Ultrasound contrast agent, Levovist microbubbles are phagocytosed by Kupffer cells-In vitro and in vivo studies

Effect of Poly(ethylene glycol) Configuration on Microbubble Pharmacokinetics

Microbubbles (MBs) hold substantial promise for medical imaging and therapy; nonetheless, knowledge gaps persist between composition, structure, and in vivo performance, especially with respect to pharmacokinetics. Of particular interest is the role of the poly(ethylene glycol) (PEG) layer, which is thought to shield the MB against opsonization and rapid clearance but is also known to cause an antibody response upon multiple injections. The goal of this study was, therefore, to elucidate the role of the PEG layer in circulation persistence of MBs in the naïve animal (prior to an adaptive immune response). Here, we directly observe the number and size of individual MBs obtained from blood samples, unifying size and concentration into the microbubble volume dose (MVD) parameter. This approach enables direct evaluation of the pharmacokinetics of intact MBs, comprising both the lipid shell and gaseous core, rather than separately assessing the lipid or gas components. We examined the in vivo circulation persistence of 3 μm diameter phospholipid-coated MBs with three different mPEG2000 content: 2 mol % (mushroom), 5 mol % (intermediate), and 10 mol % (brush). MB size and concentration in the blood were evaluated by a hemocytometer analysis over 30 min following intravenous injections of 20 and 40 μL/kg MVD in Sprague-Dawley rats. Interestingly, pharmacokinetic analysis demonstrated that increasing PEG concentration on the MB surface resulted in faster clearance. This was evidenced by a 1.6-fold reduction in half-life and area under the curve (AUC) (p < 0.05) in the central compartment. Conversely, the AUC in the peripheral compartment increased with PEG density, suggesting enhanced MB trapping by the mononuclear phagocyte system. This was supported by an in vitro assay, which showed a significant rise in complement C3a activation with a higher PEG content. In conclusion, a minimal PEG concentration on the MB shell (mushroom configuration) was found to prolong circulation and mitigate immunogenicity.

Intra-individual comparison of Sonazoid contrast-enhanced ultrasound and SonoVue contrast-enhanced ultrasound in diagnosing hepatocellular carcinoma

PURPOSE

To assess whether the diagnostic performance of Sonazoid contrast-enhanced ultrasound (SZUS) is non-inferior to that of SonoVue contrast-enhanced ultrasound (SVUS) in diagnosing hepatocellular carcinoma (HCC) in individuals with high risk.

MATERIALS AND METHODS

This prospective study was conducted from October 2020 to May 2022 and included participants with a high risk of HCC who underwent SZUS and SVUS. All lesions were confirmed by clinical or pathological diagnosis. Each nodule was classified according to the Contrast-Enhanced Ultrasound Liver Imaging Reporting and Data System version 2017 (CEUS LI-RADS v2017) for SVUS and SZUS and the modified CEUS LI-RADS (using Kupffer phase defect instead of late and mild washout) for SZUS. The diagnostic performance of both two modalities for all observations was compared. Analysis of the vascular phase and Kupffer phase imaging characteristics of CEUS was performed.

RESULTS

One hundred and fifteen focal liver lesions from 113 patients (94 HCCs, 12 non-HCC malignancies, and 9 benign lesions) were analysed. According to CEUS LI-RADS (v2017), SVUS and SZUS showed similar sensitivity (71.3% vs. 72.3%) and specificity (85.7% vs. 81.0%) in HCC diagnosis. However, the modified CEUS LI-RADS did not significantly improve the diagnostic efficacy of Sonazoid compared to CEUS LI-RADS v2017, having equivalent sensitivity (73.4% vs. 72.3%) and specificity (81.0% vs. 81.0%). The agreement between SVUS and SZUS for all observations was 0.610 (95% CI 0.475, 0.745), while for HCCs it was 0.452 (95% CI 0.257, 0.647).

CONCLUSION

Using LI-RADS v2017, SZUS and SVUS showed non-inferior efficacy in evaluating HCC lesions. In addition, adding Kupffer phase defects to SZUS does not notably improve its diagnostic efficacy.

Evaluation of Liposome-Loaded Microbubbles as a Theranostic Tool in a Murine Collagen-Induced Arthritis Model

Rheumatoid arthritis (RA) is an autoimmune disease characterized by severe inflammation of the synovial tissue. Here, we assess the feasibility of liposome-loaded microbubbles as theranostic agents in a murine arthritis model. First, contrast-enhanced ultrasound (CEUS) was used to quantify neovascularization in this model since CEUS is well-established for RA diagnosis in humans. Next, the potential of liposome-loaded microbubbles and ultrasound (US) to selectively enhance liposome delivery to the synovium was evaluated with in vivo fluorescence imaging. This procedure is made very challenging by the presence of hard joints and by the limited lifetime of the microbubbles. The inflamed knee joints were exposed to therapeutic US after intravenous injection of liposome-loaded microbubbles. Loaded microbubbles were found to be quickly captured by the liver. This resulted in fast clearance of attached liposomes while free and long-circulating liposomes were able to accumulate over time in the inflamed joints. Our observations show that murine arthritis models are not well-suited for evaluating the potential of microbubble-mediated drug delivery in joints given: (i) restricted microbubble passage in murine synovial vasculature and (ii) limited control over the exact ultrasound conditions in situ given the much shorter length scale of the murine joints as compared to the therapeutic wavelength.

Accelerated Clearance of Ultrasound Contrast Agents Containing Polyethylene Glycol is Associated with the Generation of Anti-Polyethylene Glycol Antibodies

Emerging evidence suggests that the immune system can recognize polyethylene glycol (PEG), leading to the accelerated blood clearance (ABC) of PEGylated particles. Our aim here was to study the generation of anti-PEG immunity and changes in PEGylated microbubble pharmacokinetics during repeated contrast-enhanced ultrasound imaging in rats. We administered homemade PEGylated microbubbles multiple times over a 28-d period and observed dramatically accelerated clearance (4.2 × reduction in half-life), which was associated with robust anti-PEG IgM and anti-PEG IgG antibody production. Dosing animals with free PEG as a competition agent before homemade PEGylated microbubble administration significantly prolonged microbubble circulation, suggesting that ABC was largely driven by circulating anti-PEG antibodies. Experiments with U.S. Food and Drug Administration-approved Definity microbubbles similarly resulted in ABC and the generation of anti-PEG antibodies. Experiments repeated with non-PEGylated Optison microbubbles revealed a slight shift in clearance, indicating that immunologic factors beyond anti-PEG immunity may play a role in ABC, especially of non-PEGylated agents.

Synthesis and characterization of transiently stable albumin-coated microbubbles via a flow-focusing microfluidic device

We describe a method for synthesizing albumin-shelled, large-diameter (>10 μm), transiently stable microbubbles using a flow-focusing microfluidic device (FFMD). The microfluidic device enables microbubbles to be produced immediately before insonation, thus relaxing the requirements for stability. Both reconstituted fractionated bovine serum albumin (BSA) and fresh bovine blood plasma were investigated as shell stabilizers. Microbubble coalescence was inhibited by the addition of either dextrose or glycerol and propylene glycol. Microbubbles were observed to have an acoustic half-life of approximately 6 s. Microbubbles generated directly within a vessel phantom containing flowing blood produced a 6.5-dB increase in acoustic signal within the lumen. Microbubbles generated in real time upstream of in vitro rat aortic smooth muscle cells under physiologic flow conditions successfully permeabilized 58% of the cells on insonation at a peak negative pressure of 200 kPa. These results indicate that transiently stable microbubbles produced via flow-focusing microfluidic devices are capable of image enhancement and drug delivery. In addition, successful microbubble production with blood plasma suggests the potential to use blood as a stabilizing shell.

Enhanced intracellular delivery of a model drug using microbubbles produced by a microfluidic device

Focal drug delivery to a vessel wall facilitated by intravascular ultrasound and microbubbles holds promise as a potential therapy for atherosclerosis. Conventional methods of microbubble administration result in rapid clearance from the bloodstream and significant drug loss. To address these limitations, we evaluated whether drug delivery could be achieved with transiently stable microbubbles produced in real time and in close proximity to the therapeutic site. Rat aortic smooth muscle cells were placed in a flow chamber designed to simulate physiological flow conditions. A flow-focusing microfluidic device produced 8 μm diameter monodisperse microbubbles within the flow chamber, and ultrasound was applied to enhance uptake of a surrogate drug (calcein). Acoustic pressures up to 300 kPa and flow rates up to 18 mL/s were investigated. Microbubbles generated by the flow-focusing microfluidic device were stabilized with a polyethylene glycol-40 stearate shell and had either a perfluorobutane (PFB) or nitrogen gas core. The gas core composition affected stability, with PFB and nitrogen microbubbles exhibiting half-lives of 40.7 and 18.2 s, respectively. Calcein uptake was observed at lower acoustic pressures with nitrogen microbubbles (100 kPa) than with PFB microbubbles (200 kPa) (p < 0.05, n > 3). In addition, delivery was observed at all flow rates, with maximal delivery (>70% of cells) occurring at a flow rate of 9 mL/s. These results demonstrate the potential of transiently stable microbubbles produced in real time and in close proximity to the intended therapeutic site for enhancing localized drug delivery.

What about non-alcoholic fatty liver disease as a new criterion to define metabolic syndrome?

Non-alcoholic fatty liver disease (NAFLD) is currently not a component of the diagnostic criteria for metabolic syndrome (MetS); however, the development of NAFLD has some common mechanisms with the development of MetS, as they share the pathophysiologic basis of insulin resistance. It is also recognized that NAFLD is the hepatic manifestation of MetS. To define MetS, the presence of at least three of the proposed criteria is required, and sometimes it is sufficient to have only one laboratory value, modified by diet or drugs, for the classification of MetS. Ultrasonographically-detected NAFLD (US-NAFLD) is more stable, only changing during the middle- to long-term. Although controversies over MetS continue, and considering that abdominal ultrasonography for diagnosing NAFLD has high specificity and guidelines to modify the natural course of NAFLD by diet composition or lifestyle have not yet been established, why should we not introduce US-NAFLD as a new criterion to define MetS?

Liquid Flooded Flow-Focusing Microfluidic Device for in situ Generation of Monodisperse Microbubbles

Current microbubble-based ultrasound contrast agents are administered intravenously resulting in large losses of contrast agent, systemic distribution, and strict requirements for microbubble longevity and diameter size. Instead we propose in situ production of microbubbles directly within the vasculature to avoid these limitations. Flow focusing microfluidic devices (FFMDs) are a promising technology for enabling in situ production as they can produce microbubbles with precisely controlled diameters in real-time. While the microfluidic chips are small, the addition of inlets and interconnects to supply the gas and liquid phase greatly increases the footprint of these devices preventing the miniaturization of FFMDs to sizes compatible with medium and small vessels. To overcome this challenge, we introduce a new method for supplying the liquid (shell) phase to an FFMD that eliminates bulky interconnects. A pressurized liquid-filled chamber is coupled to the liquid inlets of an FFMD, which we term a flooded FFMD. The microbubble diameter and production rate of flooded FFMDs were measured optically over a range of gas pressures and liquid flow rates. The smallest FFMD manufactured measured 14.5 × 2.8 × 2.3 mm. A minimum microbubble diameter of 8.1 ± 0.3 μm was achieved at a production rate of 450,000 microbubbles/s (MB/s). This represents a significant improvement with respect to any previously reported result. The flooded design also simplifies parallelization and production rates of up to 670,000 MB/s were achieved using a parallelized version of the flooded FFMD. In addition, an intravascular ultrasound (IVUS) catheter was coupled to the flooded FFMD to produce an integrated ultrasound contrast imaging device. B-mode and IVUS images of microbubbles produced from a flooded FFMD in a gelatin phantom vessel were acquired to demonstrate the potential of in situ microbubble production and real-time imaging. Microbubble production rates of 222,000 MB/s from a flooded FFMD within the vessel lumen provided a 23 dB increase in B-mode contrast. Overall, the flooded design is a critical contribution towards the long- term goal of utilizing in situ produced microbubbles for contrast enhanced ultrasound imaging of, and drug delivery to, the vasculature.

Does hepatic vein transit time performed with contrast-enhanced ultrasound predict the severity of hepatic fibrosis?

Previously published data suggest a hepatic vein transit time (HVTT) threshold of more than 24 s can distinguish mild to moderate from advanced fibrosis. In this study, we attempted to validate HVTT as a noninvasive index of hepatic fibrosis. Patients were scanned using real-time, pulse-inversion mode following bolus injections of the contrast agent Definity. HVTT was correlated with the degree of fibrosis obtained from contemporaneous liver biopsy. The study population included 40 patients with chronic liver disease and five healthy volunteers. Mean HVTT correlated with histologic grade as follows: absence/minimal fibrosis (n = 18), 25.6 ± 11.8 s; moderate fibrosis (n = 17), 21.5 ± 5.9 s; and severe fibrosis (n = 8), 20.9 ± 5.5 s, (p = .615). Poor sensitivity (57%) and specificity (43%) prevent validation of the previously published HVTT threshold as a surrogate marker of hepatic fibrosis. Further work investigating the different interaction of Definity, SonoVue and Levovist with the reticulo-endothelial system may help explain the discrepant results reported here.

Diagnosis and evaluation of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of elevated liver function tests results, after the commonly investigated causes have been excluded, and frequently coexists with type 2 diabetes mellitus (T2DM) because the conditions have common risk factors. As both T2DM and NAFLD are related to adverse outcomes of the other, diagnosis and valuation of fatty liver is an important part of the management of diabetes. Although noninvasive methods, such as biomarkers, panel markers, and imaging, may support a diagnostic evaluation of NAFLD patients, accurate histopathological findings cannot be achieved without a liver biopsy. As it is important to know whether steatohepatitis and liver fibrosis are present for the management of NAFLD, liver biopsy remains the gold standard for NAFLD diagnosis and evaluation. Therefore, new investigations of the pathogenesis of NAFLD are necessary to develop useful biomarkers that could provide a reliable noninvasive alternative to liver biopsy.

Evaluation of hepatocellular carcinoma by contrast-enhanced sonography: correlation with pathologic differentiation

OBJECTIVES

The purpose of this study was to determine whether contrast-enhanced sonography can be used to differentiate histopathologic grades of hepatocellular carcinoma.

METHODS

This study included 54 patients with hepatocellular carcinomas. All patients underwent fundamental and contrast-enhanced sonographic examinations. Auto-tracking contrast quantification software was used to determine the contrast arrival time, time to peak, peak intensity, contrast-enhanced time, wash-out time, enhancement slope, and clearance slope of the lesions. All lesions were confirmed by surgery. The hepatocellular carcinoma lesions were divided into 2 groups according to the World Health Organization grading system: group 1 (well-differentiated hepatocellular carcinomas) and group 2 (moderately to poorly differentiated carcinomas). The enhancement parameters between the groups were compared using a Student t test.

RESULTS

Fourteen of 20 well-differentiated lesions showed a "fast-in, slow-out" enhancement pattern, whereas 6 showed a "fast-in, fast-out" pattern. Thirty-three of 34 moderately to poorly differentiated lesions showed a fast-in, fast-out pattern, whereas only 1 showed a fast-in, slow-out pattern. The differences in the time to peak, contrast-enhanced time, wash-out time, enhancement slope, and clearance slope between the groups were statistically significant (P < .05), whereas the differences in the arrival time and peak intensity were not significant (P > .05).

CONCLUSIONS

The contrast patterns of well-differentiated and moderately to poorly differentiated hepatocellular carcinomas were quite different on contrast-enhanced sonography. The time to peak, contrast-enhanced time, and wash-out time of the well-differentiated hepatocellular carcinomas were longer than those of the moderately to poorly differentiated carcinomas, whereas the enhancement slope and clearance slope of the well-differentiated lesions were lower those that of the moderately to poorly differentiated lesions.

Crucial role of impaired Kupffer cell phagocytosis on the decreased Sonazoid-enhanced echogenicity in a liver of a nonalchoholic steatohepatitis rat model

AIMS

To evaluate the dynamics of Kupffer cell (KC) phagocytosis by performing both in vivo and in vitro studies using Sonazoid (GE Healthcare, Oslo) in a rat nonalcoholic steatohepatitis (NASH) model.

METHODS

Contrast enhanced ultrasonography (CEUS) was performed on a rat NASH model induced by a methionine choline deficient diet (MCDD) and control rats, and Sonazoid was used to measure the signal intensity in the liver parenchyma. The uptake of Sonazoid by the KCs was observed by intravital microscopy. Their phagocytic capability was evaluated in vitro using isolated and cultured KCs. The uptake of fluorescein isothiocyanate (FITC)-labeled latex beads was observed and quantitatively analyzed by flow cytometry.

RESULTS

In the MCDD group, liver parenchymal enhancement was reduced 20 min after the Sonazoid injection. Microscopic observation of the isolated and cultured KCs revealed that the number of phagocytosed Sonazoid microbubbles was significantly decreased. Confocal laser scanning microscopic (CLSM) observation showed a decrease in the uptake of the latex beads. A decreased phagocytic capacity in the MCDD group was suggested by the quantitative analysis using flow cytometry, as well as by intravital microscopy.

CONCLUSIONS

CEUS with Sonazoid is a powerful evaluation tool to diagnose NASH from an early stage of the disease.

Nonalcoholic fatty liver disease: a review and update

The spectrum of nonalcoholic fatty liver disease (NAFLD) ranges from asymptomatic steatosis to nonalcoholic steatohepatitis (NASH) and cirrhosis. Hepatic steatosis occurs when free fatty acids, released in the setting of insulin resistance and the metabolic syndrome, are taken up by the liver. Additional biochemical insults, including oxidative stress, upregulation of inflammatory mediators, and dysregulated apoptosis, can result in inflammation (producing NASH) and fibrosis. Noninvasive methods (e.g., abdominal ultrasonography) are safe ways to support a diagnosis of hepatic steatosis, but advanced liver histopathologic findings including NASH and fibrosis cannot be identified without pursuing liver biopsy. Recent advances in serologic and imaging methods aim to determine severity of inflammation and fibrosis noninvasively. Currently, therapeutic options for NAFLD are limited to medications that reduce risk factors, but the future holds promise for therapies that might slow the progression of this increasingly prevalent disorder.

Diagnosis of liver cirrhosis with contrast-enhanced ultrasound

The assessment of the extent of liver fibrosis is very important for the prognosis and clinical management of chronic liver diseases. Although liver biopsy is the gold standard for the assessment of liver fibrosis, new non-invasive diagnostic methods are urgently needed in clinical work due to certain limitations and complications of biopsy. Noninvasive imaging studies play an important role in the diagnosis of focal liver disease and diffuse liver diseases. Among them, ultrasonography is the first choice for study of the liver in clinical work. With the development of ultrasound contrast agents and contrast specific imaging techniques, contrast-enhanced ultrasound (CEUS) shows good performance and great potential in the evaluation of liver fibrosis. Researchers have tried different kinds of contrast agent and imaging method, such as arrival time of contrast agent in the hepatic vein, and quantitative analysis of the enhancement level of liver parenchyma, to evaluate the degree of liver fibrosis during the past 10 years. This review mainly summarizes the clinical studies concerning the assessment of liver fibrosis using CEUS.

Preclinical acute toxicology study of surfactant-stabilized ultrasound contrast agents in adult rats

Gas-filled microbubbles are used as contrast agents in diagnostic ultrasound imaging. A preclinical, acute toxicity study of 2 surfactant-stabilized ultrasound contrast agents (ST68 and ST44) was conducted. Subjects were 104 Sprague-Dawley rats (experimental doses, 0.1, 0.2, 0.8, and 1.0 mL/kg; control, 1.0 mL/kg saline) that were studied for 14 days after contrast; clinical signs, weight, blood, and urine were evaluated. Histopathology was performed following euthanasia. Of the 40 animals receiving ST44, 4 died prematurely and a dose dependency was demonstrated (P = .011), whereas in the ST68 groups only 1 death occurred (no dose dependency; P = .48). Only the weight of rats injected with ST44 varied significantly (P = .0003). This dependency was also found for 3 of 5 urine parameters and 4 of 36 blood parameters (P < .05). For ST68, only 1 urine parameter showed significance (P < .0001). Giant cell infiltration in the lungs was significantly higher than controls in the ST44 0.1 mL/kg and the ST68 0.8-1.0 mL/kg groups (P < .01). It is concluded that the prudent choice for future nonrodent, toxicology studies and potentially for human clinical trials is ST68 (given the deaths in the ST44 groups).

Definition of contrast enhancement phases of the liver using a perfluoro-based microbubble agent, perflubutane microbubbles

To define the contrast enhancement phases in the liver with perflubutane microbubbles, the liver enhancement time-intensity curves were investigated in 14 healthy volunteers. The agent was injected intravenously as a bolus and the liver was imaged with an ultrasound scanner as long as 4h after the injection. Time-intensity curves from the hepatic artery, the intrahepatic portal vein, the hepatic vein and the parenchyma of the liver were obtained from the liver ultrasound images. The arrival of the agent in the hepatic artery, the portal vein and the hepatic vein were visually distinguishable and the mean arrival times were 19.2, 24.3 and 32.2 s after the injection, respectively. The signal intensity in these vessels increased rapidly after the arrival of the contrast and gradually reverted to baseline after the peak. In contrast, within 5 min after the injection, the intensity in the parenchyma increased and reached a plateau, which persisted for at least 2h. The contrast enhancement phases in the liver with perflubutane microbubbles could be defined as two major phases-a vascular phase, in which the vessels are enhanced between 15 s and 10 min after injection, and a Kupffer phase, in which the parenchyma is enhanced 10 min after injection. The vascular phase is divided into three subphases: the arterial phase (15 to 45 s after injection); the portal phase (45 s to 1 min after injection); and the vasculo-Kupffer phase (1 to 10 min after injection).

Optical microscopic findings of the behavior of perflubutane microbubbles outside and inside Kupffer cells during diagnostic ultrasound examination

PURPOSE

To investigate the behavior of perflubutane microbubbles outside and inside Kupffer cells during diagnostic ultrasound (US) examination, and to determine the thresholds of the acoustic pressure of different kinds of behavior.

METHODS

Acoustic behavior of perflubutane microbubbles inside and outside Kupffer cells in an acoustic field induced by a clinical US transducer and equipment was optically observed in vitro. The acoustic pressure was measured simultaneously by a calibrated hydrophone and an oscilloscope.

RESULTS

The acoustic behavior of microbubbles was optically categorized as stabilization, oscillation, transposition, shrinkage, and destruction. The mechanical index (MI) displayed on the US equipment correlated well with the acoustic pressure at the level of microbubbles measured hydrophonically. At a frame rate of 15 Hz with a frequency of 3.5 MHz and pulse repetition frequency of 3 KHz, the thresholds in term of MI for free microbubbles to begin oscillation, reach best oscillation, transposition, shrinkage, and destruction were 0.21, 0.44, 0.53, 0.75, and 1.03, respectively. Although adherent and phagocytosed microbubbles showed more stability enduring insonation compared with free microbubbles, the thresholds of shrinkage and destruction were MI 1.03 and 1.18 for adherent microbubbles, and 1.18 and 1.37 for phagocytosed microbubbles, respectively. Neither oscillation nor transposition of microbubbles inside Kupffer cells was observed microscopically. No cell damage because of microbubbles destruction was found in the present study.

CONCLUSION

Perflubutane microbubbles outside and inside Kupffer cells respond to external US insonation with same parameters of a clinical contrast-enhanced US study according to the acoustic pressure. Free microbubbles behave as stabilization, oscillation, transposition, shrinkage, and destruction under insonation. The adherent and phagocytosed microbubbles are more stable under insonation than free microbubbles, but still respond showing shrinkage and destruction when MI is over 1.03.

Decreased phagocytic activity of Kupffer cells in a rat nonalcoholic steatohepatitis model

AIM: To investigate Kupffer cell dynamics and phagocytic activity, using a rat nonalcoholic steatohepatitis (NASH) model.

METHODS: Male F344 rats were fed either a control diet or a choline-deficient L-amino acid-defined (CDAA) diet, followed by contrast enhanced ultrasonography (CEUS) using Levovist^®. The uptake of latex beads by the Kupffer cells was determined by fluorescent microscopy. The status of the Kupffer cells was compared between the two groups, using the immunohistochemical staining technique.

RESULTS: After 4 or more wk of the CDAA diet, CEUS examination revealed a decrease in the signal intensity, 20 min after intravenous Levovist^®. Fluorescent microscopic examination showed that the uptake of latex beads by the Kupffer cells was reduced at week 1 and 2 in the study group, compared with the controls, with no further reduction after 3 wk. Immunohistochemical staining revealed no significant difference in the Kupffer cell counts between the control group and the CDAA group.

CONCLUSION: CEUS examination using Levovist^® demonstrated reduced contrast effect and phagocytic activity in the liver parenchymal phase, although the Kupffer cell numbers were unchanged, indicating reduced phagocytic function of the Kupffer cells in the rat NASH model. We believe that CEUS examination using Levovist^® is a useful screening modality, which can detect NASH in fatty liver patients.

How to characterize non-hypervascular hepatic nodules on contrast-enhanced computed tomography in chronic liver disease: feasibility of contrast-enhanced ultrasound with a microbubble contrast agent

BACKGROUND AND AIM

Although hypervascular appearance is characteristic in hepatocellular carcinoma (HCC), hepatic nodules without hypervascular appearance are sometimes found in patients with chronic liver disease (CLD). The aim of the present study was to clarify the efficacy of contrast-enhanced ultrasound (CEUS) with Levovist to characterize small, non-hypervascular hepatic nodules on contrast-enhanced computed tomography (CECT) in patients with CLD.

METHODS

The subject was 41 hepatic nodules (<30 mm, 18.5 +/- 5.6 mm) which showed non-hypervascular appearance on CECT in 35 patients with CLD; their histological results were 31 HCC (15 well, 14 moderate, and two poor) and 10 regenerative nodules (RN). CEUS with Levovist was performed under intermittent scanning (1-s interval) using APLIO at the early phase and the liver-specific phase, and the contrast enhancement of the nodule was assessed in comparison to that of the surrounding liver parenchyma. The contrast-enhanced findings with the time-intensity analysis were compared with the histological results.

RESULTS

Twelve nodules with weak enhancement in the liver-specific phase were HCC, regardless of their early-phase appearances. The other 29 nodules with equivalent or weak enhancement in the early phase and equivalent enhancement in the liver-specific phase were 19 HCC and 10 RN. Among them, the maximum-intensity ratio of tumor to non-tumor in the early phase was significantly higher in HCC than in RN (P < 0.01, n = 16), and the receiver-operating characteristic analysis showed a sensitivity of 1.0 and a specificity of 0.83 for their characterization.

CONCLUSION

CEUS with Levovist may be an alternative to biopsy to characterize small, non-hypervascular hepatic nodules on CECT in patients with CLD.

Decrease in accumulation of ultrasound contrast microbubbles in non-alcoholic steatohepatitis

AIM

Non-alcoholic steatohepatitis (NASH) is one of the representative liver diseases in developed countries. Diagnosis of NASH is dependent on histological findings from liver biopsy.

METHODS

The usefulness of contrast ultrasound with Levovist for diagnosis of NASH is described. 2.5 g of ultrasound contrast agent Levovist was injected intravenously. The liver was scanned at 5, 10, 15, 20, 30, 40 and 50 min and changes in microbubble accumulation were evaluated. The signal intensity from regions of interest (ROI) on the contrast images was measured and estimated using time intensity curves (TICs). Twenty-one patients with NASH, 33 with non-alcoholic fatty liver disease (NAFLD) and 10 healthy volunteers (HV) were studied. The signal intensity was measured quantitatively at 5 and 20 min after injection.

RESULTS

There was a statistically significant decrease in NASH, when compared with NAFLD and HV groups. These changes in signal intensity were not correlated to the degree of fibrosis and steatosis in histological study. The sensitivity, specificity and overall accuracy obtained from the receiver operating characteristic (ROC) curve were 100% when the cut-off value was set at 43.6 of signal intensity at 20 min.

CONCLUSION

The Levovist contrast study is a useful screening examination which picks up NASH among fatty liver patients.

Grey scale enhancement by a new self-made contrast agent in early cirrhotic stage of rabbit liver

Background

The development of new ultrasound contrast agents (UCAs) has become one of the most promising fields in ultrasound medicine. This paper evaluates a new self-made contrast agent enhancement effect developed to study the fibrotic stages of the liver in perfusion models in vivo.

Methods

We constructed experimental models of hepatic fibrosis involving five stages from F0 to F4 via administration of CCL₄ (0.01 ml/kg BW) every 3 days for 3 months. The intrahepatic circulatory time of the contrast agent was analyzed via an image and Cine-loop display. Calculations of the perfusion-related parameters including the peak signal intensity (PSI) and peak signal intensity time (PIT) of the portal vein and parenchyma were obtained from an analysis of the time-acoustic intensity curve.

Results

Hepatic artery to vein transmit time (HA-HVTT) was significantly shorter at F4 stage (mean 5.1 seconds) compared with those in other stages (mean 8.3 s, 7.5 s, 6.9 s, 6.6 s, P < 0.01). The average PSI difference of PV-parenchyma was 13.62 dB in F4 stage, demonstrating significant differences between F4 stage and other early stages (P < 0.001).

Conclusion

These results indicate that the new self-made contrast agent is capable of indicating intrahepatic hemodynamic changes. HA-HVTT and the PSI difference of the microbubble perfusion in liver parenchyma and PV were considered to differentiate the degree of hepatic fibrosis between F4 and other early stages.

Dynamic US contrast study of the liver: Vascular and delayed parenchymal phase

We evaluated the time-intensity curves of the ultrasound contrast agent, Levovist, in the aorta, portal vein and liver parenchyma in order to define distribution of the agent when it is administered by an intravenous bolus injection. Twelve healthy volunteers were studied. All 12 subjects were examined for the study of vascular phase and five of the subjects were examined for the study of delayed parenchymal phase. To evaluate vascular enhancement, transverse abdominal scanning was performed. To evaluate parenchymal enhancement, liver scanning was done just once at 14 time points up to 60 min after injection. The time-intensity curves in the aorta and the portal vein indicated the conventional curves of blood pool agents such as iodine CT agents and gadolinium MRI agents. They showed steep initial rises and peaks at 20 s and 30 s after injection, respectively. Parenchymal enhancement reached a peak five minutes after injection, with a plateau for 20 min subsequently. It has been proved that there are two phases of Levovist contrast ultrasonography, the vascular phase and the delayed parenchymal phase.