Microbubble-based Contrast Agents Research Articles

Contrast-enhanced ultrasonography for the management of portal hypertension in cirrhosis.

Portal hypertension is a major pathophysiological condition in patients with cirrhosis. This accounts for the occurrence and severity of the various manifestations. The degree is determined by the portal pressure or hepatic venous pressure gradients, both of which are obtained by invasive interventional radiological procedures. Ultrasound (US) is a simple and minimally invasive imaging modality for the diagnosis of liver diseases. Owing to the availability of microbubble-based contrast agents and the development of imaging modes corresponding to contrast effects, contrast-enhanced US (CEUS) has become popular worldwide for the detailed evaluation of hepatic hemodynamics, diffuse liver disease, and focal hepatic lesions. Recent advancements in digital technology have enabled contrast-based demonstrations with improved resolution, leading to a wider range of applications. This review article describes the current role, benefits, and limitations of CEUS in the management of portal hypertension.

New frontiers in liver ultrasound: From mono to multi parametricity.

Modern liver ultrasonography (US) has become a “one-stop shop” able to provide not only anatomic and morphologic but also functional information about vascularity, stiffness and other various liver tissue properties. Modern US techniques allow a quantitative assessment of various liver diseases. US scanning is no more limited to the visualized plane, but three-dimensional, volumetric acquisition and consequent post-processing are also possible. Further, US scan can be consistently merged and visualized in real time with Computed Tomography and Magnetic Resonance Imaging examinations. Effective and safe microbubble-based contrast agents allow a real time, dynamic study of contrast kinetic for the detection and characterization of focal liver lesions. Ultrasound can be used to guide loco-regional treatment of liver malignancies and to assess tumoral response either to interventional procedures or medical therapies. Microbubbles may also carry and deliver drugs under ultrasound exposure. US plays a crucial role in diagnosing, treating and monitoring focal and diffuse liver disease. On the basis of personal experience and literature data, this paper is aimed to review the main topics involving recent advances in the field of liver ultrasound.

Developing a Microbubble-Based Contrast Agent for Synchrotron In-Line Phase Contrast Imaging.

X-ray phase contrast imaging generates contrast from refraction of X-rays, enhancing soft tissue contrast compared to conventional absorption-based imaging. Our goal is to develop a contrast agent for X-ray in-line phase contrast imaging (PCI) based on ultrasound microbubbles (MBs), by assessing size, shell material, and concentration. Polydisperse perfluorobutane-core lipid-shelled MBs were synthesized and size separated into five groups between 1 and 10μm. We generated two size populations of polyvinyl-alcohol (PVA)-MBs, 2-3μm and 3-4μm, whose shells were either coated or integrated with iron oxide nanoparticles (SPIONs). Microbubbles were then embedded in agar at three concentrations: 5×107, 5×106 and 5×105 MBs/ml. In-line phase contrast imaging was performed at the Canadian Light Source with filtered white beam micro-computed tomography. Phase contrast intensity was measured by both counting detectable MBs, and comparing mean pixel values (MPV) in minimum and maximum intensity projections of the overall samples. Individual lipid-MBs 6-10μm, lipid-MBs 4-6μm and PVA-MBs coated with SPIONs were detectable at each concentration. At the highest concentration, lipid-MBs 6-10μm and 4-6μm showed an overall increase in positive contrast, whereas at a moderate concentration, only lipid-MBs 6-10μm displayed an increase. Negative contrast was also observed from two largest lipid-MBs at high concentration. These data indicate that lipid-MBs larger than 4μm are candidates for PCI, and 5×106 MBs/ml may be the lowest concentration suitable for generating visible phase contrast in vivo. Identifying a suitable MB for PCI may facilitate future clinical translation.

Contrast-enhanced US in Local Ablative Therapy and Secondary Surveillance for Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) has a high incidence of recurrence following therapy. Therefore, secondary surveillance (scheduled follow-up imaging after treatment) is an important part of disease management. The recent approval in the United States for use of a microbubble-based contrast agent for US liver imaging promotes the increased use of contrast-enhanced US (CEUS) in patients with HCC. Although the criteria for the diagnosis of HCC at CEUS are well described, there is a paucity of published literature describing the role of CEUS in ablative therapy and secondary surveillance. In the setting of ablative therapy, CEUS can have vital roles, including patient selection, intraprocedural guidance, and immediate postprocedural assessment. Although CEUS is not widely used, the authors found that it can be used to accurately detect residual or recurrent tumor, characterize the geographic pattern of recurrence (intrazonal, extrazonal, segmental, or remote), and assess for tumor in vein. In addition, similar to primary surveillance, secondary surveillance includes assessment of the entire liver for evaluation of new nodules. Arterial phase hyperenhancement is the reference standard characteristic of disease recurrence at secondary surveillance with CEUS. ©RSNA, 2019 See discussion on this article by Rodgers.

Size determination of microbubbles in optical microscopy: a best-case scenario

Microbubble-based ultrasound contrast agents are used in clinical settings to enhance backscattered ultrasound signals from blood during perfusion and blood flow measurements. The dynamics of microbubbles contained in ultrasound contrast agents are typically studied with a high-speed camera attached to a microscope. Such microbubbles, with resting diameters between 1 µm and 7 µm, are considered in optical focus if the bubble centers are in the focal plane of the objective lens. Nonetheless, when a three-dimensional object, a stack of infinitely thin two-dimensional layers, is imaged through a microscope, the image formed onto the charge coupled device element consists of contributions from all layers. If a bubble is larger than the depth of focus, the part of the bubble above the focal plane influences the image formation and therefore the bubble size measured. If a bubble is of a size in the order of the wavelengths of the light used, the system resolution and the segmentation method influence the bubble size measured. In this study, the projections of three dimensional microbubbles (hollow spheres) were computed with an ideal, weighted three-dimensional point spread function to find out under which circumstances the optical image formation leads to a significant deviation in measurement of the actual size. The artificial images were subjected to segmentation techniques for objectively comparing original microbubble sizes with measured microbubble sizes. Results showed that a systematic error was observed for objects in focus with radius ≤ 1.65µm. Also it was concluded that even though a three-dimensional object is in focus, there is discrepancy of up to 0.66% in size measurement. In addition, size measurement of an object for the same shift above and below focus could differ by up to 3.6%. Moreover, defocusing above 25% severely deviates size measurements while defocusing up to 90% could result in mean percentage error of up to 67.96.

Assessment of renal perfusion impairment in a rat model of acute renal congestion using contrast-enhanced ultrasonography

Renal congestion is caused by elevated central venous pressure (CVP), and decreases glomerular filtration in patients with congestive heart failure. Since real-time contrast-enhanced ultrasonography (CEUS) using microbubble-based contrast agents can visualize the perfused microvascular bed, we sought to evaluate the impairment of renal perfusion during acute renal congestion with CEUS. In Wister rats, CEUS of kidney was performed with the direct monitoring of CVP and intra-renal pressure (IRP). When CVP was elevated to 10 and 15mmHg after the bolus injection of normal saline via the femoral vein, peak intensity (PI, dB) and time to PI (TTP) in the renal cortex and medulla were compared with control rats. There was a strong correlation between IRP and CVP (r=0.95, p<0.0001). In the congestion model, more time was required for enhancement of the parenchyma, especially in the medulla compared to control; TTP of the medulla and cortex at 15mmHg CVP (CVP15) was significantly prolonged compared with controls (medulla, 4351±98 vs. 1415±267ms, p=0.003; cortex, 3219±106 vs. 1335±264ms, p=0.005). In addition, medullary PI at CVP15 decreased, but not significantly, compared to those of controls and at 10mmHg CVP (20.1±0.9, 22.8±1.6, 21.6±0.2dB). In contrast, cortical PIs at CVP15 were significantly lower than that of control (24.6±1.0 vs. 31.4±1.0dB, p=0.007). CEUS revealed that impaired renal parenchymal flow in an acute congestion model is accompanied with increased renal interstitial pressure.

Extended Lifetime In Vivo Pulse Stimulated Ultrasound Imaging.

An on-demand long-lived ultrasound contrast agent that can be activated with single pulse stimulated imaging (SPSI) has been developed using hard shell liquid perfluoropentane filled silica 500-nm nanoparticles for tumor ultrasound imaging. SPSI was tested on LnCAP prostate tumor models in mice; tumor localization was observed after intravenous (IV) injection of the contrast agent. Consistent with enhanced permeability and retention, the silica nanoparticles displayed an extended imaging lifetime of 3.3±1 days (mean±standard deviation). With added tumor specific folate functionalization, the useful lifetime was extended to 12 ± 2 days; in contrast to ligand-based tumor targeting, the effect of the ligands in this application is enhanced nanoparticle retention by the tumor. This paper demonstrates for the first time that IV injected functionalized silica contrast agents can be imaged with an in vivo lifetime ~500 times longer than current microbubble-based contrast agents. Such functionalized long-lived contrast agents may lead to new applications in tumor monitoring and therapy.

Ultrasonography for Noninvasive Assessment of Portal Hypertension.

Portal hypertension is a major pathophysiology in patients with cirrhosis. Portal pressure is the gold standard to evaluate the severity of portal hypertension, and radiological intervention is the only procedure for pressure measurement. Ultrasound (US) is a simple and noninvasive imaging modality available worldwide. B-mode imaging allows broad applications for patients to detect and characterize chronic liver diseases and focal hepatic lesions. The Doppler technique offers real-time observation of blood flow with qualitative and quantitative assessments, and the application of microbubble-based contrast agents has improved the detectability of peripheral blood flow. In addition, elastography for the liver and spleen covers a wider field beyond the original purpose of fibrosis assessment. These developments enhance the practical use of US in the evaluation of portal hemodynamic abnormalities. This article reviews the recent progress of US in the assessment of portal hypertension.

Pipe Phantoms With Applications in Molecular Imaging and System Characterization.

Pipe (vessel) phantoms mimicking human tissue and blood flow are widely used for cardiovascular related research in medical ultrasound. Pipe phantom studies require the development of materials and liquids that match the acoustic properties of soft tissue, blood vessel wall, and blood. Over recent years, pipe phantoms have been developed to mimic the molecular properties of the simulated blood vessels. In this paper, the design, construction, and functionalization of pipe phantoms are introduced and validated for applications in molecular imaging and ultrasound imaging system characterization. There are three major types of pipe phantoms introduced: 1) a gelatin-based pipe phantom; 2) a polydimethylsiloxane-based pipe phantom; and 3) the "Edinburgh pipe phantom." These phantoms may be used in the validation and assessment of the dynamics of microbubble-based contrast agents and, in the case of a small diameter tube phantom, for assessing imaging system spatial resolution/contrast performance. The materials and procedures required to address each of the phantoms are described.

Coating microbubbles with nanoparticles for medical imaging and drug delivery.

Coating microbubbles with nanoparticles for medical imaging and drug delivery.

Quantitative Nonlinear Contrast-Enhanced Ultrasound of the Breast.

Breast cancer is the most frequent type of cancer among women (25% of all cancers). The angiogenic process that fuels the growth of tumors is a potential early indicator for differentiating between malignant and benign tumors. Recently, the use of microbubble-based contrast agents combined with ultrasound has allowed the development of contrast agent-specific imaging modes that provide visualization of tumor neovascularity. Contrast-enhanced Doppler, harmonic, and subharmonic imaging are some of the imaging modes that have been investigated for visualizing and quantifying the vascularity in breast tumors.

Ultrasonic Contrast Portography for Demonstration of Intrahepatic Porto-systemic Shunts

Spontaneous intrahepatic porto-systemic shunts (IHPSS) can be disclosed with ultrasound (US) and color Doppler ultrasound (CDU). However, direct evidence of the shunt on US or CDU may not be convincing. In this report we demonstrate the presence of IHPSS by ultrasonic contrast portography with intravenous injection of microbubble-based contrast agent (MBCA). With this technique, the MBCA was depicted to enter the hepatic vein through the shunt, and then flowed into the inferior vena cava.

Role of contrast-enhanced ultrasonography with Sonazoid for hepatocellular carcinoma: evidence from a 10-year experience.

Hepatocellular carcinoma (HCC) represents primary liver cancer. Because the development of HCC limits the prognosis as well as the quality of life of the patients, its management should be properly conducted based on an accurate diagnosis. The liver is the major target organ of ultrasound (US), which is the simple, non-invasive, and real-time imaging method available worldwide. Microbubble-based contrast agents are safe and reliable and have become popular, which has resulted in the improvement of diagnostic performances of US due to the increased detectability of the peripheral blood flow. Sonazoid (GE Healthcare, Waukesha, WI, USA), a second-generation contrast agent, shows the unique property of accumulation in the liver and spleen. Contrast-enhanced US with Sonazoid is now one of the most frequently used modalities in the practical management of liver tumors, including the detection and characterization of the nodule, evaluation of the effects of non-surgical treatment, intraoperative support, and post-treatment surveillance. This article reviews the 10-year evidence for contrast-enhanced US with Sonazoid in the practical management of HCC.

Fluorine in medical microbubbles – Methodologies implemented for engineering and investigating fluorocarbon-based microbubbles

Abstract Gaseous microbubbles are being used in cardiovascular diagnostic procedures. They have further potential in diagnosis of tumours, vascular and blood flow abnormalities, as well as for targeted, ultrasound-triggered drug delivery and as intravascular mechanical devices. All the commercially available microbubble-based contrast agents comprise a fluorinated inner gas in their composition. Fluorinated components (fluorocarbon gases, self-assembling perfluoroalkylated surfactants) can play a key role in the engineering, investigation and development of microbubbles. Fluorocarbon gases provide osmotic stabilization and a co-surfactant contribution to interfacial tension reduction. Perfluoroalkylated surfactants self-assemble in aqueous media to form bubble shells with exceptional elasticity and resilience, and, optionally, effective anchorage for surface functionalization. This paper critically reviews the foremost methods used for preparing and monitoring microbubble suspensions. In particular, it identifies some common pitfalls encountered in the determination of microbubble sizes. The paper also reviews the methods used for collecting reliable data on the bubble morphology and shell structure that are required for understanding, controlling and improving their functional properties. Models for bubble shell studies include spontaneously adsorbed Gibbs films and spread Langmuir monolayers.

Role of intra-operative contrast-enhanced ultrasound (CEUS) in robotic-assisted nephron-sparing surgery.

This review examines studies of intra-operative contrast-enhanced ultrasound (CEUS) and its emerging role and advantages in robotic-assisted nephron-sparing surgery. Contrast-enhanced ultrasound is a technology that combines the use of second-generation contrast agents consisting of microbubbles with existent ultrasound techniques. Until now, this novel technology has aided surgeons with procedures involving the liver. However, with recent advances in the CEUS technique and the introduction of robotics in nephron-sparing surgery, CEUS has proven to be efficacious in answering several clinical questions with respect to the kidneys. In addition, the introduction of the microbubble-based contrast agents has increased the image quality and signal uptake by the ultrasound probe. This has led to better, enhanced scanning of the macro and microvasculature of the kidneys, making CEUS a powerful diagnostic modality. This imaging method is capable of further lowering the learning curve and warm ischemia time (WIT) during robotic-assisted nephron-sparing surgery, with its increased level of capillary perfusion and imaging. CEUS has the potential to increase the sensitivity and specificity of intra-operative images, and can significantly improve the outcome of robotic-assisted nephron-sparing surgery by increasing the precision and diagnostic insight of the surgeon. The purpose of this article is to review the practical and potential uses of CEUS as an intra-operative imaging technique during robotic-assisted nephron-sparing surgery.

Contrast-Enhanced Ultrasound

The recent decade has witnessed the great improvement of contrast-enhanced ultrasound (CEUS) and its extensive use in clinical practice, which is undoubtedly the major breakthrough in the field of diagnostic ultrasound in recent years. The concept of CEUS can be looked back to 60s in the last century, whereas only in 2000s CEUS regained increasing attention in both clinical practice and basic research. The current popularization of CEUS is largely due to the emergence of low acoustic power contrast-specific imaging mode and microbubble-based contrast agent filled with inert gas. After administration of ultrasound contrast agent intravenously, the low acoustic power contrast-specific imaging mode facilitates visualization of the nonlinear signals from the microbubbles in the circulation and suppresses the linear signals from the surrounding tissues, which leads to an improved signal-to-noise ratio and facilitates depiction of macro- and microcirculation of the region of interest (ROI) noninvasively. The low acoustic power also limits the damage to the microbubbles under acoustic push; thus, more microbubbles will remain in the circulation and a long time CEUS depiction is available [1].

Microbubbles as a scattering contrast agent for grating-based x-ray dark-field imaging

In clinically established—absorption-based—biomedical x-ray imaging, contrast agents with high atomic numbers (e.g. iodine) are commonly used for contrast enhancement. The development of novel x-ray contrast modalities such as phase contrast and dark-field contrast opens up the possible use of alternative contrast media in x-ray imaging. We investigate using ultrasound contrast agents, which unlike iodine-based contrast agents can also be administered to patients with renal impairment and thyroid dysfunction, for application with a recently developed novel x-ray dark-field imaging modality. To produce contrast from these microbubble-based contrast agents, our method exploits ultra-small-angle coherent x-ray scattering. Such scattering dark-field x-ray images can be obtained with a grating-based x-ray imaging setup, together with refraction-based differential phase-contrast and the conventional attenuation contrast images. In this work we specifically show that ultrasound contrast agents based on microbubbles can be used to produce strongly enhanced dark-field contrast, with superior contrast-to-noise ratio compared to the attenuation signal. We also demonstrate that this method works well with an x-ray tube-based setup and that the relative contrast gain even increases when the pixel size is increased from tenths of microns to clinically compatible detector resolutions about up to a millimetre.

Diagnostic value of endoscopic ultrasound-guided directional eFLOW in solid pancreatic lesions.

Ultrasound using microbubble-based contrast agents is useful for vascular imaging. Directional eFLOW (D-eFLOW) is a novel technology for vascular assessment that provides high spatial and temporal resolution. The purpose of this study was to investigate the utility of endoscopic ultrasound (EUS)-guided D-eFlow before and after administration of an ultrasound contrast agent (USCA) for assessing the vascularity of solid pancreatic lesions. D-eFlow was compared to power Doppler EUS (PD-EUS) or color Doppler EUS (CD-EUS) before and after USCA injection. We also evaluated the Visual Vascular Assessment (ViVA) scale for the estimation of vascularity and investigated its reliability using the interclass correlation coefficient (ICC). From January 2007 to March 2007, 35 patients (mean age, 64.5years old; age range, 28-81years) underwent EUS followed by D-eFLOW EUS, PD-EUS, and CD-EUS before and after administration of USCA. The pancreatic parenchymal ViVA score, pancreatic vascular pattern, and ICC were evaluated for all lesions. Concerning the sensitivity for detection of the hypovascular pattern in pancreatic adenocarcinoma, D-eFLOW (before and after USCA) had similar sensitivity to PD-EUS (before and after USCA) and CD-EUS (before and after USCA). D-eFLOW after contrast showed the highest accuracy (82.3%) and negative predictive value (53.8%) among all the modalities investigated. There was a good correlation among the ViVA scores for D-eFLOW before contrast, those for D-eFLOW EUS, and those for PD-EUS and CD-EUS. The reliability of the ViVA scale was excellent with an ICC of 0.81. In conclusion, D-eFLOW EUS is a sensitive, reliable, and highly accurate method of assessment of pancreatic vascularity. D-eFLOW EUS with contrast was more sensitive than PD-EUS and CD-EUS for assessment of pancreatic vascularity.

Abstract P4-03-10: Sonographic-pathological correlation in contrast-enhanced ultrasonography in the diagnosis of breast cancers.

Abstract Background: As contrast-enhanced ultrasonography (CEUS) in the diagnosis of breast masses has been performed less frequently than other imaging modalities, it's efficacy evaluation has not been established. CEUS with Sonazoid, which is microbubble-based contrast agent, allows visualization of the mass bloodstream, therefore the classification of enhancement patterns in CEUS could increase diagnostic yield for breast masses. To achieve this, a clear standard for the CEUS evaluation is needed. The purpose of this study was to identify CEUS findings for malignancies and clarify sonographic-pathological correlation of breast cancers. Material and Method: Present study included 20 patients with invasive ductal cancer who underwent operation for primary therapy without any chemotherapy or hormonal therapy. We contrasted CEUS features with Sonazoid with surgical specimens retrospectively. As malignant findings, the presence of focal perfusion defects inside masses and enhancement of outside masses were chosen. Result: All of the 20 cases displayed focal perfusion defects. 9 cases of those could be successfully assessed in the same sections histopathologically and ultrasonographically. Histopathological findings showed those defects to be fibrotic foci inside masses in 7cases (77.7%). While, 6 cases of all (30%) showed stains outside tumor, and only one case was found out to be fibrotic growth with cancer cells. Conclusion: focal perfusion defects of breast masses in CEUS were considered to be specific for malignancy, and they seemed to be fibrotic foci histopathologically. Desmoplastic reaction has been observed in epithelial solid tumor biology, and if those defects reflect the desmoplasia defects could be the proof of malignancy. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-03-10.

Double contrast-enhanced two-dimensional and three-dimensional ultrasonography for evaluation of gastric lesions

To investigate the value of two-dimensional (2D) and three-dimensional (3D) double contrast-enhanced ultrasonography (DCUS) imaging for evaluation of gastric lesions. 2D and 3D DCUS imaging with both oral and intravenous administrations of contrast agents was used to assess gastroscopiclly-confirmed gastric lesions in 46 patients with benign and malignant diseases. Initially, liquid-based ultrasound contrast agent (Xinzhang®) was given orally at dose of 500-600 mL for conventional ultrasound examination of the gastric lesions, and then a microbubble-based contrast agent (SonoVue) was injected intravenously at dose of 1.2-2.4 mL in bolus fashion to assess the perfusion pattern of the lesions using contrast imaging modes. The parameters derived from time-intensity curves including the arrival time (AT), time to peak (TTP), peak intensity (PI) and enhanced intensity (EI) were measured on the 2D DCUS imaging. 3D DCUS of the lesions was acquired to demonstrate the value of this imaging mode. There were 22 cases with benign lesions including chronic gastritis (n = 5), gastric ulcer (n = 9), gastric polyps (n = 3), gastric stromal tumors (n = 5), and 24 cases with malignant lesions including gastric cancer (n = 20), gastric cardia carcinoma (n = 3) and post-operative recurrent gastric cancer (n = 1) in the study. The oral contrast-enhanced ultrasonography (CEUS) imaging of the stomach clearly demonstrated the anatomy of the stomach and morphologic features of gastric lesions. With optimal scanning window and imaging display under oral CEUS, intravenous CEUS clearly showed the perfusion of gastric lesions with various characteristic manifestations. Both 2D and 3D DCUS images clearly demonstrated normal gastric wall as a three-layer structure, from the inside out, hyperechoic mucosa, hypoechoic muscularis and hyperechoic serosa, respectively. There were statistical significant differences of AT (8.68 ± 2.06 vs 10.43 ± 2.75, P = 0.017), PI (34.64 ± 6.63 vs 29.58 ± 8.22, P = 0.023) and EI (29.72 ± 6.69 vs 22.66 ± 7.01, P = 0.001) between malignant lesions and normal gastric wall. However, no differences of AT, PI and EI between benign lesions and normal gastric wall tissue were found. 3D DCUS could intuitively display morphological features and vascularities of the lesions with multiplanar and volume views. 3D DCUS imaging provided comprehensive information complementary to 2D imaging. The crater or wellhead appearances and feeding vessels as well as distorted nourishing vasculature of gastric carcinoma were better seen with 3D imaging than 2D imaging. DCUS imaging can simultaneously display the anatomic and perfusion features of gastric lesions. 3D DCUS can provide additional information to 2D DCUS for evaluation of gastric lesions.