Stimulated acoustic emission to image a late liver and spleen-specific phase of Levovist in normal volunteers and patients with and without liver disease

Internalization of targeted microbubbles by endothelial cells and drug delivery by pores and tunnels

Ultrasound insonification of microbubbles can locally enhance drug delivery by increasing the cell membrane permeability. To aid development of a safe and effective therapeutic microbubble, more insight into the microbubble-cell interaction is needed. In this in vitro study we aimed to investigate the initial 3D morphology of the endothelial cell membrane adjacent to individual microbubbles (n = 301), determine whether this morphology was affected upon binding and by the type of ligand on the microbubble, and study its influence on microbubble oscillation and the drug delivery outcome. High-resolution 3D confocal microscopy revealed that targeted microbubbles were internalized by endothelial cells, while this was not the case for non-targeted or IgG1-κ control microbubbles. The extent of internalization was ligand-dependent, since α_vβ₃-targeted microbubbles were significantly more internalized than CD31-targeted microbubbles. Ultra-high-speed imaging (~17 Mfps) in combination with high-resolution confocal microscopy (n = 246) showed that microbubble internalization resulted in a damped microbubble oscillation upon ultrasound insonification (2 MHz, 200 kPa peak negative pressure, 10 cycles). Despite damped oscillation, the cell's susceptibility to sonoporation (as indicated by PI uptake) was increased for internalized microbubbles. Monitoring cell membrane integrity (n = 230) showed the formation of either a pore, for intracellular delivery, or a tunnel (i.e. transcellular perforation), for transcellular delivery. Internalized microbubbles caused fewer transcellular perforations and smaller pore areas than non-internalized microbubbles. In conclusion, studying microbubble-mediated drug delivery using a state-of-the-art imaging system revealed receptor-mediated microbubble internalization and its effect on microbubble oscillation and resulting membrane perforation by pores and tunnels.

Imaging Methods for Ultrasound Contrast Agents

Microbubble contrast agents were introduced more than 25 years ago with the objective of enhancing blood echoes and enabling diagnostic ultrasound to image the microcirculation. Cardiology and oncology waited anxiously for the fulfillment of that objective with one clinical application each: myocardial perfusion, tumor perfusion and angiogenesis imaging. What was necessary though at first was the scientific understanding of microbubble behavior in vivo and the development of imaging technology to deliver the original objective. And indeed, for more than 25 years bubble science and imaging technology have evolved methodically to deliver contrast-enhanced ultrasound. Realization of the basic bubbles properties, non-linear response and ultrasound-induced destruction, has led to a plethora of methods; algorithms and techniques for contrast-enhanced ultrasound (CEUS) and imaging modes such as harmonic imaging, harmonic power Doppler, pulse inversion, amplitude modulation, maximum intensity projection and many others were invented, developed and validated. Today, CEUS is used everywhere in the world with clinical indications both in cardiology and in radiology, and it continues to mature and evolve and has become a basic clinical tool that transforms diagnostic ultrasound into a functional imaging modality. In this review article, we present and explain in detail bubble imaging methods and associated artifacts, perfusion quantification approaches, and implementation considerations and regulatory aspects.

Characterization of Contrast Agent Microbubbles for Ultrasound Imaging and Therapy Research

The high efficiency with which gas microbubbles can scatter ultrasound compared with the surrounding blood pool or tissues has led to their widespread employment as contrast agents in ultrasound imaging. In recent years, their applications have been extended to include super-resolution imaging and the stimulation of localized bio-effects for therapy. The growing exploitation of contrast agents in ultrasound and in particular these recent developments have amplified the need to characterize and fully understand microbubble behavior. The aim in doing so is to more fully exploit their utility for both diagnostic imaging and potential future therapeutic applications. This paper presents the key characteristics of microbubbles that determine their efficacy in diagnostic and therapeutic applications and the corresponding techniques for their measurement. In each case, we have presented information regarding the methods available and their respective strengths and limitations, with the aim of presenting information relevant to the selection of appropriate characterization methods. First, we examine methods for determining the physical properties of microbubble suspensions and then techniques for acoustic characterization of both suspensions and single microbubbles. The next section covers characterization of microbubbles as therapeutic agents, including as drug carriers for which detailed understanding of their surface characteristics and drug loading capacity is required. Finally, we discuss the attempts that have been made to allow comparison across the methods employed by various groups to characterize and describe their microbubble suspensions and promote wider discussion and comparison of microbubble behavior.

Ultrasound imaging beyond the vasculature with new generation contrast agents

Current commercially available ultrasound contrast agents are gas-filled, lipid- or protein-stabilized microbubbles larger than 1 µm in diameter. Because the signal generated by these agents is highly dependent on their size, small yet highly echogenic particles have been historically difficult to produce. This has limited the molecular imaging applications of ultrasound to the blood pool. In the area of cancer imaging, microbubble applications have been constrained to imaging molecular signatures of tumor vasculature and drug delivery enabled by ultrasound-modulated bubble destruction. Recently, with the rise of sophisticated advancements in nanomedicine, ultrasound contrast agents, which are an order of magnitude smaller (100-500 nm) than their currently utilized counterparts, have been undergoing rapid development. These agents are poised to greatly expand the capabilities of ultrasound in the field of targeted cancer detection and therapy by taking advantage of the enhanced permeability and retention phenomenon of many tumors and can extravasate beyond the leaky tumor vasculature. Agent extravasation facilitates highly sensitive detection of cell surface or microenvironment biomarkers, which could advance early cancer detection. Likewise, when combined with appropriate therapeutic agents and ultrasound-mediated deployment on demand, directly at the tumor site, these nanoparticles have been shown to contribute to improved therapeutic outcomes. Ultrasound's safety profile, broad accessibility and relatively low cost make it an ideal modality for the changing face of healthcare today. Aided by the multifaceted nano-sized contrast agents and targeted theranostic moieties described herein, ultrasound can considerably broaden its reach in future applications focused on the diagnosis and staging of cancer.

Natural history of postvascular-phase iso-enhanced lesions on the sonogram in chronic liver diseases

BACKGROUND AND AIM

This study examined the natural history of postvascular-phase iso-enhanced lesions (PIELs) on contrast-enhanced sonograms to determine the potential risk and predictive factors for developing hepatocellular carcinoma (HCC) in chronic liver diseases.

METHODS

This prospective study included 87 PIELs on contrast-enhanced sonograms (postvascular-phase: 10 min post-injection of perflubutane microbubbles) in 72 patients with chronic liver diseases (45 males and 27 females; age 65.0 ± 10.8y; PIEL diameter 12.5 ± 4.2 mm). The PIELs were followed up by ultrasound/contrast-enhanced ultrasound, computed tomography, or magnetic resonance imaging at 3 to 6 months intervals.

RESULTS

Twenty patients developed HCCs during the study period (median, 22.0 months). The cumulative risk of HCC occurrence was 7.9% at 1 year and 36.0% at 3 years. The presence of coexistent HCC (hazard ratio [HR], 4.975; 95% confidence interval [CI], 1.729-14.316; P = 0.003) and alpha-fetoprotein > 20 ng/mL (HR, 4.104; 95% CI, 1.621-10.392; P = 0.003) were significant factors for the risk of HCC occurrence. Fourteen of these lesions were diagnosed as HCCs that developed from iso-enhanced lesions. Cumulative HCC occurrence rates from PIEL > 14 mm was 23.5% at 1 year and 46.3% at 3 years. Cox regression analysis showed that PIEL > 14 mm (HR, 6.780; 95% CI, 2.060-22.32; P = 0.002) and alpha-fetoprotein > 20 ng/mL (HR, 4.892; 95% CI, 1.559-15.350; P = 0.007) were statistically significant factors for HCC occurrence.

CONCLUSIONS

Patients with coexistent HCC, alpha-fetoprotein > 20 ng/mL, or PIEL > 14 mm should be carefully monitored because of the high potential for HCC occurrence.

Noninvasive diagnosis of compensated cirrhosis using an analysis of the time-intensity curve portal vein slope gradient on contrast-enhanced ultrasonography

Purpose

We measured the slope gradients (SGs) of the vascular time–intensity curves (TICs) of the intrahepatic vessels on contrast-enhanced ultrasonography (CEUS). The aim of this study was to assess the diagnostic accuracy of the SG of each hepatic vessel, particularly the portal vein (PV), for detecting cirrhosis and to compare this method with conventional modalities.

Methods

Fifty-one preoperative patients underwent CEUS, and the TICs were plotted. The SGs of the hepatic artery, PV and hepatic vein were obtained from the linear functions between the slope of the arrival time of the contrast agent and the peak enhancement time of each vessel. The transit times and levels of biochemical markers were also measured. The patients were divided into three groups according to the Metavir score: F0/1 group (n = 14), F2/3 group (n = 21) and F4 group (n = 16).

Results

The PVSG significantly decreased in the F4 group (F0/1: 29.1 ± 2.27, F2/3: 23.1 ± 1.86, F4: 14.7 ± 2.13). The PVSG demonstrated high accuracy for diagnosing cirrhosis and was correlated with the levels of ICG-R15 and hyaluronic acid (Spearman rank correlation; ρ = −0.5691, p < 0.001 and ρ = −0.4652, p = 0.0006).

Conclusions

The PVSG has the potential to be a diagnostic marker for identifying patients with well-compensated cirrhosis.

Quantitative contrast-enhanced ultrasound imaging: a review of sources of variability

Ultrasound provides a valuable tool for medical diagnosis offering real-time imaging with excellent spatial resolution and low cost. The advent of microbubble contrast agents has provided the additional ability to obtain essential quantitative information relating to tissue vascularity, tissue perfusion and even endothelial wall function. This technique has shown great promise for diagnosis and monitoring in a wide range of clinical conditions such as cardiovascular diseases and cancer, with considerable potential benefits in terms of patient care. A key challenge of this technique, however, is the existence of significant variations in the imaging results, and the lack of understanding regarding their origin. The aim of this paper is to review the potential sources of variability in the quantification of tissue perfusion based on microbubble contrast-enhanced ultrasound images. These are divided into the following three categories: (i) factors relating to the scanner setting, which include transmission power, transmission focal depth, dynamic range, signal gain and transmission frequency, (ii) factors relating to the patient, which include body physical differences, physiological interaction of body with bubbles, propagation and attenuation through tissue, and tissue motion, and (iii) factors relating to the microbubbles, which include the type of bubbles and their stability, preparation and injection and dosage. It has been shown that the factors in all the three categories can significantly affect the imaging results and contribute to the variations observed. How these factors influence quantitative imaging is explained and possible methods for reducing such variations are discussed.

Hepatic vein transit times of a microbubble agent in assessing response to antiviral treatment in patients with chronic hepatitis C

Microbubble measurement of hepatic vein transit times (HVTT) may have the potential to assess severity of hepatitis C virus (HCV)-related liver disease, where there is a shorter HVTT with more severe disease. We investigated the utility of this test as a marker of response to antiviral treatment. Thirty-seven patients with biopsy-proven HCV-related disease undergoing antiviral treatment were studied. All had baseline scans and then repeat scans 6 months after the end of treatment. HVTT using Levovist were obtained from the right and middle hepatic veins, and the shorter time was used for analysis. The aspartate aminotransferase to platelet ratio index (APRI) scores were calculated retrospectively. There were seven patients with mild hepatitis, 23 with moderate/severe hepatitis and seven with cirrhosis. The mean baseline HVTT in responders ± SE increased from 27.3 ± 2.29 s to 33.5 ± 2.8 s posttreatment (P = 0.01). In the 10 nonresponders, the HVTT remained the same; 43.3 ± 9 s baseline compared to 44 ± 7.8 s posttreatment (P = 0.84). This trend was also seen with the APRI score where in responders, the mean score decreased from 1.1 ± 0.2 to 0.74 ± 1 (P = 0.03) and in nonresponders, the score remained unchanged; 0.88 ± 0.2 compared to 0.84 ± 0.2 (P = 0.31). HVTT measurement lengthened, while APRI scores decreased in patients who responded to antiviral treatment while both remained the same, shortened (HVTT) or increased (APRI), respectively, in patients who were nonresponders. These results are encouraging and indicate that these tests could be potentially used as markers of response to treatment and could obviate the need for serial biopsies in antiviral future treatment studies.

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.

Liver fibrosis staging with contrast-enhanced ultrasonography: prospective multicenter study compared with METAVIR scoring

We prospectively assessed contrast-enhanced sonography for evaluating the degree of liver fibrosis as diagnosed via biopsy in 99 patients. The transit time of microbubbles between the portal and hepatic veins was calculated from the difference between the arrival time of the microbubbles in each vein. Liver biopsy was obtained for each patient within 6 months of the contrast-enhanced sonography. Histological fibrosis was categorized into two classes: (1) no or moderate fibrosis (F0, F1, and F2 according to the METAVIR staging) or (2) severe fibrosis (F3 and F4). At a cutoff of 13 s for the transit time, the diagnosis of severe fibrosis was made with a specificity of 78.57%, a sensitivity of 78.95%, a positive predictive value of 78.33%, a negative predictive value of 83.33%, and a performance accuracy of 78.79%. Therefore, contrast-enhanced ultrasound can help with differentiation between moderate and severe fibrosis.

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.

Levovist ultrasonography imaging in intracystic hemorrhage of simple liver cyst

The differential diagnosis between intracystic hemorrhage and cystadenocarcinoma of the liver is often difficult even with the use of various imaging modalities. A 73-year-old woman was admitted to our hospital with the complaint of right upper quadrant pain. Ultrasonography (US) demonstrated a heterogeneous echogenic cyst measuring 11 cm × 8 cm in size in S2 of the liver, indicated intracystic hemorrhage of simple liver cyst or cystadenocarcinoma, but the differential diagnosis was considerably difficult. Levovist (Schering, Berlin, Germany) US revealed no enhancement of the intracystic structures, suggesting a clot in the case of intracystic hemorrhage. An operation was performed and the resected lesion showed a solitary benign liver cyst, measuring 5.5 cm × 4.7 cm × 8.5 cm containing a large blood clot. The patient had an uneventful recovery after the surgery. Levovist US may play an important role in discrimination between intracystic hemorrhage of simple hepatic cysts and cystadenocarcinoma of the liver.

Phagocytosis of ultrasound contrast agent microbubbles by Kupffer cells

Delayed parenchymal phase images of the liver more than 5 min after IV injection of ultrasound contrast agents are thought to be related to the phagocytosis of contrast agent microbubbles by macrophages. In this study, we examined whether liver-specific macrophages, Kupffer cells, phagocytosed the microbubbles and whether their elimination affected the delayed parenchymal images of the liver. Phase-contrast microscope observations showed that Kupffer cells phagocytosed various contrast agents in vitro. Among the contrast agents used, 99% of Sonazoid and Optison, and 47% of Levovist were phagocytosed, whereas only 7.3% of SonoVue and 0% of Imavist were phagocytosed. Elimination of Kupffer cells in vivo by gadolinium chloride (GdCl(3)) resulted in decreased intensity of the delayed parenchymal images with Sonazoid and Levovist, while SonoVue showed no changes compared with control. Our findings suggested that Kupffer cells phagocytosed contrast agents and they were responsible for the delayed images of contrast ultrasound in the liver.

Contrast-enhanced Ultrasound in Obstetrics and Gynecology

Ultrasonography is a well-established imaging modality for evaluation of gynecologic tumors. In recent years, more sophisticated technologies like the use of intravascular contrast agents led to an improvement in the ability of the practitioner to differentiate benign from malignant masses. When we consider the safety of contrast-enhanced ultrasonography in obstetrics and gynecology, we must discuss about the effect of ultrasound contrast media on embryo and fetus. The use of ultrasound contrast media in pregnant women always concerns in the obstetricians because of the principle of not exposing a fetus to any drug. Therefore, the literature was reviewed for information about those safety and efficacy because of the uncertainty about the use of contrast media during pregnancy. Based on the limited information available, mutagenic and teratogenic effects have not been described after administration of ultrasound contrast media. No effect on the fetus has been seen after contrast media. The small potential risk associated with the nonthermal bioeffects via acoustic cavitation may be considered to prohibit the use in first trimester pregnant women. In previous studies including human trials, no evidence of adverse effect was reported. Contrast-enhanced ultrasonography could prove a useful adjunct in multiple gestations and in evaluation of uteroplacental circulation. It appears to be very promising potential in obstetrics.

Hepatic vein transit time of SonoVue: a comparative study with Levovist

PURPOSE

To prospectively compare transit times of Levovist and SonoVue in healthy volunteers and patients with biopsy-proved hepatitis C-related liver disease.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Forty patients and 25 healthy volunteers were examined. Subjects fasted, a bolus of SonoVue (0.6 mL) was injected into a cubital fossa vein, and hepatic venous time-intensity profiles were measured with spectral Doppler tracing. This was repeated with two injections of Levovist (2 g) and another injection of SonoVue. Time-intensity curves of spectral Doppler signals of right and middle hepatic veins were analyzed. A sustained signal intensity increase of 10% above baseline levels indicated hepatic vein transit time (HVTT). Carotid artery audio intensity was measured in volunteers. Analysis of variance and t tests were used for statistical analysis.

RESULTS

Twelve patients had mild hepatitis; 18, moderate or severe hepatitis; and 10, cirrhosis. Mean HVTTs in control, mild hepatitis, moderate or severe hepatitis, and cirrhosis groups were 38.3 seconds +/- 2.4 (standard error), 47.5 seconds +/- 6.5, 29.5 seconds +/- 10.8, and 17.6 seconds +/- 5.0, respectively, with Levovist (P < .001) and 29.4 seconds +/- 6.9, 27.4 seconds +/- 9.3, 22.9 seconds +/- 4.7, and 16.4 seconds +/- 4.9, respectively, with SonoVue (P < .001). HVTT decreased as severity increased at imaging with both contrast agents. There was no significant difference in HVTT between mild and moderate hepatitis groups with SonoVue; however, there were significant differences in HVTT between all patient groups with Levovist. HVTT of SonoVue was shorter than that of Levovist in all groups (P < .001) except the cirrhosis group; in this group, HVTT of the two contrast agents was similar (P = .05). No difference was observed in mean cardiopulmonary transit time for SonoVue or Levovist (9.1 seconds +/- 2.4 [standard error] and 8.4 seconds +/- 2.5, respectively, P = .18).

CONCLUSION

HVTT was significantly shorter with SonoVue than with Levovist; there was no significant difference in cardiopulmonary transit time.

Evaluation of pathological features of hepatocellular carcinoma by contrast-enhanced ultrasonography: comparison with pathology on resected specimen

Features of hepatocellular carcinoma (HCC) observed by contrast-enhanced ultrasonography (CEUS) were compared to pathological features of corresponding resected HCC specimens, to evaluate the ability of CEUS to depict the pathological features of HCC. We investigated 50 HCC nodules that were treated by surgical resection. All nodules had been examined by CEUS with intravenous contrast agent (Levovist) before surgery. CEUS findings were divided into three phases for evaluation and classification of enhancement patterns: two vascular phases (arterial phase and portal venous phase) and the delayed phase. Pathological examination focused on differentiation and on the presence or absence of a tumor capsule, intratumoral septum, and intratumoral necrosis. All 21 nodules that showed a linear or annular vessel around the tumor margin in the arterial phase had capsular formation. Of the 27 nodules that showed heterogeneous perfusion in the portal venous phase, 21 (77.8%) had an intratumoral septum and 23 (85.2%) showed intratumoral necrosis. All nodules that were depicted as a defect with an unclear margin in the delayed phase were well-differentiated HCCs, whereas all nodules that were depicted as a defect with a clear margin were moderately or poorly differentiated HCCs. From our observations, the arterial, portal venous, and delayed phases of CEUS could reflect different pathological aspects of HCC. Some pathological characteristics of HCC might be evaluated preoperatively and non-invasively, by means of combined analysis of three phases of CEUS findings.

Importance of evaluating all vascular phases on contrast-enhanced sonography in the differentiation of benign from malignant focal liver lesions

OBJECTIVE

Our objective was to evaluate the accuracy of a blood-pool sonographic contrast agent in the late phase compared with the three vascular phases for differentiation between benign and malignant focal liver lesions.

SUBJECTS AND METHODS

In 152 patients (105 with chronic liver disease), 152 solid focal liver lesions characterized either by fine-needle biopsy or by dynamic CT or MRI were studied. The final diagnoses were metastasis for 24, hepatocellular carcinoma for 75, focal nodular hyperplasia for 13, regenerating or dysplastic nodule for 14, hemangioma for 22, cholangiocarcinoma for two, and another focal liver lesion for two. Real-time sonography was performed after a bolus injection of 2.4 mL of SonoVue, using a low mechanical index (< 0.2). All lesions were evaluated in the arterial, portal, and late phases; classified as benign or malignant; and correlated with final diagnoses.

RESULTS

For discrimination between malignant and benign focal liver lesions, evaluation of all vascular phases improved the sensitivity from 78.4% to 98% and the accuracy from 80.9% to 92.7%, compared with evaluation of the late phase alone. The increase in accuracy was higher in patients with chronic liver disease (16.3%) than in those without (2.1%).

CONCLUSION

Evaluation of SonoVue enhancement in all three vascular phases is superior to evaluation of SonoVue enhancement in the late phase alone, especially in patients with chronic liver disease.

Bolus versus Continuous Infusion of Microbubble Contrast Agent for Liver US: Initial Experience

Institutional review board approval and informed consent were obtained. To prospectively assess if continuous infusion of galactose-palmitic acid can prolong the duration of hepatic enhancement at ultrasonography over bolus injection, 11 patients received two injections--one bolus injection (2 mL/sec) and one continuous infusion (1.5 mL/min)--with the same dose of galactose-palmitic acid (4 g, 300 mg/dL). Two unenhanced baseline sweep scans (mechanical index of 0.7 and 1.3) of the relevant liver lobe were acquired followed by contrast-enhanced sweeps after bolus injection and continuous infusion. Each sweep was saved as cine loops and analyzed with a personal computer. Duration of enhancement more than 3 dB was prolonged by continuous infusion from 4.3 minutes +/- 2.4 (+/-standard deviation) at bolus injection to 10.1 minutes +/- 3.0 (P < .005). Maximal parenchymal enhancement was 11.0 dB +/- 3.2 (bolus injection) and 9.2 dB +/- 3.8 (infusion, P < .05). Peak liver-to-lesion contrast was 14.2 dB +/- 6.3 (bolus injection) and 13.2 dB +/- 7.1 (infusion, not significant). Continuous infusion of galactose-palmitic acid markedly prolongs but slightly diminishes hepatic enhancement; liver-to-lesion contrast remains unchanged.

Differential diagnosis of nodular lesions in cirrhotic liver by post-vascular phase contrast-enhanced US with Levovist: comparison with superparamagnetic iron oxide magnetic resonance images

BACKGROUND

We investigated the diagnostic utility of post-vascular phase contrast-enhanced ultrasonography (US) and superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance imaging (MRI) as compared to the histological diagnosis of differential grades of hepatocellular carcinomas (HCCs).

METHODS

Forty-nine patients with histologically characterized liver nodules (well-differentiated HCC, n = 20; moderately differentiated HCC, n = 19; poorly differentiated HCC, n = 1; dysplastic nodule, n = 9) received contrast-enhanced US and SPIO-MRI. Subsequently, we quantitatively evaluated the relationships between the images of the nodules and their histological diagnosis and differential grades.

RESULTS

The ratio of the echogenicity of the tumorous area to that of the nontumorous area with post-vascular phase contrast-enhanced US (post-vascular phase ratio) decreased as nodules became less differentiated (P < 0.05; Kruskal-Wallis test). The ratio of the intensity of the nontumorous area to that of the tumorous area on SPIO-enhanced MR images (SPIO intensity index) also decreased as nodules became less differentiated (P < 0.01). The post-vascular phase ratio correlated with the SPIO intensity index for HCCs and dysplastic nodules (r = 0.76). The conformity of the result from the post-vascular phase contrast-enhanced US and SPIO-MRI was 96%.

CONCLUSIONS

Contrast-enhanced US is a valuable method for predicting the histological grade of HCCs in cirrhotic patients, and may be a good alternative to SPIO-enhanced MRI.

1.5 Harmonic Imaging Sonography with microbubble contrast agent improves characterization of hepatocellular carcinoma

AIM: To investigate the usefulness of 1.5 Harmonic Imaging Sonography with the use of the contrast agent Levovist for the diagnosis of hepatocellular carcinoma (HCC) and for the evaluation of therapeutic response.

METHODS: Phantom experiments were performed to compare the contrast effects of 2^nd harmonic imaging and 1.5 Harmonic Imaging Sonography. 1.5 Harmonic Imaging Sonography was employed to examine 36 patients with HCC (42 nodules) before and after the treatment and to compare against the findings obtained using other diagnostic imaging modalities.

RESULTS: In 1.5 Harmonic Imaging Sonography, the tumor vessels of HCCs were clearly identified during the early phase, and late-phase images clearly demonstrated the differences in contrast enhancement between the tumor and surrounding hepatic parenchyma. Blood flow within the tumor was detected in 36 nodules (85.7%) during the early phase and in all 42 nodules (100%) during the late phase using 1.5 Harmonic Imaging Sonography, in 38 nodules (90.5%) using contrast-enhanced CT, in 34 nodules (81.0%) using digital subtraction angiography (DSA), and in 42 nodules (100%) using US CO₂ angiography. Following transcatheter arterial embolization, 1.5 Harmonic Imaging Sonography detected blood flow and contrast enhancement within the tumors that were judged to contain viable tissue in 20 of 42 nodules (47.6%). However, 6 of these 20 cases were not judged in contrast-enhanced CT. 1.5 Harmonic Imaging Sonography was compared with the US CO2 angiography findings as the gold standard, and the sensitivity and specificity of these images for discerning viable and nonviable HCC after transcatheter arterial embolization were 100% and 100%, respectively.

CONCLUSION: 1.5 Harmonic Imaging Sonography permits the vascular structures of HCCs to be identified and blood flow within the tumor to be clearly demonstrated. Furthermore, 1.5 Harmonic Imaging Sonography is potentially useful for evaluating the therapeutic effects of transcatheter arterial embolization on HCC.

Ultraschallkontrastmittel: Substanzklassen, Pharmakokinetik, klinische Anwendungen, Sicherheitsaspekte

Ultrasound contrast agents (UCA) have undergone constant development and improvement in recent years. Greater mechanical stability and improved acoustic properties, combined with new contrast-specific ultrasound sequences, have broadened the potential fields for investigation considerably. Contrast-enhanced ultrasound studies will no longer be complementary investigations, but will be considered as primary techniques. This review article provides a survey of the different drugs used, their chemical properties, and their pharmacokinetic aspects. Summarized are the most important established and published indications for the use of UCA together with an outlook for future applications. Finally this paper discusses the safety profile of these agents, which has become important due to the increasing use of these agents.

Ultrasonographic contrast media: has the time come in obstetrics and gynecology?

OBJECTIVE

The aim of this work was to review the technical aspects and clinical applications of contrast media (microbubbles and nanomolecular agents) in obstetric and gynecologic ultrasonographic imaging.

METHODS

With the use of a computerized database (MEDLINE) and several Web-based search engines (Google Scholar and Copernic), relevant articles on ultrasonographic contrast media were reviewed. References cited in these articles and not obtained via the search engines were also reviewed.

RESULTS

Ultrasonographic contrast media constitute a new and expanding technology. They are frequently used, for example, in adult cardiology. Extensive research in laboratory setups, animals, and human subjects has shown their safety and huge potential as an adjunctive tool in clinical practice. They increase signals returning from insonated tissues and are particularly effective as intravascular agents, enhancing color and Doppler signals, for instance. Preliminary results in tumor imaging are encouraging. The ultrasonographic contrast media permit pharmacokinetic perfusion studies, which may be of enormous clinical importance in the study of early cancer development. Targeted imaging and therapies are becoming a reality. Microbubbles have already brought a new dimension to diagnostic ultrasonographic imaging. Many authors have described the clinical value of these agents in liver, prostate, and breast imaging, among others. Newer types of media, the nanomolecules, are now emerging as the latest in imaging enhancers as well as therapeutic agent carriers.

CONCLUSIONS

Although showing potential in imaging of the uterus and fallopian tubes as well as some obstetric applications, the contrast media, in particular the nanomolecules, seem to be most promising in ovarian cancer.

Signal intensity of the liver parenchyma in microbubble contrast agent in the late liver phase reflects advanced fibrosis of the liver

BACKGROUND

Microbubble of Levovist accumulates in liver parenchyma, and the phenomenon has been reported as late liver-specific parenchymal. The aim of the present study was to compare the parenchymal enhancement effect of Levovist with the degree of liver dysfunction.

PATIENTS AND METHODS

Sixty consecutive patients who consented to be treated were enrolled in this study. Pulse-inversion ultrasonography (US) in the liver parenchymal phase of enhancement with Levovist was performed in a preoperative examination. The mechanical index of pulse-inversion US was set at 1.3. The gray-scale intensity of the non-tumor area of the liver parenchyma at the level of the focal zone was measured. The hepatic fibrosis index was measured in each liver by morphometric analysis. The correlation between the gray-scale intensity of the non-tumor area of the liver parenchyma and the hepatic fibrosis index was assessed.

RESULTS

There was a significant inverse correlation between the gray scale of the liver parenchyma and the hepatic fibrosis index (r = -0.809, P < 0.01). The average signal intensity of the liver parenchyma was 144.5 in a normal liver, 133.6 in chronic hepatitis, and 102.6 in liver cirrhosis, demonstrating a significant difference between a normal and cirrhotic liver (P < 0.01).

CONCLUSIONS

The signal intensity of a microbubble disruption of the liver parenchyma in the late phase of enhancement with Levovist was considered to reflect the degree of hepatic fibrosis.

[Contrast ultrasound imaging in focal liver lesions: diagnostic value and guidelines]

The recent introduction of high quality scanners and contrast agents for ultrasound deeply modifies diagnosis strategy in focal liver lesions by using validated criteria. Non-linear imaging methods using low mechanical index (MI<0.2) and second generation contrast agents allow real-time continuous imaging with concomitant limitation in background tIssue signal and also in agent collapse for a high quality contrast imaging giving dramatic improvement in detection and characterization of lesions. Interpretation is based on the presence of contrast agent within the lesion or not (hyper-, hypo- or isosignal) and the delay after injection (arterial, portal or parenchymal or late phase) as previously used by non-ultrasound methods. This allows an easy differentiation of benign from malignant lesions. Moreover, this allows complete characterization in 85 to 95% of all focal liver lesions and 75% in hepatocellular carcinomas. Those results markedly improve ultrasound accuracy compared to conventional sonography and so put contrast-enhanced sonography among recommended non-invasive imaging methods for focal liver lesions with changes in diagnostic strategy according to the lesion type and actual place of US methods. It is recommended to use contrast ultrasound methods in cancer staging for an optimal detection of liver metastases as well as in characterization of lesions detected during conventional sonography with a consecutive decrease of cost-diagnosis ratio.

Kontrastverst�rkte Sonographie der Leber

The detection rate of liver lesions using ultrasonography is 53-77%, rendering this method inferior to CT and MRI. Despite well-known limitations, development of stable second-generation contrast agents in conjunction with new techniques of contrast display has led to increased diagnostic accuracy. Characterization of focal liver lesions with ultrasound contrast agents follows known features of iodine- and gadolinium-containing contrast agents, but compared to CT and MRI sensitive visualization of intratumoral vessels takes place in real time. In addition to very high diagnostic accuracy in differentiating benign from malignant lesions, detectability of tumors of nonhepatocellular origin is increased significantly and direct assessment of treatment success with minimally invasive tumor ablative interventions in the liver is possible. The active principle of ultrasound contrast agents, examination technique as well as distinguishing features and appearance of various, frequently observed focal liver lesions are illustrated by cases from our department.

Improved characterization of liver lesions with liver-phase uptake of liver-specific microbubbles: prospective multicenter study

PURPOSE

To evaluate in a prospective multicenter study whether conventional ultrasonographic (US) characterization of liver lesions can be improved by imaging during the liver-specific phase of SH U 508A uptake in the microbubble-specific agent detection imaging mode.

MATERIALS AND METHODS

One hundred forty-two patients with liver lesions underwent conventional gray-scale and color Doppler US and SH U 508A-enhanced US. Two radiologists blindly read digital cine clips and assigned scores for confidence in diagnosis of benignancy or malignancy, diagnosis of specific lesion types, and relative difference in SH U 508A uptake between the lesion and the liver parenchyma (ie, subjective conspicuity score [SCS]). Comparisons were made to see whether the addition of agent detection imaging led to improved diagnostic performance.

RESULTS

Receiver operating characteristic analysis revealed improved discrimination of benign and malignant lesions for readers 1 (P =.049) and 2 (P <.001). The number of patients with a correct diagnosis of benignancy or malignancy assigned by readers 1 and 2, respectively, improved from 114 and 113 to 125 and 128 with agent detection imaging (reader 1: P =.027; reader 2: P =.008; McNemar test). Specific diagnoses were made more accurately with agent detection imaging: At McNemar testing, the number of correct lesion type determinations increased from 83 to 92 (P =.022) for reader 1 and from 85 to 99 (P <.001) for reader 2. Both readers assigned high scores for differences in SH U 508A uptake between the liver parenchyma and the lesion for metastases and cholangiocarcinomas and low scores for uptake differences in most of the benign lesions. Hepatocellular carcinomas (HCCs), hemangiomas, and adenomas had more variable uptake differences. Fourteen of 22 hemangiomas were assigned an SCS of less than 50%, and 22 (reader 1) and 15 (reader 2) of 31 HCCs were assigned an SCS of greater than 50%.

CONCLUSION

With use of SH U 508A-enhanced agent detection imaging, liver lesion characterization and diagnostic performance are significantly improved.

Focal hepatic lesions: contrast-enhancement patterns at pulse-inversion harmonic US using a microbubble contrast agent

Objective

To analyze the contrast-enhancement patterns obtained at pulse-inversion harmonic imaging (PIHI) of focal hepatic lesions, and to thus determine tumor vascularity and the acoustic emission effect.

Materials and Methods

We reviewed pulse-inversion images in 90 consecutive patients with focal hepatic lesions, namely hepatocellular carcinoma (HCC) (n=43), metastases (n=30), and hemangioma (n=17). Vascular and delayed phase images were obtained immediately and five minutes following the injection of a microbubble contrast agent. Tumoral vascularity at vascular phase imaging and the acoustic emission effect at delayed phase imaging were each classified as one of four patterns.

Results

Vascular phase images depicted internal vessels in 93% of HCCs, marginal vessels in 83% of metastases, and peripheral nodular enhancement in 71% of hemangiomas. Delayed phase images showed inhomogeneous enhancement in 86% of HCCs; hypoechoic, decreased enhancement in 93% of metastases; and hypoechoic and reversed echogenicity in 65% of hemangiomas. Vascular and delayed phase enhancement patterns were associated with a specificity of 91% or greater, and 92% or greater, respectively, and with positive predictive values of 71% or greater, and 85% or greater, respectively.

Conclusion

Contrast-enhancement patterns depicting tumoral vascularity and the acoustic emission effect at PIHI can help differentiate focal hepatic lesions.

Evidence for spleen-specific uptake of a microbubble contrast agent: a quantitative study in healthy volunteers

PURPOSE

To evaluate the pharmacokinetics of the microbubble contrast agent BR1.

MATERIALS AND METHODS

Twenty healthy volunteers were injected via arm vein with a 1.2-mL bolus of BR1. Ultrasonographic images of liver and right kidney and of spleen and left kidney were obtained intermittently for 5 minutes with low-mechanical-index software (to minimize microbubble destruction) that shows stationary microbubbles in green. Percentage total uptake was calculated as the number of green pixels in the region of interest for each organ over time, divided by the total pixels. Relative uptake, the ratio of total uptake in liver to that in right kidney and of total uptake in spleen to that in left kidney, and differential uptake, the difference in total uptake between liver and right kidney and between spleen and left kidney, were calculated. Total uptake for each organ was plotted against time, and the gradient of a best-fit straight line was calculated. Wilcoxon signed rank test was used to compare mean uptake values in each subject. Mann-Whitney U test was used for comparisons in sex and age.

RESULTS

Total uptake declined over 5 minutes in left and right kidney and in liver (from 88% +/- 10% [1 minute] to 67% +/- 14% [5 minutes]), but not in spleen (range, 90%-99%). Mean relative uptake +/- 1 SD for spleen increased from 2.3 +/- 0.7 (1 minute) to 3.7 +/- 2.3 (5 minutes) (P =.005) but for liver was constant: 2.1 +/- 0.9 (1 minute) and 2.3 +/- 0.4 (5 minutes) (P =.06). Mean differential uptake +/- 1 SD for spleen increased from 51.3% +/- 14.9% (1 minute) to 65.0% +/- 9.1% (5 minutes) (P =.002). Significant difference was seen over time in total uptake gradients between spleen and left kidney (P =.014) but not between liver and right kidney or right and left kidney. No difference was seen between men and women or with age.

CONCLUSION

BR1 produces spleen-specific enhancement that is longer (5 minutes) than the blood pool phase.

[Ultrasound contrast agents]

Ultrasound contrast agents consist of tiny gas bubbles encapsulated by a stabilising membrane or shell. When combined with recent contrast-specific ultrasound techniques, they provide substantial enhancement of vessels and solid organs. The clinical use and the diagnostic value of ultrasound contrast agents are in principle comparable to those of contrast agents for CT and MRI. They add an additional dimension of information to sonography, which results in considerable improvement of diagnostic accuracy in many cases. This paper reviews the physicochemical properties of various microbubble contrast agents, discusses non-linear bubble behaviour and contrast-specific imaging techniques. An overview of the most important radiological clinical applications in the liver, kidney and spleen is given.

Temperature monitoring using ultrasound contrast agents: in vitro investigation on thermal stability

Invasiveness of temperature monitoring devices is presently one of the most serious limitations to the application of oncological hyperthermia (HT). A promising approach aims at detecting temperature variations by monitoring the mean grey level (MGL) of the ultrasonographic image of the tissue. Gaseous ultrasound contrast agents (UCA), enhancing Ultrasonic (US) imaging, are expected to be sensitive to temperature, and are therefore a good candidate as temperature monitoring medium. The present study evaluates the 'in vitro' temporal and thermal stability and the correlation between temperature and MGL using a gaseous UCA (SonoVue) as phantom. No statistical differences were detected between the MGL value of the phantom kept at 43.5 degrees C before (215.2+/-3.5) and after 1 h (214.8+/-2.5), showing good stability at HT temperatures. Data of MGL image vs. temperature were obtained during both heating and cooling experiments in the HT range (30-43 degrees C). A good linearity of MGL vs. temperature (R2=0.976) was found with a good accuracy (2.5%) and a sensitivity of about 6.6 MGL/degrees C.

Ultrasound contrast agents can influence the respiratory burst activity of human neutrophil granulocytes

Activated leucocytes can bind and, subsequently, phagocytose microbubbles that are used as ultrasound (US) contrast agents. The purpose of this study was to investigate whether or not microbubbles can influence the inflammatory response of human neutrophil granulocytes. Granulocytes isolated from healthy volunteers were activated with various stimuli, for example, the bacterial peptide N-formyl-methyonyl-leucyl-phenylalanine (fMLP), the calcium ionophore A23187, the protein kinase C activator phorbol myristate acetate (PMA) and the cytokine tumor necrosis factor alpha (TNF-alpha), and incubated with albumin or phospholipid microbubbles. Neutrophil respiratory burst activity and elastase release were quantified. Albumin (Optison) and phospholipid (SonoVue) contrast agents induced an extensive oxidative response of human granulocytes to all the stimuli used, and these effects could be significantly impaired by preincubation of the cells with cytochalasin B. Left heart contrast agents used for contrast-enhanced US assessment can activate human neutrophil granulocytes, inducing an extensive respiratory burst to secondary stimuli. The potential clinical relevance of this effect needs to be elucidated.

A review of nonconventional ultrasound techniques and contrast-enhanced ultrasonography of noncardiac canine disorders

Modern ultrasound contrast media are gas-containing stabilized microbubbles that remain intact in the circulating blood for several minutes after intravenous injection and increase the intensity of the backscattered ultrasound. When the microbubbles disappear from the blood, they can be detected in the parenchyma of the liver and the spleen for about 30 more minutes (late liver- and spleen-specific phase). The insonated microbubbles produce second harmonic ultrasound frequencies, whose detection requires nonconventional ultrasound modalities such as pulsed inversion imaging. Nonconventional ultrasound techniques can also be used without microbubbles because second harmonics can be generated by ultrasound in tissues as well. The physical principles and advantages of nonconventional ultrasound techniques are described. The circulating microbubbles can be used not only to enhance weak Doppler signals, but also to perform dynamic contrast studies. Contrast-enhanced dynamic ultrasound studies--similar to contrast-enhanced CT and MRI examinations--have been used in humans to characterize lesions noninvasively (i.e., without biopsies) found during conventional ultrasound examinations. To map the distribution of contrast medium in a nodule or in an organ, specific scanning techniques such as stimulated acoustic emission have been developed. Stimulated acoustic emission occurs when high acoustic pressure ultrasonic waves disrupt the stationary or slowly moving microbubbles. This results in the release of a large amount of harmonic ultrasound frequencies. When the stimulated acoustic emission technique is used for dynamic studies, scanning must be interrupted several times to allow the microvasculature of the lesion to refill with microbubbles (interval delay imaging). The contrast patterns of malignant and benign hepatic nodules in humans have been the most intensively studied. Another type of dynamic study in humans measures the transit time of the contrast medium; that is, how fast the peripherally injected microbubbles reach the hepatic veins. Hepatic cirrhosis can be differentiated from other diffuse parenchymal liver diseases by a shorter transit time. Introducing nonconventional ultrasound techniques and ultrasound contrast media in veterinary diagnostic imaging may have potential value; however, intensive research should be carried out before ultrasound contrast agents can routinely be used in clinical practice.

Improved detection of hepatic metastases with pulse-inversion US during the liver-specific phase of SHU 508A: multicenter study

PURPOSE

To compare conventional B-mode ultrasonography (US) alone with the combination of conventional B-mode US and contrast material-enhanced (SHU 508A) late-phase pulse-inversion US for the detection of hepatic metastases by using dual-phase spiral computed tomography (CT) as the standard of reference.

MATERIALS AND METHODS

One hundred twenty-three patients underwent conventional US, US in the liver-specific phase of SHU 508A, and single-section spiral CT. US and CT images were assessed by blinded readers. Differences in sensitivity, specificity, and the number and smallest size of metastases at conventional and contrast-enhanced US were compared by using CT as the standard of reference. Lesion conspicuity was assessed objectively (quantitatively) and subjectively by one reader before and after contrast material administration.

RESULTS

In 45 of 80 (56%) patients with metastases, more metastases were seen at contrast-enhanced US than at conventional US. In three of these patients, conventional US images appeared normal. The addition of contrast-enhanced US improved sensitivity for the detection of individual metastases from 71% to 87% (P <.001). On a patient basis, sensitivity improved from 94% to 98% (P =.44), and specificity improved from 60% to 88% (P <.01). Contrast enhancement improved the subjective conspicuity of metastases in 66 of 75 (88%) patients and the objective contrast by a mean of 10.8 dB (P <.001). Contrast-enhanced US showed more metastases than did CT in seven patients, and CT showed more than did contrast-enhanced US in one of 22 patients in whom an independent reference (magnetic resonance imaging, intraoperative US, or pathologic findings) was available.

CONCLUSION

Contrast-enhanced US improved sensitivity and specificity in the detection of hepatic metastases.

Ultrasound contrast imaging research

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

Pulse-inversion harmonic imaging improves lesion conspicuity during US-guided biopsy

PURPOSE

To assess the feasibility of percutaneous biopsy of low-conspicuity focal liver lesions with use of pulse-inversion harmonic imaging (PIHI) guidance in the late phase after injection of microbubble contrast agent.

MATERIALS AND METHODS

Twelve patients referred for ultrasound (US)-guided biopsy had liver lesions lacking adequate conspicuity to undergo biopsy under conventional ultrasound (US) guidance. They underwent biopsy procedures performed with the use of PIHI guidance in the late phase after injection of Levovist. The conspicuity of lesions, procedure time, number of passes, and success and complication rates were documented and compared to a control group. The control group consisted of retrospective analysis of 19 patients who had undergone conventional US-guided biopsy procedures performed by the same radiologist.

RESULTS

After contrast material injection, all lesions had sufficient increases in conspicuity to be targeted under PIHI guidance. Procedure time was prolonged in the PIHI group (66 minutes; range, 30-120 min; vs control, 33 min; range, 15-77 min; P <.01, Wilcoxon signed-rank test). The number of passes was greater in the PIHI group (1.9 +/- 0.3; vs control, 1.4 +/- 0.6; P <.01, chi(2) test). No statistically significant difference was observed when comparing success and complication rates.

CONCLUSION

PIHI in the late phase after injection of Levovist generated clear delineation of focal liver lesions in all cases, allowing an accurate and safe sampling. This technique broadens the scope of US-guided biopsy to lesions lacking adequate conspicuity on conventional US.

Kinetics of a US contrast agent in benign and malignant adnexal tumors

PURPOSE

To evaluate the effects of a microbubble contrast agent on the power Doppler ultrasonographic (US) examination of adnexal tumors, with a special focus on the timing of the transit of the microbubble bolus.

MATERIALS AND METHODS

Seventy patients who were suspected of having ovarian tumors were examined preoperatively with contrast material-enhanced US. Images obtained during a 5-minute examination were stored digitally, and the behavior of the contrast agent was evaluated objectively with measurement of the time-dependent image intensity at the region of interest with a computer program. A time-intensity curve in each case was derived and analyzed. The Mann-Whitney U test was used to compare intensity changes and tumor parameters in benign and malignant adnexal tumors.

RESULTS

Both the baseline and maximum power Doppler intensities, as well as the absolute and relative (percent) rise in intensity, were significantly higher (P <.001) in malignant as compared with benign tumors. The arrival time was shorter (17.5 vs 22.5 seconds; P =.005) and the duration of contrast agent effect was longer (190.4 vs 103.6 seconds; P <.001) in malignant tumors than they were in benign tumors. The area under the time-intensity curve was significantly greater in malignant tumors compared with that in benign tumors (P <.001).

CONCLUSION

After microbubble contrast agent injection, malignant and benign adnexal lesions behave differently in degree, onset, and duration of Doppler US enhancement.

Detection of hepatic VX2 tumors in rabbits: comparison of conventional US and phase-inversion harmonic US during the liver-specific late phase of contrast enhancement

OBJECTIVE

To compare phase-inversion sonography during the liver-specific phase of contrast enhancement using a microbubble contrast agent with conventional B-mode sonography for the detection of VX2 liver tumors.

MATERIALS AND METHODS

Twenty-three rabbits, 18 of which had VX2 liver tumor implants, received a bolus injection of 0.6 g of Levovist (200 mg/ml). During the liver-specific phase of this agent, they were evaluated using both conventional sonography and contrast-enhanced phase-inversion harmonic imaging (CEPIHI). Following sacrifice of the animals, pathologic analysis was performed and the reference standard thus obtained. The conspicuity, size and number of the tumors before and after contrast administration, as determined by a sonographer, were compared between the two modes and with the pathologic findings.

RESULTS

CE-PIHI demonstrated marked hepatic parenchymal enhancement in all rabbits. For VX2 tumors detected at both conventional US and CE- PIHI, conspicuity was improved by contrast-enhanced PIHI. On examination of gross specimens, 52 VX2 tumors were identified. Conventional US correctly detected 18 of the 52 (34.6%), while PIHI detected 35 (67.3%) (p < 0.05). In particular, conventional US detected only three (8.3%) of the 36 tumors less than 10 mm in diameter, but CE-PIHI detected 19 such tumors (52.8%) (p < 0.05).

CONCLUSION

Compared to conventional sonography, PIHI performed during the liver-specific phase after intravenous injection of Levovist is markedly better at detecting VX2 liver tumors.

Correlation between microbubble contrast-enhanced color doppler sonography and immunostaining for Kupffer cells in assessing the histopathologic grade of hepatocellular carcinoma: preliminary results

PURPOSE

The aim of this study was to determine the histopathologic grades of hepatocellular carcinomas (HCCs) on the basis of the presence of Kupffer cells, using color Doppler sonography with the liver-specific microbubble contrast agent Levovist.

METHODS

Color Doppler sonograms generated by stimulated acoustic emission were obtained 7 minutes after intravenous injection of 5 ml of Levovist (300 mg/dl) in patients with histopathologically confirmed HCCs. CT scans were also obtained and evaluated, and hematoxylin and eosin staining for morphologic examination and immunostaining (anti-CD68) for detecting Kupffer cells were performed for confirmation of the sonographic findings.

RESULTS

Eighteen tumors had a defect in the color Doppler signal (color void) that corresponded with the baseline gray-scale image of the tumor. On histopathologic examination, these 18 tumors were all found to be either poorly or moderately differentiated HCCs with either a marked reduction in the number of or the absence of Kupffer cells. The remaining 2 tumors showed color signals. Histopathologic examination of these 2 tumors disclosed well-differentiated components within the tumors, with Kupffer cells in the tumor tissue.

CONCLUSIONS

Color Doppler sonography using a liver-specific microbubble ultrasound contrast agent appears to reflect the histopathologic features of HCCs and may thus be useful for differentiating liver tumors and determining a treatment strategy.

Hepatocellular adenoma: diagnostic difficulties and novel imaging techniques

We report the case of a 30-year-old eastern European female who presented with right upper quadrant pain. Clinical examination was unremarkable and liver function tests were normal. CT identified a 5 cm lesion in segment V of the liver, which was of homogeneous low density with no calcification or significant enhancement. MRI showed the lesion to be hypointense to liver on T(1) weighted sequences and isointense on T(2) weighted sequences. Rapid arterial enhancement with gadolinium-DTPA faded without leaving a definite central scar. Ultrasound showed the lesion to be echogenic with minimal vascularity. Administration of a liver-specific microbubble contrast agent showed low uptake relative to the surrounding liver. Phosphorus-31 MR spectroscopy, localized to the lesion itself, revealed a markedly increased phosphomonoester resonance with a decreased phosphodiester resonance, compatible with increased cell turnover. Biopsy confirmed the lesion to be a hepatocellular adenoma. The diagnosis of a hepatic adenoma is difficult with tissue diagnosis the gold standard, but it may be suggested by a combination of imaging modalities. We have described two new imaging techniques not previously described in characterization of hepatic adenomata, namely ultrasound with contrast agent and MR spectroscopy.

Heterogeneous delayed enhancement of the liver after ultrasound contrast agent injection--a normal variant

We report a characteristic heterogeneous delayed liver enhancement pattern that we have encountered in a total of 6 of approximately 1500 subjects who underwent contrast-enhanced liver ultrasonography. The heterogeneous enhancement occurred several min after contrast injection and persisted for up to 1 h. It was seen in diseased as well as healthy livers and appears to represent a "normal variant" of liver enhancement. It was observed with two different contrast agents. The cause of the described effect is unknown; it may be related to the formation of large bubbles and vascular entrapment of these bubbles in the liver.

The disappearance of ultrasound contrast bubbles: observations of bubble dissolution and cavitation nucleation

The destruction process of biSphere and Optison ultrasound (US) contrast microbubbles were studied at 1.1 MHz. High-amplitude tone bursts caused shell disruption and/or fragmentation of the microbubbles, leading to dissolution of the freed gas. The bubble destruction and subsequent dissolution process was imaged with a high pulse-repetition frequency (PRF) 10-cycle, 5-MHz bistatic transducer configuration. Three types of dissolution profiles were measured: In one case, biSphere microbubbles showed evidence of dissolution through resonance, during which a temporary increase in the scattering amplitude was observed. In another case, both biSphere and Optison microbubbles showed evidence of fragmentation, during which the scattering amplitude decreased rapidly. Finally, in some cases, we observed the impulsive growth and subsequent rapid decay of signals that appear to be due to cavitation nucleation. Simulations of bubble dissolution curves show good agreement with experiments.