Reinhard Schlief

Stimulated acoustic emission to image a late liver and spleen-specific phase of Levovist® in normal volunteers and patients with and without liver disease

Quantitative studies were performed to investigate liver- specific uptake of the microbubble Levovist, using stimulated acoustic emission (SAE), which can detect microbubbles even when stationary or slow-moving. These comprised studies of biodistribution comparing the liver and kidney in five normal volunteers, reproducibility in 34 patients, comparison between cirrhotics and controls (n = 9 each) and maximal depth of effect at different frequencies (180 measurements in 31 patients). Stimulated acoustic emission lasted beyond 30 min, with strongly liver-specific properties in each volunteer and was highly reproducible. No difference in the amount of SAE in the superficial liver was seen between cirrhotic and normal livers, but attenuation was higher in cirrhotics. This demonstrates a frequency-dependent effect on liver SAE penetration. We conclude that the liver uptake of Levovist lasts over 30 min, is reproducible, occurs even where diffuse liver disease is present and can be used to assess tissue attenuation in a novel fashion.

Successful Opacification of the Left Heart Chambers on Echocardiographic Examination after Intravenous Injection of a New Saccharide Based Contrast Agent

A new monosaccharide microparticle based echocardiographic contrast agent (SH U 508) was injected intravenously into five healthy male volunteers following which the heart was imaged in an apical four‐chamber view. Volumes of 2, 4, 8, and 16 mL of SH U 508 were incrementally injected into each volunteer. Concentrations of 50, 100, 200, 300, and 400 mg microparticles per mL of suspension were used in five successive examinations. Left heart opacification of diagnostic value was obtained during the whole cardiac cycle with concentrations of 300 and 400 mg/mL. There was no interference in imaging of the left ventricular walls due to increased attenuation. SH U 508 showed a good tolerance. No side effect was observed and no clinical relevant changes were observed in the heart rate, blood pressure, ECC, blood chemistry, hematology or urinalysis findings. This new agent may greatly extend the role of cardiac ultrasound and may also permit the examination of the arterial circulation in other organs.

Quantitative echo contrast concentration measurement by Doppler sonography

The hypothesis investigated in this study is that Doppler ultrasound can be used to make quantitative echo contrast concentration measurements in flow systems. Our motivation was to demonstrate the utility and some of the pitfalls of using scattered ultrasound intensity to quantify echo contrast in chambers and vessels. Doppler ultrasound was used rather than conventional imaging techniques because of its natural association with the assessment of flow in chambers and vessels. We compared the intensity of audio Doppler to various steady-state concentrations echo contrast in a carefully controlled in vitro flow system. A total of 62 paired audio Doppler intensity and echo contrast concentration measurements were made. A weak positive correlation was found between the absolute echo contrast concentration and audio Doppler intensity (r = 0.510, p = 0.001). The correlation was weak because of the many unknowns and effervescent nature of microbubble echo contrast agents. However, audio Doppler intensity was shown to correlate strongly with the relative concentration of echo contrast over short time periods (r = 0.958, p = 0.0001). The results show that Doppler intensity can be used to quantitatively measure the relative, but not the absolute concentration of echo contrast in in vitro flow systems.

Harmonic Power Doppler Contrast Echocardiography: Preliminary Clinical Results

Background: In fundamental and second harmonic echocardiography new contrast media opacify the cavities and reduce the difference in the gray level between the cavity and the myocardium thus obscuring the borders of the myocardium. Objectives: The aim of the study was to examine the potential usefulness of second harmonic power Doppler imaging (HPD) in providing adequate delineation of the myocardium from the left ventricular (LV) and right ventricular (RV) cavities during intravenous contrast echocardiography. Using HPD, microbubbles in a cavity or a tissue are imaged as colored pixels superimposed on a conventional B‐scan image. Methods: In a pilot study, three healthy volunteers and two patients with ischemic heart disease were investigated using an ATL‐HDI 3000 echo system. Four chamber views were obtained using fundamental B‐scan, harmonic B‐scan two‐dimensional echocardiography (H2D) and HPD following intravenous injections of 3 g Levovist*. Results: Using intermittent scanning/recording, H2D and HPD provided intensive and homogenous contrast effects in the RV and LV cavities. Good delineation of the myocardium was found in all subjects using HPD, whereas in two of three volunteers and in one of two patients ventricular septal and apical endocardial borders were obscured during H2D. No obvious change in myocardial backscatter was visually found with H2D. However, in all three healthy volunteers and in one of two patients, HPD recordings demonstrated patchy and reticular patterns in the myocardium, which were different from the homogenous signals in the LV cavity. These are consistent with imaging of intramyo‐cardial coronary vessels. Conclusions: HPD with intravenous Levovist is feasible. This technique demonstrated good delineation of ventricular cavities from the myocardium as well as presence of visible contrast in the myocardium. This pilot study justifies further clinical trials to evaluate the clinical benefit of this approach.

Improved sensitivity of color Doppler by SH U 454

SH U 454, a suspension of galactose microparticles, provides microbubbles (97% less than 7 microns) in variable, reproducible concentrations. Its influence on color Doppler imaging was evaluated in a flow model study and in a clinical study. In the flow model, increasing attenuation (up to 11.4 dB/MHz) impaired the signal to noise ratio and decreased the sensitivity for detecting flow velocities. Thus, flow signals were obtained with flow velocities greater than 3 cm/s (0.1 dB/MHz), greater than 9 cm/s (5.7 dB/MHz) and greater than 17 cm/s (11.4 dB/MHz). After injection of SH U 454 (200 mg/ml), velocities down to 3 cm/s were detected even with high attenuation (11.4 dB/MHz). Color Doppler imaging was performed before and after intravenous injection of 2 ml, 3 ml and 4 ml of SH U 454 (200 mg/ml) in 22 adult patients, and the maximal color-coded areas of diastolic blood flow were determined in the right atrium and ventricle. In 19 of 22 patients, the displayed color-coded areas increased after injection of SH U 454. The diastolic blood flow was imaged on 14 +/- 8% (mean +/- 1 standard deviation) of the cross-sectional area of the right ventricle (4-chamber view) without SH U 454, compared with 39 +/- 15% with 3 ml of SH U 454 (p less than 0.001). For the right atrium, the area displayed by color Doppler increased from 9 +/- 13 to 62 +/- 25% (p less than 0.001). The variability of the measurements from patient to patient after injection of SH U 454 was 5.9 +/- 4% as compared with 10.7 +/- 6.9% without SH U 454 (p less than 0.05). These findings indicate that the intravenous injection of SH U 454 increases the sensitivity of color Doppler imaging for detection of blood flow by improving the signal to noise ratio.

The Effects of the Microbubble Suspension SH U 454 (Echovist®) on Ultrasound-Induced Cell Lysis In a Rotating Tube Exposure System

Human erythrocytes resuspended at different hematocrits in autologous plasma at 37°C were exposed to therapeutic intensities of continuous‐wave 0.75‐MHz ultrasound in vitro in a rotating tube exposure apparatus designed to maximize the destructive effects of cavitational activity. Provided that large numbers of additional gas bubbles had not been introduced during the various preparative and manipulatory procedures, the addition of Echovist® at final concentrations comparable with those currently being used for clinical investigations resulted in a statistically significant increase in the amount of cell lysis in vitro in those samples having hematocrits < 2%. The amount of cell lysis produced at any given ultrasound intensity decreased with increasing hematocrit in both the controls and the cell suspensions containing Echovist® until it was virtually zero in both cases at hematocrits of 5.5% or greater. The addition of Echovist® to samples that already contained large numbers of stabilized gas bubbles and/or had hematocrits > 5.5% produced no detectable cell lysis even at ultrasonic intensities as high as 3 W/cm2 spatial average, temporal average (SATA). It is therefore unlikely that Echovist® would cause appreciable amounts of cell lysis when the gas bubbles were being exposed to ultrasound under the conditions used for clinical investigations in vivo. (ECHOCARDIOGRAPHY, Volume 8, July 1991)

Improved Doppler signal intensity in coronary arteries after intravenous peripheral injection of a lung-crossing contrast agent (SHU 508A)

OBJECTIVES We tested the hypothesis that SHU 508A, a new lung-crossing contrast agent capable of increasing the Doppler signal to noise ratio in the right heart as well as left heart cavities after intravenous injection, could increase Doppler signal intensity in coronary arteries, thus improving the feasibility and quality of transesophageal Doppler echocardiographic evaluation of coronary blood flow velocity. BACKGROUND Coronary blood flow velocity can be evaluated by transesophageal Doppler echocardiography. However, an adequate Doppler tracing is obtainable in a relatively low percent of patients. METHODS Transesophageal Doppler echocardiography of coronary arteries was performed in 35 patients before and after SHU 508A injection at four different dosages (200 mg/ml in 5 ml, 200 mg/ml in 10 ml, 300 mg/ml in 5 ml and 300 mg/ml in 10 ml). Color Doppler mapping of coronary flow and pulsed wave Doppler measurement of coronary blood flow velocity were attempted in all patients. RESULTS Color Doppler flow mapping of 105 evaluated coronary segments (left main, left anterior descending and circumflex in 35 patients) was not detectable or was weak in 88% of patients before and 33% of patients after echo contrast injection (p < 0.0001); it was optimal (that is, well delineated with complete flow mapping of the explored vessel) in only 11% of patients before and 67% after echo contrast injection (p < 0.0001). In addition, pulsed wave Doppler signal quality improved after echo contrast injection: Pulsed wave Doppler recording of coronary blood flow velocity was not obtainable or was weak in 78% of cases before and 34% after echo contrast injection (p < 0.0001); pulsed wave Doppler recording of coronary blood flow velocity was optimal (that is, there was a complete and well defined outline of diastolic coronary blood flow velocity in 23% of cases before and 66% after echo contrast injection [p < 0.0001]. Both length and width of color Doppler mapping in the left anterior descending coronary artery increased after SHU 508A injection (from 5.75 +/- 5.32 and 1.51 +/- 1.17 to 17.04 +/- 8.76 and 4.21 +/- 1.78 mm, respectively, mean +/- SD, p < 0.0001). CONCLUSIONS The feasibility and quality of recording coronary blood flow velocity by transesophageal Doppler echocardiography are considerably improved by intravenous injection of SHU 508A. The improved feasibility of this new semi-invasive method for evaluating coronary blood flow velocity and flow reserve can considerably increase its research and clinical utilization.

Stimulated Acoustic Emission Nonbackscatter Contrast Effect of Microbubbles Seen with Harmonic Power Doppler Imaging.

Transient imaging has been introduced to enhance the signal intensities when using echo contrast agents. However, this phenomenon is not clearly understood. To evaluate the mechanisms of this phenomenon, isolated pig hearts were investigated with different echo imaging techniques in the beating, working heart as well as in an asystolic state without any motion of the heart. The hearts of five German farm pigs (21 ± 2.5 kg) were surgically explanted and inserted in an artificial circulation providing physiological flow and pressures. Levovist in the dosage of 0.05–0.3 g was injected into the left atrium and contrast effects evaluated in the left ventricular (LV) cavity and in the myocardium with an ultrasound imager (ATL, HDI 3000) equipped with a prototype software for harmonic imaging. Harmonic B‐scans and power Doppler registrations were performed with continuous and intermittent recordings (ECG triggered at end‐systole) in the beating heart and using an external trigger in the asystolic heart in which perfusion was interrupted for 20 seconds. In the beating pig heart, transient harmonic power Doppler imaging provided intensive opacification of the LV cavity and visible myocardial uptake when ECG triggering was performed. In the asystolic pig heart, with uninterrupted perfusion, both triggered and nontriggered registrations showed contrast signals in the LV cavity and in the myocardium. These findings cannot be explained with the known physics of ultrasound contrast media. Stimulated acoustic emission occurring during disintegration of the microbubbles in the acoustic field would explain this phenomenon, which has not yet been described for Levovist.

The Doppler kinetics of microbubble echo contrast

The right and left heart kinetics of a saccharide-based microbubble echo contrast agent were measured in 11 anesthetized dogs using Doppler intensity as a measure of microbubble concentration while controlling for the dose administered, weight of the subject and cardiac output. A two-phase Doppler time-intensity curve was noted in all vascular regions. A brief first pass effect (phase 1) was found to depend on the contrast dose, cardiac output and subject size. This was followed by a much longer nearly steady-state elevation in the Doppler intensity compared with baseline (phase 2). The kinetics of phase 2 were found to be the same in all vascular distributions and independent of cardiac output. The phase 2 kinetics depend on the contrast dose, subject size and elimination characteristics of the contrast agent. The clinically important conclusions are: (1) the magnitude of Doppler enhancement and duration of the contrast effect can be predicted using the simple formulas presented; (2) the flow-dependent portion of the arterial contrast effect is effectively over only a few seconds after intravenous injection; and (3) the kinetics of phase 2 are the same throughout the body.

Wideband harmonic imaging: A novel contrast ultrasound imaging technique

Abstract. A novel ultrasonic imaging method, wideband harmonic imaging, for nonlinear imaging of microbubble contrast agents is evaluated. In wideband harmonic mode, two pulses of alternate phase are send out. The image is then processed from the sum of both pulses, resulting in an image of nonlinear scatterers such as microbubbles. A prototype ultrasound system, Siemens Elegra, was evaluated with in vitro investigations and animal trials, using conventional, harmonic and wideband harmonic settings with the galactose based ultrasound contrast agent Levovist. Wideband harmonic imaging offers superior sensitivity for ultrasound contrast agents compared to conventional imaging and harmonic imaging. At low transmit power settings (MI 0.1–0.5) the nonlinear response is already sufficient to generate a image of the blood pool distribution of Levovist in the rabbit kidney including the microvasculature, with clear delineation of vessels and perfused parenchyma. At high transmit amplitudes, nonlinear tissue response reduced the apparent image contrast between contrast agent and tissue. The results suggest that wideband harmonic imaging is currently the most sensitive contrast imaging technique, maintaining highest spatial resolution. This may add to image quality and offer new clinical potential for the use of ultrasound contrast agents such as Levovist.