Potential advantage of flash echocardiography for digital subtraction of B-mode images acquired during myocardial contrast echocardiography

Relationship between cavitation and loss of echogenicity from ultrasound contrast agents

Ultrasound contrast agents (UCAs) have the potential to nucleate cavitation and promote both beneficial and deleterious bioeffects in vivo. Previous studies have elucidated the pulse-duration-dependent pressure amplitude threshold for rapid loss of echogenicity due to UCA fragmentation. Previous studies have demonstrated that UCA fragmentation was concomitant with inertial cavitation. The purpose of this study was to evaluate the relationship between stable and inertial cavitation thresholds and loss of echogenicity of UCAs as a function of pulse duration. Determining the relationship between cavitation thresholds and loss of echogenicity of UCAs would enable monitoring of cavitation based upon the onscreen echogenicity in clinical applications. Two lipid-shelled UCAs, echogenic liposomes (ELIP) and Definity®, were insonified by a clinical ultrasound scanner in duplex spectral Doppler mode at four pulse durations ('sample volumes') in both a static system and a flow system. Cavitation emissions from the UCAs insonified by Doppler pulses were recorded using a passive cavitation detection system and stable and inertial cavitation thresholds ascertained. Loss of echogenicity from ELIP and Definity® was assessed within regions of interest on B-mode images. A numerical model based on UCA rupture predicted the functional form of the loss of echogenicity from ELIP and Definity®. Stable and inertial cavitation thresholds were found to have a weak dependence on pulse duration. Stable cavitation thresholds were lower than inertial cavitation thresholds. The power of cavitation emissions was an exponential function of the loss of echogenicity over the investigated range of acoustic pressures. Both ELIP and Definity® lost more than 80% echogenicity before the onset of stable or inertial cavitation. Once this level of echogenicity loss occurred, both stable and inertial cavitation were detected in the physiologic flow phantom. These results imply that stable and inertial cavitation are necessary in order to trigger complete loss of echogenicity acoustically from UCAs and this finding can be used when planning diagnostic and therapeutic applications.

Semi-automated analysis of dynamic changes in myocardial contrast from real-time three-dimensional echocardiographic images as a basis for volumetric quantification of myocardial perfusion

AIMS

Despite the potential of real-time three-dimensional (3D) echocardiography (RT3DE) to assess myocardial perfusion, there is no quantification method available for perfusion analysis from RT3DE images. Such method would require 3D regions of interest (ROI) to be defined and adjusted frame-by-frame to compensate for cardiac translation and deformation. Our aims were to develop and test a technique for automated identification of 3D myocardial ROI suitable for translation-free quantification of myocardial videointensity over time, MVI(t), from contrast-enhanced RT3DE images.

METHODS AND RESULTS

Twelve transthoracic RT3DE (Philips) data sets obtained in pigs during transition from no contrast to steady-state enhancement (Definity) were analysed using custom software. Analysis included: (i) semi-automated detection of left ventricular endo- and epicardial surfaces using level-set techniques in one frame to define a 3D myocardial ROI, (ii) rigid 3D registration to reduce translation and rotation, (iii) elastic 3D registration to compensate for deformation, and (iv) quantification of MVI(t) in the 3D ROI from the registered and non-registered data sets to assess the effectiveness of registration. For each MVI(t) curve we computed % variability during steady-state enhancement (100 x SD/mean) and goodness of fit (r2) to the indicator dilution equation MVI(t) = A[1-exp(-betat)]. Analysis of myocardial contrast throughout contrast inflow was feasible in all data sets. Three-dimensional registration improved MVI(t) curves in terms of both % variability (2.8 +/- 1.8 to 1.5 +/- 0.9%; P < 0.05) and goodness of fit (r2 from 0.79 +/- 0.2 to 0.90 +/- 0.1; P < 0.05).

CONCLUSION

This is the first study to describe a new technique for semi-automated volumetric quantification of myocardial contrast from RT3DE images that includes registration and thus provides the basis for 3D measurement of myocardial perfusion.

Evaluation of colon cancer vascularity by flash echo imaging

OBJECTIVE

Tumor vascularity is strongly related to the prognoses of patients with various malignant primary tumors, including colorectal cancer. The aim of this study was to confirm the usefulness of harmonic flash echo imaging (H-FEI) for the preoperative evaluation of tumor vascularity in colorectal cancer by comparison with CD34 staining of resected specimens.

MATERIAL AND METHODS

Seventeen patients undergoing surgical resection for advanced colorectal cancer (9 M, 8 F) were enrolled in this study. An ultrasound system transmitting ultrasound pulses at 2.3 MHz and receiving them at 4.6 MHz (second harmonic) was used for H-FEI. After intravenous injection of ultrasonic contrast medium (SHU 508A), intermittent harmonic scanning was carried out for 120 s at intervals of 4 s. On the tumor image of the strongest enhancement in each patient, 5 regions of interest were taken to decide the mean echo intensity of the tumor. Immunohistochemistry using antibodies against CD34 was carried out on resected specimens. The mean microvessel density was decided by counting microvessels on 5 fields (x 400) of CD34-stained specimens.

RESULTS

The mean value of H-FEI intensity was 5.44+/-1.10, and the mean microvessel count with CD34 staining was 35.0+/-7.95. A significant positive linear correlation was observed between the intensity of H-FEI determined preoperatively and the microvessel count in CD34-stained specimens (r=0.741, p=0.0006).

CONCLUSION

Vascularity of colon cancer can be evaluated non-invasively using H-FEI.

Contrast ultrasound in the assessment of patients presenting with suspected cardiac ischemia

Echocardiography is a portable technology that can be used to assess myocardial, pericardial, and valvular structure and function. Doppler echocardiography provides the ability to evaluate blood flow in large vessels and within cardiac chambers. Recently, the advent of microbubble contrast agents, which can opacify the systemic circulation, has improved the ability of echocardiography to evaluate left-ventricular function by improving delineation of the left-ventricular endocardial border. Furthermore, these microbubbles can be used to assess myocardial perfusion and quantify myocardial blood flow. Myocardial contrast echocardiography has been studied in multiple clinical situations, including the acute evaluation of patients presenting with suspected cardiac ischemia. Ongoing research is focused on the development of microbubbles that are capable of detecting molecular and cellular events within the circulation, which may allow distinction of acute vs. remote ischemic insults to the myocardium. This multifaceted technology promises to be of increasing clinical utility--not only for the heart, but for any organ accessible to ultrasound.

Parametric detection and measurement of perfusion defects in attenuated contrast echocardiographic images

OBJECTIVE

Attenuation of radio frequency (RF) signals limits the use of contrast echocardiography. The harmonic-to-fundamental ratio (HFR) of the RF signals compensates for attenuation. We tested whether HFR analysis measures the left ventricular nonperfused area under simulated experimental attenuation.

METHODS

Radio frequency image data from short axis systolic projections were obtained from 11 open-chest dogs with left anterior descending or left circumflex coronary artery occlusion followed by left atrial bolus injection of a perflutren microbubble contrast agent. Clinical attenuation was simulated by calibrated silicone pads interposed between the epicardial surface and the transducer to induce mild (7-dB) and severe (14-dB) reduction of the backscattered RF signals. Harmonic-to-fundamental ratio values were calculated for each image pixel for 0-, 7-, and 14-dB attenuation conditions and reproducibly showed a "perfused area" and a "nonperfused area." A reference nonperfused area was obtained by manual delineation in high-quality contrast scans.

RESULTS

Correlations of the HFR-detected and manually outlined perfusion defect areas were R = 0.92 for 0 dB, R = 0.94 for 7 dB, and R = 0.90 for 14 dB; the mean difference was less than 0.36 cm(2) (negligible) in all 3 attenuation settings. Conclusions. Attenuation compensation by our HFR method allows precise measurement of myocardial perfusion defect areas in contrast scans with simulated high level of attenuation.

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.

Bioeffects of albumin-encapsulated microbubbles and real-time myocardial contrast echocardiography in an experimental canine model

Myocardial contrast echocardiography has been used for assessing myocardial perfusion. Some concerns regarding its safety still remain, mainly regarding the induction of microvascular alterations. We sought to determine the bioeffects of microbubbles and real-time myocardial contrast echocardiography (RTMCE) in a closed-chest canine model. Eighteen mongrel dogs were randomly assigned to two groups. Nine were submitted to continuous intravenous infusion of perfluorocarbon-exposed sonicated dextrose albumin (PESDA) plus continuous imaging using power pulse inversion RTMCE for 180 min, associated with manually deflagrated high-mechanical index impulses. The control group consisted of 3 dogs submitted to continuous imaging using RTMCE without PESDA, 3 dogs received PESDA alone, and 3 dogs were sham-operated. Hemodynamics and cardiac rhythm were monitored continuously. Histological analysis was performed on cardiac and pulmonary tissues. No hemodynamic changes or cardiac arrhythmias were observed in any group. Normal left ventricular ejection fraction and myocardial perfusion were maintained throughout the protocol. Frequency of mild and focal microhemorrhage areas in myocardial and pulmonary tissue was similar in PESDA plus RTMCE and control groups. The percentages of positive microscopical fields in the myocardium were 0.4 and 0.7% (P = NS) in the PESDA plus RTMCE and control groups, respectively, and in the lungs they were 2.1 and 1.1%, respectively (P = NS). In this canine model, myocardial perfusion imaging obtained with PESDA and RTMCE was safe, with no alteration in cardiac rhythm or left ventricular function. Mild and focal myocardial and pulmonary microhemorrhages were observed in both groups, and may be attributed to surgical tissue manipulation.

Value of adenosine infusion for infarct size determination using real-time myocardial contrast echocardiography

Background

Myocardial contrast echocardiography has been used for determination of infarct size (IS) in experimental models. However, with intermittent harmonic imaging, IS seems to be underestimated immediately after reperfusion due to areas with preserved, yet dysfunctional, microvasculature. The use of exogenous vasodilators showed to be useful to unmask these infarcted areas with depressed coronary flow reserve. This study was undertaken to assess the value of adenosine for IS determination in an open-chest canine model of coronary occlusion and reperfusion, using real-time myocardial contrast echocardiography (RTMCE).

Methods

Nine dogs underwent 180 minutes of coronary occlusion followed by reperfusion. PESDA (Perfluorocarbon-Exposed Sonicated Dextrose Albumin) was used as contrast agent. IS was determined by RTMCE before and during adenosine infusion at a rate of 140 mcg·Kg^-1·min^-1. Post-mortem necrotic area was determined by triphenyl-tetrazolium chloride (TTC) staining.

Results

IS determined by RTMCE was 1.98 ± 1.30 cm² and increased to 2.58 ± 1.53 cm² during adenosine infusion (p = 0.004), with good correlation between measurements (r = 0.91; p < 0.01). The necrotic area determined by TTC was 2.29 ± 1.36 cm² and showed no significant difference with IS determined by RTMCE before or during hyperemia. A slight better correlation between RTMCE and TTC measurements was observed during adenosine (r = 0.99; p < 0.001) then before it (r = 0.92; p = 0.0013).

Conclusion

RTMCE can accurately determine IS in immediate period after acute myocardial infarction. Adenosine infusion results in a slight better detection of actual size of myocardial damage.

Effects of Ultrasound Contrast Agents on Doppler Tissue Velocity Estimation

The combination of Doppler tissue imaging and myocardial contrast echocardiography has the potential to provide information about motion and perfusion of the myocardium in a single examination. The purpose of this study was to establish how the presence of ultrasound contrast agent (UCA) affects measurements of Doppler tissue velocities in vivo and in vitro. We performed echocardiography in 12 patients with ischemic heart disease before and immediately after a slow intravenous infusion of the UCA Optison, using color Doppler tissue imaging to examine the effect of contrast agents in vivo. The myocardial peak systolic velocities and their integrals were analyzed in digitally stored cineloops before and after contrast administration. To distinguish between methodologic and physiologic factors affecting the measurement of tissue velocity in vitro, experiments with a rotating disk and a flow cone phantom were also carried out for the 3 contrast agents: Optison, Sonovue, and Sonazoid. In vivo results show that the values for peak systolic velocity increased by about 10% during contrast infusion, from mean 5.2 +/- 1.8 to 5.7 +/- 2.3 cm/s (P = .02, 95% confidence interval 2%-16%). The increase in myocardial peak systolic velocities was verified in experimental models in which the UCA increased the estimated mean velocity in the order of 5% to 20% for the motion interval of 5 to 7 cm/s, corresponding to the myocardial velocities studied in vivo. The response was similar for all 3 contrast agents and was not affected by moderate variations in concentration of the agent. We have shown that the presence UCA will affect Doppler tissue measurements in vivo and in vitro. The observed bias is presumed to be an effect of harmonic signal contribution from rupturing contrast agent microbubbles and does not indicate biologic or physiologic effects.

Myocardial Contrast Echocardiography for Distinguishing Ischemic From Nonischemic First-Onset Acute Heart Failure

Background— Distinguishing ischemic from nonischemic origin in patients presenting with acute heart failure (AHF) not resulting from acute myocardial infarction has both therapeutic and prognostic implications. The aim of the study was to assess whether myocardial contrast echocardiography (MCE) can identify underlying coronary artery disease (CAD) as the cause of AHF.

Methods and Results— Fifty-two consecutive patients with AHF with no prior clinical history of CAD and no clinical evidence of acute myocardial infarction underwent resting echocardiography and MCE both at rest and after dipyridamole stress at a mean of 9±2 days after admission. All patients underwent coronary arteriography before discharge. Of the 52 patients, 22 demonstrated flow-limiting CAD (>50% luminal diameter narrowing). Sensitivity, specificity, and positive and negative predictive values of MCE for the detection of CAD were 82%, 97%, 95%, and 88%, respectively. Among clinical, ECG, biochemical, resting echocardiographic, and MCE markers of CAD, MCE was the only independent predictor of CAD ( P <0.0001). Quantitative MCE demonstrated significantly ( P <0.0001) lower myocardial blood flow velocity reserve in vascular territories subtended by >50% CAD (0.59±0.46) compared with patients with normal coronary arteries (1.99±1.00). However, myocardial blood flow velocity reserve in patients with no significant CAD was significantly ( P =0.03) lower compared with control (2.91±0.41). Myocardial blood flow velocity reserve correlated significantly ( P <0.0001) with increasing severity of CAD.

Conclusions— MCE, which is a bedside technique, may be used to detect CAD in patients presenting with AHF without a prior history of CAD or evidence of acute myocardial infarction. Quantitative MCE may further risk-stratify patients with AHF but no CAD.

Effect of Microbubble Exposure to Ultrasound on Quantitation of Myocardial Perfusion

BACKGROUND

The purpose of this study was to determine whether acoustic disruption of microbubbles in the left ventricular (LV) cavity prior to entry in the coronary circulation or their gradual destruction in the myocardium during myocardial contrast echocardiography (MCE) affects quantitative parameters of myocardial perfusion.

METHODS

MCE was performed in 12 open chest dogs with both intermittent high-power imaging (IHPI) and real-time low-power imaging (RLPI). To assess the affects of microbubble destruction in the LV cavity, MCE parameters of myocardial perfusion were compared for imaging planes that included versus avoided the LV cavity. To assess the effects of gradual disruption of microbubbles in the microcirculation during RLPI, MCE parameters from frames acquired continuously were compared to that from acquiring only end-systolic frames.

RESULTS

Destruction of microbubbles in the LV cavity did not alter perfusion data for either form of imaging unless RLPI was performed using long (6-frame) destructive pulse sequences. With RLPI, a gradual decay in microbubble signal occurred during their myocardial transit, the degree of which was related to the acoustic power. Signal decay during microbubble transit resulted in an overestimation of the microvascular blood velocity (beta-value) and an underestimation of the microvascular blood volume (A-value).

CONCLUSIONS

MCE parameters of perfusion at low power can be significantly altered by microbubble destruction in the LV cavity and in the myocardial microcirculation during RLPI. Short microbubble destruction pulse sequences and imaging only at end-systole can reduce these effects.

Instantaneous quantitative video intensity heterogeneity: evaluation with low mechanical index contrast echocardiography

BACKGROUND

Instantaneous video intensity of myocardium has been poorly characterized. Myocardial video intensity is usually displayed in the fitted curve from the exponential equation, y = a(1 - e (-bt)). However, information from the fitted curve will be as accurate as the original video intensity data from the perfusion image. Therefore, we sought to characterize the intramyocardial instantaneous video intensity from low mechanical index (MI) contrast echo imaging for variation.

METHOD

Low-MI imaging using a nonlinear cancellation technique was performed on 10 subjects with normal myocardium. Quantitative video intensity was analyzed in five segments in the epicardium and subendocardium, as well as in systole and diastole.

RESULTS

Video intensity varied between the epicardium and endocardium in each of the region that was analyzed, with the greatest variation in the inferior region (P < 0.0001). Diastolic and systolic differences were also present.

CONCLUSION

Instantaneous video intensity is heterogeneous within the myocardium. Differences can result from attenuation, myocardial fiber structure, and even isotropic effects of the contrast agent, and should be taken into account when data are fitted into an exponential function.

Spectral normalization for ultrasonic contrast microbubble detection

Ultrasonic contrast agents consisting of microbubbles are used to assess tissue perfusion. The microbubbles are highly reflective and nonlinear and thus produce harmonics that are stronger than those from tissues. However, the magnitude of harmonic signals resulting from a region with microbubbles also depends on the acoustic pressure of incident ultrasound and the attenuation of intervening tissues in the ultrasound path. Therefore, the harmonic magnitude, as used in traditional harmonic imaging, may not be a reliable indicator of the presence or absence of microbubbles, and hence, tissue perfusion. To compensate for these effects, we present two parameters defined as the ratio of the harmonic to the fundamental component (HFR) and the ratio of the harmonic to squared fundamental (HSFR). A simplified model is used to illustrate the usefulness of these two parameters. Experiments show that both parameters improve detection of microbubbles and that HSFR performs better than HFR.

Assessment of Regional Myocardial Blood Flow with Myocardial Contrast Echocardiography: An Experimental Study

OBJECTIVES

The aim of this study was to verify the accuracy of using myocardial contrast echocardiography (MCE), to quantify regional myocardial blood flow (MBF), and to evaluate myocardial viability in comparison to that measured by radiolabeled microsphere and pathologic examination.

METHODS

Epicardial MCE was obtained in five myocardial ischemic dogs with constant microbubble intravenous infusion. After the video intensity (VI, y) versus pulsing interval plots derived from each myocardial pixel were fitted to an exponential function: y = A(1 - e(-beta t)), the MBF was calculated as the product of A (microvascular cross-sectional area or myocardial blood volume) and beta (mean myocardial microbubble velocity). The MBF was also obtained by radiolabeled microsphere method.

RESULTS

The MBF derived by radiolabeled microsphere method in the normal, ischemic, and infarcted region was 1.5 +/- 0.3, 0.7 +/- 0.3, and 0.3 +/- 0.2 ml/min per gram, respectively; P < 0.01. The product of A and beta in those regions was 52.5 +/- 15.1, 24.4 +/- 3.9, and 3.7 +/- 3.8, respectively; P < 0.01. The normalized product of A and beta correlated well with normalized MBF (r = 0.81, P = 0.001).

CONCLUSION

Our initial study demonstrated that MCE has an ability to assess MBF in ischemic myocardium in the experimental model. It may provide a potential capability to detect viable myocardium noninvasively after total persistent coronary occlusion in the clinical setting.

Myocardial contrast echocardiography in the detection of coronary stenosis

The need for the capillary bed to maintain normal hydrostatic pressure results in capillary derecruitment distal to a stenosis during hyperemia. This pathophysiologic behavior is seen irrespective of the method by which coronary driving pressure is reduced. The functional consequences of the decrease in MBV are an increase in myocardial vascular resistance and a concomitant reduction in hyperemic MBF. These phenomena form the basis for the detection of CAD with MCE, which isa unique noninvasive tool that allows the separate assessment of both MBV and MBF velocity. Because of its excellent spatial and temporal resolution, portability, widespread availability,and relatively low cost, MCE should provide an attractive method for the noninvasive detection of CAD and for the quantification of stenosis severity.

Evaluation of stunned and infarcted canine myocardium by real time myocardial contrast echocardiography

Differentiation between stunned and infarcted myocardium in the setting of acute ischemia is challenging. Real time myocardial contrast echocardiography allows the simultaneous assessment of myocardial perfusion and function. In the present study we evaluated infarcted and stunned myocardium in an experimental model using real time myocardial contrast echocardiography. Sixteen dogs underwent 180 min of coronary occlusion followed by reperfusion (infarct model) and seven other dogs were submitted to 20 min of coronary occlusion followed by reperfusion (stunned model). Wall motion abnormality and perfusional myocardial defect areas were measured by planimetry. Risk and infarct areas were determined by tissue staining. In the infarct model, the wall motion abnormality area during coronary occlusion (5.52 1.14 cm(2) ) was larger than the perfusional myocardial defect area (3.71 1.45 cm (2); P < 0.001). Reperfusion resulted in maintenance of wall motion abnormality (5.45 1.41 cm (2); P = 0.43 versus occlusion) and reduction of perfusional myocardial defect (1.51 1.29 cm (2); P = 0.004 versus occlusion). Infarct size determined by contrast echocardiography correlated with tissue staining (r = 0.71; P = 0.002). In the stunned model, the wall motion abnormality area was 5.49 0.68 cm (2) during occlusion and remained 5.1 0.63 cm (2) after reperfusion (P = 0.07). Perfusional defect area was 2.43 0.79 cm (2) during occlusion and was reduced to 0.2 0.53 cm(2) after reperfusion (P = 0.04). 2,3,5-Triphenyl tetrazolium chloride staining confirmed the absence of necrotic myocardium in all dogs in the stunned model. Real time myocardial contrast echocardiography is a noninvasive technique capable of distinguishing between stunned and infarcted myocardium after acute ischemia.

A comparison of the fragmentation thresholds and inertial cavitation doses of different ultrasound contrast agents

Contrast bubble destruction is important in several new diagnostic and therapeutic applications. The pressure threshold of destruction is determined by the shell material, while the propensity for of the bubbles to undergo inertial cavitation (IC) depends both on the gas and shell properties of the ultrasound contrast agent (UCA). The ultrasonic fragmentation thresholds of three specific UCAs (Optison, Sonazoid, and biSpheres), each with different shell and gas properties, were determined under various acoustic conditions. The acoustic emissions generated by the agents, or their derivatives, characteristic of IC after fragmentation, was also compared, using cumulated broadband-noise emissions (IC "dose"). Albumin-shelled Optison and surfactant-shelled Sonazoid had low fragmentation thresholds (mean = 0.13 and 0.15 MPa at 1.1 MHz, 0.48 and 0.58 MPa at 3.5 MHz, respectively), while polymer-shelled biSpheres had a significant higher threshold (mean = 0.19 and 0.23 MPa at 1.1 MHz, 0.73 and 0.96 MPa for thin- and thick-shell biSpheres at 3.5 MHz, respectively, p<0.01). At comparable initial concentrations, surfactant-shelled Sonazoid produced a much larger IC dose after shell destruction than did either biSpheres or Optison (p<0.01). Thick-shelled biSpheres had the highest fragmentation threshold and produced the lowest IC dose. More than two and five acoustic cycles, respectively, were necessary for the thin- and thick-shell biSpheres to reach a steady-state fragmentation threshold.

Quantitative parameters of myocardial perfusion with contrast echocardiography in human beings: Influence of triggering mode

To facilitate quantitation of myocardial contrast echocardiography (MCE) in human beings, dual- or triple-triggered flash imaging has been advocated. However, the effect of this modality on quantitative blood-flow parameters of MCE is not known. Accordingly, MCE was quantitated in 71 myocardial regions of 22 patients (age: 57 +/- 16 years) during continuous infusion of Optison (12-18 mL/h). Two sets of images with end-systolic gating (1:1, 1:2, 1:3, 1:4, 1:6, and 1:8) from the apical 4-chamber view were acquired: single and dual triggering for the first 15 patients; and single and triple triggering for the other 7 patients. During gated imaging, MCE of the first, second, and third frame were quantitated. Curves of intensity versus pulsing intervals were fitted to an exponential function: y = A (1-e(-betat)). Where beta is myocardial blood velocity or the rate of rise of myocardial contrast intensity (MCI), and A is myocardial blood volume or the plateau of MCI reached. Continuous imaging, and the second and third frame in 1:1 gating only, provided similar intensity to precontrast imaging. Beyond 1:1 gating, MCI of the second frame in dual triggering mode gradually increased with incremental pulsing interval. This was still present but less pronounced in triple triggering. During dual and triple triggering, a lower beta was observed compared with single triggering. Application of image subtraction with the flash procedure further decreased beta, A, and the A(*)beta product, a quantitative parameter of blood flow by MCE. Thus, flash subtraction imaging alters the quantitative parameters of myocardial blood velocity and flow derived from MCE. Continuous imaging, and the second or third frame in flash imaging at 1:1 gating only, result in MCI similar to precontrast imaging and can be used for background subtraction to quantitate MCE parameters.

Effect of destructive pulse duration on the detection of myocardial perfusion in myocardial contrast echocardiography: In vitro and in vivo observations

Myocardial perfusion is detected with contrast echocardiography by comparing a contrast-enhanced image with a baseline obtained before contrast injection (true baseline) or after myocardial bubble destruction after a high-power destructive pulse (postdestructive pulse baseline). Although it is assumed that all bubbles are destroyed by a destructive pulse insuring optimal contrast detection, this assumption has not been tested. In 18 participants we compared the videointensity (VI) differences among the contrast-enhanced image, the postdestructive pulse baseline, and the true baseline using both triggered high-mechanical index imaging and real-time imaging. VI difference was significantly greater for the true baseline with both techniques at all ventricular levels. The benefit of using a true baseline was less when the duration of the destructive pulse was increased. Similarly, we quantified VI in a flow phantom using continuous Optison (commercially available perfluoropropane-filled albumin microbubbles) (Amersham, Princeton, NJ) infusion and variable durations of destructive pulses. VI decreased with the duration of the destructive pulse and reached a plateau after a duration of 8 to 15 frames. The plateau reached after a long destructive pulse was dependent on flow rate and concentration and never reached a true baseline, unless concentration (<100 microL/L) and flow rate (<0.5 cm/s) were very low.

IN CONCLUSION

(1) in clinical studies, the difference in VI between contrast-enhanced and baseline images is greater when true baseline is used; (2) the longer the destructive pulse, the closer the postdestructive pulse baseline to true baseline; and (3) this effect exists in all regions of the left ventricle.

C-peptide exerts beneficial effects on myocardial blood flow and function in patients with type 1 diabetes

Myocardial dysfunction, perfusion abnormalities, and the extent to which these abnormalities may be reversed by C-peptide administration was assessed in type 1 diabetic patients. Eight patients were studied before and during a 0.84-mg/kg dipyridamole administration using a randomized double-blind crossover protocol with infusion of C-peptide (6 pmol x kg(-1) x min(-1)) or saline during 60 min on two different days. Myocardial function was measured as peak myocardial velocity during systole (Vs) and early diastole (Vd) by pulsed tissue Doppler imaging. Myocardial contrast echocardiography was used for assessment of myocardial blood volume (SI(max)) and myocardial blood flow index (MBFI) calculated from the relation between trigger interval and signal intensity. Eight age-matched healthy volunteers served as control subjects. In the basal state, Vd (13.8 +/- 0.6 vs. 15.6 +/- 0.5 cm/s, P < 0.04) and SI(max) (6.6 +/- 0.6 vs. 8.2 +/- 0.6 a.u. P < 0.04) were reduced in patients compared with control subjects. Dipyridamole administration significantly increased indexes of myocardial function and blood flow to a similar extent in patients and control subjects. During C-peptide administration, Vs and Vd increased by 12% (P = 0.03), SI(max) increased from 6.6 +/- 0.6 to 8.1 +/- 0.7 a.u. (P < 0.02), and MBFI increased from 3.3 +/- 0.4 to 5.3 +/- 0.9 (P < 0.05). The results demonstrate that type 1 diabetic patients have impaired myocardial function and perfusion in the basal state that can be improved by short-term replacement of C-peptide.

Combined assessment of microvascular integrity and contractile reserve improves differentiation of stunning and necrosis after acute anterior wall myocardial infarction

OBJECTIVES

We sought to determine the relative accuracy of myocardial contrast echocardiography (MCE) and low-dose dobutamine echocardiography (LDDE) in predicting recovery of left ventricular (LV) function in patients with a recent anterior wall myocardial infarction (MI).

BACKGROUND

Left ventricular dysfunction after acute MI may be secondary to myocardial stunning or necrosis. Myocardial contrast echocardiography allows real-time echocardiographic perfusion assessment from a venous injection of a fluorocarbon-based contrast agent. Although this technique is promising, it has not been compared with LDDE.

METHODS

Forty-six patients underwent baseline wall motion assessment, MCE, and LDDE two days after admission, as well as follow-up echocardiography after a mean period of 53 days.

RESULTS

Perfusion by MCE predicted recovery of segmental function with a sensitivity of 69%, specificity of 85%, positive predictive value of 74%, negative predictive value of 81%, and overall accuracy of 78%. Contractile reserve by LDDE predicted recovery of segmental function with a sensitivity of 50%, specificity of 88%, positive predictive value of 72%, negative predictive value of 73%, and overall accuracy of 73%. Concordant test results occurred in 74% of segments and further increased the overall accuracy to 85%. The mean wall motion score at follow-up was significantly better in perfused versus nonperfused segments (1.9 vs. 2.6, p < 0.0001) and in segments with contractile reserve, compared with segments lacking contractile reserve (1.9 vs. 2.5, p < 0.0001).

CONCLUSION

Myocardial contrast echocardiography compares favorably with LDDE in predicting recovery of regional LV dysfunction after acute anterior wall MI. Concordant contractile reserve and myocardial perfusion results further enhance the diagnostic accuracy.

The disappearance of ultrasound contrast bubbles: observations of bubble dissolution and cavitation nucleation

The destruction process of biSphere and Optison ultrasound (US) contrast microbubbles were studied at 1.1 MHz. High-amplitude tone bursts caused shell disruption and/or fragmentation of the microbubbles, leading to dissolution of the freed gas. The bubble destruction and subsequent dissolution process was imaged with a high pulse-repetition frequency (PRF) 10-cycle, 5-MHz bistatic transducer configuration. Three types of dissolution profiles were measured: In one case, biSphere microbubbles showed evidence of dissolution through resonance, during which a temporary increase in the scattering amplitude was observed. In another case, both biSphere and Optison microbubbles showed evidence of fragmentation, during which the scattering amplitude decreased rapidly. Finally, in some cases, we observed the impulsive growth and subsequent rapid decay of signals that appear to be due to cavitation nucleation. Simulations of bubble dissolution curves show good agreement with experiments.

Dual-spectra ultrasonography: an attenuation-compensating technique for myocardial perfusion analysis

OBJECTIVE

To validate the harmonic-fundamental frequency ratio peak for user-independent differentiation of myocardial perfusion under clinically relevant levels of signal attenuation.

METHODS

Radio frequency data were obtained by using apical long-axis scans in 11 open-chest pigs during continuous infusion of a contrast agent after left anterior descending artery occlusion. Silicone pads were interposed between the transducer and the heart to simulate levels of thoracic wall attenuation. Samples of image data from perfused and nonperfused regions were collected; values using harmonic-fundamental frequency ratio peak and conventional harmonic gray scale intensity techniques were calculated.

RESULTS

At each attenuation level, the harmonic-fundamental frequency ratio peak value of perfused myocardium was higher than that of nonperfused myocardium (P < .0001). The variance of these values was smaller than that of the gray scale intensity values (P < .0001), with smaller overlap between harmonic-fundamental frequency ratio peak values differentiating perfused and nonperfused regions. In the receiver operating characteristic curves, this analysis had better diagnostic performance than gray scale analysis. In the optimal cutoff value, harmonic-fundamental frequency ratio peak analysis provided 87% sensitivity and 91% specificity; gray scale analysis had 80% sensitivity and 78% specificity.

CONCLUSIONS

Harmonic-fundamental frequency ratio peak analysis differentiated perfused from nonperfused myocardium under clinically relevant attenuation conditions and provided higher sensitivity and specificity for perfusion determination in attenuated myocardium than did gray scale intensity analysis.

Skeletal muscle microvascular recruitment by physiological hyperinsulinemia precedes increases in total blood flow

Supraphysiological doses of insulin enhance total limb blood flow and recruit capillaries in skeletal muscle. Whether these processes change in response to physiological hyperinsulinemia is uncertain. To examine this, we infused either saline (n = 6) or insulin (euglycemic clamp, 3.0 mU x min(-1) x kg(-1), n = 9) into anesthetized rats for 120 min. Femoral artery flow was monitored continuously using a Doppler flow probe, and muscle microvascular recruitment was assessed by metabolism of infused 1-methylxanthine (1-MX) and by contrast-enhanced ultrasound (CEU). Insulin infusion raised plasma insulin concentrations by approximately 10-fold. Compared with saline, physiological hyperinsulinemia increased femoral artery flow (1.02 +/- 0.10 vs. 0.68 +/- 0.09 ml/min; P < 0.05), microvascular recruitment (measured by 1-MX metabolism [6.6 +/- 0.5 vs. 4.5 +/- 0.48 nmol/min; P < 0.05] as well as by CEU [167.0 +/- 39.8 vs. 28.2 +/- 13.8%; P < 0.01]), and microvascular flow velocity (beta, 0.14 +/- 0.02 vs. 0.09 +/- 0.02 s(-1)). Subsequently, we studied the time dependency of insulin's vascular action in a second group (n = 5) of animals. Using CEU, microvascular volume was measured at 0, 30, and 90 min of insulin infusion. Insulin augmented microvascular perfusion within 30 min (52.8 +/- 14.8%), and this persisted at 90 min (64.6 +/- 9.9%). Microvascular recruitment occurred without changes to femoral artery flow or beta. We conclude that insulin increases tissue perfusion by recruiting microvascular beds, and at physiological concentrations this precedes increases in total muscle blood flow by 60-90 min.

Quantification of myocardial perfusion and determination of coronary stenosis severity during hyperemia using real-time myocardial contrast echocardiography

Although regional myocardial perfusion can be currently quantified with myocardial contrast echocardiography (MCE) by using intermittent harmonic imaging (IHI), the method is tedious and time-consuming in the clinical setting. We hypothesized that regional myocardial perfusion can be quantified and the severity of coronary stenosis determined during hyperemia with MCE using real-time imaging (RTI) where microbubbles are not destroyed. Six open-chest dogs were studied during maximal hyperemia induced by adenosine in the absence or presence of coronary stenoses varying from mild to severe. Myocardial blood flow (MBF) was measured at each stage by using radiolabeled microspheres. MCE was performed using both IHI and RTI. Data for the latter were acquired in both end-systole and end-diastole. No differences were found between myocardial flow velocity (MFV) derived from IHI and RTI when end-systolic frames were used for the latter. MFV was consistently higher for RTI (P <.01) when end-diastolic frames were used. A linear relation was noted between MFV and radiolabeled microsphere-derived MBF ratios from the stenosed and the normal beds when end-systolic frames were used for RTI (r = 0.78, P <.001), whereas no relation was found when end-diastolic frames were used (r = 0.08, P =.78). The scatter for assessing MBF (A.beta) was minimal for IHI and RTI (9%-10%) with end-systolic frames, whereas that for RTI with end-diastolic frames was large (30%). Furthermore the correlation with radiolabeled microsphere-derived MBF was significantly (P <.01) weaker with RTI when end-diastolic frames were used (r = 0.53) than when end-systolic frames (r = 0.94) or IHI was used (r = 0.99). Data acquisition for IHI was 10 minutes, whereas it was 8 seconds for RTI. Thus, RTI can be used to quantify regional myocardial perfusion and stenosis severity during MCE. Only end-systolic frames, however, provide accurate data. RTI offers a rapid and easy means of assessing regional myocardial perfusion with MCE.

Full-motion pulse inversion power Doppler contrast echocardiography differentiates stunning from necrosis and predicts recovery of left ventricular function after acute myocardial infarction

OBJECTIVES

The goal of this study was to determine, in patients with a recent myocardial infarction (MI) and residual wall motion abnormalities within the distribution of the infarct-related artery, whether normal perfusion by myocardial contrast echocardiography (MCE) would accurately predict recovery of segmental left ventricular (LV) function.

BACKGROUND

Left ventricular dysfunction after acute MI may be secondary to myocardial stunning or necrosis. Recent technical innovations in contrast echocardiography, including pulse inversion imaging and power Doppler, now allow full-motion echocardiographic perfusion assessment from a venous injection of fluorocarbon-based contrast agent.

METHODS

Thirty-four patients with recent MI underwent baseline wall motion assessment and MCE two days after admission and follow-up echocardiography a mean of 55 days later.

RESULTS

Perfusion by MCE predicted recovery of segmental function with a sensitivity of 77%, specificity of 83%, positive predictive value of 90% and overall accuracy of 79%. The mean wall motion score at follow-up was significantly better in perfused, compared with nonperfused, segments (1.4 vs. 2.2, p < 0.0001). Additionally, 90% of perfused segments improved, while the majority of nonperfused segments remained unchanged.

CONCLUSIONS

Full-motion MCE utilizing an intravenous fluorocarbon-based agent and pulse inversion power Doppler techniques, identifies stunned myocardium, and accurately predicts recovery of segmental LV function in patients with recent MI.

Vibro-acoustography: quantification of flow with highly-localized low-frequency acoustic force

The intersection of two ultrasound beams with slightly different frequencies results in generation of a localized radiation force and stimulates emission of audio signals from targeted objects. Vibro-acoustography uses this phenomenon to probe elastic properties of objects. Vibro-acoustography of contrast microbubbles in degassed water produced quantitative flow measurements from analysis of their acoustic emission. We used a dual-beam transducer generating bursts of 40-kHz vibrations. The vibrations resulted from interference of 3.48-MHz and 3.52-MHz confocal beams intersecting at the center of a thin plastic conduit. We tested flows of 13,48, 85, and 120 mL/min of contrast microbubbles at concentrations from 1.2 x 10(5) to 6 x 10(9) bubbles/mL. The amplitude of the acoustic emission was linear with microbubble concentrations up to a value of 3.6 x 10(5) bubbles/mL. A replenishment method for microbubble contrast and flow rate analysis was used with radiation force bursts deployed at 0.05, 0.1, 0.2, (.5, 1, and 2-second pulsing intervals. The relation between the pulsing intervals and the peak amplitude was fitted by an exponential curve and a rate constant calculated for each tested flow rate. The rate constant values were linearly correlated with the tested flows. The vibro-acoustography method provides objective, quantitative, and highly-localized assessment of flow using contrast microbubbles.

Detection and quantification of coronary stenosis severity with myocardial contrast echocardiography

The development of microbubble contrast agents and new imaging modalities now allows the assessment of myocardial perfusion during echocardiography. These microbubbles are excellent tracers of red blood cell kinetics. Apart from providing a spatial assessment of myocardial perfusion, myocardial contrast echocardiography (MCE) can also be used to quantify the 2 specific components of myocardial blood flow-flow velocity and myocardial blood volume. The method to quantify myocardial blood flow velocity is based on rapid destruction of microbubbles by ultrasound, and subsequent assessment of the rate of replenishment of microbubbles into the myocardial microcirculation within the ultrasound beam elevation. Assessment of steady state myocardial video intensity (VI) provides a measure of myocardial or capillary blood volume. Perfusion defects that develop distal to a stenosis during hyperemia are therefore due to capillary derecruitment. We have shown that the degree of derecruitment (and therefore the severity of a perfusion defect) is proportional to stenosis severity. Because the capillary bed also provides the greatest resistance to hyperemic flow, decreases in capillary blood volume distal to a stenosis during hyperemia result in increases in microvascular resistance, which is the mechanism underlying the progressive decrease in flow reserve in the presence of a stenosis. Consequently, both the severity of a perfusion defect and quantification of abnormal myocardial blood flow reserve on MCE can be used to determine stenosis severity. As imaging methods with MCE continue to be refined, the optimal imaging algorithms for clinical practice still need to be determined. MCE, however, holds promise as a noninvasive, instantaneous, on-line method for the detection and quantification of coronary artery disease.

Ultraharmonic myocardial contrast imaging: in vivo experimental and clinical data from a novel technique

Myocardial contrast echocardiography (MCE) with high-mechanical-index (MI), triggered harmonic imaging is the best-established technique to date for the assessment of myocardial perfusion. A high signal-to-noise ratio, which is significantly influenced by precontrast tissue signals, is an important prerequisite. Our goal was to evaluate the efficacy of ultraharmonic MCE, a technique that rejects tissue signals by receiving signals beyond the second but below the third harmonic. Imaging was performed in 6 closed-chest dogs and in 15 healthy volunteers (11 of whom also had dipyridamole stress). Analyses of videointensity (VI) confirmed uniformly low precontrast tissue VI, a significant increase of postcontrast VI (before and after dipyridamole), and a significant decrease in VI after microbubble destruction. We conclude that ultraharmonic MCE produces low precontrast tissue signals, thus optimizing postcontrast myocardial opacification, and exhibits efficient microbubble destruction with use of multiple-frame triggering. Thus this new technique opens up a new possibility of further optimizing coronary microcirculation imaging with microbubbles.

Assessment of no-reflow phenomenon after acute myocardial infarction with harmonic angiography and intravenous pump infusion with Levovist: comparison with intracoronary contrast injection

Myocardial contrast echocardiography (intracoronary application) has emerged as an accurate method to detect the "no-reflow phenomenon." To investigate the diagnostic value of harmonic angiography after intravenous infusion of Levovist in assessing "no-reflow," both intracoronary and intravenous contrast injections were performed in a group of patients with acute myocardial infarction. Seventeen consecutive patients with a successfully reperfused acute myocardial infarction within 6 hours of symptom onset were selected for this study. All patients underwent contrast echocardiography with harmonic angiography with Levovist (400 mg/mL, intravenous pump infusion, trigger intervals 1:4 to 1:8) and sonicated albumin (0.5 to 1 mL, intracoronary bolus) on day 1 after the achievement of a sustained coronary reflow. Myocardial perfusion was qualitatively assessed with a 12-segment model. The endocardial length of the residual contrast defect after reflow was also calculated. Forty-four of 204 segments were not analyzed after intravenous contrast echocardiography and 37 after intracoronary contrast echocardiography because of artifacts. Intracoronary and intravenous injections showed a perfusion defect in 31 (19%) segments, with a concordance of 89% (kappa coefficient, 0.72). Concordance in anteroseptal, anterolateral, and inferolateral segments was 95% (kappa = 0.92), 88% (kappa = 0.66), and 83% (kappa = 0.57), respectively. With intracoronary injection used as the reference method, intravenous injection had a sensitivity of 74% and a specificity of 93% for diagnosing contrast defects. The endocardial extent of no-reflow was 18 +/- 19 after intravenous and 21 +/- 17 after intracoronary contrast echocardiography (P = not significant). Intravenous contrast echocardiography with Levovist reliably identifies the no-reflow phenomenon after successful reperfusion, especially in acute anteroseptal myocardial infarction.

In vitro quantification of flow using continuous infusion of Levovist and pairs of harmonic power Doppler images

To evaluate the potential of harmonic power Doppler to quantify perfusion using a continuous infusion of contrast, two dialysis cartridges were perfused with different flow rates adjusted between 0 to 300 mL/min, corresponding to flow ratios comprised between 300:0 and 150:150. The contrast agent (Levovist, Schering) was injected at constant rates (0.6 to 5 g/h). Sequential pairs of images showing simultaneously the cross-sections of the two filters were acquired with a HDI 5000 (ATL) and the Doppler data were processed with HDI lab software (ATL). The absolute values of the signal in the different regions-of-interest (ROI) were not closely related to flow rate. At the opposite, the rapid signal decrease between the first and the second image of each pair was inversely proportional to the flow rate. An index of perfusion [PerI = image 1/(image 1 -- image 2)] was defined. It correlated closely with the absolute and relative flow rates. For the latter, the slopes of regression were found to be independent of the infusion rate of Levovist. Thus, the use of pairs of images combined with a continuous infusion of Levovist provide a quantification of perfusion.

Assessment of myocardial perfusion by harmonic power Doppler imaging at rest and during adenosine stress: comparison with (99m)Tc-sestamibi SPECT imaging

BACKGROUND

Harmonic power Doppler imaging (HPDI) is a novel technique for assessing myocardial perfusion by contrast echocardiography in humans. The purpose of this study was to compare myocardial perfusion by HPDI with that obtained by (99m)Tc-sestamibi single photon emission computed tomography (SPECT) during rest and pharmacological stress.

METHODS AND RESULTS

HPDI was performed on 123 patients who were referred for SPECT imaging for known or suspected coronary artery disease. Images were obtained at baseline and during adenosine infusion (0.14 mg. kg(-)(1). min(-)(1)x6 minutes) in 3 apical views. Myocardial perfusion by HPDI was graded for each coronary territory as absent, patchy, or full. The persistence of absent or patchy myocardial perfusion by HPDI between rest and adenosine was interpreted as a fixed defect, whereas any decrease in perfusion grade was interpreted as a reversible defect. Overall concordance between HPDI and SPECT was 83 (81%) of 103 for normal versus abnormal perfusion. Agreement between the 2 methods for each of the 3 coronary territories was 81% (kappa=0.57) for the left anterior descending artery, 76% (kappa=0.52) for the right coronary artery, and 72% (kappa=0.40) for the left circumflex artery. Discrepancies between the 2 techniques were most notable in the circumflex territory, where fixed defects were observed in 33% by HPDI but in only 14% by SPECT (chi(2)=15.8, P=0.0001).

CONCLUSIONS

This study demonstrates that HPDI can reliably detect myocardial perfusion during pharmacological stress, although there was a significantly higher number of falsely abnormal results in the circumflex territory.

Quantification of microbubble destruction of three fluorocarbon-filled ultrasonic contrast agents

The assessment of myocardial blood velocity using ultrasonic contrast agents is based on the premise that the vast majority of contrast microbubbles within a myocardial region can be destroyed by an acoustic pulse of sufficient magnitude. Determination of the period of time after destruction that a region of myocardium needs to reperfuse may be used to assess myocardial blood velocity. In this study, we investigated the acoustic pressure sensitivity of three solutions of intravenous fluorocarbon-filled contrast agents and the magnitude of acoustic pulse required to destroy the contrast agent microbubbles. A novel tissue-mimicking phantom was designed and manufactured to investigate the relationships between mean integrated backscatter, incident acoustic pressure and number of frames of insonation for three fluorocarbon-filled contrast agents (Definity(R), Optison(R), and Sonazoid(R), formerly NC100100). Using a routine clinical ultrasound (US) scanner (Acuson XP-10), modified to allow access to the unprocessed US data, the contrast agents were scanned at the four acoustic output powers. All three agents initially demonstrated a linear relationship between mean integrated backscatter and number of frames of insonation. For all three agents, mean integrated backscatter decreased more rapidly at higher acoustic pressures, suggesting a more rapid destruction of the microbubbles. In spite of the fact that there was no movement of microbubbles into or out of the beam, only the results from Definity(R) suggested that a complete destruction of the contrast agent microbubbles had occurred within the total duration of insonation in this study.

Contrast echocardiography: current and future applications

Recent updates in the field of echocardiography have resulted in improvements in image quality, especially in those patients whose ultrasonographic (ultrasound) evaluation was previously suboptimal. Intravenous contrast agents are now available in the United States and Europe for the indication of left ventricular opacification and enhanced endocardial border delineation. The use of contrast enables acquisition of ultrasound images of improved quality. The technique is especially useful in obese patients and those with lung disease. Patients in these categories comprise approximately 10% to 20% of routine echocardiographic examinations. Stress echocardiography examinations can be even more challenging, as the image acquisition time factor is critically important for accurate detection of coronary disease. Improvements in image quality with intravenous contrast agents can facilitate image acquisition and enhance delineation of regional wall motion abnormalities at the peak level of exercise. Recent phase III clinical trial data on the use of Optison and several other agents (currently under evaluation) have revealed that for approximately half of patients, image quality substantively improves, which enables the examination to be salvaged and/or increases diagnostic accuracy. For the "difficult-to-image" patient, this added information results in (1) enhanced laboratory efficiency, (2) a reduction in downstream testing, and (3) possible improvements in patient outcome. In addition, substantial research efforts are underway to use ultrasound contrast agents for assessment of myocardial perfusion. The detection of myocardial perfusion during echocardiographic examinations will permit the simultaneous assessment of global and regional myocardial structure, function, and perfusion-all of the indicators necessary to enable the optimal noninvasive assessment of coronary artery disease. Despite the added benefit in improved efficacy of testing, few data exist regarding the long-term effectiveness of these agents. Currently under evaluation are the clinical and economic outcome implications of intravenous contrast agent use for daily clinical decision making in a variety of patient subsets. Until these data are known, this document offers a preliminary synthesis of available evidence on the value of intravenous contrast agents for use in rest and stress echocardiography. At present, it is the position of this guideline committee that intravenous contrast agents demonstrate substantial value in the difficult-to-image patient with comorbid conditions limiting an ultrasound evaluation of the heart. For such patients, the use of intravenous contrast agents should be encouraged as a means to provide added diagnostic information and to streamline early detection and treatment of underlying cardiac pathophysiology. As with all new technology, this document will require updates and revisions as additional data become available.