Background subtraction from time-intensity curves in videodensitometry: a pitfall in flow assessment using contrast echocardiography

Guidelines and Good Clinical Practice Recommendations for Contrast Enhanced Ultrasound (CEUS) in the Liver - Update 2020 - WFUMB in Cooperation with EFSUMB, AFSUMB, AIUM, and FLAUS

The present, updated document describes the fourth iteration of recommendations for the hepatic use of contrast enhanced ultrasound (CEUS), first initiated in 2004 by the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB). The previous updated editions of the guidelines reflected changes in the available contrast agents and updated the guidelines not only for hepatic but also for non-hepatic applications.The 2012 guideline requires updating as previously the differences of the contrast agents were not precisely described and the differences in contrast phases as well as handling were not clearly indicated. In addition, more evidence has been published for all contrast agents. The update also reflects the most recent developments in contrast agents, including the United States Food and Drug Administration (FDA) approval as well as the extensive Asian experience, to produce a truly international perspective.These guidelines and recommendations provide general advice on the use of ultrasound contrast agents (UCA) and are intended to create standard protocols for the use and administration of UCA in liver applications on an international basis to improve the management of patients.

Guidelines and Good Clinical Practice Recommendations for Contrast-Enhanced Ultrasound (CEUS) in the Liver-Update 2020 WFUMB in Cooperation with EFSUMB, AFSUMB, AIUM, and FLAUS

The present, updated document describes the fourth iteration of recommendations for the hepatic use of contrast-enhanced ultrasound, first initiated in 2004 by the European Federation of Societies for Ultrasound in Medicine and Biology. The previous updated editions of the guidelines reflected changes in the available contrast agents and updated the guidelines not only for hepatic but also for non-hepatic applications. The 2012 guideline requires updating as, previously, the differences in the contrast agents were not precisely described and the differences in contrast phases as well as handling were not clearly indicated. In addition, more evidence has been published for all contrast agents. The update also reflects the most recent developments in contrast agents, including U.S. Food and Drug Administration approval and the extensive Asian experience, to produce a truly international perspective. These guidelines and recommendations provide general advice on the use of ultrasound contrast agents (UCAs) and are intended to create standard protocols for the use and administration of UCAs in liver applications on an international basis to improve the management of patients.

Guidelines and good clinical practice recommendations for Contrast Enhanced Ultrasound (CEUS) in the liver - update 2012: A WFUMB-EFSUMB initiative in cooperation with representatives of AFSUMB, AIUM, ASUM, FLAUS and ICUS

Initially, a set of guidelines for the use of ultrasound contrast agents was published in 2004 dealing only with liver applications. A second edition of the guidelines in 2008 reflected changes in the available contrast agents and updated the guidelines for the liver, as well as implementing some non-liver applications. Time has moved on, and the need for international guidelines on the use of CEUS in the liver has become apparent. The present document describes the third iteration of recommendations for the hepatic use of contrast enhanced ultrasound (CEUS) using contrast specific imaging techniques. This joint WFUMB-EFSUMB initiative has implicated experts from major leading ultrasound societies worldwide. These liver CEUS guidelines are simultaneously published in the official journals of both organizing federations (i.e., Ultrasound in Medicine and Biology for WFUMB and Ultraschall in der Medizin/European Journal of Ultrasound for EFSUMB). These guidelines and recommendations provide general advice on the use of all currently clinically available ultrasound contrast agents (UCA). They are intended to create standard protocols for the use and administration of UCA in liver applications on an international basis and improve the management of patients worldwide.

Liver dysplasia: US molecular imaging with targeted contrast agent enables early assessment

PURPOSE

To investigate the ability of vascular endothelial growth factor receptor type 2 (VEGFR2)-targeted ultrasonographic (US) microbubbles for the assessment of liver dysplasia in transgenic mice.

MATERIALS AND METHODS

Animal experiments were approved by the governmental review committee. Nuclear factor-κB essential modulator knock-out mice with liver dysplasia and wild-type mice underwent liver imaging by using a clinical US system. Two types of contrast agents were investigated: nontargeted, commercially available, second-generation microbubbles (SonoVue) and clinically translatable PEGylated VEGFR2-targeted microbubbles (BR55). Microbubble kinetics was investigated over the course of 4 minutes. Targeted contrast material-enhanced US signal was quantified 5 minutes after injection. Competitive in vivo binding experiments with BR55 were performed in knock-out mice. Immunohistochemical and hematoxylin-eosin staining of liver sections was performed to validate the in vivo US results. Groups were compared by using the Mann-Whitney test.

RESULTS

Peak enhancement after injection of SonoVue and BR55 did not differ in healthy and dysplastic livers (SonoVue, P = .46; BR55, P = .43). Accordingly, immunohistochemical findings revealed comparable vessel densities in both groups. The specificity of BR55 to VEGFR2 was proved by in vivo competition (P = .0262). While the SonoVue signal decreased similarly in healthy and dysplastic livers during the 4 minutes, there was an accumulation of BR55 in dysplastic livers compared with healthy ones. Furthermore, targeted contrast-enhanced US signal indicated a significantly higher site-specific binding of BR55 in dysplastic than healthy livers (P = .005). Quantitative immunohistologic findings confirmed significantly higher VEGFR2 levels in dysplastic livers (P = .02).

CONCLUSION

BR55 enables the distinction of early stages of liver dysplasia from normal liver.

Coronary structure and perfusion in health and disease

Blood flow is distributed through the heart muscle via a system of vessels forming the coronary circulation. The perfusion of the myocardium can be hampered by atherosclerosis creating localized obstructions in the epicardial vessels or by microvascular disease. In early stages of the disease, these impediments to blood flow are offset by dilation of the resistance vessels, which normally compensates for a decrease in perfusion pressure or increased metabolism. However, this dilatory reserve can become exhausted, which in general occurs first at the deeper layers of the heart wall where intramural vessels are subjected to compressive forces related to heart contraction. In the catheterization laboratory, guide wires of 0.33 mm diameter are available that are equipped with a pressure and flow velocity sensor at the tip, which can be positioned distal to the stenosis. These signals provide information about the impediment of the stenosis on coronary flow and allow for the evaluation of the status of the microcirculation. However, the interpretation of these signals is strongly model-dependent and therefore it is of paramount importance to develop realistic models reflecting the anatomy and unique physiology of the coronary circulation.

In vivo perfusion estimation using subharmonic contrast microbubble signals

OBJECTIVE

The purpose of this study was to quantify perfusion in vivo using contrast-enhanced subharmonic imaging (SHI).

METHODS

A modified LOGIQ 9 scanner (GE Healthcare, Milwaukee, WI) operating in gray scale SHI mode was used to measure SHI time-intensity curves in vivo. Four dogs received intravenous contrast bolus injections (dose, 0.1 mL/kg), and renal SHI was performed. After 3 contrast agent injections, a microvascular staining technique based on stable (nonradioactive) isotope-labeled microspheres (BioPhysics Assay Laboratory Inc, Worcester, MA) was used to quantify the degree of perfusion in 8 sections of each kidney. Low perfusion states were induced by ligating surgically exposed segmental renal arteries followed by contrast agent injections and microvascular staining. Digital clips were transferred to a personal computer, and SHI time-intensity curves were acquired in each section using Image-Pro Plus software (Media Cybernetics, Silver Spring, MD). Subharmonic fractional blood volumes were calculated, and the perfusion was estimated from the initial slope of the fractional blood volume uptake averaged over 3 injections. Subharmonic perfusion data were compared with the gold standard (ie, the microspheres) using linear regression analysis.

RESULTS

In vivo gray scale SHI clearly showed flow and, thus, perfusion in the kidneys with almost complete suppression of tissue signals. In total, 270 SHI time-intensity curves were acquired, which reduced to 94 perfusion estimates after averaging. Subharmonic perfusion estimates correlated significantly with microsphere results (r = 0.57; P < .0001). The best SHI perfusion estimates occurred for high perfusion states in the anterior of the kidneys (r = 0.73; P = .0001). The corresponding root mean square error was 2.4%.

CONCLUSIONS

Subharmonic perfusion estimates have been obtained in vivo. The perfusion estimates were in reasonable to good agreement with a microvascular staining technique.

On the usefulness of the mechanical index displayed on clinical ultrasound scanners for predicting contrast microbubble destruction

OBJECTIVE

The purpose of this study was to evaluate the mechanical index (MI) displayed on clinical ultrasound scanners as a predictor of exposure conditions related to the destruction of sonographic microbubble contrast agents.

METHODS

Sonazoid (GE Healthcare, Oslo, Norway) and Optison (GE Healthcare, Princeton, NJ) microbubbles were injected into a tissue-mimicking flow phantom. Gray scale imaging was performed with 4 different scanners and 3 different transducers (3.5 MHz curved linear, 2.5 MHz convex, and 7.5 MHz linear array), and the MI displayed by the scanner was varied from 0.2 to 1.5 by changing the system output power. All other scanning parameters were kept constant. Downstream changes in echogenicity were monitored with a PowerVision 7000 scanner (Toshiba America Medical Systems, Tustin, CA) as an indirect measure of bubble destruction. Video intensity changes within the flow tube were determined as a function of MI for the different scanner/transducer combinations, and the best linear fit was determined.

RESULTS

At a displayed MI of 0.7, different scanner/transducer combinations exhibited a range in video intensity from +16% to -3% of baseline for Sonazoid and from +8% to -71% for Optison. At an MI of 0.3, reductions in video intensity of up to 32% were produced. These results indicate a wide range in bubble destruction at identical MI values. Likewise, regression analysis found no linear fits for all scanner/transducer combinations (r2 < 0.046).

CONCLUSIONS

The MI displayed on clinical ultrasound scanners does not predict the degree of microbubble destruction and should not be used by itself to define exposure conditions for destruction of microbubble contrast agents.

Different behaviors of microbubbles in the liver: time-related quantitative analysis of two ultrasound contrast agents, Levovist and Definity

The differences in time-related changes of liver images were compared quantitatively between Levovist and Definity. A total of 40 rabbits were assigned to eight groups according to the timing of taking enhanced liver images at 1, 3, 5, 7, 9, 11, 13 and 15 min by intermittent harmonic imaging using Levovist or Definity (30 microL/kg) and another 40 rabbits for Definity (50 microL/kg). Intensity changes between before and after enhancement in the portal vein (I-PV) and liver parenchyma (I-LP) were analyzed. I-PV was greater than I-LP at the 1- and 3-min phases of enhancement and I-LP became greater than I-PV with Levovist after 5 min. However, I-PV was higher than I-LP in all phases with Definity. Different time-intensity curves of these two agents will indicate discrete behaviors of microbubble hemodynamics in the liver; Levovist becomes accumulated in the liver, whereas Definity acts as a blood pool contrast agent, without accumulation.

Measurement of radial artery contrast intensity to assess cardiac microbubble behavior

OBJECTIVES

We sought to determine whether analysis of the contrast signal from the radial artery is better able to reflect changes in left ventricular (LV) microbubble dynamics than the signal from the LV itself.

BACKGROUND

Assessment of microbubble behavior from images of the LV may be affected by attenuation from overlying microbubbles and nonuniform background signal intensities. The signal intensity from contrast in a peripheral artery is not affected by these artifacts and may, thus, be more accurate.

METHODS

After injection of a contrast bolus into a peripheral vein, signal intensity was followed simultaneously in the LV and radial artery. The measurements were repeated using continuous, triggered, low and high mechanical index harmonic imaging of the LV.

RESULTS

Peak and integrated signal intensities ranged from 25 dB and 1550 dB/s, respectively, with radial artery imaging to 5.6 dB and 471 dB/s with ventricular imaging. Although differences in microbubble behavior during the different imaging protocols could be determined from both the LV and radial artery curves, analysis of the radial artery curves yielded more consistent and robust differences.

CONCLUSIONS

The signal from microbubbles in the radial artery is not affected by shadowing and is, thus, a more accurate reflection of microbubble behavior in the LV than the signal from the LV itself. This may have important implications for the measurement of myocardial perfusion by contrast echocardiography.

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.

Harmonic imaging of the brain parenchyma using a perfluorobutane-containing ultrasound contrast agent

We evaluated the signal-enhancing effect of the novel perfluorobutane-based ultrasound contrast agent BR 14 (Bracco Research, Switzerland) in grey-scale harmonic imaging of the brain parenchyma. Six sedated male beagle dogs were investigated with transcranial grey-scale harmonic imaging (SONOS 5500, 1.8/3.6 MHz). After bolus injection of two different doses of BR 14, acoustic densitometry was performed to quantify changes in regional contrast intensity. In the dogs' brain parenchyma, the mean relative peak increase in acoustic intensity was +61% after administration of 0.05 ml/kg BW of BR 14 and +24% after 0.2 ml/kg BW. In the masticatory muscle, application of the higher dose resulted in a stronger increase in contrast intensity compared to the lower dose. Evaluation of the contralateral base of the skull showed a dose-dependent decrease in acoustic intensity. Bolus injection of BR 14 produces an increase in acoustic intensity, which can be used for the visualization of contrast agent in the brain parenchyma. Using high dosages, a strong signal-enhancing effect in the regions near the ultrasound probe leads to a consecutive attenuation of signals from structures being located beyond ("shadowing-effect"). This is the explanation for the paradoxical result that the higher dose leads to a lower peak signal increase in the brain parenchyma.

A new ultrasound contrast imaging approach based on the combination of multiple imaging pulses and a separate release burst

A new ultrasound contrast imaging technique is described that optimally employs the rupture of the contrast agent. It is based on a combination of multiple high frequency, broadband, imaging pulses and a separate release burst. The imaging pulses are used to survey the target before and after the rupture and release of free gas bubbles. In this way, both processes (imaging and release) can be optimized separately. The presence of the contrast agent is simply detected by correlating or subtracting the signal responses of the imaging pulses. Because the time delay between the imaging pulses can be very short, the subtraction is less affected by tissue motion and can be done in real time. In vitro measurements showed that by using a release burst, the detection sensitivity increased 12 to 43 dB for different types of contrast agents. In the presence of a moving phantom, the increase in sensitivity was 22 dB. This new method is very sensitive for contrast agent detection in fundamental imaging mode and, therefore, non-linear propagation effects do not limit the maximum obtainable agent-to-tissue ratio. However, because of the inherent destruction of the contrast agent, it has to operate in an intermittent way. Through experiments, we have demonstrated the potential of the method to achieve simultaneous high sensitivity for contrast detection, i.e., high agent-to-tissue ratio, and high spatial resolution performance for different types of contrast agents.

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.

Confounding effects of myocardial background intensity and attenuation in contrast echocardiography: an in vivo study

It has been shown in vitro that the time-intensity data of echo contrast agents may be influenced by the background intensity of the myocardium and attenuation at high contrast agent concentrations. In the present study, these effects are evaluated from in vivo data. An effect of background intensity of the myocardium on the determination of the transit rate of the contrast agent could not be demonstrated unambiguously. A statistically significant relation between transit rate and background intensity was found only for intermediate flows in the transmural region. The magnitude of this relation was such that it does not provide a serious source of error. Attenuation and shadowing typically underestimate the transit rate of the contrast agent, which results in overestimation of flow. It is recommended that the lowest doses of contrast agent inducing myocardial opacification should be applied.

Persistent opacification of the left ventricle and myocardium with a new echo contrast agent

Echo contrast agents with long survival times open up new fields of application in the investigation of tissue perfusion and cardiovascular function. The purpose of this study was to characterize the time-course of the opacification of the heart cavities and myocardium with a new long-lasting second-generation, phospholipid-based echo contrast agent containing perfluoropentane (BY963-C5F12), and to compare its contrast potency with that of air-filled phospholipid monolayer (BY963-air). Doses of 0.03 mL/kg, 0.08 mL/kg and 0.16 mL/kg of BY963-air and BY963-C5F12 were administered intravenously to six conscious dogs weighing 25-36 kg. A transthoracic echocardiography was performed to evaluate peak intensity and area under the curve (AUC) from regions-of-interest placed in the right ventricle, left ventricle and left ventricular (LV) myocardium using acoustic densitometry. All injections were well tolerated, without wall-motion abnormalities or ECG changes. The LV cavity and myocardium were uniformly and well opacified for both echo contrast agents. However, at all administered doses, the contrast efficacy and duration were much more pronounced using BY963-C5F12 than with BY963-air. For the myocardium, the average peak intensity increased from 11.9+/-2.8 to 15.0+/-2.7 (not significant) following injection of BY963-air and from 12.8+/-3.2 to 18.7+/-2.8 (p < 0.01) following IV administration of BY963-C5F12; the latter corresponding to an increase in myocardial opacification of 46%. In conclusion, these results show the high myocardial opacification of BY963-C5F12 as compared to BY963-air. The simple incorporation of a perfluorocarbon gas into the phopholipid monolayer BY963 instead of air alters the acoustic properties of this contrast agent, resulting in qualitatively different application potentials for tissue opacification.

Conventional and hypobaric activation of an ultrasound contrast agent

Hypobaric activation is a new injection technique for use with the contrast agent EchoGen and, in this study, the agent's ability to produce parenchymal enhancement in vivo, with and without prior hypobaric activation, was investigated. Injections, ranging in dose from 0.05 to 0.5 mL/kg, were administrated through a peripheral vein to eight woodchucks with multiple hepatomas. At the 0.10 mL/kg dose level, seven of eight injections following hypobaric activation (88%) resulted in definite parenchymal enhancement. Conversely, dosages of 0.10 mL/kg without prior hypobaric activation produced no grey-scale changes. Only at the 0.4 and 0.5 mL/kg dosage level did the conventional administration technique obtain similar results (4 of 5 injections increased the echogenicity for a 0.4 mL/kg dose). These differences were statistically significant (p = 0.031). In vitro experiments were conducted to establish the physical mechanisms behind hypobaric activation. Relative measurements of contrast microbubble sizes were performed with a phase Doppler particle analyzer after hypobaric and after conventional (bolus) activation. Hypobaric activation produced approximately 20 times more microbubbles per unit volume than the conventional method. In conclusion, this investigation has demonstrated the benefits of prior hypobaric activation when performing in vivo contrast studies with EchoGen and determined the physical mechanisms behind this new injection technique. Hypobaric activation of EchoGen increases contrast enhancement and reduces dose size.

Contrast ultrasonography for 2-D opacification of heart cavities, peripheral vessels, kidney and muscle

Contrast ultrasonography of peripheral vessels and peripheral organs has been only sparsely used to evaluate peripheral tissue blood flow. The purpose of the study was to characterize intraluminal opacification of renal and femoral arteries and veins, of skeletal muscle and renal parenchyma after intraarterial (IA) injection of BY963, a newly developed ultrasound contrast agent being evaluated in Phase II and III trials, and to compare it with opacification of heart cavities after intravenous injection (IV) in dogs. A further purpose was to quantitate possible opacification losses during the first transcapillary passage of BY963 through pulmonary and peripheral microcirculation. BY963 was administered at the dose of 5 mL/animal/vascular territory (0.2 mL/kg). The peak intensity (intensity units = IU) and the area-under-the-curve (AUC, IU x heart cycles) were estimated from regions-of-interest placed in the right ventricle (RV), left ventricle (LV), main renal artery and vein, kidney, femoral artery and vein and adductor muscle. Following single IV injection, the average peak intensity and AUC values were 33 +/- 3 (mean +/- SE) and 674 +/- 109 for the RV, and 27 +/- 2 and 870 +/- 74 for the LV (p < 0.05), respectively. Following single IA injection in the descending aorta, the average peak intensities and AUC values were 35 +/- 2 and 613 +/- 139 in the renal artery and 26 +/- 4 (p < 0.05) and 639 +/- 151 in the renal vein (nonsignificant), respectively. For the femoral vessels, the average peak intensities and AUC values were 30 +/- 3 and 469 +/- 63 in the femoral artery, and 21 +/- 2 (p < 0.05) and 517 +/- 44 in the femoral vein (nonsignificant), respectively. The values for the output-to-input intensity ratios for peak intensity and AUC were 0.82 +/- 0.06 and 1.36 +/- 0.12 for the LV/RV ratio, 0.73 +/- 0.08 and 1.02 +/- 0.05 for the renal vein/renal artery ratio, and 0.71 +/- 0.09 and 1.16 +/- 0.13 for the femoral vein/femoral artery ratio, respectively (nonsignificant). In conclusion, these results demonstrate the high opacification potency of BY963 in the LV, renal and femoral veins, being of the same order of magnitude as that in the RV, renal and femoral arteries, respectively. Finally, the loss of opacification properties of BY963 during the first transcapillary (pulmonary or peripheral-capillary) passage is minimal.

Ultrasound contrast agent in intravascular echography: an in vitro study

The intravascular ultrasound image of the intraluminal contour depends on the difference between acoustic impedances of the media which create the endoluminal interface. There are several limitations to the visualization and detection of this interface. These limitations are due to artifacts encountered during image formation and to anatomical complexity. The purpose of this study is to obtain intraluminal contour enhancement using ultrasound contrast agent (UCA). Therefore, our objective was to address the feasibility of this technique by documenting the following: (i) the acoustic properties of UCA at 30 MHz; (ii) in vitro experimentation with tube or postnecrotic artery; and (iii) suitable digital processing. The images obtained with UCA (enhanced image quality) and subtracted from those without UCA provided, after simple digital processing, accurate visualization of the arterial lumen. The image obtained exhibits an even, high-contrast intraluminal edge. Such characteristics facilitate contour extraction by the automated contour detection procedures.