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At least 793 records · Page 44Linked to original sources

PubMed1999

Intraoperative multiplane transesophageal echocardiography for guiding direct myocardial gene transfer of vascular endothelial growth factor in patients with refractory angina pectoris.

Gene transfer for therapeutic angiogenesis represents a novel treatment for patients with chronic angina refractory to standard medical therapy and not amenable to conventional revascularization. We sought to assess the role of intraoperative multiplane transesophageal echocardiography (MPTEE) in guiding injection of naked DNA encoding vascular endothelial growth factor (VEGF) into the left ventricular (LV) myocardium of patients with refractory angina. After exposing the LV myocardium via a limited lateral thoracotomy, each of 17 patients in this series received 4 separate injections of VEGF DNA into different myocardial sites. Initial injections in the first patient produced intracavitary microbubbles, indicating injection of DNA into the LV chamber. Subsequently, each injection was preceded by a test injection of agitated saline. The absence of microbubbles while visualizing the LV cavity during the test injection verified that the ensuing injection of DNA would not be inadvertently squandered in the LV chamber itself. Intracavitary LV microbubbles were observed by MPTEE in 13 of 64 (20.3%) saline test injections and in 8 of 16 (50.0%) patients in which saline test injection was used, leading to adjustments in needle position. MPTEE imaging detected a previously unknown large, apical left ventricular thrombus in one patient, thereby preventing inadvertent injection of VEGF DNA through the myocardium into the thrombus. Imaging during and after injection verified no deleterious impact on LV function. We conclude that MPTEE is a useful tool for ensuring that myocardial gene therapy performed by direct needle injection results in gene transfer to the LV myocardium.

Aged↗

PubMed1995

Quantitative aspects in myocardial contrast echocardiography.

Myocardial tissue perfusion is not currently quantified in the clinical setting. Thus the aim of this paper is to review the quantitative information on myocardial perfusion provided by contrast echocardiography. In a circulatory model-without the capillary network interposed between injection and sampling point of contrast-the transit time of microbubbles (source of the echo contrast effect) is inversely related to absolute flow, thus providing accurate quantitation. A similar situation is represented by blood flow inside a vessel or a cardiac cavity, where, if the prerequisites for quantitation are respected, it is possible to measure blood flow by contrast echocardiography. In the coronary circulation, the transit time of contrast microbubbles varies according to their interaction with coronary microcirculation, and to the characteristics of contrast agents as flow tracers. Echo contrast agents with small microbubbles have been injected into the coronary branches of experimental animals, under both coronary autoregulation and maximal coronary dilation, providing good estimates of coronary blood flow. The accuracy of these measurements might improve when new contrast agents, with characteristics closer to those of a flow tracer, are available. If a tracer is injected before a bifurcation, and provided it mixes adequately, the amount of tracer distributed to each branch is proportional to the corresponding blood flow. A similar situation is encountered when an echo contrast agent is injected into the aortic root or into the left main coronary artery. Here, the ratio between myocardial signal intensity in the different perfusion territories reflects the corresponding ratio of blood flows. The validity of this approach has been previously demonstrated in experimental animals and validated in patients with coronary stenoses. The injection of contrast agents into the coronary circulation at baseline and under coronary hyperaemia has the potential for measuring coronary blood flow reserve. However, what is still unclear is whether contrast echo changes reflect changes in coronary blood flow (i.e. flow reserve), coronary blood volume (i.e. coronary recruitment) or both, and also whether they influence the different types of contrast agent. Finally, myocardial contrast echocardiography can provide information on the spatial distribution of myocardial perfusion, i.e. the presence, site and extent of perfused myocardium. Thus, in models where myocardial perfusion may be either present or absent, contrast echo can provide an accurate estimate of perfusion abnormalities.

Blood Flow Velocity↗

PubMed1986

Spontaneous contrast visualization on the right side of the heart during echocardiography.

Microbubble contrast visualization within the right heart is almost always due to intravenous injections containing microbubbles. In the absence of immediate administration of agitated solutions, several other mechanisms for the occurrence of echo contrast spontaneously in the cardiovascular system have been postulated. Often overlooked as a source of contrast are microbubbles from remotely injected solutions that persist in the circulation because of markedly delayed clearance. Two patients were observed with apparently spontaneous contrast detected in the right heart chambers, both of whom had congestive heart failure, tricuspid regurgitation, and pulmonary hypertension. Regardless of the exact mechanism involved, the finding of this phenomenon reflects the presence of right heart failure and a low flow state.

Aged↗

PubMed1990

Assessment of myocardial perfusion with contrast two-dimensional echocardiography.

Myocardial contrast echocardiography (MCE) is a new technique capable of assessing regional myocardial perfusion in vivo in real time. At present, this technique involves the intraaortic or intracoronary injection of microbubbles of air. As these microbubbles traverse the myocardium, they produce opacification of the myocardium in concomitantly performed echocardiographic images. In animal models, MCE has been demonstrated to assess accurately the in vivo risk area (region of the myocardium at risk for necrosis after acute coronary occlusion). It has also been shown to provide quantitative information on regional myocardial blood flow (both antegrade and collateral). This technique has been demonstrated to be safe in humans. In clinical studies it has been shown to be a useful adjunct to cardiac catheterization, particularly in the assessment of coronary blood flow reserve and collateral blood flow. MCE is also used in the operating room to assess regional myocardial perfusion before and after bypass graft operations. The microbubbles used for MCE were shown to opacify the left ventricular cavity after their injection into a peripheral vein. If myocardial opacification after venous injection can be achieved, MCE will have the potential for the simultaneous noninvasive in vivo assessment of regional myocardial perfusion and function in humans.

Animals↗

PubMed2002

Venous air emboli occur during release of positive end-expiratory pressure and repositioning after sitting position surgery.

UNLABELLED: We studied the effect of positive end-expiratory pressure (PEEP) release and positioning on the occurrence of venous air embolism (VAE). Eighteen consecutive patients (8 women, 10 men; ASA grade I-III) undergoing neurosurgery in the sitting position were studied. After induction of anesthesia ventilation was controlled with a PEEP of 5 cm H(2)O in an oxygen-air gas mixture. A transesophageal echocardiographic (TEE) probe was inserted. Preoperatively, a patent foramen ovale was excluded in all patients. TEE monitoring was performed during surgery, during PEEP release at the end of surgery with the patient still in the sitting position, and during change of the patient position into the supine position. The severity of VAE was differentiated as follows: grade 1 = only microbubbles; grade 2 = microbubbles and decrease of end-tidal carbon dioxide partial pressure (PETCO(2)) by more than 1.5 mm Hg; grade 3 = microbubbles combined with a decrease of PETCO(2) by more than 1.5 mm Hg, and a decrease of mean arterial blood pressure by at least 20 mm Hg. During surgery, VAE with a grade of 1, 2 or 3 occurred in 7, 4, and 2 patients, respectively. After PEEP release, VAE of grades 1, 2, and 3 were observed in 7, 2, and 1 patients, respectively. During repositioning from sitting to supine position, VAE of grades 1, 2, and 3 was observed in 6, 1, and 1 patients, respectively. The patient with VAE grade 3 needed inotropic support until 2 h after surgery to maintain sufficient blood pressure. No patient showed any sign of paradoxical arterial embolism or cardiac dysfunction. We conclude that VAE occurs not only during surgery in the sitting position, but also with release of PEEP and during repositioning to the supine position. IMPLICATIONS: This study shows that venous air embolism (VAE) occurs not only during surgery in the sitting position but also during positive end-expiratory pressure release and repositioning of the patient into the supine position. Continuous monitoring for VAE should be performed until the patient is returned to the supine position.

Adult↗

PubMed2003

Embolism bubble adhesion force in excised perfused microvessels.

BACKGROUND: The mechanics of gas embolism bubble adhesion to the vessel wall is poorly understood. New strategies to treat gas embolism may result from an understanding of adhesion forces, including the molecular determinants of bubble adhesion. The authors conducted experiments to measure the adhesion force of bubbles contacting the vessel wall. METHODS: Microbubbles were injected into excised arterioles. Bubbles resided for 5, 10, 20, or 30 min with the endothelium intact or damaged and with a physiologic salt solution, physiologic salt solution with 5% bovine serum albumin, or rat serum as the perfusate. Inflow pressure was raised until the bubble dislodged. The differential pressure across the microbubble, deltaP, was recorded at the moment of bubble movement. Bubble diameter, D, and length, L, were determined by videomicroscopy. The adhesion force per unit surface area of a bubble contacting the vessel wall, K = deltaPD/4 L, was calculated for each experiment. RESULTS: K at 10 min contact time (physiologic salt solution, 141 +/- 29; serum, 153 +/- 57 dyne/cm2) was higher than at 5 min (physiologic salt solution, 56 +/- 22; serum, 71 +/- 29 dyne/cm2), 20 min (physiologic salt solution, 46 +/- 29) and 30 min (physiologic salt solution, 14 +/- 5) (P < 0.05). Endothelium removal reduced K at 10 min (physiologic salt solution, 68 +/- 46; serum, 60 +/- 14 dyne/cm2) (P < 0.05). K was higher with 5% bovine serum albumin present at 10 min (349 +/- 149, P < 0.05), correlating with in vivo estimates. CONCLUSIONS: The adhesion force developed between a microbubble and the vessel wall depends on multiple factors, including bubble residence time, presence of the endothelium, and perfusion solution.

Acetylcholine↗

PubMed1997

Recent advances in myocardial contrast echocardiography.

In the past few years, significant advances have been made in the production of microbubbles that are more stable in the circulation. Our understanding of the interactions between microbubbles and ultrasound has also led to the development of new ultrasound imaging techniques that result in excellent myocardial opacification after an intravenous administration of microbubbles. This review focuses on advances made with these technologies in the setting of acute coronary syndromes and chronic coronary artery disease.

Cardiomyopathies↗

PubMed1998

Direct video-microscopic observation of the dynamic effects of medical ultrasound on ultrasound contrast microspheres.

RATIONALE AND OBJECTIVES: Ultrasound can cause destruction of microbubble contrast agents used to enhance medical ultrasound imaging. This study sought to characterize the dynamics of this interaction by direct visual observation of microbubbles during insonification in vitro by a medical ultrasound imaging system. METHODS: Video microscopy was used to observe air-filled sonicated albumin microspheres adsorbed to a solid support during insonation. RESULTS: Deflation was not observed at lowest transmit power settings. At higher intensities, gas left the microparticle gradually, apparently dissolving into the surrounding medium. Deflation was slower for higher microsphere surface densities. Intermittent ultrasound imaging (0.5 Hz refresh rate) caused slower deflation than continuous imaging (33 Hz). CONCLUSIONS: Higher concentrations of microbubbles, lower ultrasound transmit power settings, and intermittent imaging each can reduce the rate of destruction of microspheres resulting from medical ultrasound insonation.

Adsorption↗

PubMed1998

Binding and lysing of blood clots using MRX-408.

RATIONALE AND OBJECTIVES: A thrombus-specific ultrasound contrast agent, MRX-408, has been developed recently. This agent consists of phospholipid-coated microbubbles with a ligand capable of targeting the GPIIb/IIIa receptor, thereby allowing the microbubbles to bind with thrombi rich in activated platelets. In vitro and in vivo animal experiments have been conducted to examine imaging enhancement and sonothrombolysis using this agent compared with a nontargeted agent. METHODS: For clot binding, blood-smeared slides were incubated with microbubbles and examined under a light microscope. Change in backscatter signals from the blood clots after binding was examined by both an ultrasound scanner and two single-element transducers arranged in a transmitter-receiver pair. For clot lysis, either 1-MHz or 20-KHz ultrasound was used to enhance the lysing effects of MRX-408 with or without urokinase. RESULTS: Evidence of binding was demonstrated under a microscope. In vitro experiments showed that the "acoustic signature", or properties, of blood clots changed after binding. Clots became more echogenic and nonlinear. In vivo fundamental ultrasound imaging confirmed that as a result of binding, blood clots were more visible, the area of detection was improved, and shadowing behind clots was more noticeable. Under 1-MHz ultrasound and 30 minutes of treatment, lysis efficiency reached 34% with MRX-408, whereas there was no visible clot lysis with saline. CONCLUSION: The results of these preliminary studies show that as a contrast agent, MRX-408 enhanced clots under ultrasound imaging and facilitated sonothrombolysis with or without thrombolytic drugs.

Animals↗

PubMed2002

Optimizing an ultrasound contrast agent's stability using in vitro attenuation measurements.

RATIONALE AND OBJECTIVES: To evaluate the changes in the microbubble population of a currently available ultrasound contrast agent (USCA) through attenuation measurements to optimize its clinical use. MATERIALS AND METHODS: The microbubble population from a galactose-based USCA (Levovist, Schering AG, Germany) was characterized in vitro using attenuation measurements. The effect of dose (0.1, 0.5, and 1 mL), concentrations (200, 300, and 400 mg mL(-1)) and time since reconstitution (2, 12, 22, and 32 minutes) was evaluated using two broadband pulses at different peak negative pressures (0.39 and 0.49 MPa) for a total of 72 injections. RESULTS: Two minutes after reconstitution, a linear relationship was found between attenuation measurements and the amount of USCA (slope 0.92 dB x mg x cm(-1) ml(-1), R = 0.86). For a given dose and concentration, the microbubble stability was significantly reduced with the increase of the time since reconstitution, particularly for the lower concentrations. CONCLUSIONS: The persistence and contrast effect of Levovist can be improved by using recommended minimum time since reconstitution and maximum concentration.

Contrast Media↗

PubMed2000

Reversal of intrapulmonary arteriovenous shunting detected by two-dimensional contrast-enhanced echocardiography after liver transplantation.

BACKGROUND: Intrapulmonary arteriovenous shunting (IPS), occasionally associated with advanced liver disease, may reverse after liver transplantation (LTx). Two-dimensional contrast-enhanced echocardiography, a convenient noninvasive study, has never been used to demonstrate disappearance of IPS after LTx. METHODS: For an 8-month-old girl undergoing living-related LTx, two-dimensional contrast-enhanced echocardiography was performed with the microbubble injection. The opacification of the microbubble in the left heart emerging within 3-6 beats after detection in the right heart was compared with that in the right heart. RESULTS: Microbubble opacification in the left heart was almost the same as that in the right heart (grade 3) shortly after LTx. However, the contrast in the left heart diminished (grade 1) as the respiratory condition improved and subsequently disappeared (grade 0). CONCLUSIONS: Two-dimensional contrast-enhanced echocardiography may be a feasible noninvasive method to evaluate the degree of IPS in the peritransplant period and observe disappearance of IPS after LTx.

Arteriovenous Shunt, Surgical↗

PubMed2000

Quantification of the physiological relevance of a coronary stenosis using myocardial contrast echocardiography.

MCE can be used in the catheterization laboratory or in the operating room to provide rapid assessments of the functional significance of a coronary stenosis from direct arterial injections of microbubbles. In the past few years, the development of more stable microbubble contrast agents, and a better understanding of the interactions between ultrasound and microbubbles have led to the development of a truly non-invasive approach to quantify MBF using venous infusions. Furthermore, additional insights into the physiology of coronary stenosis, particularly as it affects MBV, have been obtained using MCE.

Blood Flow Velocity↗

PubMed2001

Thresholds for inertial cavitation in albunex suspensions under pulsed ultrasound conditions.

Stabilized microbubbles used as echo-contrast agents can be destroyed by ultrasonic irradiation. We have identified two pressure thresholds at which these microbubbles undergo inertial cavitation (here, defined as the collapse of gas bubbles followed by emission of an acoustic broadband noise). The first threshold (P1) corresponds to the pressure at which all the microbubbles in a cavitation field lose their property as an effective scatterer because of fragmentation or deflation. The second threshold (P2) is associated with the acoustic reactivation of the remnants of the contrast agents and is related to the onset of more violent inertial cavitation. P1 and P2 were measured as a function of the concentration of Albunex (Molecular Biosystems Inc., San Diego, CA) contrast agent, the number of transmitting acoustic cycles, and the pulse repetition frequency (PRF). The ultrasound frequency used was 1.1 MHz, and the peak negative acoustic pressures ranged from 0 to 8 MPa. Our results, measured in Isoton II (Coulter Diagnostics, Miami, FL) and whole blood solutions, showed that P1 increased with increasing Albunex concentration and decreased with increasing PRF, whereas P2 decreased with increasing Albunex concentration and was independent of the PRF. Both P1 and P2 decreased with increasing number of acoustic cycles N for N < 10 and were independent of the number of cycles for N > 10. Ultrasound images of Albunex acquired by a commercial scanner showed echo enhancement not only at pressure levels below P1 but also at levels above P2. The threshold P2 was achieved at ultrasound energies above the diagnostic level. Inertial cavitation produced at P2 was associated with a higher level of hemolysis compared with P1. The results of this investigation have potential significance for both diagnostic and therapeutic ultrasound applications.

Albumins↗

PubMed2001

Mechanisms of contrast agent destruction.

Various applications of contrast-assisted ultrasound, including blood vessel detection, perfusion estimation, and drug delivery, require controlled destruction of contrast agent microbubbles. The lifetime of a bubble depends on properties of the bubble shell, the gas core, and the acoustic waveform impinging on the bubble. Three mechanisms of microbubble destruction are considered: fragmentation, acoustically driven diffusion, and static diffusion. Fragmentation is responsible for rapid destruction of contrast agents on a time scale of microseconds. The primary characteristics of fragmentation are a very large expansion and subsequent contraction, resulting in instability of the bubble. Optical studies using a novel pulsed-laser optical system show the expansion and contraction of ultrasound contrast agent microbubbles with the ratio of maximum diameter to minimum diameter greater than 10. Fragmentation is dependent on the transmission pressure, occurring in over 55% of bubbles insonified with a peak negative transmission pressure of 2.4 MPa and in less than 10% of bubbles insonified with a peak negative transmission pressure of 0.8 MPa. The echo received from a bubble decorrelates significantly within two pulses when the bubble is fragmented, creating an opportunity for rapid detection of bubbles via a decorrelation-based analysis. Preliminary findings with a mouse tumor model verify the occurrence of fragmentation in vivo. A much slower mechanism of bubble destruction is diffusion, which is driven by both a concentration gradient between the concentration of gas in the bubble compared with the concentration of gas in the liquid, as well as convective effects of motion of the gas-liquid interface. The rate of diffusion increases during insonation, because of acoustically driven diffusion, producing changes in diameter on the time scale of the acoustic pulse length, thus, on the order of microseconds. Gas bubbles diffuse while they are not being insonified, termed static diffusion. An air bubble with initial diameter of 2 microns in water at 37 degrees C is predicted to fully dissolve within 25 ms. Clinical ultrasound contrast agents are often designed with a high molecular weight core in an attempt to decrease the diffusion rate. C3F8 and C4F10 gas bubbles of the same size are predicted to fully dissolve within 400 ms and 4000 ms, respectively. Optical experiments involving gas diffusion of a contrast agent support the theoretical predictions; however, shelled agents diffuse at a much slower rate without insonation, on the order of minutes to hours. Shell properties play a significant role in the rate of static diffusion by blocking the gas-liquid interface and decreasing the transport of gas into the surrounding liquid. Static diffusion decreases the diameter of albumin-shelled agents to a greater extent than lipid-shelled agents after insonation.

Animals↗

PubMed1999

Effect of a Residual Stenosis by Quantitative Angiography on the Myocardial Contrast Defect Observed Following Coronary Reperfusion Using Intermittent Harmonic Ultrasound Imaging and Intravenous Perfluorocarbon Ultrasound Contrast.

Intermittent harmonic imaging following intravenously injected perfluorocarbon-containing microbubbles can detect myocardial perfusion abnormalities caused by ischemia. It is unknown whether this technique can differentiate viable, ischemic myocardium from infarcted myocardium immediately following coronary reperfusion. The objective of this paper was to determine whether intermittent harmonic imaging with intravenous microbubbles could define myocardial perfusion abnormalities following reperfusion. In 26 dogs, a prolonged total coronary occlusion (mean occlusion time 2.1 +/- 0.4 hours) was followed by coronary reperfusion. Wall thickening (WT) and peak myocardial video intensity (PMVI) within and outside the risk area (PMVI ratio) were measured following intravenous perfluorocarbon microbubbles under resting conditions and during a 5 µg/kg per minute dobutamine [low dose dobutamine (LDD)] infusion in the presence and absence of a >/= 50% diameter stenosis in the reperfused vessel. Infarct size was determined postmortem. The resting contrast defect in all dogs correlated closely (r = 0.93) with infarct size when no residual stenosis was present but correlated more closely with risk area (r = 0.88) when a >/= 50% diameter residual stenosis was present. In dogs with infarction involving > 50% of the risk area, the PMVI ratio was lower under resting conditions (0.51 +/- 0.27) than in dogs with no or partial infarction when no residual stenosis was present. However, in dogs with no or partial infarction, the PMVI ratio fell significantly when a >/= 50% diameter stenosis was present, both under resting conditions and during LDD. We conclude that the myocardial contrast defect observed with intermittent harmonic imaging and intravenous ultrasound contrast is affected by both the infarct size and the presence of a significant residual stenosis.

Journal Article↗

PubMed1999

Real-Time Contrast Echo Assessment of Myocardial Perfusion at Low Emission Power: First Experimental and Clinical Results Using Power Pulse Inversion Imaging.

Power pulse inversion (PPI) has been developed for echocontrast specific imaging in order to reduce destruction of microbubbles. The purpose of this study was to evaluate PPI for real-time contrast echocardiography. Therefore, in vitro studies in a physiological flow-phantom and clinical examinations in patients with coronary artery disease were performed. The in vitro rersults of this study indicate that PPI allows real-time imaging at low emission power and is almost nondestructive to contrast microbubbles of Definity. At this low emission power a strong linear relationship between the dosage of the contrast agent and the resulting PPI signal intensity was found (R = 0.998, p < 0.001). In the clinical examinations real-time imaging using low mechanical index PPI resulted in strong myocardial signals and a complete filling of the cavities indicating absence of bubble destruction. Most striking was the ability of PPI to display myocardial thickening and wall motion simultaneously with the assessment of myocardial contrast replenishment following ultrasound induced bubble destruction by high power frames. We conclude that PPI allows nondestructive contrast imaging both in experimental and clinical settings. Therefore, real-time imaging of myocardial perfusion and real-time assessment of contrast replenishment following ultrasound induced destruction of microbubbles is feasible. Moreover, PPI allows simultaneous assessment of perfusion and myocardial function.

Journal Article↗

PubMed1999

Characteristics of SonoVuetrade mark.

The advances made by ultrasonography in the last decade, in parallel with the development of ultrasound contrast agents, have opened a wide range of potential breakthroughs in the field of ultrasound imaging. SonoVue(trade mark) is a new echocontrast agent made of microbubbles stabilized by phospholipids and containing sulphur hexafluoride (SF6), an innocuous gas. The suspension of the microbubbles is stable over the time following reconstitution. The bubble concentration of SonoVue(trade mark) is between 100 and 500 million per ml. The mean bubble diameter is 2.5 µm and more than 90% of the bubbles are smaller than 8 µm. Following intravenous injection, the bubble suspension is submitted to pressure increases. SF(6), a high molecular weight gas with low solubility in water, was selected since laboratory tests showed that it confers to the bubbles a good resistance to pressure changes as those that occur in the left ventricle, in the pulmonary capillaries, or in the coronary circulation. The high bubble concentration, combined with a favorable size distribution profile, provides SonoVue(trade mark) with a strong echogenicity. SonoVue(trade mark) shows a peak in the backscatter coefficient at about 3 MHz. With regard to the gas contained in the bubbles, its pharmacokinetics have been assessed during a study in human volunteers. Following intravenous administration of 0.3 ml/kg of SonoVue(trade mark) (i.e., approximately ten times the imaging dose), the blood level curve showed a distribution half-life of about 1 minute and an elimination half-life of about 6 minutes. More than 80% of the administered gas is exhaled via the lungs after 11 minutes. Extensive studies in animals and humans have confirmed the outstanding safety profile of this second generation contrast agent and its capability in providing a clinically useful ultrasound signal enhancement for the evaluation of cardiac function and extracardiac vessel abnormalities. Thanks to the long persistence of SF(6) microbubbles, SonoVue(trade mark) is also potentially useful in the assessment of myocardial perfusion, as well as microcirculatory disorders.

Journal Article↗

PubMed2000

Role of intravenous ultrasound contrast in stress echocardiography.

Intravenous newer generation perfluorocarbon containing microbubbles have been shown to enhance endocardial borders, especially during harmonic imaging. Although this significantly improves the detection of wall-motion abnormalities during stress echocardiography, intermittent imaging consistently results in myocardial contrast following intravenous infusions or injections of perfluorocarbon microbubbles. Detection of myocardial perfusion abnormalities during both exercise and pharmacologic stress echocardiography appears to be feasible clinically with either intravenous injections or continuous infusions of microbubbles using intermittent harmonic imaging. Accelerated intermittent harmonic imaging allows one to rapidly acquire both myocardial perfusion and wall motion during exercise and dobutamine stress echocardiography.

Cardiotonic Agents↗