Ultrasound contrast agents: balancing safety versus efficacy

A new sonoablation using acoustic droplet vaporization and focused ultrasound: A feasibility study

BACKGROUND

Histotripsy and boiling histotripsy are two methods of mechanical ablation that use high-pressure focused ultrasound (FUS).

PURPOSE

Here, a new bubble sonoablation technique was investigated using low-pressure FUS in combination with local injection of perfluoropentane (PFP) in rabbit liver.

METHODS

Fifteen healthy New Zealand white rabbits were treated with FUS alone, FUS + PFP or PFP alone. FUS was performed using a single-element focused transducer (frequency 596 kHz, 0.27 ms pulses, 0.54% duty cycle, and peak negative pressure 2.0 MPa). Ten minutes before FUS treatment, the PFP droplet was locally injected into the rabbit liver, where the ultrasound was focused. Contrast-enhanced ultrasound (CEUS) of the liver was performed, and the temperature at the liver surface in the targeted liver region was recorded during treatment. The livers were collected for pathological examination. Statistical significance was set at p < 0.05. Paired t-tests were used to compare the pre- and post-treatment values. One-way analysis of variance was performed to compare multiple groups, and the least significant difference method was used for further comparisons between the two groups.

RESULTS

Analysis of CEUS data showed that the values of area under the curve (AUC) were significantly different in the PFP + FUS group pre- (10453.644 ± 1182.93) and post-treatment (4058.098 ± 2720.41), and the AUC values of PFP + FUS post-treatment (4058.098 ± 2720.41) were also significantly lower than those of the FUS (9946.694 ± 1071.54) and the PFP (10364.794 ± 2181.53) groups. The peak intensity values also showed the same results, the value of peak intensity of PFP+FUS post-treatment was 82.958 ± 13.99, whereas there was no difference between FUS (106.61 ± 7.61) and PFP (104.136 ± 10.55). Hematoxylin and eosin (H&E) staining revealed that the pathological damage ratings of the PFP + FUS, PFP, and FUS groups were grade 3, grade 1, and grade 0, respectively. Specifically, the area of liver necrosis in the PFP + FUS group (0.99 ± 0.29 cm2 ) was 198 times higher than that in the PFP group (0.005 ± 0.008 cm2 ), whereas no necrosis was observed in the livers treated with FUS alone. Simultaneously, the number of vacuoles in the liver of the PFP + FUS group (35.50 ± 23.31) was approximately five times that of the PFP group (7.00 ± 12.88), whereas no vacuoles were found in the liver treated with FUS alone.

CONCLUSION

PFP droplets combined with FUS can destroy liver tissue and cause tissue necrosis in the droplet injection area, without affecting the structure of surrounding tissue.

Contrast-enhanced ultrasound of the kidneys: principles and potential applications

Contrast-enhanced ultrasound (CEUS) is an extension and an enhanced form of ultrasound that allows real-time evaluation of the various structures in different vascular phases. The last decade has witnessed a widespread expansion of CEUS applications beyond the liver. It has shown fair potential in kidneys and its diagnostic efficacy is comparable to CT and MRI. Ultrasound is the well-accepted screening modality for renal pathologies, however, it underperforms in the characterization of the renal masses. CEUS can be beneficial in such cases as it can help in the characterization of such incidental masses in the same sitting. It has an excellent safety profile with no risk of radiation or contract-related nephropathy. It can aid in the correct categorization of renal cysts into one of the Bosniak classes and has proven its worth especially in complex cysts or indeterminate renal masses (especially Bosniak Category IIF and III). Few studies also describe its potential role in solid masses and in differentiating benign from malignant masses. Other areas of interest include infections, infarctions, trauma, follow-up of local ablative procedures, and VUR. Through this review, the readers shall get an insight into the various applications of CEUS in kidneys, with imaging examples.

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

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

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

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

Review of ultrasound contrast agents in current clinical practice with special focus on DEFINITY® in cardiac imaging

Echocardiography is the most widely used noninvasive modality to evaluate the structure and function of the cardiac muscle in daily practice. However, up to 15-20% of echocardiograms are considered suboptimal. To enable accurate assessment of cardiac function and wall motion abnormality, the use of ultrasound microbubble contrast has shown substantial benefits in cases of salvaging nondiagnostic studies and enhancing the diagnostic accuracy in daily practice. DEFINITY^® is a perflutren based, lipid shelled microbubble contrast agent, which is US FDA approved for left ventricular opacification. The basis of ultrasound microbubbles, its development, and the clinical role of DEFINITY (characteristics, indications and case examples, side effect profile and existing evidence) is the subject of discussion in this review.

Safety of Perfluorobutane (Sonazoid) in Characterizing Focal Liver Lesions

Background:

The purpose of this study was to report the safety of perfluorobutane (Sonazoid) as a vascular-phase imaging agent in characterizing focal liver lesions (FLLs).

Materials and Methods:

From May 2014 to April 2015, a total of 54 individuals who received Sonazoid contrast-enhanced ultrasound (CEUS) were enrolled at 5 hospitals of 4 medical centers. All individuals were included in safety evaluation. A prospective study to evaluate the adverse effect (AE) incidences after intravenous administration of Sonazoid.

Results:

Sonazoid was well tolerated. Treatment-emergent adverse events (TEAEs) representing AE were recorded for 13 (24.1%) patients. The most common AE was abdominal pain (9.3%), followed by heart rate irregularity (5.6%). The majority of these patients (69.2%) experienced TEAEs that were mild in intensity. Sonazoid causes no significant AEs after intravenous injection. The only noteworthy AEs are related to tolerable myalgia (3.7%), abdominal pain (1.9%), and headache (1.9%). None of the 54 patients showed serious adverse effects.

Conclusion:

Sonazoid shows good safety and tolerance of intravenous use during CEUS of the liver for evaluation of FLLs.

Anaphylactic shock with an ultrasound contrast agent

Echo contrast agents, such as SonoVue^®, (Bracco, Milan, Italy) are often used to enhance diagnosis. Although their use is safe, some rare side effects could be severe or even fatal. We are reporting a case of severe systemic allergic reaction after infusion of SonoVue^®. After a brief review of the literature, the aim of this paper is to draw attention to this risk and recall the safety instructions coming with the use of ultrasound contrast agents.

Safety of Perflutren Ultrasound Contrast Agents: A Disproportionality Analysis of the US FAERS Database

INTRODUCTION

Perflutren microbubble/microsphere ultrasound contrast agents have a black-box warning based on case reports of serious cardiopulmonary events. There have been several subsequent observational safety studies. Large spontaneous reporting databases may help detect/refine signals of rare adverse events that elude other data sources/study designs.

OBJECTIVE

The objective of this study was to supplement existing knowledge of the reported safety of perflutren using statistical analysis of spontaneous reports.

METHODS

We analyzed information from the US Food and Drug Administration Adverse Event Reporting System using a disproportionality analysis. Analysis of overall reporting for perflutren was supplemented by subset (age, indication) analysis. A signal of disproportionate reporting (SDR) was defined as EB05 >2.

RESULTS

Overall, 18/380 Preferred Terms and 1/83 Standardized Medical Queries had SDRs. Most were small (EB05 = 2-4). Back pain and flank pain were the largest SDRs followed by events compatible with signs/symptoms of hypersensitivity. The general pattern of SDRs in the subset analysis was consistent with the overall analysis. Almost all events with SDRs were literally or conceptually labeled. Except for chest pain (higher in the age <65 years subgroup) and back pain (higher in the age ≥65 years subgroup), there were no statistically significant differences between age subsets. Except for the Preferred Terms Pruritus and Urticaria and the narrow Standardized Medical Queries Ventricular tachyarrhythmia, Angioedema, Oropharyngeal allergic conditions, and Hypersensitivity (higher in the stress test subgroup), there were no statistically significant reporting differences between indication subsets. There were no SDRs associated with the major cardiovascular events of death, myocardial infarction/ischemia, angina, arrhythmias, or convulsions in any analysis.

CONCLUSIONS

Our combined signal detection/evaluation analysis did not identify SDRs of novel adverse events or major cardiovascular events associated with perflutren ultrasound contrast agents. The negative results for major cardiovascular events extend previous signal evaluation exercises supporting the relative cardiovascular safety of these agents.

Detection of Intraneural Median Nerve Microvascularity Using Contrast-Enhanced Sonography: A Pilot Study

OBJECTIVES

Demonstrating vascularity within the human median nerve may be difficult using power Doppler sonography. To this end, a pilot study documenting contrast-enhanced vascularity of the median nerve was conducted.

METHODS

Patients undergoing contrast-enhanced transthoracic echocardiography were recruited for this study (n = 24). During echocardiography, a simultaneous contrast-enhanced sonographic examination of the median nerve was conducted. The study and study protocol were built from preclinical evidence. Image analysis was based on the power Doppler pixel intensity within a defined region of interest to obtain quantitative data representing the average pixel intensity, maximum pixel intensity, and power Doppler pixel dot count. Semiquantitative data representing the power Doppler dot count grading were also obtained.

RESULTS

Spearman correlations between analytical methods showed strong positive, statistically significant (P< .05) correlations between the average pixel intensity and maximum pixel intensity and between the power Doppler dot count and dot count grading. Statistically significant increases in the average pixel intensity and power Doppler dot count were seen at all but 1 time point throughout the contrast-enhanced sonographic examination when compared to precontrast administration. Statistically significant increases in the maximum pixel intensity were seen at all but 4 time points.

CONCLUSIONS

These pilot results represent early evidence that contrast-enhanced sonography can be used to image median nerve vascularity. In this convenience sample, median nerve contrast-enhanced sonographic data collection was feasible, safe, and consistent.

Transrectal Elastographic Biopsy and Contrast-Enhanced Transrectal Biopsy May Offer Improvements Over the Current Transrectal Systemic Biopsy Technique

Prostate cancer is a common cause of cancer-related death of men in the United States. The purpose of this review is to compare the validity of transrectal ultrasound–guided systemic biopsy with contrast-enhanced transrectal ultrasound–guided systemic biopsy and transrectal elastography–guided systemic biopsy for the detection of prostate cancer. Adding contrast-enhanced or transrectal elastography core targeting to transrectal ultrasound–guided biopsy is a feasible approach to increase detection rates of higher-grade prostate cancers. Because contrast-enhanced imaging of the prostate is not approved for use in the United States, elastography is the most effective sonographic solution to improve prostate cancer detection with current screening techniques.

Advantages and Limitations of Focal Liver Lesion Assessment with Ultrasound Contrast Agents: Comments on the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) Guidelines

Contrast-enhanced ultrasound (CEUS) represents a significant breakthrough in sonography. Due to US contrast agents (UCAs) and contrast-specific techniques, sonography offers the potential to show enhancement of liver lesions in a similar way as contrast-enhanced cross-sectional imaging techniques. The real-time assessment of liver perfusion throughout the vascular phases, without any risk of nephrotoxicity, represents one of the major advantages that this technique offers. CEUS has led to a dramatic improvement in the diagnostic accuracy of US and subsequently has been included in current guidelines as an important step in the diagnostic workup of focal liver lesions (FLLs), resulting in a better patient management and cost-effective therapy. The purpose of this review was to provide a detailed description of contrast agents used in different cross-sectional imaging procedures for the study of FLLs, focusing on characteristics, indications and advantages of UCAs in clinical practice.

Contrast-enhanced ultrasound in liver cancer

Contrast-enhanced ultrasound (CEUS) is a sure, noninvasive, repeatable imaging technique widely used in the characterization of benign and malignant liver lesions. The European Federation of Societies for Ultrasound in Medicine and Biology guidelines suggest the typical CEUS features of liver lesions as criteria for the noninvasive diagnosis in cirrhotic and not-cirrhotic patients. The clinical application of CEUS in the liver study is summarized in this review; the contrast-enhanced patterns of the most frequent liver lesions are described (hepatocellular and cholangiocellular carcinoma, liver metastases, hemangioma, focal nodular hyperplasia, adenoma). The role of this imaging technique in the diagnostic algorithm of liver malignancy is illustrated and the CEUS application in hepatologic and oncological settings is depicted.

Safety of ultrasound contrast agents in the pediatric oncologic population: a single-institution experience

OBJECTIVE

Little information is available regarding the safety of ultrasound contrast agents in children. The purpose of this article was to assess the safety profile of the i.v. administration of ultrasound contrast agents in the pediatric oncology population.

MATERIALS AND METHODS

Patients with pediatric solid malignancies who were enrolled on institutional clinical trials conducted between June 2003 and January 2013 and who met our institutional screening criteria for contrast-enhanced ultrasound (CEUS) were eligible. After providing informed consent or assent for CEUS, subjects received i.v. bolus injections of one of two contrast agents for imaging of the primary tumor or a metastatic target lesion. Hemodynamic parameters, including heart rate, cardiac rhythm, and oxygen saturation, were monitored immediately before and for 30 minutes after the administration of the contrast agent. Interviews with the subject or a guardian were conducted by the principal investigator or a radiologist coinvestigator before and after the examination to assess for any adverse effects.

RESULTS

Thirty-four subjects (21 male and 13 female) ranging in age from 8 months to 20.7 years (median, 8.7 years) underwent 134 CEUS. No detrimental change in hemodynamic status occurred in any subject. Three subjects (3/134, 2.2%) reported mild transient side effects on one occasion each, two (2/134, 1.5%) had taste alteration, and one (1/134, 0.8%) reported mild transient tinnitus and lightheadedness. These reactions did not recur in these subjects on subsequent CEUS examinations.

CONCLUSION

The i.v. administration of ultrasound contrast agents is safe and well tolerated in the pediatric oncology population. Further studies in children are needed to confirm our findings.

Encapsulated microbubbles and echogenic liposomes for contrast ultrasound imaging and targeted drug delivery

Micron- to nanometer-sized ultrasound agents, like encapsulated microbubbles and echogenic liposomes, are being developed for diagnostic imaging and ultrasound mediated drug/gene delivery. This review provides an overview of the current state of the art of the mathematical models of the acoustic behavior of ultrasound contrast microbubbles. We also present a review of the in vitro experimental characterization of the acoustic properties of microbubble based contrast agents undertaken in our laboratory. The hierarchical two-pronged approach of modeling contrast agents we developed is demonstrated for a lipid coated (Sonazoid™) and a polymer shelled (poly D-L-lactic acid) contrast microbubbles. The acoustic and drug release properties of the newly developed echogenic liposomes are discussed for their use as simultaneous imaging and drug/gene delivery agents. Although echogenicity is conclusively demonstrated in experiments, its physical mechanisms remain uncertain. Addressing questions raised here will accelerate further development and eventual clinical approval of these novel technologies.

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

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

Evaluation of ultrasound-assisted thrombolysis using custom liposomes in a model of retinal vein occlusion

PURPOSE

To study the potential efficacy of ultrasound (US) assisted by custom liposome (CLP) destruction as an innovative thrombolytic tool for the treatment of retinal vein occlusion (RVO).

METHODS

Experimental RVO was induced in the right eyes of 40 rabbits using laser photothrombosis; the US experiment took place 48 hours later. Rabbits were randomly divided into four equal groups: US+CLP group, US+saline group, CLP+sham US group, and no treatment group. The latter three groups acted as controls. Fundus fluorescein angiography and Doppler US were used to evaluate retinal blood flow.

RESULTS

CLP-assisted US thrombolysis resulted in restoration of flow in seven rabbits (70%). None of the control groups showed significant restoration of retinal venous blood flow.

CONCLUSIONS

US-assisted thrombolysis using liposomes resulted in a statistically significant reperfusion of retinal vessels in the rabbit experimental model of RVO. This approach might be promising in the treatment of RVO in humans. Further studies are needed to evaluate this approach in patients with RVO. Ultrasound assisted thrombolysis can be an innovative tool in management of retinal vein occlusion.

Effects of ultrasound and ultrasound contrast agent on vascular tissue

BACKGROUND

Ultrasound (US) imaging can be enhanced using gas-filled microbubble contrast agents. Strong echo signals are induced at the tissue-gas interface following microbubble collapse. Applications include assessment of ventricular function and virtual histology.

AIM

While ultrasound and US contrast agents are widely used, their impact on the physiological response of vascular tissue to vasoactive agents has not been investigated in detail.

METHODS AND RESULTS

In the present study, rat dorsal aortas were treated with US via a clinical imaging transducer in the presence or absence of the US contrast agent, Optison. Aortas treated with both US and Optison were unable to contract in response to phenylephrine or to relax in the presence of acetylcholine. Histology of the arteries was unremarkable. When the treated aortas were stained for endothelial markers, a distinct loss of endothelium was observed. Importantly, terminal deoxynucleotidyl transferase mediated dUTP nick-end-labeling (TUNEL) staining of treated aortas demonstrated incipient apoptosis in the endothelium.

CONCLUSIONS

Taken together, these ex vivo results suggest that the combination of US and Optison may alter arterial integrity and promote vascular injury; however, the in vivo interaction of Optison and ultrasound remains an open question.

Contrast-enhanced sonography of malignant pediatric abdominal and pelvic solid tumors: preliminary safety and feasibility data

BACKGROUND

Little information exists regarding pediatric contrast-enhanced US.

OBJECTIVE

To assess the safety and feasibility of contrast-enhanced US of pediatric abdominal and pelvic tumors.

MATERIALS AND METHODS

This prospective study included eight boys and five girls (mean age, 10.8 years) with abdominal or pelvic tumors. Cohorts of three subjects underwent US with perflutren contrast agent at escalating dose levels. Neurological and funduscopic examination, electrocardiography and continuous pulse oximetry were performed before and after contrast administration. Three radiologists independently scored six imaging parameters on pre- and postcontrast sonography. Inter-reviewer agreement was measured by the Kappa statistic.

RESULTS

No neurological, retinal, electrocardiographical or pulse oximetry changes were attributable to the contrast agent. Two subjects reported minor, transient symptoms. Postcontrast US parameter scores improved slightly in 8 of 12 subjects. Postcontrast ultrasound inter-reviewer agreement improved slightly for detection of tumor margins (precontrast = 0.20, postcontrast = 0.26), local tumor invasion (precontrast = -0.01, postcontrast = 0.10) and adenopathy (precontrast = 0.35, postcontrast = 0.44).

CONCLUSIONS

Although our sample size is small, perflutren contrast agents appear to be safe and well tolerated in children. Contrast-enhanced sonography of pediatric abdominal and pelvic tumors is feasible, but larger studies are needed to define their safety and efficacy in children.

Contrast-enhanced sonography in pediatrics

Microbubble US contrast agents are composed of an outer shell of protein, phospholipid or polymer that encase air or perfluorocarbon gas. These contrast agents have been widely used in adult cardiology patients to improve endocardial border delineation and have been proved safe and well tolerated in this patient population. There is also a growing body of literature elucidating the value of contrast-enhanced sonography to distinguish benign from malignant liver lesions in adults and to characterize non-hepatic adult malignancies. Because these agents have not been approved for pediatric use in many countries, less is known of the value of contrast-enhanced sonography in children. In this review I will discuss several proven and potential pediatric applications of contrast-enhanced sonography.

Imaging of the ovine corpus luteum microcirculation with contrast ultrasound

Ultrasound contrast agents have been the subject of microvascular imaging research. The sheep corpus luteum (CL) is a microvascular tissue that provides a natural angiogenic and antiangiogenic process, which changes during the luteal phase of the estrous cycle of the ewe. It can also be controlled and monitored endocrinologically, providing a very attractive in vivo model for the study and development of microvascular measurement. The perfusion of the fully developed CL between days 8 and 12 of the estrous cycle was studied in six ewes. A Philips iU22 ultrasound scanner (Bothell, WA, USA) with the linear array probe L9-3 was used to capture contrast-enhanced images after an intravenous bolus injection of 2.4 mL SonoVue (Bracco S.P.A., Milan, Italy). Time-intensity curves of a region of interest inside the CL were formed from linearized image data. A lagged-normal model to simulate the compartmental kinetics of the microvascular flow was used to fit the data, and the wash-in time was measured. Good contrast enhancement was observed in the CLs of all animals and the wash-in time averaged at 5.5 s with 9% uncertainty. The regression coefficient was highly significant for all fits. These data correlated with stained endothelial area in the histology performed postmortem. Two ewes were injected with prostaglandin F2alpha to induce CL regression, which resulted in an increase of wash-in time after a few hours. The CL of the ewe is thus proposed as an ideal model for the study and development of microvascular measurements using contrast ultrasound. Our initial results demonstrate a highly reproducible model for the study of the microvascular hemodynamics in a range of tissues and organs.

Molecular imaging of inflammation and intraplaque vasa vasorum: a step forward to identification of vulnerable plaques?

Current developments in cardiovascular biology and imaging enable the noninvasive molecular evaluation of atherosclerotic vascular disease. Intraplaque neovascularization sprouting from the adventitial vasa vasorum has been identified as an independent predictor of intraplaque hemorrhage and plaque rupture. These intraplaque vasa vasorum result from angiogenesis, most likely under influence of hypoxic and inflammatory stimuli. Several molecular imaging techniques are currently available. Most experience has been obtained with molecular imaging using positron emission tomography and single photon emission computed tomography. Recently, the development of targeted contrast agents has allowed molecular imaging with magnetic resonance imaging, ultrasound and computed tomography. The present review discusses the use of these molecular imaging techniques to identify inflammation and intraplaque vasa vasorum to identify vulnerable atherosclerotic plaques at risk of rupture and thrombosis. The available literature on molecular imaging techniques and molecular targets associated with inflammation and angiogenesis is discussed, and the clinical applications of molecular cardiovascular imaging and the use of molecular techniques for local drug delivery are addressed.

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).