probes on the left circumflex coronary artery. Aortic root injections of agitated sodium diatrizoate and saline solution were used for myocardial contrast. Data were collected at baseline (n = 16), during coronary occlusion (n = 18), immediately after coronary release (n = 18), and 5 minutes after coronary artery release (n = 12). Baseline coronary flow was 23.8 +/- 5.9 ml/min, decreasing to 0 ml/min during coronary occlusion. Immediately after coronary release flow was 96.6 +/- 41 ml/min (p less than 0.001 compared with baseline), and 5 minutes after coronary release flow was 68.2 +/- 27.9 ml/min (p less than 0.001 compared with baseline). The myocardial image intensity change after injection of contrast material was 74.25 +/- 30.6 ml/min at baseline and declined to 10.4 +/- 10.9 ml/min during coronary occlusion (p less than 0.001 compared with baseline). During reperfusion hyperemia image intensity change was 102.3 +/- 33.3 ml/min (p less than 0.001 compared with occlusion, p less than 0.02 compared with baseline, p less than 0.001 compared with remote regions). Considering all observations, myocardial image intensity change after contrast injection correlated positively with coronary flow (r = 0.67, p less than 0.001). Correlations within individual dogs ranged from r = 0.70 to 0.98. We conclude that image intensity change after aortic root injection of echocardiographic contrast correlates with coronary blood flow. Objective measurements of contrast intensity reflect increases in coronary flow associated with reactive hyperemia after coronary occlusion and release.

Myocardial risk area and peak gray level measurement by contrast echocardiography: effect of microbubble size and concentration, injection rate, and coronary vasodilation

Contrast agents were injected via the intracoronary route in eight dogs during two-dimensional echocardiographic imaging to determine the influence of microbubble size and concentration, injection rate, and coronary vasodilation on risk area and peak gray level measurement. At an injection rate at 13 cc/sec, the average background-subtracted peak gray level intensity of hand-agitated diatrizoate meglumine/diatrizoate sodium was significantly (p less than 0.01) higher than that of hand-agitated diatrizoate meglumine/diatrizoate sodium + 0.9% saline, sonicated diatrizoate meglumine/diatrizoate sodium, and sonicated 70% sorbitol. These differences were abolished by the use of 38 cc/sec injection rates and intracoronary injection of adenosine. Perfusion area determinations as assessed by planimetry were unaffected by the contrast agent used, the injection rate, or by intracoronary administration of adenosine. We conclude that risk area measurement by the ultrasound contrast technique is not affected by varying contrast agents, injection rates, or vasodilation. However, peak gray level intensity is variable among contrast agents and may result in variability of time-activity curve analysis.

Echocardiographic contrast agents: effect of microbubbles and carrier solutions on left ventricular contractility

Recently, there has been a resurgence of interest in the use of contrast-enhanced echocardiography as a means of noninvasively assessing myocardial perfusion. However, if injections of echocardiographic contrast agents are to be used for this purpose it is essential that they are not intrinsically toxic to the heart. In this study, the left ventricular end-systolic wall stress-rate-corrected velocity of fiber shortening relation, a load independent index of contractility, was studied in nine dogs. Two-dimensional and targeted M-mode echocardiographic as well as central aortic pressure tracings were made during echocardiographically gated, pressure- and volume-controlled aortic root injections of nonsonicated and sonicated Renografin-76, saline and dextrose 70% (n = 6), and sonicated and hand-agitated Renografin-76/saline mixture (n = 5). Two of nine dogs received all agents. Off-line computer videodensitometric analysis documented myocardial perfusion. In all cases, data were obtained at control and 5 and 15 seconds after injection. Additional data were collected at 25 seconds after injection for the Renografin-76/saline mixture. Alterations in contractility were measured relative to control as changes in rate-corrected velocity of fiber shortening after afterload (measured as end-systolic wall stress) was eliminated as a confounding variable. Under no condition did saline or Renografin-76 cause alterations in left ventricular contractility. Nonsonicated and sonicated dextrose 70% increased left ventricular contractility at 15 seconds but not at 5 seconds after injection. Hand-agitated Renografin-76/saline mixture induced a negative inotropic effect at 5 and 15 seconds after injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative evaluation of regional myocardial blood flow by videodensitometric analysis of digital subtraction coronary arteriography in humans

Videodensitometric analysis of digital subtraction coronary arteriography, a new approach for calculating contrast disappearance half-life (T1/2), was assessed in determining regional myocardial blood flow quantitatively. Forty-one patients with coronary artery disease and 12 with angiographically normal coronary arteries underwent digital subtraction coronary arteriography by manual injection of contrast medium into the left main coronary artery. The T1/2 was calculated from a time-density curve generated in the four sectors of the myocardium perfused by the left anterior descending coronary artery. The mean T1/2 value of the four sectors correlated inversely with the great cardiac vein flow measured by the thermodilution method (r = -0.89), and appeared to be a reliable index of myocardial blood flow. The relation of mean T1/2 with percent stenosis of the left anterior descending coronary artery was curvilinear (r = 0.88) and an abnormally high T1/2 occurred in patients with coronary stenosis greater than 75%. In patients with comparable stenosis of the left anterior descending artery, the apical T1/2 was significantly increased in those with impaired apical wall motion, while it was significantly decreased in those with coronary collateral vessels. These findings suggest that regional myocardial blood flow begins to decrease in vessels with greater than 75% stenosis, and that myocardial contraction and collateral flow are additional factors that modify regional myocardial blood flow. Thus, the contrast disappearance half-life (T1/2) derived by computerized washout analysis of digital subtraction coronary arteriograms proved useful as an index for quantitative evaluation of regional myocardial blood flow.

Intraoperative cardioplegic contrast echocardiography for assessing myocardial perfusion during open heart surgery

Aortic root hypothermic, hyperkalemic cardioplegic perfusion has been shown to preserve ventricular function during open heart surgery. However, significant coronary artery stenoses may prevent adequate perfusion of myocardial regions distal to the lesions, leading to intraoperative ischemia and damage. The purpose of this study was to evaluate for the first time in human patients the use of intraoperative contrast cardioplegic echocardiography for identifying potentially jeopardized myocardial regions as defined by cardiac catheterization. Forty-two patients, 23 men and 19 women, aged 28 to 83 years (mean 56.7 +/- 2), who had undergone cardiac catheterization and coronary arteriography, underwent open heart surgery; 30 had coronary artery disease. Echocardiograms of the left ventricle, performed on the open heart in the papillary muscle short-axis plane during routine aortic root cardioplegia were divided into three regions according to the coronary anatomy: septal (left anterior descending artery), anterolateral (left circumflex) and inferoposterior (right coronary artery). Intraoperatively, myocardial segments at greatest potential ischemic risk were identified by several findings alone or in combination: lack of spontaneous contrast and delayed whiting out or persistent fine fibrillation. The ability of intraoperative echographic interpretation to identify high risk segments based on preoperative catheterization findings was excellent. Thus, the sensitivity of cardioplegic contrast echocardiography for predicting significant (greater than 70% stenosis) coronary lesions was 96, 100 and 58% for left anterior descending, left circumflex and right coronary artery regions, respectively. Specificity was 94, 78 and 100% for anterior descending, circumflex and right coronary artery regions, respectively. Overall sensitivity and specificity for all regions was 82 and 92%, respectively. Importantly, the echocardiogram was most helpful in observing septal region perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Retrograde coronary venous contrast echocardiography: assessment of shunting and delineation of regional myocardium in the normal and ischemic canine heart

Coronary venous injections of sonicated Renografin-76 were performed in seven closed chest dogs during two-dimensional echocardiography to study the ability of this new technique to opacify regional myocardium before and after occlusion of the left anterior descending coronary artery. The balloon of a 4F double lumen catheter was inflated in the great cardiac vein for each contrast injection to prevent backflow through the coronary sinus into the right atrium. Retrograde injections before coronary artery occlusion generally resulted in patchy myocardial contrast uptake. Injections after coronary occlusion always resulted in confluent and transmural myocardial opacification which occupied 42.8 +/- 8.6% (range 26 to 54) (mean +/- standard deviation) of the myocardial circumference. Retrograde opacification always extended into adjacent myocardium beyond the ischemic zone, which was assessed in echocardiograms with antegrade contrast injections into the left main coronary artery and which measured 30 +/- 6.3% of the ventricular circumference. Shunting from the coronary venous system to cardiac chambers was evaluated in a parasternal four chamber view and was graded on a scale of 0 to 4+. Contrast appearance was equally intense in the right atrium and right ventricle (3.5 +/- 0.6+, range 2+ to 4+), less intense in the left ventricular cavity (1.5 +/- 0.6+, range 1+ to 3+) and absent in the left atrium. Postmortem anatomic validation with retrograde great cardiac vein injections of indocyanine green corroborated and in vivo contrast appearance in chambers. Retrograde coronary venous contrast echocardiography appears capable of providing in vivo information about the extent and location of myocardial zones that can be reached by retrograde infusions of therapeutic agents and about the ability of these agents to reach ischemic myocardium. In addition, this new method allows for in vivo evaluation of shunts between coronary veins and cardiac chambers, which may influence the efficacy of retrograde interventions.

Assessment of location and size of myocardial infarction with contrast-enhanced echocardiography. II. Application of digital imaging techniques

Contrast echocardiography can be used to identify nonperfused regions of myocardium and localize and quantify infarcted myocardium. Analysis is usually undertaken by visual inspection of an analog two-dimensional echocardiographic image. The purpose of our study was to apply digital imaging techniques to contrast-enhanced echocardiograms for the determination of myocardial infarct size. Myocardial contrast was produced by an injection into the aortic root of a mixture of hydrogen peroxide and blood. Sixteen open chest dogs were studied 4 hours after coronary artery occlusion. Echocardiograms were evaluated by two independent observers. The results were compared with infarct location and size determined with nitro-blue tetrazolium staining of the corresponding slice of the left ventricle. Both the routine analog echocardiographic image and the digital subtraction image were analyzed. For the latter, three precontrast and three postcontrast echocardiographic enddiastolic fields were digitized in a 256 X 256 X 6 bit matrix and then averaged. Average pre- and postcontrast images were mathematically subtracted to form the digital subtraction image. There was excellent correlation between the percent of infarct determined with digital subtraction contrast echocardiography and results of nitro-blue tetrazolium staining (r = 0.97, SEE = 0.04, p less than 0.001). Using linear regression, the relation between infarct size by the two studies was best described by the equation DSI = 0.92 NBT + 0.03, where DSI = digital subtraction image and NBT = infarct size by nitro-blue tetrazolium. Inter- and intraobserver variability were also excellent (r = 0.93 and 0.96, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Computer methods for myocardial contrast two-dimensional echocardiography

Two computer-aided videodensitometric methods that may be used in conjunction with two-dimensional contrast echocardiography were examined to quantify the time course of echographic opacification in the myocardium after experimental injections of contrast agents (hand-agitated Renografin-saline and sonicated sorbitol 70% solutions) into the left main coronary artery. Echographic studies of myocardial cross sections were digitized with an image processing computer using a 128 X 128 resolution matrix. Both stop frame and continuous cycle modes of acquisition were performed. A set of computer programs was developed to extract and analyze time-intensity curves from the digitized images. These included cardiac outline delineation, segmental division, regional intensity computation and exponential curve analysis. The stop frame method was applied to experimental studies in 17 closed chest dogs during control states and after coronary occlusions. Significant differences were found in the decay half-lives of echo intensity between normal (24 +/- 8 seconds) and acutely ischemic (293 +/- 165 seconds; p less than 0.001) myocardium for the Renografin-saline solution. Interobserver reproducibility of the measured half-lives was r = 0.91 and standard error of the estimate = 5 seconds. The continuous cycle method of analysis was examined in five closed chest dogs (with up to six injections per dog), applying the sonicated sorbitol 70% solution in only the control state. The mean half-life was 4.2 +/- 1.1 seconds. These computer-based videodensitometric methods might be applied to a wide variety of experimental studies in two-dimensional contrast echocardiography that attempt to quantify myocardial perfusion and function.