Improved myocardial contrast with second harmonic transient ultrasound response imaging in humans using intravenous perfluorocarbon-exposed sonicated dextrose albumin.

OBJECTIVES: The objectives of this study were to determine whether a new method of ultrasound imaging (transient response imaging) could improve the myocardial contrast after intravenous injections of perfluorocarbon-exposed sonicated dextrose albumin microbubble contrast medium in humans. BACKGROUND: We have shown in animals that very low doses of intravenous contrast medium can produce transient but significantly better myocardial contrast when diagnostic ultrasound pulses are interrupted (delivered only once per cardiac cycle) instead of conventional 25- to 30-Hz frame rate imaging. METHODS: In 14 patients with normal rest wall motion, the peak myocardial contrast produced by transient response imaging was compared with that produced by conventional harmonic ultrasound imaging after injections of low doses (0.0025 to 0.01 ml/kg) of intravenous contrast medium. All studies were performed with second harmonic imaging (2.0 to 2.5 MHz-transmitted frequency). Blood pressure, oxygen saturation, respiratory rate and pulse were monitored before and after each injection. RESULTS: The intravenous contrast medium in the doses given produced no hemodynamic changes and no significant side effects in any patients. Overall, the mean (+/-SD) anterior and posterior myocardial contrast produced was significantly greater with transient response imaging than with conventional harmonic ultrasound imaging (anterior: 37 +/- 20 U transient response imaging vs. 18 +/- 14 U conventional harmonic imaging; posterior: 17 +/- 14 U transient response imaging vs. 5 +/- 5 U conventional; p< 0.01). With the sample size of 14 patients, the study had 80% power to detect a true difference of 18 U for anterior myocardial contrast and 90% power to detect a difference of 12 U for posterior contrast. Visually evident anterior or apical myocardial contrast was observed in 14 of 15 patients with transient response imaging but in only 7 patients with conventional harmonic imaging. Posterior or basal myocardial contrast was evident in 10 patients with transient response imaging but in only 1 patient with conventional harmonic imaging. CONCLUSIONS: Transient response imaging produces significantly better myocardial contrast than conventional harmonic imaging in humans and can be produced safely with minute quantities of intravenous perfluorocarbon.

Detection of myocardial perfusion in multiple echocardiographic windows with one intravenous injection of microbubbles using transient response second harmonic imaging.

OBJECTIVES: The purpose of this study was to prove that transient response harmonic imaging could detect normal and abnormal myocardial perfusion in multiple echocardiographic windows with one intravenous injection of microbubbles in humans. BACKGROUND: Myocardial ultrasound contrast can be produced from intravenous perfluorocarbon-exposed sonicated dextrose albumin, and ultrasound can be significantly improved by briefly suspending the interval between frame rates. Whether this contrast can noninvasively quantify myocardial perfusion in humans is unknown. METHODS: In 28 patients, harmonic transient response imaging was used to image the heart in multiple different imaging planes after one intravenous injection of ultrasound contrast agent. Twenty-five of these 28 patients had a repeat injection during dipyridamole stress. In the primary view, the ultrasound transmission rate was one frame per cardiac cycle; in secondary and tertiary views, the transmission rate was once every multiple cardiac cycles. Regional myocardial contrast was visually assessed and quantified off-line. Quantitative rest thallium and dipyridamole stress sestamibi imaging was also performed. RESULTS: Perfusion abnormalities were evident in the secondary and tertiary views only with one frame every multiple cardiac cycles. Regional peak myocardial videointensity (PMVI) correlated closely with regional tracer uptake in individual patients both at rest (r = 0.84) and during stress (r = 0.88). A PMVI ratio (abnormal region divided by the region with highest nuclear uptake) < 0.6 in any view had a 92% sensitivity and a 84% specificity in identifying a regional nuclear perfusion abnormality. CONCLUSIONS: Transient response imaging produces myocardial contrast in multiple views with one intravenous injection of contrast agent and can accurately identify regional myocardial perfusion abnormalities.

Real-time perfusion imaging with low mechanical index pulse inversion Doppler imaging.

OBJECTIVES: We sought to determine how successful pulse inversion Doppler (PID) imaging would be in detecting myocardial perfusion defects during dobutamine stress echocardiography. BACKGROUND: By transmitting multiple pulses of alternating polarity (PID) at a low mechanical index, myocardial contrast enhancement from intravenously injected microbubbles can be detected using real-time frame rates. Pulse inversion Doppler imaging was performed in 117 patients during dobutamine stress echocardiography by using an intravenous bolus of a perfluorocarbon-filled, albumin-(Optison: n = 98) or liposome- (Definity: n = 19) encapsulated microbubble and a mechanical index of <0.3. The visual identification of myocardial contrast defects and wall motion abnormalities was determined by blinded review. Forty of the patients had quantitative angiography (QA) performed to correlate territorial contrast defects with stenosis diameter >50%. RESULTS: There was a virtual absence of signal from the myocardium before contrast injections in all patients. Bright myocardial opacification at peak stress was observed in at least one coronary artery territory at frame rates up to 25 Hz in 114 of the 117 patients during dobutamine stress echocardiography. Regional myocardial contrast defects at peak stress were observed in all 30 patients with >50% stenosis in at least one vessel (13 with single-vessel and 17 with multivessel disease). Contrast defects were observed in 17 territories subtended by >50% diameter stenosis that had normal wall motion at peak stress. Overall agreement between QA and myocardial contrast enhancement on a territorial basis was 83%, as compared with 72% for wall motion. CONCLUSIONS: Pulse inversion Doppler imaging allows the detection of myocardial perfusion abnormalities in real-time during stress echocardiography and will further add to the quality and sensitivity of this test.

Real-time assessment of myocardial perfusion and wall motion during bicycle and treadmill exercise echocardiography: comparison with single photon emission computed tomography.

OBJECTIVES: We sought to determine the feasibility and accuracy of real-time imaging of myocardial contrast echocardiography (MCE) in detecting myocardial perfusion defects during exercise echocardiography compared with radionuclide tomography. BACKGROUND: Ultrasound imaging at a low mechanical index and frame rate (10 to 20 Hz) after intravenous injections of perfluorocarbon containing microbubbles has the potential to evaluate myocardial perfusion and wall motion (WVM) simultaneously and in real time. METHODS: One hundred consecutive patients with intermediate-to-high probability of coronary artery disease underwent treadmill (n = 50) or supine bicycle (n = 50) exercise echocardiography. Segmental perfusion with MCE and WM w ere assessed in real time before and at peak exercise using low mechanical index (0.3) and frame rates of 10 to 20 Hz after 0.3 ml bolus injections of intravenous Optison (Mallinckrodt Inc., San Diego, California). All patients had a dual isotope (rest thallium-201, stress sestamibi) study performed during the same exercise session, and 44 patients had subsequent quantitative coronary angiography. RESULTS: In the 100 patients, agreement between MCE and single photon emission computed tomography (SPECT) was 76%, while it was 88% between MCE and WM assessment. Compared with quantitative angiography, sensitivity of MCE, SPECT and WM was comparable (75%), with a specificity ranging from 81% to 100%. The combination of MCE and WM had the best balance between sensitivity and specificity (86% and 88%,respectively) with the highest accuracy (86%). CONCLUSIONS: The real-time assessment of myocardial perfusion during exercise stress echocardiography can be achieved with imaging at low mechanical index and frame rates. The combination of WM and MCE correlates well with SPECT and is a promising important addition to conventional stress echocardiography.

Effect of blood and microbubble oxygen and nitrogen content on perfluorocarbon-filled dextrose albumin microbubble size and efficacy: in vitro and in vivo studies.

We hypothesized, on the basis of in vitro observations, that a higher oxygen partial pressure within perfluorocarbon-containing microbubbles (PCMB) would enhance inward nitrogen diffusion after venous injection, leading to improved myocardial contrast. The in vitro studies measured PCMB size and concentration after injection into arterial blood that was obtained during inhalation of either room air or 100% oxygen. We then compared the myocardial contrast produced from PCMB sonicated in the presence of either a nitrogen-free environment (100% oxygen) or room air in three closed chest dogs. PCMB exposed to oxygenated blood in vitro were significantly smaller after insonation than PCMB exposed to arterial blood obtained during room air inhalation, confirming the important role of dissolved nitrogen in stabilizing PCMB size. In vivo studies demonstrated that intravenous PCMB sonicated with 100% oxygen produced significantly greater anterior and posterior myocardial contrast than PCMB sonicated in the presence of room air.

The effect of ultrasound frame rate on perfluorocarbon-exposed sonicated dextrose albumin microbubble size and concentration when insonifying at different flow rates, transducer frequencies, and acoustic outputs.

The purpose of this article was to compare the effects of 1 and 30 Hz frame rates on perfluorocarbon-exposed sonicated dextrose albumin microbubble size and concentration in a flow cell containing either saline or blood at 37 degrees C. Microbubble size and concentration of perfluorocarbon-exposed sonicated dextrose albumin were measured after insonation at different acoustic outputs, transducer frequencies, and flow rates with the use of the two different frame rates and compared with no ultrasound exposure. At 2.0 MHz insonation frequency, microbubble concentration was significantly reduced with the use of a 30 Hz frame rate and peak negative pressures of 1.1 megaPascal (mPa). This destruction did not occur when using a lower acoustic output, a 1 Hz frame rate, or when flow rate was increased to 100 cc/min. One-hertz frame rates at 2.0 MHz resulted in a significantly larger mean microbubble size than 30 Hz or no ultrasound in both saline and blood, which was in part due to selective destruction of smaller microbubbles. These findings indicate that 30 Hz frame rates destroy perfluorocarbon-exposed sonicated dextrose albumin microbubbles only at higher diagnostic acoustic outputs. A 1 Hz frame rate prevents this destruction, especially destruction of larger (> 5.0 microns) microbubbles.

Effect of transducer standoff on the detection, spatial extent, and quantification of myocardial contrast defects caused by coronary stenoses.

Intermittent harmonic imaging during a continuous infusion of microbubbles may be able to quantify myocardial perfusion abnormalities. Measurements of the spatial extent of these perfusion abnormalities depends on homogenous destruction of the microbubbles in the elevation plane of the transducer. We hypothesized that uneven microbubble destruction caused by attenuation of beam intensity could alter quantitative measurements of perfusion abnormalities during stress. To test this hypothesis, we measured the spatial extent of perfusion defects at peak dobutamine stress with a continuous intravenous infusion of perfluorocarbon-exposed sonicated dextrose albumin and intermittent harmonic imaging in dogs with nonflow-limiting coronary stenoses in the left anterior descending artery. The spatial extent of perfusion defects was also measured during total occlusion of the artery. Measurements were made at standoffs of 2- to 3-cm and 4- to 5-cm distance from transducer surface to myocardium. These spatial extents were correlated with risk area determined after death. The risk area during left anterior descending occlusion at a standoff of 2 to 3 cm was significantly larger at a 1500-ms pulsing interval (6.5 +/- 2.6 cm(2) for 2- to 3-cm standoff versus 3.7 +/- 1.4 cm(2) for 4- to 5-cm standoff; P =.01). The spatial extent at the 2- to 3-cm standoff more closely approximated risk area measured with Monastral Blue (7.8 +/- 2.7 cm(2)). Myocardial perfusion abnormalities during peak dobutamine stress were significantly smaller with the 4- to 5-cm standoff and undetectable in 4 of the 5 dogs. We conclude that ultrasound beam attenuation can reduce the size of a myocardial perfusion abnormality observed with intermittent harmonic imaging during a continuous infusion of microbubbles. This may reduce the sensitivity of this technique when transthoracic imaging is used.

Myocardial cavitational activity during continuous infusion and bolus intravenous injections of perfluorocarbon-containing microbubbles.

The 20-MHz component of broadband noise from inertial cavitation within the anterior myocardium of an open-chest dog was recorded during intravenous infusions or injections of perfluorocarbon-containing microbubbles during insonation with a 1.7-MHz harmonic transducer. Intramyocardial cavitational activity was evident even at a mechanical index of 0.2, but it increased significantly as frame rate and mechanical index were increased. The amount of myocardial contrast intensity produced by the microbubbles was increased by variables that reduced cavitational activity (eg, reducing frame rate to 1 every cardiac cycle or decreasing mechanical index). At a mechanical index of 0.2, myocardial contrast could still be observed at 10-Hz frame rates. These results confirm that intramyocardial cavitational activity is present during ultrasound imaging of microbubbles; imaging techniques that reduce cavitational activity increase the magnitude of myocardial contrast.

Inhibition of carotid artery neointimal formation with intravenous microbubbles.

Because therapeutic gene products such as synthetic antisense oligodeoxynucleotides (ODN) bind to albumin-coated microbubbles, we sought to determine whether IV perfluorocarbon-exposed sonicated dextrose albumin (PESDA) microbubbles could target their delivery to the carotid artery following balloon injury. In 5 pigs, the concentration of ODN taken up within the carotid vascular wall was found to be significantly increased when the IV antisense (ODN) was administered bound to PESDA (ODN-PESDA), and while transcutaneous low-frequency (20 kHz) ultrasound was applied over the carotid artery. Based on these results, a chronic model was then developed, in which 21 pigs received either IV ODN-PESDA, ODN alone, or control, following carotid balloon injury. At 30 days following balloon injury, percent area stenosis was only 8 +/- 2% in the ODN-PESDA groups compared to 19 +/- 8% and 28 +/- 3% in the other groups (p < 0.01). IV PESDA may be a method of noninvasively targeting the delivery of therapeutic genes.

Detection of angiographically significant coronary artery disease with accelerated intermittent imaging after intravenous administration of ultrasound contrast material.

BACKGROUND: Accelerated intermittent harmonic imaging (AII) is used to detect myocardial perfusion abnormalities after intravenous injection of ultrasound contrast medium. A low mechanical index and frame rates of 10 to 20 Hz are used to allow simultaneous wall motion analysis. The purpose of this study was to determine whether the myocardial contrast enhancement achieved with AII can be used to detect angiographically significant coronary artery disease during stress echocardiography. METHODS: We gave intravenous perfluorocarbon containing microbubbles to 45 patients (total of 270 regions) during dobutamine (n = 27) or exercise (n = 18) stress testing with AII. Quantitative angiography was performed on all patients after the stress echocardiograms were interpreted. RESULTS: Quantitative angiography showed >50% diameter stenosis of at least 1 vessel in 32 patients (total of 118 regions). There were visually evident contrast defects in 100 (85%) of these regions, and wall motion was abnormal in 64 (54%). Overall, there was agreement between regional perfusion and quantitative angiographic findings in 217 of the 270 regions (kappa = 0.61; 80% agreement). Agreement with findings at quantitative angiography was good for both dobutamine stress (kappa = 0.66; 83% agreement) and exercise (kappa = 0.53; 77% agreement). The greatest incremental benefit of AII versus wall motion was gained during dobutamine stress. The contrast studies depicted 90% of the regions supplied by a vessel with >50% stenosis, whereas wall motion depicted only 32% (P =.001). CONCLUSIONS: The results of this study indicated that accelerated intermittent perfusion imaging during stress echocardiography can improve the sensitivity of the study in detecting angiographically significant coronary artery disease, especially during dobutamine stress.

Myocardial perfusion abnormalities during low-dose dobutamine after coronary reperfusion can be demonstrated with intravenous perfluorocarbon-exposed sonicated dextrose albumin ultrasound contrast.

We measured background-subtracted peak myocardial videointensity (PMVI) in the left anterior descending and left circumflex perfusion zones in open-chest dogs after intravenous injection of perfluorocarbon-exposed sonicated dextrose albumin ultrasound contrast (PESDA) after reperfusion of a coronary occlusion. These measurements were repeated during low-dose dobutamine (LDD). The ratio of PMVI in the reperfused zone (RZ) compared with the adjacent normal zone (NZ) was measured at baseline and during LDD. Dogs with a >50% diameter residual stenosis were group I (n = 10), and those with <50% residual stenosis were group II (n = 13). Wall-thickening (WT) responses to LDD were not different between groups. Although the PMVI ratio (PMVI(RZ)/PMVI(NZ)) was the same in both groups at baseline, it decreased by >0.1 during LDD in 8 of 10 in group I compared with only 3 of 13 in group II dogs (p = 0.01). PMVI in the RZ increased by > or = 1.5 U in 12 of 13 group II dogs during LDD, but only in 3 of 10 group I dogs. Therefore, intravenous PESDA can be combined with WT responses to define both myocardial function and flow after reperfusion.

Effectiveness of transcranial and transthoracic ultrasound and microbubbles in dissolving intravascular thrombi.

OBJECTIVE: To examine the effectiveness of 1 -MHz and 40-kHz ultrasound with and without microbubbles in fragmenting thrombi in attenuated conditions. METHODS: First, an vitro transcranial model was used to examine the ability of these frequencies to fragment thrombi in the presence or absence of perfluorocarbon-exposed sonicated dextrose albumin microbubbles. Second, an in vivo transthoracic model was used to test the effectiveness of these same frequencies with intravenous perfluorocarbon-exposed sonicated dextrose albumin in fragmenting left circumflex coronary thrombotic occlusions. RESULTS: In the in vitro model, both transcranial 1-MHz and 40-kHz ultrasonic frequencies were effective at fragmenting thrombi only in the presence of microbubbles. In the in vivo model, 1-MHz ultrasound with intravenous perfluorocarbon-exposed sonicated dextrose albumin angiographically recanalized only 4 of 14 occlusions but was consistently effective at improving myocardial blood flow to the risk area even in the absence of angiographic recanalization. Both 40-kHz and 1-MHz ultrasound with perfluorocarbon-exposed sonicated dextrose albumin improved regional wall-thickening and electrocardiographic abnormalities (P < .05 compared with control or ultrasound alone). CONCLUSIONS: Transcranial and transthoracic ultrasound in the presence of intravenous microbubbles can improve flow to ischemic regions and should be considered as a supplement to current pharmacologic therapy.

Noninvasive in vivo clot dissolution without a thrombolytic drug: recanalization of thrombosed iliofemoral arteries by transcutaneous ultrasound combined with intravenous infusion of microbubbles.

BACKGROUND: Previous in vivo studies have shown that microbubbles not only enhance the effectiveness of thrombolytic agents in the presence of ultrasound but may also augment clot dissolution without thrombolytic drugs. METHODS AND RESULTS: The objective of this study was to examine the efficacy of arterial clot disruption by a noninvasive, nonlytic approach with intravenous administration of perfluorocarbon-exposed sonicated dextrose albumin (PESDA) and transcutaneous delivery of ultrasound alone. Pairs of iliofemoral arteries in 10 rabbits were randomized to receive transcutaneous ultrasound treatment or no ultrasound treatment after an acute artery thrombotic occlusion and intravenous PESDA infusion. Five arteries from 3 additional rabbits served as controls (ultrasound alone). All 10 iliofemoral arteries treated with PESDA + ultrasound were recanalized by angiography after ultrasound treatment. None of the 10 contralateral arteries treated with PESDA alone and none of the 5 arteries treated with ultrasound alone were patent after 1 hour. D-Dimer levels did not change after intravenous PESDA + ultrasound-mediated reperfusion. CONCLUSIONS: In vivo arterial clot dissolution can be achieved with intravenous microbubbles and transcutaneous ultrasound delivery alone. This technique has potential for clinical application in patients with acute arterial and venous thrombotic occlusions.