Pitfalls in quantitative contrast echocardiography: the steps to quantitation of perfusion

The diagnostic accuracy of contrast echocardiography in patients with suspected cardiac masses: A preliminary multicenter, cross-sectional study

Background

To evaluate the diagnostic accuracy of contrast echocardiography (CE) in patients with suspected cardiac masses.

Methods

A multicenter, prospective study involving 108 consecutive patients with suspected cardiac masses based on transthoracic echocardiography performed between November 2019 and December 2020 was carried out. CE examinations were performed in all patients. The echocardiographic diagnosis was established according to the qualitative (echogenicity, boundary, morphology of the base, mass perfusion, pericardial effusion, and motility) and quantitative (area of the masses and peak intensity ratio of the masses and adjacent myocardium A1/A2) evaluations.

Results

Final confirmed diagnoses were as follows: no cardiac mass (n = 3), pseudomass (n = 3), thrombus (n = 36), benign tumor (n = 30), and malignant tumor (n = 36). ROC analysis revealed the optimal A1/A2 with cutoff value of 0.295 for a cardiac tumor from a thrombus, with AUC, sensitivity, specificity, PPV, and NPV of 0.958 (95% confidence interval (CI): 0.899–0.988), 100, 91.7, 95.7, and 100%, respectively. CE was able to distinguish malignant from benign tumors with an AUC of 0.953 (95% CI: 0.870–0.990). Multivariate logistic regression analysis revealed that tumor area, base, and A1/A2 were associated with the risk of malignant tumor (OR = 1.003, 95% CI: 1.00003–1.005; OR = 22.64, 95% CI: 1.30–395.21; OR = 165.39, 95% CI: 4.68–5,850.94, respectively). When using A1/A2 > 1.28 as the only diagnostic criterion to identify the malignant tumor, AUC, sensitivity, specificity, PPV, and NPV were 0.886 (95% CI: 0.784–0.951), 80.6, 96.7, 96.7, and 80.7%, respectively.

Conclusion

CE has the potential to accurately differentiate cardiac masses by combining qualitative and quantitative analyses. However, more studies with a large sample size should be conducted to further confirm these findings.

Clinical trial registration

http://www.chictr.org.cn/, identifier: ChiCTR1900026809.

Response of contrast agents to ultrasound

Microbubbles are used as ultrasonic contrast agents that enhance the ultrasound signals of the vascular bed. The recent development of site-targeted microbubbles opened up the possibility for molecular imaging as well as localised drug and gene delivery. Initially the microbubbles' physical properties and their response to the ultrasound beam were not fully understood. However, the introduction of fast acquisition microscopy has allowed the observation of the microbubble behaviour in the presence of ultrasound. In addition, acoustical techniques can determine the scatter of single microbubbles. Sonoporation experiments promise high-specificity drug and gene delivery, but the responsible physical mechanisms, particularly for in vivo applications, are not fully understood. An improvement of microbubble technology may address variability related problems in both imaging and drug/gene delivery.

Value of vasodilator stress myocardial contrast echocardiography and magnetic resonance imaging for the differential diagnosis of ischemic versus nonischemic cardiomyopathy

OBJECTIVE

Noninvasive differentiation of ischemic versus nonischemic cardiomyopathy (CM) remains challenging because of the low specificity of imaging-based tests in these patients. We hypothesized that myocardial contrast echocardiography (MCE) and cardiac magnetic resonance (CMR), combined with vasodilator stress, could provide accurate alternatives for determining the cause of CM.

METHODS

To allow side-by-side comparisons between these techniques with coronary angiography as a reference, we studied 16 patients referred for coronary angiography after abnormal nuclear perfusion studies. Both MCE and CMR images were acquired within 48 hours with infusion of adenosine. MCE included flash-echo imaging during intravenous infusion of echocardiographic contrast solution. CMR included gadolinium injections for first-pass perfusion and delayed enhancement imaging. MCE and CMR images were reviewed by experienced investigators, blinded to the findings of the other modality and angiography. For each technique, each myocardial segment was classified as normal or abnormal. Sensitivity and specificity of each technique were calculated against the angiography reference. These calculations were also performed using a perfusion territory as a unit of analysis.

RESULTS

Six of 16 patients had normal coronary arteries, and three patients had stenosis < 50%. By using this threshold for abnormal perfusion, segment-by-segment comparisons with angiography resulted in sensitivity of 0.88, 0.61, and 0.71 and specificity of 0.74, 0.86, and 0.94 for CMR perfusion, delayed enhancement scans, and MCE sequences, respectively. Using stenosis > 70% as a threshold resulted in a small decrease in both sensitivity and specificity (0.02-0.04) for all three techniques. Analysis of the ability of these techniques to detect an abnormality in at least one perfusion territory yielded sensitivity of 1.00, 1.00, and 0.86 and specificity of 0.78, 0.78, and 0.89, correspondingly, which were threshold-independent.

CONCLUSIONS

Both CMR and MCE perfusion imaging may be used to differentiate between ischemic and nonischemic CM. These emerging diagnostic tools may prove useful in strategizing treatment in these patients and thus avoiding unnecessary invasive procedures.

Three-Dimensional Echocardiographic Evaluation of Myocardial Perfusion

One of the most intriguing developments in ultrasound imaging of the heart was the use of contrast media to assess myocardial perfusion, which sparked tremendous interest and over the years generated a significant body of research. Although most published work has been based on the use of contrast for 2D perfusion imaging, there are a few recent studies aimed at exploring the idea of 3D assessment of myocardial perfusion, which has the potential to overcome many of the limitations of the 2D methodology. We provide a brief overview of the 2D work that provided the scientific basis for the emerging 3D methodology and discuss the unique features and promises as well as the challenges posed by this novel approach.

Clinical utility of contrast-enhanced echocardiography

Over the past three decades, echocardiography has become a major diagnostic tool in the arsenal of clinical cardiology for real-time imaging of cardiac dynamics. More and more, cardiologists' decisions are based on images created from ultrasound wave reflections. From the time ultrasound imaging technology provided the first insight into a human heart, our diagnostic capabilities have increased exponentially as a result of our growing knowledge and developing technologies. One of the most intriguing developments that brought about a decade-long combination of expectations and disappointments was the introduction of echocardiographic contrast agents. Despite repeated waves of controversy regarding the readiness of this technology for clinical use, it has overcome multiple hurdles and currently provides useful clinical information that helps cardiologists to diagnose heart disease accurately. Since the initial reports on the use of ultrasound contrast media such as agitated saline or renografin, the major advances in the field of contrast echocardiography have included (1) the development of stable perfluorocarbon-filled microbubbles, frequently referred to as second-generation contrast agents; and (2) the development of contrast-targeted nonlinear imaging modes, such as harmonic imaging, pulse inversion, and power modulation, which allow consistent real-time visualization of these agents. These contrast agents in conjunction with the new imaging technology constitute powerful tools that improve our ability to evaluate left ventricular function and myocardial perfusion, and allow differential diagnosis of thrombi and intravascular masses. In this manuscript, we briefly review some of the literature that has provided the scientific basis for the use of echocardiographic contrast agents in the context of these important variables.

Interrupted Infusion of Echocardiographic Contrast as a Basis for Accurate Measurement of Myocardial Perfusion: Ex Vivo Validation and Analysis Procedures

BACKGROUND

Echocardiographic quantification of myocardial perfusion is based on analysis of contrast replenishment after destructive high-energy ultrasound impulses (flash-echo). This technique is limited by nonuniform microbubble destruction and the dependency on exponential fitting of a small number of noisy time points. We hypothesized that brief interruptions of contrast infusion (ICI) would result in uniform contrast clearance followed by slow replenishment and, thus, would allow analysis from multiple data points without exponential fitting.

METHODS

Electrocardiographic-triggered images were acquired in 14 isolated rabbit hearts (Langendorff) at 3 levels of coronary flow (baseline, 50%, and 15%) during contrast infusion (Definity) with flash-echo and with a 20-second infusion interruption. Myocardial videointensity was measured over time from flash-echo sequences, from which characteristic constant beta was calculated using an exponential fit. Peak contrast inflow rate was calculated from ICI data using analysis of local time derivatives. Computer simulations were used to investigate the effects of noise on the accuracy of peak contrast inflow rate and beta calculations.

RESULTS

ICI resulted in uniform contrast clearance and baseline replenishment times of 15 to 25 cardiac cycles. Calculated peak contrast inflow rate followed the changes in coronary flow in all hearts at both levels of reduced flow (P < .05) and had a low intermeasurement variability of 7 +/- 6%. With flash-echo, contrast clearance was less uniform and baseline replenishment times were only 4 to 6 cardiac cycles. beta Decreased significantly only at 15% flow, and had intermeasurement variability of 42 +/- 33%. Computer simulations showed that measurement errors in both perfusion indices increased with noise, but beta had larger errors at higher rates of contrast inflow.

CONCLUSION

ICI provides the basis for accurate and reproducible quantification of myocardial perfusion using fast and robust numeric analysis, and may constitute an alternative to the currently used techniques.

The powerful microbubble: from bench to bedside, from intravascular indicator to therapeutic delivery system, and beyond

This review discusses the development, current applications, and therapeutic potential of ultrasound contrast agents. Microbubbles containing gases act as true, intravascular indicators, permitting a noninvasive, quantitative analysis of the spatial and temporal heterogeneity of blood flow and volumes within the microvasculature. These shelled microbubbles are near-perfect reflectors of acoustic ultrasound energy and, when injected intravenously into the bloodstream, reflect ultrasound waves within the capillaries without disrupting the local environment. Accordingly, microbubble ultrasound contrast agents are clinically useful in enhancing ultrasound images and improving the accuracy of diagnoses. More recently, ultrasound contrast agents have been used to directly visualize the vasa vasorum and neovascularization of atherosclerotic carotid artery plaques, thus suggesting a new paradigm for diagnosis and treatment of atherosclerosis. Future applications of these microscopic agents include the deliver of site-specific therapy to targeted organs in the body. Medical therapies may use these microbubbles as carriers for newer therapeutic options.

Differential diagnosis of cardiac masses using contrast echocardiographic perfusion imaging

OBJECTIVES

We investigated the usefulness of echocardiographic contrast perfusion imaging in differentiating cardiac masses.

BACKGROUND

Two-dimensional echocardiography is the primary diagnostic modality for cardiac masses. However, differentiation between the different types of cardiac masses may be difficult at times. We hypothesized that echocardiographic contrast perfusion imaging would differentiate the neo-vascularization of malignancies from the avascularity of thrombi and the sparse vascularity of stromal tumors.

METHODS

Sixteen patients with cardiac masses underwent power-modulation imaging after echocardiographic intravenous contrast administration. Pixel intensities in the mass and an adjacent section of myocardium were analyzed visually and by dedicated software. All masses had a pathologic diagnosis or resolved after anticoagulation. In a subset of patients, video-intensity curves of contrast replenishment in the mass and myocardium over time were generated. The post-impulse steady-state pixel intensity (A) and initial rate of contrast replenishment after impulse (beta) were compared with an index of blood vessel area on pathology.

RESULTS

In seven of 16 patients, contrast enhancement resulted in greater pixel intensity in the mass than in the adjacent myocardium. All of these masses were classified pathologically as malignant (n = 6) or benign and vascular (n = 1). Nine masses demonstrated decreased pixel intensity, compared with the myocardium, and were diagnosed pathologically as myxomas (n = 2) or thrombi (n = 5), or they resolved with anticoagulation (n = 2). For the subset of patients, beta correlated with the vessel area index (r = 0.60).

CONCLUSIONS

Echocardiographic contrast perfusion imaging aids in the differentiation of cardiac masses. Compared with the adjacent myocardium, malignant and vascular tumors hyper-enhanced, whereas stromal tumors and thrombi hypo-enhanced.

Harmonic imaging for endocardial visualization and myocardial contrast echocardiography during transesophageal echocardiography

BACKGROUND

Although harmonic imaging (HI) improves endocardial visualization and is necessary for myocardial perfusion imaging, it has yet to be implemented in transesophageal echocardiography. Our goal was to determine whether HI implemented in a prototype transesophageal echocardiography probe improved endocardial visualization and allowed perfusion imaging.

METHODS

In 23 patients, fundamental and harmonic images were obtained in the transgastric short-axis (TSAX) and midesophageal 4-chamber views, and reviewed for endocardial visualization by 3 readers blinded to imaging mode. In 14 additional patients, perfusion imaging was performed in the TSAX view during contrast infusion.

RESULTS

HI improved overall endocardial visualization, most noticeably in the anterior and lateral segments (P <.004) in the TSAX view, and in the lateral segments (P <.01) in the midesophageal 4-chamber view. The salvage rate was 8.3% in the TSAX view and 12.6% in the midesophageal 4-chamber view. Myocardial perfusion was consistently confirmed in the inferior (86%), posterior (100%), and lateral (79%) segments, but rarely in the septal (21%), anteroseptal (0%), and anterior (14%) segments.

CONCLUSION

Use of HI with transesophageal echocardiography improves endorcardial visualization and allows partial assessment of myocardial perfusion.

Simultaneous real-time echocardiographic imaging of myocardial perfusion and regional function using color-encoded, contrast-enhanced power modulation

We hypothesized that color-encoded, contrast-enhanced, power modulation imaging could allow simultaneous quantification of myocardial perfusion and regional left ventricular function. We studied 12 anesthetized, closed-chest pigs at baseline, during acute ischemia, and during reperfusion, and 8 patients after acute myocardial infarction. Color kinesis was used to color encode endocardial motion during real-time contrast perfusion imaging with high-energy ultrasound pulses. Wall motion was assessed by calculating regional fractional area changes. Translation-free perfusion analysis was performed in automatically identified myocardial regions of interest. Steady-state intensity and postimpulse rate of contrast replenishment were calculated. In all animals, ischemia caused reversible changes in the images and the perfusion- and function-calculated indices. A significant decrease in pixel intensity (14%) and contrast replenishment rate (66%) in left anterior descending coronary artery segments, in agreement with fluorescent microspheres measurements, coincided with a decrease in fractional area change (34%). For patients, respective perfusion and function indices were 61%, 51%, and 58% lower in segments where perfusion defects, regional wall-motion abnormalities, or both were noted in gray scale images. Color-encoded, contrast-enhanced power modulation allows simultaneous real-time imaging and quantitative analysis of myocardial perfusion and regional left ventricular function.

Quantification of regional myocardial perfusion using semiautomated translation-free analysis of contrast-enhanced power modulation images

Quantitative analysis of myocardial perfusion is currently based on manual tracing and frame-by-frame realignment of regions of interest. We developed a technique for semiautomated identification of myocardial regions from power modulation images as a potential tool for quantification of myocardial contrast enhancement. This approach was tested in 13 anesthetized pigs during continuous intravenous infusion of contrast at baseline, left anterior descending coronary artery occlusion, and reperfusion. Regional pixel intensity was calculated for each consecutive end-systolic frame after a high-energy ultrasound impulse, and fitted with an exponential function. Perfusion defects caused by occlusion of left anterior descending coronary artery were confirmed by a significant decrease in both postimpulse steady-state intensity and the initial rate of contrast replenishment (P <.05), which were reversed with reperfusion. Automated measurements of myocardial intensity correlated highly with conventional manual tracing (r = 0.90 to 0.97), and resulted in improved signal-to-noise ratios. This technique allows translation-free quantification of regional myocardial perfusion, without the need for manual tracing.

Contrast-enhanced Doppler perfusion index: clinical and experimental evaluation

OBJECTIVE

To assess the potential of the power Doppler signal intensity rate of enhancement due to contrast agent wash-in for assessment of hepatic hemodynamics.

METHODS

With the use of standardized settings, power Doppler sonography was performed before and after administration of a contrast agent. Video-recorded examinations were digitized for offline analysis on a personal computer. The temporal changes of the power Doppler signal intensity were quantified to provide contrast agent wash-in curves. The contrast-enhanced Doppler perfusion index was defined by the ratio of the wash-in gradient of the hepatic artery and portal vein as contrast-enhanced Doppler perfusion index = hepatic artery gradient/(hepatic artery gradient + portal vein gradient). The contrast-enhanced Doppler perfusion index was evaluated at 4 contrast agent doses in each of 14 patients with liver metastases and 3 patients with hemangiomas. An in vitro flow model was used to determine the relationships between the power Doppler rate of enhancement and flow in vessels of 4, 8, and 12 mm in diameter.

RESULTS

In vivo, there was a significantly higher (P < .0001) mean contrast enhanced Doppler perfusion index in patients with liver metastases (mean, 0.59; 95% confidence interval, 0.54-0.63), compared with patients with hemangiomas (mean, 0.33; 95% confidence interval, 0.24-0.41). The corresponding coefficients of variations were 25% for patients with liver metastases and 31% for patients with hemangiomas. In vitro, the power Doppler rate of enhancement was proportional to flow speed and independent of vessel diameter.

CONCLUSIONS

Measurement of the contrast-enhanced Doppler perfusion index may have potential in assessment of hepatic hemodynamics and focal liver disease.

Comparison between echo contrast agent-specific imaging modes and perfusion-weighted magnetic resonance imaging for the assessment of brain perfusion

BACKGROUND AND PURPOSE

Contrast burst imaging (CBI) and time variance imaging (TVI) are new ultrasonic imaging modes enabling the visualization of intravenously injected echo contrast agents in brain parenchyma. The aim of this study was to compare the quantitative ultrasonic data with corresponding perfusion-weighted MRI data (p-MRI) with respect to the assessment of brain perfusion.

METHODS

Twelve individuals with no vascular abnormalities were examined by CBI and TVI after an intravenous bolus injection of 4 g galactose-based microbubble suspension (Levovist) in a concentration of 400 mg/mL. Complementary, a dynamic susceptibility contrast MRI, ie, p-MRI, of each individual was obtained. In both ultrasound (US) methods and p-MRI, time-intensity curves were calculated offline, and absolute time to peak intensities (TPI), peak intensities (PI), and peak width (PW) of US investigations and TPI, relative cerebral blood flow (CBF) and relative cerebral blood volume (CBV) of p-MRI examinations were determined in the following regions of interest (ROIs): lentiform nucleus (LN), white matter (WM), posterior (PT), and anterior thalamus (AT). In addition, the M(2) segment of the middle cerebral artery (MCA) was evaluated in the US, and the precentral gyrus (PG) was examined in the p-MRI examinations. In relation to a reference parenchymal ROI (AT), relative TPIs were compared between the US and p-MRI methods and relative PI of US investigations with the ratio of CBF (rCBF) of p-MRI examinations in identical ROIs.

RESULTS

Mean TPIs varied from 18.3+/-5.0 (AT) to 20.1+/- 5.8 (WM) to 17.2+/-4.9 (MCA) seconds in CBI examinations and from 19.4+/-5.3 (AT) to 20.4+/-4.3 (WM) to 17.3+/-4.0 (MCA) seconds in TVI examinations. Mean PIs were found to vary from 581.9+/-342.4 (WM) to 1522.9+/-574.2 (LN) to 3400.9+/- 621.7 arbitrary units (MCA) in CBI mode and from 7.5+/-4.6 (WM) to 17.5+/-4.9 (LN) to 46.3+/-7.1 (MCA) arbitrary units in TVI mode. PW ranged from 7.3+/-4.5 (AT) to 9.1+/-4.0 (LN) to 24.3+/-12.8 (MCA) seconds in CBI examinations and from 7.1+/-3.9 (AT) to 8.7+/-3.5 (LN) to 26.7+/-18.2 (MCA) seconds in TVI examinations. Mean TPI was significantly shorter and mean PI and mean PW were significantly higher in the MCA compared with all other ROIs (P<0.05). Mean TPI of the p-MRI examinations ranged from 22.0+/-6.9 (LN) to 23.0+/-6.8 (WM) seconds; mean CBF ranged from 0.0093+/- 0.0041 (LN) to 0.0043+/-0.0021 (WM). There was no significant difference in rTPI in any ROI between US and p-MRI measurements (P>0.2), whereas relative PIs were significantly higher in areas with lower insonation depth such as the LN compared with rCBF.

CONCLUSIONS

In contrast to PI, TPI and rTPI in US techniques are robust parameters for the evaluation of cerebral perfusion and may help to differentiate physiological and pathological perfusion in different parenchymal regions of the brain.

Second harmonic imaging of the human brain: the practicability of coronal insonation planes and alternative perfusion parameters

BACKGROUND AND PURPOSE

Second harmonic imaging (SHI) is a novel ultrasound technique that allows the evaluation of brain tissue perfusion. The purpose of this study was to assess normal cerebral echo contrast characteristics in 3 regions of interest (ROIs) in the transverse axial and coronal insonation planes through the temporal bone window. Materials and Methods- SHI examinations were performed in 25 patients without cerebrovascular disease (aged 50+/-19 years) in a transverse axial and a coronal diencephalic insonation plane through the temporal bone window. After intravenous administration of 2.5 g (400 mg/mL) of a galactose-based echo contrast agent, 62 time-triggered images with a transmission rate of 1 frame per 2.5 seconds were recorded for offline analysis. Time-intensity curves, including peak intensity (PI) (dB) and positive gradient (PG) (dB/s), were calculated to quantify ultrasound intensity in 3 different ROIs in both planes of the following sections: the thalamus (ROI(thal)), the lentiform nucleus (ROI(ncl)), and the area supplied by the middle cerebral artery (ROI(mca)).

RESULTS

Characteristic time-intensity curves with high PIs and steep PGs were recorded in each ROI. Statistical analysis of the aforementioned parameters showed no significant difference for comparison of the 3 ROIs in the transverse axial versus the coronal insonation plane. Comparison of different ROIs in the transverse axial insonation plane revealed that PI was significantly higher in ROI(thal) than in ROI(mca) (7.8 versus 5.5 dB; P<0.05) and significantly higher in ROI(ncl) than in ROI(thal) (9.3 versus 7.8 dB; P<0.05). In contrast, PG was comparable in ROI(thal) and in ROI(mca) (0.21 versus 0.25 dB/s; P=0.42).

CONCLUSIONS

SHI is a promising technique for the evaluation of cerebral parenchymal perfusion. Comparison of the transverse axial and coronal insonation planes shows similar time-intensity curves with comparable values for PIs and PGs. Coronal insonation allows the evaluation of perfusion abnormalities near the vertex and skull base, areas that cannot be depicted in the transverse axial plane. Comparison of the different ROIs indicates that the PG is a more robust and reliable parameter than the PI.

Rapid quantitative assessment of myocardial perfusion: spectral analysis of myocardial contrast echocardiographic images

We described a novel rapid spectral analysis technique performed on raw digital in-phase quadrature (IQ) data that quantitatively differentiated perfused from nonperfused myocardium based on the simultaneous comparison of local fundamental and harmonic frequency band intensity levels. In open-chest pigs after ligation of the left anterior descending coronary artery (LAD) and continuous venous contrast infusion, the fundamental-to-harmonic intensity ratio (FHIR) for samples placed within the left ventricular (LV) cavity (10.8 +/- 1.7 dB) and perfused myocardium (13.7 +/- 1.6 dB) were significantly (P <.001) lower than for nonperfused myocardium (27.1 +/- 2.9 dB). In attenuated images, the FHIR for the LV cavity and perfused myocardium were also significantly (P <.05) lower than for the nonperfused myocardium (21.4 +/- 3.0 dB, 34.4 +/- 3.2 dB, and 40.2 +/- 4.4 dB, respectively). Spectral properties of contrast microbubbles, as characterized by the FHIR, allow for rapid quantitative assessment of myocardial perfusion from data contained in a single-image frame, without requiring background image subtraction and image averaging.

Influence of transducer frequency and imaging modality on the intraoperative assessment of myocardial perfusion with transesophageal echocardiography

OBJECTIVE

To determine factors that improve intraoperative myocardial perfusion assessment with conventional ultrasound imaging and intravenous ultrasound agents.

DESIGN

Prospective cohort study with repeated interventions on each patient.

SETTING

Single university hospital.

PARTICIPANTS

Fourteen patients scheduled for elective coronary artery bypass graft surgery.

INTERVENTIONS

Myocardial perfusion was evaluated with contrast transesophageal echocardiography during conventional imaging after central venous injections of the contrast agent Optison (0.3 mL) before cardiopulmonary bypass. Eight patients received the injection during continuous sampling at each of 4 transducer frequency settings (3.5, 5.0, 6.0, 7.0 MHz). In another 6 patients, injections were administered during continuous and intermittent sampling (electrocardiogram-gated) at 3.5 and 5.0 MHz. Generalized estimating equations were used to compare mean responses, with p < or = 0.05 considered significant.

MEASUREMENTS AND MAIN RESULTS

All recorded images were analyzed with off-line videodensitometry. Background-corrected peak pixel intensity (PPI(corr)) and rate of change in pixel intensity (PPI(corr)/T(PPI)) were determined for each injection. PPI(corr) was greater at 3.5 MHz than at 5.0, 6.0, and 7.0 MHz (p < 0.001). PPI(corr)/T(PPI) was greater at 3.5 MHz than at 5.0 (p < 0.001), 6.0 (p = 0.003), and 7.0 MHz (p < 0.001). PPI(corr) was greater for gated than for nongated sampling conditions at 3.5 (p < 0.05) and 5.0 MHz (p < 0.05).

CONCLUSION

To optimize myocardial contrast opacification, intraoperative transesophageal echocardiography should be performed with intermittent sampling at a transducer frequency close to the intrinsic frequency of the contrast agent.

Contrast agent stability: a continuous B-mode imaging approach

The stability of contrast agents in suspensions with various dissolved gas levels has not been reported in the literature. An in vitro investigation has been carried out that studied the combined effect of varying the acoustic pressure along with degassing the suspension environment. In this study, the contrast agents were introduced into suspensions with different oxygen concentration levels, and their relative performance was assessed in terms of decay rate of their backscatter echoes. The partial pressures of oxygen in those solutions ranged between 1.5 and 26 kPa. Two IV and one arterial contrast agents were used: Definity, Quantison, and Myomap. It was found that Quantison and Myomap released free bubbles at high acoustic pressure that also dissolved faster in degassed suspensions. The backscatter decay for Definity did not depend on the air content of the suspensions. The destruction of bubbles was dependent on acoustic pressure. Different backscatter performance was observed by different populations of bubbles of the last two agents. The physical quantity of "overall backscatter" (OB) was defined as the integral of the decay rate over time of the backscatter of the contrast suspensions, and improved significantly the understanding of the behaviour of the agents. A quantitative analysis of the backscatter properties of contrast agents using a continuous imaging approach was difficult to achieve. This is due to the fact that the backscatter in the field of view is representative of a bubble population affected by the ultrasound (US) field, but this bubble population is not representative of the contrast suspension in the whole tank. Single frame insonation is suggested to avoid the effects of decay due to the ultrasonic field, and to measure a tank-representative backscatter. The definition of OB was useful, however, in understanding the behaviour of the agents.

Combined assessment of myocardial perfusion and regional left ventricular function by analysis of contrast-enhanced power modulation images

BACKGROUND

Echocardiographic contrast media have been used to assess myocardial perfusion and to enhance endocardial definition for improved assessment of left ventricular (LV) function. These methodologies, however, have been qualitative or have required extensive offline image analysis. Power modulation is a recently developed imaging technique that provides selective enhancement of microbubble-generated reflections. Our goal was to test the feasibility of using power modulation for combined quantitative assessment of myocardial perfusion and regional LV function in an animal model of acute ischemia.

METHODS AND RESULTS

Coronary balloon occlusions were performed in 18 anesthetized pigs. Transthoracic power modulation images (Agilent 5500) were obtained during continuous intravenous infusion of the contrast agent Definity (DuPont) at baseline and during brief coronary occlusion and reperfusion and were analyzed with custom software. At each phase, myocardial perfusion was assessed by calculation, in 6 myocardial regions of interest, of mean pixel intensity and the rate of contrast replenishment after high-power ultrasound impulses. LV function was assessed by calculation of regional fractional area change from semiautomatically detected endocardial borders. All ischemic episodes caused detectable and reversible changes in perfusion and function. Perfusion defects, validated with fluorescent microspheres, were visualized in real time and confirmed by a significant decrease in pixel intensity in the left anterior descending coronary artery territory after balloon inflation and reduced rate of contrast replenishment. Fractional area change decreased significantly in ischemic segments and was restored with reperfusion.

CONCLUSIONS

Power modulation allows simultaneous online assessment of myocardial perfusion and regional LV wall motion, which may improve the echocardiographic diagnosis of myocardial ischemia.

Ultrasonic assessment of physiological echo-contrast agent distribution in brain parenchyma with transient response second harmonic imaging

OBJECTIVES

The present study was designed to provide normal data of transient response second harmonic imaging (TRSHI) examinations of cerebral echo contrast enhancement using different modes of electrocardiogram (ECG) gating and echo-contrast agent doses.

MATERIALS AND METHODS

Fifty-five patients were examined in an axial diencephalic plane of section using the transtemporal acoustic bone window. TRSHI examinations (ECG gating: systolic, frame-rate once every 2 cardiac cycles = "basical instrument setting") could be performed in 50 individuals with adequate insonation conditions after application of 4 g of a galactose-based microbubbles suspension in a concentration of 400 mg/ml. For comparison, diastolic ECG gating (20 patients), cardiac-cycle triggering frequency of once every 2 seconds (15 patients), or an echo contrast agent dose of 2 g Levovist (15 patients) were used. Analysis of peak intensities (PIs) and areas under the curve (AUCs) was done in posterior (region of interest [ROI]a) and anterior (ROIb) parts of the thalamus, in the lentiform nucleus (ROIc), and the white matter (ROId).

RESULTS

In 41 patients with basical instrument setting, characteristic time intensity curve (TIC) could be detected in all ROIs. In ROIa (90%) and ROIb (82%), focal contrast enhancement was most difficult to visualize, and in ROIc and ROId, characteristic TICs were observable in more than 90% of the examinations. Background subtracted PIs and AUCs were significantly higher in ROIc (mean PI: 12.2 +/- 8 acoustic units [AUs]; mean AUC: 598.8 +/- 451.1 AU x Cardiac cycles), and ROId (11.8 +/- 6.9; 559.2 +/- 404) as compared to ROIa (8.3 +/- 5.2; 368.9 +/- 242.7) and ROIb (7.1 +/- 4.7; 298.2 +/- 199.1) (P < .0001). Values for corresponding examinations with a diastolic ECG gating and a cardiac cycle triggering frequency of once every 2 seconds were not different as compared to the basical instrument setting. A 4 g Levovist dose increased the portion of typical TIC in all ROIs. PI of 4 g examinations were significantly higher in ROId and ROIb as compared to the 2 g examination.

CONCLUSION

Our findings indicate that TRSHI allows noninvasive assessment of focal cerebral contrast enhancement in the majority of patients with adequate insonation conditions. This study provides data about normal quantitative and qualitative TRSHI values in patients without cerebrovascular diseases. A dose of 4 g Levovist is recommended in those individuals with inaccurate echo contrast enhancement using the 2 g dose.

Contrast agent specific imaging modes for the ultrasonic assessment of parenchymal cerebral echo contrast enhancement

Previous work has demonstrated that cerebral echo contrast enhancement can be assessed by means of transcranial ultrasound using transient response second harmonic imaging (HI). The current study was designed to explore possible advantages of two new contrast agent specific imaging modes, contrast burst imaging (CBI) and time variance imaging (TVI), that are based on the detection of destruction or splitting of microbubbles caused by ultrasound in comparison with contrast harmonic imaging (CHI), which is a broadband phase-inversion-based implementation of HI. Nine healthy individuals with adequate acoustic temporal bone windows were included in the study. Contrast harmonic imaging, CBI, and TVI examinations were performed in an axial diencephalic plane of section after an intravenous bolus injection of 4 g galactose-based microbubble suspension in a concentration of 400 mg/mL. Using time-intensity curves, peak intensities and times-to peak-intensity (TPIs) were calculated off-line in anterior and posterior parts of the thalamus, in the region of the lentiform nucleus, and in the white matter. The potential of the different techniques to visualize cerebral contrast enhancement in different brain areas was compared. All techniques produced accurate cerebral contrast enhancement in the majority of investigated brain areas. Contrast harmonic imaging visualized signal increase in 28 of 36 regions of interest (ROIs). In comparison, TVI and CBI examinations were successful in 32 and 35 investigations, respectively. In CHI examinations, contrast enhancement was most difficult to visualize in posterior parts of the thalamus (6 of 9) and the lentiform nucleus (6 of 9). In TVI examinations, anterior parts of the thalamus showed signal increase in only 6 of 9 examinations. For all investigated imaging modes, PIs and TPIs in different ROIs did not differ significantly, except that TVI demonstrated significantly higher PIs in the lentiform nucleus as compared with the thalamus and the white matter (P < 0.05). The current study demonstrates for the first time that CBI and TVI represent new ultrasonic tools that allow noninvasive assessment of focal cerebral contrast enhancement and that CBI and TVI improve diagnostic sensitivity as compared with CHI.

Ultrasonic evaluation of pathological brain perfusion in acute stroke using second harmonic imaging

OBJECTIVE

To evaluate the use of transient response second harmonic imaging (HI) by means of ultrasound to assess abnormalities of cerebral echo contrast agent enhancement in patients with acute stroke.

METHODS

The study comprised 25 patients with acute onset of hemispheric stroke (<24 h) with sufficient insonation conditions and 14 control subjects without cerebrovascular disease. All stroke patients had HI, extracranial and transcranial colour coded duplex examinations of the arteries supplying the brain, and clinical examinations (European stroke scale) performed in the acute phase, on day 2, and within 1 week. Acute CT was repeated within 1 week and facultatively accompanied by angiography. Examinations using HI were performed in an axial diencephalic plane of section using the transtemporal acoustic bone window. After bolus application of galactose based microbubbles, 61 ultrasound images with a cardiac cycling triggering frequency of once every 2 seconds were recorded and evaluated off line. Focal perfusion deficit was identified if no contrast enhancement was visualised in a circumscribed region of interest and insufficient temporal bone window was excluded. In cases of reappearance of contrast enhancement reperfusion was assessed.

RESULTS

Adequate cerebral contrast enhancement could be seen in 21 subjects. In seven, a large hemispheric deficit of contrast enhancement affecting the entire middle cerebral artery (MCA) territory was detectable; the lentiform nucleus was affected in three subjects. Assessment of cerebral contrast abnormalities was possible in two patients with superficial MCA infarctions but in none of the patients with lacunar ischaemias. None of the control persons had focal deficits of cerebral echo contrast enhancement. In all patients with complete MCA infarction and striatocapsular infarction, presumed ischaemic areas in HI examinations correlated with final CT findings. Overall sensitivity and specifity of HI examinations for predicting size and localisation of the infarction were 75 and 100%, respectively. During follow up, reappearance of contrast enhancement was determined in three patients, in two patients circulatory arrest due to malignant brain oedema with missing contrast enhancement in the entire cerebral hemisphere could be seen. Extent of contrast enhancement deficits significantly correlated with the clinical status on admission and after 1 week (p<0.01).

CONCLUSIONS

Second harmonic imaging is the first ultrasonic technique that enables visualisation of pathological cerebral echo contrast enhancement. Because this method identifies deficits of focal contrast enhancement in patients with acute stroke and allows estimation of the final infarct size and clinical prognosis, it may help to select and monitor patients for invasive therapies.

An in vitro comparison of ultrasonic contrast agents in solutions with varying air levels

The performance, in particular, the stability of ultrasound (US) contrast agents has yet to be assessed. An in vitro system has been set up to investigate the properties of ultrasonic contrast agents under different suspension conditions. This is designed to contribute to the optimal use of agents in clinical practice. In this study, the contrast agents were introduced into solutions of different oxygen concentration levels, as might be encountered in blood, and their relative performance was assessed in terms of decay in the solution environment. The partial pressures of oxygen in those solutions ranged between 1.5 and 26 kPa. Three IV and one arterial contrast agents were used: Levovist, DMP115, Quantison and Myomap. Levovist showed the highest sensitivity to oxygen concentration in the solution, and the other three proved tolerant for the above values of oxygen concentrations.

Improved characterisation of focal liver tumours: dynamic power Doppler imaging using NC100100 echo-enhancer

OBJECTIVE

To assess the vascularisation of focal hepatic tumours using NC100100, enhanced power Doppler imaging.

METHODS

Twenty-two patients with focal liver tumours (12 metastases and ten hemangiomas) were studied. Using standardised settings, power Doppler imaging with ATL HDI3000 was performed before and after intravenous administration of NC100100 contrast agent. The video-recorded examinations were digitised for off-line analysis on a personal computer. Regions of interest were defined over the entire tumour and a neighbouring area of the normal liver parenchyma. The temporal changes of the mean power Doppler signal intensity (PDSI) was quantified to provide contrast agent wash-in (PDSI-time) curves for the initial 40 s.

RESULTS

Liver metastases were characterised by a rapid increase in PDSI, while the PDSI-time curves within hemangiomas were flat. The PDSI within the tumour increased significantly in ten subjects with liver metastases and only one subject with hemangioma. An enhanced rim around hemangiomas was seen in four subjects. There was no clear relationship between the contrast agent dose and the peak PDSI within metastases.

CONCLUSIONS

Power Doppler imaging with NC100100 contrast agent enhances tumour visualisation and may aid differential diagnosis of focal liver lesions.

Evaluation of an experimental system for the in vitro assessment of ultrasonic contrast agents

The ultrasonic properties of microbubble contrast agents need to be fully understood if reproducible images and quantitative results are to be produced. Additional aspects of the physical and chemical environment into which the contrast agents are introduced also need to be taken into account, and their effect on contrast agent performance evaluated. A setup that provides an accurate and reproducible data-acquisition system is presented and evaluated in this paper. The linear range of this system is assessed, as well as its accuracy and precision. A new approach to the investigation of contrast agents, based on normalised backscatter, is discussed. Also, a common technique of degassing, widely used in other areas, is described and evaluated to determine its appropriateness to contrast agent studies.

Differing susceptibility of echocardiographic contrast agents to adverse effects of biologic factors: multicenter, videodensitometric comparison of octafluoropropane-filled microspheres with air-filled microspheres for left ventricular opacification

BACKGROUND

Echocardiographic contrast enhancement of the left ventricle has diagnostic value in the assessment of regional and global left ventricular (LV) function. The efficacy of both octafluoropropane-filled human albumin microbubbles (OCTA) and of air-filled human albumin microbubbles (AIR) for LV endocardial delineation and qualitative LV opacification has previously been reported. However, pulmonary disease, obesity, impaired LV function, and decreased echogenicity may diminish the efficacy of contrast agents for LV opacification. The purpose of this study was to compare the susceptibility of 2 contrast agents currently approved by the Food and Drug Administration to these biologic factors.

METHODS

To compare quantitative LV opacification with OCTA (0.2, 0. 5, 3.0, 5.0 mL) versus AIR (0.08 mL/kg, 0.22 mL/kg), we performed videodensitometry in 199 patients (average age 59.2 +/- 13.3 years, 79% men) studied in 2 identical, prospective, multicenter, blinded trials, of whom 74 had impaired LV function, pulmonary disease, or both, 70 were obese (body mass index >30 kg/m(2)), and 45 were nonechogenic (>/=4 of 6 endocardial segments were not seen in the apical 4-chamber view). Changes in videodensity from noncontrast to contrast agent with the same gain settings were determined at end diastole and end systole (gray scale 0 to 255 U) for 2 regions of interest: left ventricle apex-to-mid-cavity and mid-cavity-to-base. The relative influence of clinically evident pulmonary disease, impaired LV function on echocardiography, and echogenicity on LV opacification produced by both contrast agents was determined by multivariate analysis.

RESULTS

Significant videodensity increases ranging from 67% to 143% were observed with both agents. At the recommended initial doses (0.5 mL for OCTA, 0.22 mL/kg for AIR), OCTA produced greater opacification than AIR in both regions of interest and at both phases of the cardiac cycle. Poor LV function was associated with decreased LV opacification for AIR but not for OCTA. Diminished echogenicity was more strongly associated with impaired opacification for AIR than for OCTA. Obesity and clinically evident pulmonary disease were associated with diminished chamber opacification with both OCTA and AIR.

CONCLUSIONS

In addition to the superiority of octafluoropropane-filled microspheres to air-filled microspheres for LV opacification, the efficacy of OCTA is relatively unaffected by impaired LV function and is less susceptible to the effects of poor echogenicity than AIR.

Second harmonic imaging In acute middle cerebral artery infarction. Preliminary results

BACKGROUND

Second harmonic imaging (SHI) is a new ultrasound technique that is able to detect microbubbles in the tissue vascular space. The aim of this pilot study was to prove that this technique may detect focal abnormalities of cerebral echo-contrast enhancement in acute hemispheric stroke.

CASE DESCRIPTIONS

Two male patients (aged 72 and 64 years) were included who presented with acute onset of severe hemiparesis and no established demarcation of the ischemic area in CT scans. After bolus application of galactose-based microbubbles, axial SHI examinations in a diencephalic plane of sections were performed using the transtemporal approach. Ultrasound investigations were recorded and evaluated offline. In both individuals demarcated focal abnormalities of cerebral contrast enhancement were detectable: in patient 1 the region of the lentiform nucleus and the adjacent parts of the temporoparietal lobe was affected, and in patient 2 a large region including the lentiform nucleus and cortical white matter was involved for at least 24 hours. Follow-up CT scans demonstrated a striatocapsular infarct in patient 1 and complete MCA infarction in patient 2, correlating with the presumed ischemic area in acute ultrasound examinations. The patient with complete MCA infarction showed missing contrast enhancement in the entire hemisphere of the affected side in follow-up SHI examinations. He died of malignant space-occupying brain edema. In the patient with the striatocapsular infarction, reappearance of echo-contrast enhancement in the ischemic area was assessable after 1 week.

CONCLUSIONS

SHI may identify focal abnormalities of cerebral echo-contrast enhancement in acute hemispheric stroke. Furthermore, this technique helps to determine size, localization, and prognosis of the ischemic region and could be useful for bedside assessment of echo-contrast agent distribution related to brain tissue perfusion.

Identifying the cause of left ventricular systolic dysfunction after coronary artery bypass surgery: the role of myocardial contrast echocardiography

OBJECTIVE

Intraoperative myocardial contrast echocardiography was used to determine whether the identification of regional myocardial flow patterns during revascularization could predict myocardial contractile function immediately after separation from cardiopulmonary bypass (CPB) and at 1 month after coronary artery bypass grafting (CABG) surgery.

DESIGN

A prospective, open-labeled, longitudinal analysis.

SETTING

Two independent university hospitals.

PARTICIPANTS

Twenty patients, during and up to 1 month after CABG.

INTERVENTIONS

The contrast agent Albunex (Mallenckrodt Medical, Inc, St Louis, MO) was injected into the aortic root during CPB.

MEASUREMENTS AND MAIN RESULTS

Myocardial contrast echocardiography opacification of flow was graded from intraoperative transesophageal echocardiographic images of the left ventricle in the short-axis, midpapillary view. The same myocardial images were also evaluated for regional wall motion abnormalities at 15, 30, and 60 minutes, 24 hours, 5 to 8 days, and 1 month after CPB. Logistic regression analysis was used to analyze the flow scores and regional function data from identical segments. Regional flow represented by contrast enhancement was assessed in 70% of the myocardial regions (55 of 80 possible segments; 95% confidence interval [CI], 61 to 76). Flow was more easily evaluated in the posterior region (95%) than in the anterior (70%) or septal regions (60%), and least likely evaluated in the lateral regions (50%). Regional wall motion was scored in 84% of the myocardial regions (469 of 560 possible regions). Function (segmental wall motion) was assessed in all regions with equal success. Segmental function and flow scores were matched to the same regions 66% of the time (53 of 80 possible series; 95% CI, 55 to 76). Regional myocardial contrast flow patterns did not predict myocardial function at 15, 30, or 60 minutes after separation from CPB. However, contrast opacification of flow did predict regional myocardial function at 1 week (p < or = 0.05) and at 1 month (p < or = 0.01) after CABG surgery. The probability that myocardial function would be normal at 1 month was 0.62 when intraoperative flow opacification was abnormal and 0.98 when flow opacification was normal. For patients with normal flow, the estimated odds of having normal myocardial function were 3.33 times those of patients with abnormal flow at 1 week (odds ratio, 3.33; 95% CI, 1.09 to 10.19) and 18.5 times those of patients with abnormal flow at 1 month (95% CI, 2.44 to 140.48).

CONCLUSION

Intraoperative application of myocardial contrast echocardiography to determine regional flow patterns after revascularization may help differentiate conditions of left ventricular systolic dysfunction immediately after separation from CPB for CABG surgery and appear to predict myocardial function at 1 month.

Evaluation of dynamic changes in microvascular flow during ischemia-reperfusion by myocardial contrast echocardiography

BACKGROUND

Dynamic changes of myocardial blood flow have been observed after reperfusion of an occluded coronary artery. MCE performed by intracoronary contrast injection can provide an estimate of microvascular flow. We hypothesized that MCE performed using intravenous infusion of a new generation contrast agent and electrocardiogram-gated harmonic imaging would be able to assess serial changes of microvascular perfusion.

OBJECTIVE

To study the potential of myocardial contrast echocardiography (MCE) to assess serial changes of microvascular flow during ischemia-reperfusion.

METHODS

Sixteen dogs underwent 90 or 180 min of left anterior descending coronary occlusion, followed by 180 min of reperfusion. Regional blood flow (RBF) was measured with fluorescent microspheres at baseline, during coronary occlusion, and at 5, 30, 90, and 180 min during reperfusion. At the same time points, MCE was performed with intravenous infusion of AF0150 (4 mg/min). Gated end-systolic images in short axis were acquired in harmonic mode and digitized on-line. Background-subtracted videointensity measured from MCE and RBF obtained from fluorescent microspheres were calculated for the risk area and for a control area, and were expressed as the ratio of the two areas.

RESULTS

After initial hyperemia, a progressive reduction in flow was observed during reperfusion. MCE correctly detected the time course of changes in flow during occlusion-reperfusion. Videointensity ratio significantly correlated with RBF data (r=0.79; p < 0.0001).

CONCLUSIONS

The progressive reduction in blood flow occurring within the postischemic microcirculation was accurately detected by MCE. This approach has potential application in the evaluation and management of postischemic reperfusion in humans.

Transient response harmonic imaging: an ultrasound technique related to brain perfusion

BACKGROUND AND PURPOSE

Gray-scale harmonic imaging is the first method to visualize blood perfusion and capillary blood flow with ultrasound after intravenous contrast agent application. The purpose of the present study was to evaluate the potential of transient response second harmonic imaging (TRsHI) to assess normal echo contrast characteristics in different brain areas by transcranial ultrasound.

METHODS

In 18 patients without cerebrovascular diseases, TRsHI examinations were performed bilaterally with the use of the transtemporal approach after application of 6.5 mL of a galactose-based microbubble suspension (400 mg/mL). The transmission rate was once every 4 cardiac cycles. Regional cerebral contrast was visually assessed and then quantified off-line with the use of time-intensity curves. In 4 different regions of interest (ROI) (posterior part of the thalamus [ROIa], anterior part of the thalamus [ROIb], lentiform nucleus [ROIc], and white matter [ROId]), the following parameters were evaluated: peak intensity, area under the curve (AUC), and time to peak intensity. AUC ratios for ROIc/a, d/a, c/b, and d/b were calculated.

RESULTS

In all patients parenchymal contrast enhancement was visually detectable. One hundred thirty-one characteristic time-intensity curves (baseline phase, peak contrast intensity, slow washout phase) were demonstrable in 144 ROIs. In ROIc and ROId, characteristic contrast curves could be observed most frequently (68/72 examinations), whereas time-intensity curves in ROIa and ROIb could not be evaluated because of inadequate contrast enhancement in 9 of 72 examinations. Time to peak intensity varied between 20 and 52 cardiac cycles; in 1 patient it was 88 cardiac cycles. In all individuals AUCs and in 16 of 18 subjects peak intensity in ROIc and ROId showed a 2- to 10-fold increase compared with ROIa and ROIb. In no examination did AUC ratios show a >2-fold side difference irrespective of the ROI.

CONCLUSIONS

The present study demonstrates for the first time that TRsHI produces accurate contrast in different brain areas and represents an ultrasonic tool related to brain perfusion. Absolute values of quantitative parameters show high variations caused by different temporal bone thicknesses and a complex relationship between echo contrast concentrations and measurements of optic intensities. Ratios between different ROIs help to compare contrast enhancement in different brain areas. Furthermore, because of the fact that attenuation of contrast enhancement in TRsHI depends strictly on the insonation depth, harmonic imaging studies of brain perfusion cannot be compared directly with other imaging techniques such as positron emission tomography.

Improved left ventricular endocardial border delineation and opacification with OPTISON (FS069), a new echocardiographic contrast agent. Results of a phase III Multicenter Trial

OBJECTIVES

The echocardiographic contrast-enhancing effects and safety profile of ALBUNEX (a suspension of air-filled albumin microspheres) were compared with the new contrast agent OPTISON (formerly FS069: a suspension of albumin microspheres containing the gas perfluoropropane) in 203 patients with inadequate noncontrast echocardiograms.

BACKGROUND

The efficacy of ALBUNEX has been limited by its short duration of action. By using perfluoropropane instead of air within the microsphere, its duration of action is increased.

METHODS

Each patient received ALBUNEX (0.8 and 0.22 mL/kg) and OPTISON (0.2, 0.5, 3.0, and 5.0 mL) on separate days a minimum of 48 hours apart. Echocardiograms were evaluated for increase in left ventricular (LV) endocardial border length, degree of LV opacification, number of LV endocardial border segments visualized, conversion from a nondiagnostic to a diagnostic echocardiogram, and duration of contrast enhancement. A thorough safety evaluation was conducted.

RESULTS

Compared with ALBUNEX, OPTISON more significantly improved every measure of contrast enhancement. OPTISON increased well-visualized LV endocardial border length by 6.0+/-5.1, 6.9+/-5.4, 7.5+/-4.7, and 7.6+/-4.8 cm, respectively, for each of the four doses, compared with only 2.2+/-4.5 and 3.4+/-4.6 cm, respectively, for the two ALBUNEX doses (p < 0.001). 100% LV opacification was achieved in 61%, 73%, 87%, and 87% of the patients with the four doses of OPTISON, but in only 16% and 36% of the patients with the two ALBUNEX doses (p < 0.001). Conversion of nondiagnostic to diagnostic echocardiograms with contrast occurred in 74% of patients with the optimal dose of OPTISON (3.0 mL) compared with only 26% with the optimal dose of ALBUNEX (0.22 mL/kg) (p < 0.001). The duration of contrast effect was also significantly greater with OPTISON than with ALBUNEX. In a subset of patients with potentially poor transpulmonary transit of contrast (patients with chronic lung disease or dilated cardiomyopathy), OPTISON more significantly improved the same measures of contrast enhancement compared with ALBUNEX and did so to the same extent as in the overall population. Side effects were similar and transient with the two agents.

CONCLUSION

OPTISON appears to be a safe, well-tolerated echocardiographic contrast agent that is superior to ALBUNEX.

Methods for quantifying ultrasound backscatter and two-dimensional video intensity: implications for contrast-enhanced sonography

Quantification of acoustic backscatter energy is believed to be useful for assessing "tissue character" and for quantifying the regional concentration of echo contrast. Measurement of ultrasonic video intensity has been the traditional means of quantifying backscatter energy, with "integrated backscatter" considered the gold standard. The purpose of this work is to review the commonly used methods for quantifying ultrasonic backscatter and to describe the difference between detected backscatter energy and the intrinsic tissue backscatter coefficient. Many of the quantification pitfalls that can lead to erroneous conclusions will also be discussed. A set of eight rubber phantoms with backscatter coefficient from -6 dB to +15 dB relative to liver were imaged at 2.5, 3.5, and 5.0 MHz. Methods for calculating the acoustic backscatter intensity from calibrated video intensity measurements and for calculating the tissue backscatter coefficient are described and tested using equipment from two different manufacturers. A commercially available automatic "acoustic densitometry" system with on-board quantitative integrated backscatter is also evaluated. Ultrasound attenuation and ultrasound system factors were found to strongly influence the detected backscatter intensity using either calibrated video intensity or on-board integrated backscatter. Special system transfer functions and attenuation correction were found to be useful in converting video intensity and integrated backscatter to a measure of the intrinsic tissue backscatter coefficient. With these correction factors, the correlation between the measured tissue backscatter coefficient and the phantom backscatter coefficient was excellent (r = 0.99, intercept 0.0, regression slope essentially 1.0) at all three imaging frequencies with traditional video intensity or on-board integrated backscatter. Uncalibrated video intensity and on-board integrated backscatter have limitations when used in isolation for tissue characterization. Rigorous attention to the imaging parameters and the use of calibration functions are necessary before video intensity measurement or integrated backscatter can be used reliably to measure the tissue backscatter coefficient.

Functional myocardial perfusion abnormality induced by left ventricular asynchronous contraction: experimental study using myocardial contrast echocardiography

OBJECTIVES

The aim of this study was to clarify how myocardial perfusion is impaired by asynchronous contraction.

BACKGROUND

False septal hypoperfusion is noted in some patients with left bundle branch block.

METHODS

Eight dogs were examined with epicardial pacing at the left ventricular posterior wall, the right ventricular anterior wall and, as a control, the right atrial appendage. The pacing rate was 80, 110 and 150 beats/min (bpm). Myocardial perfusion was assessed by contrast echocardiography.

RESULTS

Left ventricular pacing at 80 and 110 bpm did not change systolic wall thickening or contrast intensity at the pacing site, although an early excitation notch was noted at the pacing site. However, at 150 bpm, systolic thickening was impaired (23.3 +/- 4.2% vs. 37.0 +/- 2.6% during atrial pacing, p < 0.05), and the peak intensity ratio of the pacing site to the ventricular septum was significantly decreased (24.1 +/- 5.7% vs. 37.0 +/- 2.8% at a pacing rate of 80 bpm, p < 0.01). The peak intensity ratio correlated with systolic wall thickening at the pacing site (y = 0.413 x -0.028, r = 0.81, p < 0.0001). However, right ventricular pacing did not change either systolic thickening or the peak intensity ratio at any pacing rate, although an early excitation notch was noted on the ventricular septum.

CONCLUSIONS

Wall motion abnormalities after early excitation vary depending on the pacing mode. When tachycardia induces regional wall motion abnormalities, the ventricular wall of the pacing site is functionally hypoperfused.

Contrast echocardiography displays increased subendocardial perfusion after nitroglycerin administration

A mechanism proposed to contribute to the antianginal effect of nitroglycerin is a redistribution of coronary blood flow to the subendocardium. Contrast echocardiography combines ultrasound with echogenic contrast agents to assess regional myocardial perfusion. This study aims to assess the effect of nitroglycerin on myocardial transmural perfusion with contrast echocardiography in humans. Nine patients scheduled for coronary angiography received 300 microg intracoronary nitroglycerin. Contrast echocardiographic studies were performed before and immediately after the administration of intracoronary nitroglycerin. Videodensitometric analysis was performed off-line to measure subendocardial and subepicardial opacification. Subendocardial opacification greater than subepicardial opacification increased from six of 13 patients before nitroglycerin administration to 11 of 13 after nitroglycerin administration (p <0.05). Similarly, these observations increased from nine of 13 patients to 13 of 13 after nitroglycerin administration during diastole (p <0.05). Contrast echocardiography demonstrates increased subendocardial perfusion after the administration of nitroglycerin in these patients.

Measurement of right ventricular ejection fraction by contrast echocardiography

We evaluated 20 healthy subjects with no cardiac disease (8 males, 12 females, age 49+/-12) to determine the accuracy of right ventricular ejection fraction measurement with contrast echocardiography performed with D-galactose (Echovist 300). All patients underwent two dimensional echocardiography where the right ventricular ejection fraction was calculated by the Simpson's rule first without contrast, then after the injection of 5 ml D-galactose in the same position and compared to the right ventricular ejection fraction measured by the first pass radionuclide angiography on the same day. Subjects had a normal left ventricular ejection fraction of 66+/-5 and a body mass index of 28.9+/-1.2. The correlation between echocardiographic and radionuclide derived right ventricular ejection fraction significantly increased when contrast was used (r=0.81 vs. r=0.6). The r value for interobserver variability also increased significantly with contrast use (r=0.98 vs. r=0.7). We conclude that D-galactose contrast injection significantly enhances border detection and improves the accuracy of right ventricular ejection fraction calculations with echocardiography making it a simple and reliable method.

Reduced forward output states affect the left ventricular opacification of intravenously administered Albunex

Albunex is an Food and Drug Administration-approved ultrasound contrast agent used for the enhancement of left ventricular endocardial borders. To determine the efficacy of intravenously administered Albunex with regard to left ventricular opacification (LVO), a retrospective analysis of 117 patients who received 202 injections of Albunex for enhancement of endocardial borders was done (dose 0.08 to 0.22 ml /kg). Patients were routinely referred to our echocardiography laboratory for stress echocardiography for standard indications. Optimized settings for contrast enhancement (3.5 MHz transducer frequency and maximum dynamic range) were used. Four observers graded LVO on a scale from 0 to 3 (0 = no Albunex seen in the ventricular cavity; 3 = Albunex densely seen in the ventricular cavity). Overall, LVO was reported in 166 (82%) of 202 injections or in 91 (78%) of 117 patients. A significant reduction in LVO was noted in patients with mitral regurgitation, tricuspid regurgitation, atrial fibrillation, systolic dysfunction, or pulmonary hypertension (increased pulmonary artery systemic pressure). LVO was seen in 88% of the patients without these conditions. However, only 12 (44%) of 27 patients with one or more of the above conditions had LVO (p < 0.05). LVO can be achieved in the majority of patients after intravenously administered Albunex when imaged with optimal transducer settings. A subset of patients with systolic dysfunction, mitral regurgitation, tricuspid regurgitation, atrial fibrillation, or increased pulmonary artery systemic pressure has less effective LVO with Albunex. Heart disease associated with decreased forward flow appears to be associated with diminished LVO.

Contrast echocardiography: influence of ultrasonic machine settings, mixing conditions, and pressurization on pixel intensity and microsphere size of Albunex solutions in vitro

To use Albunex as a blood-flow tracer, the stability and consistency of microspheres under mixing conditions must be known. This study examined the effects of mixing conditions and machine settings on the size and echogenicity of Albunex solutions in vitro. Acoustic power, log compression, time-gain compensation, and transducer frequency were varied as Albunex solutions were imaged after mixing with magnetic stirring and pressurized. Higher acoustic power and lower transducer frequency decreased mean pixel intensity of Albunex solution images over time. Intensity, size, and number of Albunex microspheres were not significantly different between stirring speeds. The echogenicity of the Albunex solutions decreased with pressurization, and the critical pressure necessary to reduce the intensity to half its initial value increased with the logarithm of concentration (r = 0.91; p < 0.001). The microsphere size decreased with pressurization and remained smaller after pressure release (3.66 +/- 2.13 versus 1.47 +/- 0.95 microns; p < 0.01). These data indicate that acoustic power and transducer frequency may affect the physical properties of Albunex microspheres, decreasing mean videointensity. Pressure sensitivity of Albunex caused the decrease of videointensity and microsphere size.

Ultrasound contrast media and their use in obstetrics and gynecology

Contrast media have gained acceptance to enhance ultrasonography in many fields of medicine; in particular, cardiology. Several agents have been described and many more are being manufactured and tested. By increasing the number of strong sound scatterers, these agents improve images by increasing the amount of echoes. This is true both for grey-scale and color or Doppler imaging. Their use in obstetrics is very limited at the moment because of safety issues. In a laboratory setup, they have been shown to markedly enhance placental imaging. In gynecology, imaging of the uterine cavity and Fallopian tubes is greatly improved. A potential area where ultrasound contrast may find a role is gynecological oncology. Vascularity is increased in many tumors, but usually vessel diameter is small and velocity low. One can therefore expect future use of the ultrasound contrast agents in ovarian or other gynecological neoplasms.

Effects of Temperature on Albunex and FS069 Echocardiographic Contrast Agents: In Vitro Investigation Using Ultrasonic Irradiation

The effects of temperature on the stability of two contrast agents, Albunex and perfluoropropane filled albumin microspheres (FS069), were investigated by studying the variations in their reflective properties, induced by high dose ultrasound irradiation at different temperatures. Diluted contrast agents were introduced into a 3.5-mL latex balloon, placed in a plastic water tank, and continuously irradiated over a period of 6 minutes using different power levels: 0, 20, 25, and 30 dB. The irradiation was interrupted for imaging every 30 seconds for 2 seconds. The protocol was carried out at three different temperatures: 8 degrees C, 22 degrees C, and 37 degrees C. For each temperature, the concentration of contrast solution was matched to produce approximately the same initial video intensity. Time variations in mean video intensity in the balloon cross section were studied. Contrast enhancement was found to be directly related to temperature. Under continuous ultrasonic irradiation, video intensity gradually decreased over time. This decrease was dependent on both transmitted power and temperature, and was more pronounced with Albunex when compared to FS069 (P < 0.05). Abruptly dropping temperature consistently resulted in rapid, irreversible disappearance of contrast induced by Albunex. Temperature affects the reflectivity and stability of diluted Albunex and FS069. To enhance the reproducibility of contrast enhancement achieved by these agents, their temperature should be carefully controlled.

Optimizing albunex in the left ventricle: an analysis of the technical parameters of four ultrasound systems in canines and humans

Albunex, an intravascular ultrasound contrast agent, has been used clinically to enhance echocardiographic images. The purpose of this study if (1) to determine whether varying the settings on commercially available ultrasound machines has an effect on left ventricular opacification after intravenously administered Albunex and if there is an effect on left ventricular opacification and (2) to determine the ideal settings for each ultrasound scanner. Six canine hearts were imaged with 1 ml injections of intravenously administered Albunex while varying the transducer frequency, preprocessing curves, postprocessing curves, and dynamic range on a variety of ultrasound units. Subsequently 50 human subjects underwent imaging with the various machines while the dynamic range and transducer frequencies were altered. All subjects received two or three intravenous injections of 10 ml Albunex. The opacification of the left ventricular cavitary images in both parts of the study were interpreted visually on a scale of 0 to 4 (0 = none, 1 = trace, 2 = moderate, 3 = dense, and 4 = ideal) by four observers. The maximum compression and transducer frequency of 3.5 MHz showed significant improvement of left ventricular opacification in both canines and humans. These studies have shown that (1) varying the ultrasound unit's parameters affects the quality of left ventricular imaging when Albunex is used to enhance the image, and (2) higher compression and a transducer frequency of 3.5 MHz tend to enhance Albunex images of canine and human hearts.

Transesophageal echocardiography

This article presents an overview of the benefits and efficacy of transesophageal echocardiography (TEE) in the critically ill patient. The echocardiographic evaluation of ventricular function both regional and global, is discussed with special emphasis on ischemic heart disease; assessment of preload, interrogation of valvular heart disease (prosthetic and native) and its complications; endocarditis and its complications; intracardiac and extracardiac masses, including pulmonary embolism; aortic diseases (e.g., aneurysan, dissection, and traumatic tears); evaluation of patent foramen ovale and its association with central and peripheral embolic events; advancements in computer technology; and finally, the effect of TEE on critical care.

Ultrasound Densitometric Analysis: Comparison Between an Online Digital Acquisition Acoustic Program and an Offline Analog Program

Videodensitometric analysis of myocardial contrast echocardiography is traditionally performed off line. Recently, an online contrast ultrasound analysis system, Acoustic Densitometry (Hewlett-Packard), was introduced. We compared pixel intensities acquired with Acoustic Densitometry to pixel intensities derived from videodensitometry. A tissue phantom was imaged in phase I using three transducer frequencies (2.5, 3.5, and 5.0 MHz). In phase II, an in vitro flowing tube model with various concentrations of Albunex(R) was imaged at two flow rates, 0.6 and 1.2 m/sec, and at two transducer frequencies, 2.5 and 3.5 MHz. The relationship between pixel intensities yielded by the two systems for identical ultrasound signals was determined with linear regression. Intensities derived with Acoustic Densitometry strongly correlated with those derived from the offline videodensitometry system. The intensities were related by a predictive multiplicative factor based on display characteristics of the two systems. These results suggest that semiquantitative, online perfusion analysis with Acoustic Densitometry is as sensitive as analysis offline with videodensitometry. (ECHOCARDIOGRAPHY, Volume 13, September 1996)

Relation between air-filled albumin microbubble and red blood cell rheology in the human myocardium. Influence of echocardiographic systems and chest wall attenuation

BACKGROUND

We have previously shown that the intravascular rheology of sonicated air-filled albumin microbubbles is similar to that of red blood cells (RBCs) and that their myocardial transit rate is also similar to that of RBCs in the beating canine heart. In the present study, we tested the hypothesis that the myocardial transit rates of these microbubbles reflect those of RBCs in humans at different coronary flow rates.

METHODS AND RESULTS

RBC and microbubble transit rates were measured in 17 patients undergoing coronary angiography: in 8, measurements were made only at rest, whereas in 9, they were performed both at rest and during a pacing-induced increase in coronary blood flow. A gamma-variate function was used to derive mean RBC and microbubble transit rates from the time-activity and time-intensity plots after the left main injection of RBCs and microbubbles, respectively. There was linear correlation between the myocardial transit rates with both tracers with the slope of the correlation determined by the specific echocardiographic system that was used. Microbubble transit rate consistently overestimated RBC transit rate due to artificial narrowing of the time-intensity curves caused by chest wall attenuation of the echocardiographic signal, which was confirmed through in vitro experiments.

CONCLUSIONS

There is close correlation between air-filled albumin microbubbles and RBC rheology in the human myocardium. The use of these microbubbles in the cardiac catheterization laboratory could, therefore, provide further insights into myocardial blood flow/myocardial blood volume relations in humans.

Loss of contrast intensity during systole in the left ventricular cavity with the use of the contrast agent Albunex. An analysis of its correlation with pressure and velocity

RATIONALE AND OBJECTIVES

Several investigators have observed a decrease in video intensity in the left ventricular cavity during systole when using contrast echocardiography. It has been suggested that this phenomenon is related to microbubble instability. The authors propose that this phenomenon is, in part, related to the effects of pressure and velocity on the acoustic reflectance of ultrasound contrast agents.

METHODS

Using an in vitro flow tube model and varying concentrations of Albunex contrast agent, the effects of pressure and velocity on microbubble video intensity were investigated. Velocity and pressure were varied independently and the imaging tube was scanned using three transducer frequencies at different concentrations of Albunex. Contrast video intensity was analyzed using high and low velocities (at constant pressure) and high and low pressures (at constant velocity). In addition, the fluid from the system was collected and imaged in a nonflowing reservoir tank to investigate the video intensity of the microbubbles when exposed to variable velocity and pressure.

RESULTS

The video-intensity measurements were inversely and irreversibly related to ambient pressure changes (independent of velocity) in a tube model. However, video intensity varied inversely but reversibly with velocity (independent of pressure). This observation could not be explained simply by the "laminar flow" theory, by a change in transducer angulation, nor by a change in ultrasound imaging frame rate. This phenomenon was limited to Albunex microbubbles and was not observed with a contrast medium (corn starch) devoid of the acoustic properties of Albunex.

Evidence for a relation between inspired gas mixture and the left ventricular contrast achieved with Albunex in a canine model

BACKGROUND

In a previous experiment, a marked reduction in the right- and left-sided contrast effect of Albunex was noted in an intubated animal spontaneously breathing isoflurane in 100% oxygen. The theory suggests that the time course of echogenicity of microbubbles in liquid is dependent on the pressure and the gradients of dissolved gases. The present set of experiments tested whether the loss of contrast occurs at commonly used therapeutic concentrations of inspired oxygen.

HYPOTHESIS

This research tested the hypothesis that the left ventricular (LV) contrast effect achieved with intravenous injection of the ultrasound contrast agent Albunex is related to the inspired oxygen content.

METHODS

Intubated dogs were maintained in a spontaneously respiring anesthetic state on isoflurane and mixtures of oxygen (12-50%) in nitrogen. FIO2 was held steady for 15 min prior to injection of 0.08 ml/kg of Albunex. The contrast effects were recorded from a transthoracic short-axis view. Left and right ventricular brightness curves were generated from digitized sequences of end-diastolic frames. The minimum and maximum brightness and area under the time-brightness curves were determined.

RESULTS

The LV maximum brightness and area under the curve showed significant negative correlations (p = < 0.004) with the FIO2, while the minimum brightness showed a significant positive correlation (p = < 0.002). No significant correlations were found for the right ventricular brightness parameters.

CONCLUSIONS

These findings show an important relationship between the FIO2 and loss of the contrast effect of Albunex. This loss occurs at oxygen concentrations in the therapeutic range, but could be overcome by increasing the dose of Albunex. The mechanism is likely related to an outward nitrogen gradient causing a loss of echogenicity. The clinical implication is that patients on supplemental oxygen may require higher doses of Albunex to achieve optimal opacification.

Stress echocardiography, contrast echocardiography, and tissue characterization: applications for the future

During the last three decades the application of ultrasonography has expanded rapidly. The information available to the clinician from ultrasound imaging today is vastly more significant than it was in the early years of the development of this technology. In addition to automatic information, there is an increasing potential to provide functional, dynamic perfusion and even cellular information about the heart. This article attempts to summarize briefly the advances in these areas.

Intravenous perfluoropropane-exposed sonicated dextrose albumin produces myocardial ultrasound contrast that correlates with coronary blood flow

If microbubble gas blood solubility and diffusivity are reduced, the persistence (and hence ultrasound reflectivity) of the microbubble in blood is prolonged. Recently we have sonicated a multifold dilution of human albumin with 5% dextrose while exposed to gases of low blood solubility and diffusivity and produced microbubbles that consistently opacify the myocardium after intravenous injection. The objective of this study was to test the hypothesis that a gas with very low diffusivity, perfluoropropane, when introduced into dextrose albumin during sonication, would produce visually evident myocardial ultrasound contrast after intravenous injection compared to sonicating with gases that have more rapid diffusivity. Second, we sought to determine whether the degree of contrast (peak myocardial videointensity) achieved with this agent would correlate with coronary blood flow. In eight open-chest dogs, intravenous injections of dextrose albumin sonicated with either room air, sulfur hexafluoride, or perfluoropropane (PESDA) were given under baseline conditions. PESDA injections were repeated when coronary flow was increased during low-dose dobutamine infusion. Left anterior descending coronary blood flow was monitored with transit-time flow probe. Background-subtracted anterior myocardial peak videointensity was measured after each injection. Visible myocardial opacification was seen in 100% of the 0.04 to 0.08 ml/kg intravenous injections of PESDA. No significant myocardial contrast was observed with the same doses of intravenous room air- or sulfur hexafluoride-exposed sonicated dextrose albumin. There was a strong correlation between left anterior descending coronary artery flow (range 17 to 96 ml/min) and myocardial peak videointensity (r = 0.75; p < 0.0001) in all dogs. We conclude that intravenous injections of PESDA can safely produce consistent myocardial ultrasound contrast. the peak videointensity produced correlates with changes in coronary blood flow. Therefore this agent could be used to quantify coronary blood flow noninvasively.