Power Pulse Inversion Research Articles

Evaluation of chirp reversal power modulation sequence for contrast agent imaging

Over the last decade, significant research effort has been focused on the use of chirp for contrast agent imaging because chirps are known to significantly increase imaging contrast-to-noise ratio (CNR). New imaging schemes, such as chirp reversal (CR), have been developed to improve contrast detection by increasing non-linear microbubble responses. In this study we evaluated the contrast enhancement efficiency of various chirped imaging sequences in combination with well-established imaging schemes such as power modulation (PM) and pulse inversion (PI). The imaging schemes tested were implemented on a fully programmable open scanner and evaluated by ultrasonically scanning (excitation frequency of 2.5 MHz; amplitude of 350 kPa) a tissue-mimicking flow phantom comprising a 4 mm diameter tube through which aqueous dispersions (dilution fraction of 1/2000) of the commercial ultrasound contrast agent, SonoVue® were continuously circulated. The recovery of non-linear microbubble responses after chirp compression requires the development and the optimization of a specific filter. A compression filter was therefore designed and used to compress and extract several non-linear components from the received microbubble responses. The results showed that using chirps increased the image CNR by approximately 10 dB, as compared to conventional Gaussian apodized sine burst excitation but degraded the axial resolution by a factor of 1.4, at −3 dB. We demonstrated that the highest CNR and contrast-to-noise ratio (CTR) were achievable when CR was combined with PM as compared to other imaging schemes such as PI.

The Antiangiogenic Effects of a Vascular Endothelial Growth Factor Decoy Receptor Can Be Monitored in Vivo Using Contrast-Enhanced Ultrasound Imaging

The development of antiangiogenic therapies has stimulated interest in noninvasive imaging methods to monitor response. We investigated whether the effects of a vascular endothelial growth factor decoy receptor (VEGF Trap, Regeneron Pharmaceuticals, Tarrytown, NY) could be monitored in vivo using contrast-enhanced ultrasonography (CEUS). Twenty nude mice (in two groups) were implanted with a human melanoma cell line (DB-1). The active group received VEGF Trap (4 × 25 mg/kg over 2 weeks), whereas the control group received an inactive protein. An ultrasound contrast agent was injected followed by power Doppler imaging (PDI) and pulse inversion harmonic imaging (PIHI; regular and intermittent). Specimens were sectioned in the same planes as the images and stained for endothelial cells (CD31), cyclooxygenase-2 (COX-2), VEGF, and hypoxia (Glut1). Measures of tumor vascularity obtained with the different imaging modes were compared to immunohistochemical markers of angiogenesis. Mean tumor volume was smaller in the active group than in the control group (656 ± 225 vs 1,160 ± 605 mm3). Overall, PDI and VEGF correlated (r = .34; p = .037). Vascularity decreased from control to treated mice with intermittent PIHI, as did the expression of CD31 and COX-2 (p ≤ .02), whereas VEGF increased (p = .05). CEUS appears to allow in vivo monitoring of the antiangiogenic effects of VEGF Trap in the DB-1 human melanoma xenograft model.

Ecocardiografia com contraste no infarto do miocárdio

ABSTRACTThe contrast agents used in ultrasound are approved for several clinical situations. New echocardiographic techniques, such as harmonic imaging and power pulse inversion imaging, can improve the visualization of microbubbles. In this article we discuss the early development of contrast echocardiography, new technologies that help improve image acquisition and its practical role in the assessment of myocardial infarction.

Safety and Feasibility of Real Time Adenosine Myocardial Contrast Echocardiography with Emphasis on Induction of Arrhythmias: A Study in Healthy Volunteers and Patients with Stable Coronary Artery Disease

Some studies reported an increased incidence of premature ventricular complexes (PVCs) during triggered myocardial contrast echocardiography (MCE) using high-intensity ultrasound destruction. Whether PVCs are also induced by real time MCE using low emission power, is unknown. The aim of the study was to assess the occurrence of arrhythmias during real time adenosine MCE in healthy volunteers and patients with stable coronary artery disease (CAD). Fifty healthy volunteers and 26 patients with stable CAD underwent real time MCE using Sonovue and power pulse inversion (ATL 5000) at rest and during adenosine stress. The occurrence of premature atrial complexes (PAC) and PVCs was analyzed before and during MCE using ECG-tracings from videotapes. In healthy subjects, the occurrence of PVCs at baseline (0.04 +/- 0.23 PVCs/min) was similar at rest (0.04 +/- 0.23 PVCs/min, P = NS), and adenosine stress (0.03 +/- 0.14, P = NS). In CAD patients, the occurrence of PVCs at baseline was 0.30 +/- 0.76 PVC/min, compared to 0.29 +/- 0.74 at rest (P = NS), and 0.34 +/- 0.74 during adenosine stress (P = NS). The number of subjects demonstrating PVCs did not increase during MCE. The occurrence of PACs during MCE was not increased compared to baseline. Real time MCE using low emission power does not increase the occurrence of premature complexes in healthy volunteers or CAD patients.

Monitoring Angiogenesis in Human Melanoma Xenograft Model Using Contrast-Enhanced Ultrasound Imaging

The potential for noninvasive monitoring and quantification of tumor angiogenesis with contrast-enhanced ultrasound imaging has been investigated in a murine cancer model. Seventy athymic nude mice were implanted with the human melanoma cell line DB-1 but only 30 of these were available for the final study. The 30 mice were divided into three groups (10 mice/group), which were studied with contrast-enhanced ultrasound imaging 4, 5 or 6 weeks post-implantation. Power Doppler and pulse inversion harmonic imaging (PIHI) were performed (in real time and intermittently) with a Sonoline Elegra scanner (Siemens Medical Solutions, Issaquah, WA) following injection of Optison (dose: 0.4-0.6 ml/kg; GE Healthcare, Princeton, NJ). Ultrasound results were compared to immunohistochemical stains for endothelial cells (CD31), vascular endothelial growth factor (VEGF) and cyclooxygenase-2 (COX-2). Linear regression analysis indicated statistically significant correlations between the percent area stained with VEGF and ultrasound measures of tumor neovascularity obtained with all three techniques (p < 0.01). Contrast-enhanced ultrasound imaging of tumor neovascularity appears to provide a noninvasive marker of angiogenesis corresponding to the expression of VEGF in the DB-1 model and may become a useful tool for monitoring clinical anti-angiogenic therapies.

Contrast Enhanced Ultrasound for Radio Frequency Ablation of Canine Prostates: Initial Results

We determined the feasibility of contrast enhanced ultrasound for radio frequency ablation of the entire prostate as a method of minimally invasive treatment for prostate cancer in a canine model. Approval of the Institutional Animal Use and Care committee was obtained. Initially 5 dogs (group 1) were tested using variable power (5 to 30 W), time (4 to 12 minutes), bolus (0.01 to 0.04 ml/kg) and infusion (3 to 11 ml per minute at 0.015 microl/kg) injections of an ultrasound contrast agent with conventional grayscale power Doppler and pulse inversion harmonic imaging to establish optimal parameters. Subsequently 4 dogs (group 2) underwent entire prostate ablation using parameters based on group 1. The size of the thermal lesions and residual viable tissue was measured with ImageJ software (National Institutes of Health, Bethesda, Maryland) on ultrasound and pathological study. Linear regression and Student's t test were used for statistical analysis. A bolus of 0.04 ml/kg, an infusion of 11 ml per minute at 0.015 microl/kg and the contrast enhanced pulse inversion harmonic imaging mode were ranked best for guiding ablation. Thermal lesion volume was proportional to ablation power and time. There was no significant difference in measured thermal lesion size in group 1 between ultrasound and pathological findings (mean +/- SD 1.51 +/- 0.74 and 1.46 +/- 0.74 cm3, p = 0.56) or in residual viable tissue in group 2 (0.43 +/- 0.043 and 0.41 +/- 0.291 cm3, p = 0.21). The average volume of prostate ablation achieved in group 2 was 96.3%. Contrast enhanced pulse inversion harmonic imaging is able to guide, monitor and control radio frequency ablation of the entire prostate.

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.

Quantification of Myocardial Perfusion Using Intravenous Myocardial Contrast Echocardiography in Healthy Volunteers: Comparison with Positron Emission Tomography

Intravenous myocardial contrast echocardiography (ivMCE) has the potential to evaluate myocardial contraction and perfusion simultaneously. The purpose of this study was to assess quantification of myocardial blood flow (MBF) using ivMCE and to compare this with MBF as measured with positron emission tomography (PET). A total of 16 healthy volunteers underwent ivMCE using power pulse inversion and contrast agent microbubbles at rest and during pharmacologically induced vasodilation. Microbubble destruction was achieved with a burst of high-energy ultrasound, followed by imaging of contrast replenishment with low-energy ultrasound. Regions of interest were drawn and time intensity curves were calculated that were fitted to a monoexponential function. An estimate of MBF (perfusion estime) was calculated as the product of the plateau value A and the exponential beta describing the replenishment curve. MBF was measured with PET using oxygen-15-labeled water at rest and during adenosine stress. Significant correlations were found between MBF as measured with PET and perfusion estimate as measured with ivMCE in the left anterior descending coronary artery (r = 0.87, P < .01), right coronary artery (r = 0.66, P < .01), and left circumflex artery (r = 0.75, P < .01) territories. Heterogeneity, however, was significantly larger for ivMCE (coefficient of variation 32 +/- 15%) than for PET (9 +/- 6%) measurements (P < .01). Perfusion parameters as measured with ivMCE correlated with PET-derived MBF, but associated heterogeneity was significantly larger. Currently, this heterogeneity precludes true quantification of MBF using ivMCE.

Assessment of vasa vasorum density in coronary atherosclerotic lesions by means of contrast enhanced intravascular ultrasound imaging with microbubbles

The purpose of this study was to determine the impact of emission power on ultrasound (US)-induced destruction of echocontrast microbubbles during real-time power pulse inversion imaging (PPI) in myocardial contrast echocardiography (MCE) and to evaluate the magnitude of noncontrast PPI signals arising from myocardial tissue at variable emission power to define the cut-off emission power for optimal MCE using low power technologies. In vitro studies were performed in a flow phantom using Optison®, Definity™ and AFO 150. PPI signal intensity during real-time imaging at 27 Hz was compared with intermittent imaging at 0.1 Hz to evaluate bubble destruction at variable emission power (MI: 0.09 to 1.3). In healthy volunteers, PPI signal intensities during constant infusion of Optison® was studied in real-time PPI 22 HZ and during intermittent imaging triggered end-systolic frames every, every 3rd and every 5th cardiac cycle. In addition, the impact of emission power on nonlinear PPI signals from myocardial structures was studied. In vitro, there was a 40% decrease of real-time PPI signal intensity for Optison® and AFO 150 at lowest emission power (0.09), whereas no signal loss was observed for Definity™. Increase of emission power resulted in a faster decay for Optison® and AFO 150 as compared to Definity™. In vivo, real-time PPI during continuous infusion of Optison® resulted in a 40% decrease of myocardial signal intensity as compared to intermittent imaging every 5th cardiac cycle, even at lowest possible emission power (mechanical index = 0.09). There was a strong positive relationship between MI and noncontrast myocardial PPI signals in all myocardial segments. PPI signal intensity was found to be lower than 1 dB only for extremely low emission power (MI < 0.2). Destruction of microbubbles during real-time imaging by use of PPI at low emission power varies considerably for different echo contrast agents. However, bubble destruction and the onset of tissue harmonic signals focus the use of real-time perfusion imaging to very low emission power. (E-mail: [email protected])

Ex vivo 31P magnetic resonance spectroscopy (MRS) of heart grafts provides metabolic markers of early dysfunction in operating room

SPECT within 48 h of a routine heart catheterization. Segmental perfusion (18 segment model, visual grading) with MCE were assessed in real time before and at peak stress using power pulse inversion technique with low mechanical index (0.12) after continuous infusion of SonoVue (Bracco-Byk Gulden, Konstanz, Germany). Data were compared to sestamibi SPECT perfusion imaging and angiography/IVUS as “goldstandard”. Results: Perfusion by MCE predicted significant CAV defined by heart catheterization with a sensitivity of 86%, specificity of 89%, positive (PPV) and negative predictive value (NPV) of 75% and 94%, respectively. Sestamibi SPECT revealed a comparable diagnostic value (sensitivity 86%, specificity 94%, PPV 86%, NPV 94%). Comparison between both perfusion techniques showed a sensitivity of 71%, specificity 83%, PPV 62%, NPV 88%. Conclusion: Real time MCE using power pulse inversion technique correlates well with angiographic/IVUS and SPECT results and is a promising addition to conventional stress echocardiography/-SPECT for the noninvasive detection of significant CAV which might allow a reduction of the routine catheterization surveillance.

Assessment of angiogenesis: implications for ultrasound imaging

In this paper, the fundamentals of tumor angiogenesis and the implications for ultrasound imaging will be described. Twenty-eight athymic nude mice were implanted with the human melanoma cell lines DB-1 or MW-9 (14 mice/group). Ultrasound contrast agents were injected in the tail veins. Power Doppler and pulse inversion harmonic imaging (PI-HI) was performed (in real time and intermittently). Ultrasound results were compared to immunohistochemical stains for endothelial cells (CD31), vascular endothelial growth factor (VEGF), and cyclooxygenase-2 (COX-2). Linear regression analysis indicated statistically significant correlations between percent area stained with COX-2 and with VEGF relative to power Doppler ( p<0.05) and intermittent PI-HI ( p<0.05) measures of tumor neovascularity in the MW-9 and the DB-1 mice, respectively. Preliminary results from a human trial of the anti-angiogenic drug Angiostatin (Entremed, Rockville, MD) showed tumor volumes increased in two patients, while the vascularity remained virtually unchanged. Conversely, in three patients with diminished tumor volumes vascularity increased by 38%. In conclusion, contrast enhanced ultrasound imaging of tumor neovascularity may provide noninvasive markers of angiogenesis and may become a useful tool for monitoring anti-angiogenic therapies in vivo.

Real-time perfusion imaging: a new echocardiographic technique for simultaneous evaluation of myocardial perfusion and contraction.

Myocardial contrast echocardiography (MCE) with high acoustic energy and triggered harmonic imaging is the best established ultrasound technique to date for the assessment of myocardial perfusion. With this technique, however, the ultimate goal of MCE (noninvasive real-time simultaneous assessment of myocardial perfusion and function after an intravenous injection of microbubbles) is not met. Recently, technologic advances have enabled myocardial opacification to be visualized during low-energy real-time imaging. During real-time perfusion imaging, wall motion and myocardial perfusion may be assessed simultaneously, obviating the need of the presently time-consuming combination of different imaging modalities. When high-energy ultrasound bursts are periodically transmitted to produce bubble destruction during low-power imaging, the consecutive frames after destruction delineate the restoration of contrast intensity. Microbubble replenishment rate and peak intensity may be determined subsequently, and provide reliable quantitative parameters of regional microcirculatory flow. This review will introduce the modalities used for real-time perfusion imaging with focus on power pulse inversion imaging and quantitative analysis. Furthermore, we will describe the clinical role the technique may have in the identification of coronary artery disease, quantification of coronary stenosis severity, assessment of myocardial viability, determination of infarction size, and evaluation of reflow and no- or low-reflow after acute myocardial infarction.

Ultrasound contrast imaging research.

This article is a review of the research on ultrasound contrast agents in general imaging. While general imaging contrast agent applications are still undergoing investigation and waiting FDA approval in the United States, they are approved for clinical use in Europe and other countries. The contrast microbubble properties are described, including their nonlinear behavior and destruction properties. Imaging techniques like harmonic imaging, pulse inversion, power pulse inversion, agent detection imaging, microvascular imaging, and flash contrast imaging are explained. A connection is made between the aforementioned imaging techniques and the different contrast agents available. The blood flow appearance of different liver tumors in the presence of contrast agents is demonstrated with examples.

On the design of a capillary flow phantom for the evaluation of ultrasound contrast agents at very low flow velocities

Recently, a new imaging technology has become available that allows the evaluation of tissue perfusion using echo-contrast agents in real-time imaging: power pulse inversion imaging (PPI). Although numerous in vitro phantoms have been designed for different imaging modalities in ultrasound (US), there is a need for a phantom that mimics microcirculation and allows, in particular, the assessment of contrast replenishment kinetics following US-induced destruction of microbubbles using the new method. We, therefore, designed a new capillary flow phantom that takes the requirements of the new US imaging techniques and the physical properties of microbubbles into account and serves flow velocities in the range of microcirculation (1 to 10 mm/s). PPI studies were performed in the newly designed phantom. The contrast agent used was AF0150. We studied homogeneity of contrast distribution within the capillary phantom, constancy of contrast infusion, the dose-effect relationship and, finally, the feasibility of flow assessment using the method of contrast replenishment following US-induced microbubble destruction in a flow velocity range of 2.1 to 9.45 mm/s. Analysis of the replenishment kinetics was performed using the mathematical model f(t) = A(1 − e−βt), with A representing the blood volume and β the microbubble velocity. The new capillary phantom allowed homogeneous contrast opacification within the perfused capillaries independently of the flow. Constancy of signal intensity was achieved over a time period of almost 2 h, indicating constant contrast delivery. A strong linear correlation between the PPI signal and the contrast dose was found (r = 0.998). Analysis of the replenishment parameters revealed a strong linear relationship between parameter β and flow (r = 0.994) as well as A∗β and flow (r = 0.984) in the observed flow range. The newly designed perfusion phantom for the evaluation of echo-contrast replenishment kinetics fulfills, at very low flow velocities, important prerequisites such as constancy of contrast delivery, homogeneity of contrast signals, linear dose-effect relation and minimal attenuation. Thus, the new phantom allows standardized analysis of contrast replenishment kinetics using real-time perfusion imaging techniques at flow velocities comparable to those of the microcirculation. (E-mail: k-tiemann@uni-bonn.de)

Hyperglycemia worsens myocardial microcirculation reperfusion: validation by power pulse inversion imaging and neutron activated microspheres

Hyperglycemia worsens myocardial microcirculation reperfusion: validation by power pulse inversion imaging and neutron activated microspheres

Bubbles in echocardiography: climbing the learning curve

The past few years have seen the rapid development of novel imaging modes tuned to the specific detection of microbubbles; these include harmonic 13-mode, phase or pulse inversion, power modulation, coherent contrast imaging, and recently power pulse inversion. These contrast-specific imaging modes, combined with insonation at low incident pressure, result in greatly enhanced contrast between the vessels that contain the ultrasound contrast agent and the surrounding tissues, rendering perfusion defects highly visible. SonoVue (Bracco, Milan, Italy) is a new echocontrast agent with outstanding stability. Thanks to their very flexible shell, the SonoVue microbubbles are able to generate strong harmonics even when insonated at extremely low mechanical index (MI). The present review illustrates the different modalities of contrast bubble insonation (at high and low MI), which allow visualization of fixed defects and ischaemic or infarcted areas of the myocardium in real-time.

Ultrasound Imaging with SonoVue: Low Mechanical Index Real-Time Imaging

Ultrasound contrast specific imaging was improved in the last years by the introduction of a wealth of novel techniques, exploiting the nonlinear response of microbubble contrast agents. This included a number of techniques based on transmission of alternately phased positive and negative pulses ( 1 Bauer A Hauff P Lazenby J et al. Wideband harmonic imaging: a novel contrast ultrasound imaging technique. Eur Radiol. 1999; 9: S364-S367 Crossref PubMed Google Scholar , 3 Burns PN Wilson SR Simpson DH Pulse inversion imaging of liver blood flow: improved method for characterizing focal masses with microbubble contrast. Invest Radiol. 2000; 35: 58-71 Crossref PubMed Scopus (326) Google Scholar ) (Phase Inversion, Pulse Inversion, Power Pulse Inversion, Wideband harmonic, Coherent Contrast Imaging) as well as techniques based on alternating transmit power (Power Modulation, B Flow) and using higher harmonics ( 2 Bouakaz A Frigstad S Ten Cate FJ de Jong N Super harmonic imaging: a new imaging technique for improved contrast detection. Ultrasound Med Biol. 2002; 28: 59-68 Abstract Full Text Full Text PDF PubMed Scopus (192) Google Scholar ) (Ultraharmonic Imaging). Other techniques are based on the destruction of microbubbles (Agent Destruction Imaging) or can be used to image microbubbles in this way (power/Color Doppler -Loss of correlation) ( 6 Schlachetzki F Hoelscher T Dorenbeck U et al. Sonographic parenchymal and brain perfusion imaging: preliminary results in four patients following decompressive surgery for malignant middle cerebral artery infarct. Ultrasound Med Biol. 2001; 27: 21-31 Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar ) and therefore are limited to a relatively high mechanical index. The destructive techniques are further limited to low framerate or triggered imaging ( 5 Masugata H Lafitte S Peters B Strachan GM DeMaria AN Comparison of real-time and intermittent triggered myocardial contrast echocardiography for quantification of coronary stenosis severity and transmural perfusion gradient. Circulation. 2001; 104: 1550-1556 Crossref PubMed Scopus (63) Google Scholar ), thereby losing one of the key advantages of ultrasound: its realtime capability.

Bubbles and microcirculatory disorders.

Doppler methods are in daily clinical use for the assessment of blood flow in various vessels. With the adjunct of an ultrasound (US) contrast agent, weaker signals, for instance in smaller vessels, can be detected. However, even in the presence of an US contrast agent, colour, spectral or even power Doppler can only detect blood flow in vessels exceeding 200‐300 µm. The microvasculature is not detectable because the flow velocity in capillaries, at approximately 1 mm/s, is actually lower than the tissue motion velocity and is therefore filtered out by the equipment. It was recently demonstrated that using US contrast agents, together with novel bubble-specific imaging modes, allows the blood flow detection threshold to be lowered and the presence of microbubbles even in very small vessels to be detected. Detection of flow in such smaller vessels increases considerably the clinical utility of US, in particular for the detection of reductions in vascularity, for instance in ischaemic or infarcted tissues, or increases in vascularity, for instance in tumor angiogenesis. These bubble-specific methods, which have emerged from extensive research carried out on US contrast agents during the last decade, make use of the nonlinear properties of bubbles. Harmonic B-mode, harmonic power Doppler, phase or pulse inversion, power pulse inversion, coherent contrast imaging, and power modulation are some of the most popular of these novel imaging methods. By detecting specifically bubble signals and reducing the background signals from the surrounding structures, these methods dramatically enhance the image contrast-to-tissue ratio. Studies making use of contrast agents in combination with harmonic power Doppler have shown that vessels of approximately 40 µm in diameter can be detected in the kidney [1]. Pulse inversion imaging provides an even better resolution than harmonic imaging. Moreover, it allows the use of low-power pulses, thus preventing bubble destruction. In the following article, the new opportunities offered by the combination of new US contrast agents and novel imaging modes will be illustrated by a number of studies carried out with SonoVue, a novel ultrasound contrast medium constituted by phospholipid-stabilized microbubbles of sulfur hexafluoride (SF6) [2].

The impact of emission power on the destruction of echo contrast agents and on the origin of tissue harmonic signals using power pulse-inversion imaging

The purpose of this study was to determine the impact of emission power on ultrasound (US)-induced destruction of echocontrast microbubbles during real-time power pulse inversion imaging (PPI) in myocardial contrast echocardiography (MCE) and to evaluate the magnitude of noncontrast PPI signals arising from myocardial tissue at variable emission power to define the cut-off emission power for optimal MCE using low power technologies. In vitro studies were performed in a flow phantom using Optison®, Definity™ and AFO 150. PPI signal intensity during real-time imaging at 27 Hz was compared with intermittent imaging at 0.1 Hz to evaluate bubble destruction at variable emission power (MI: 0.09 to 1.3). In healthy volunteers, PPI signal intensities during constant infusion of Optison® was studied in real-time PPI 22 HZ and during intermittent imaging triggered end-systolic frames every, every 3rd and every 5th cardiac cycle. In addition, the impact of emission power on nonlinear PPI signals from myocardial structures was studied. In vitro, there was a 40% decrease of real-time PPI signal intensity for Optison® and AFO 150 at lowest emission power (0.09), whereas no signal loss was observed for Definity™. Increase of emission power resulted in a faster decay for Optison® and AFO 150 as compared to Definity™. In vivo, real-time PPI during continuous infusion of Optison® resulted in a 40% decrease of myocardial signal intensity as compared to intermittent imaging every 5th cardiac cycle, even at lowest possible emission power (mechanical index = 0.09). There was a strong positive relationship between MI and noncontrast myocardial PPI signals in all myocardial segments. PPI signal intensity was found to be lower than 1 dB only for extremely low emission power (MI < 0.2). Destruction of microbubbles during real-time imaging by use of PPI at low emission power varies considerably for different echo contrast agents. However, bubble destruction and the onset of tissue harmonic signals focus the use of real-time perfusion imaging to very low emission power. (E-mail: k-tiemann@uni-bonn.de)

Feasibility of the flash-replenishment concept in renal tissue: which parameters affect the assessment of the contrast replenishment?

The purpose of the study was to evaluate whether power pulse inversion (PPI) and pulse inversion (PI) techniques allow the measurement of indices of microcirculatory flow in real-time at low emission power using contrast microbubbles. PPI and PI imaging were performed in a kidney perfusion model during continuous infusion of Definity™ (0.12 mL/min). At steady state of tissue enhancement, contrast was destroyed by emission of echo bursts at high emission power (MI = 1.3). Consecutively, contrast replenishment was assessed at low emission power (MI = 0.09) in real-time imaging modes (PPI: 12 Hz; PI: 25 Hz). Regions-of-interest (ROI) of variable sizes were placed in the renal cortex and bigger arteries to compare replenishment of macro- and microcirculation. Nonlinear curve fitting was performed using the mathematical model y= s+ A(1− e − βt ), with A as the parameter describing blood volume and β as a parameter describing the speed of microbubble contrast replenishment. Replenishment curves could be visually appreciated and quantitatively analyzed in all renal segments. A was significantly higher in bigger arteries compared to renal cortex ( p < 0.001). β was found to be significantly higher in the arteries as compared to the cortex ( p < 0.001). The SD of β diminishes with increasing size of the ROI. The acquisition of replenishment curves following ultrasound (US)-induced destruction of contrast microbubbles is feasible at low power using PPI and PI. Assessment of replenishment kinetics allows the differentiation between macro- and microcirculation. Size and position of the ROI have an important impact on the generation of replenishment curves in both imaging modalities, which has to be taken into account. (E-mail:k-tiemann@Uni-Bonn.de)