Jolette K. Wojdyla

Detection of individual microbubbles of ultrasound contrast agents: imaging of free-floating and targeted bubbles.

Rationale and Objectives:During echo examinations with microbubble contrast, individual “dots” of ultrasound reflection can be visualized. To address the question whether these signals represent individual microbubbles, very dilute suspensions of ultrasound contrast agents or individual microbubbles attached to Petri dishes were prepared and studied by ultrasound imaging. Methods:Microbubble suspensions were diluted in saline and evaluated by a clinical ultrasound imaging system. Microbubble concentration was verified by Coulter counter. Single microbubble preparation on a Petri dish was established by streptavidin–biotin interaction under microscopy control and subjected to ultrasound imaging. Results:Ultrasound of dilute microbubble dispersions demonstrated distinct white foci; concentration of these sites was consistent with signals from individual microbubbles as determined by Coulter. Individual microbubbles immobilized on polystyrene were also visualized by ultrasound. Conclusion:Ultrasound medical systems can resolve backscatter signals from individual microbubbles of ultrasound contrast, both in solution and in the targeted immobilized state, implying picogram sensitivity.

Detection of individual microbubbles of an ultrasound contrast agent: fundamental and pulse inversion imaging.

The use of ultrasound contrast materials in diagnostic imaging has been steadily increasing, with several agents recently approved for clinical application (1). When contrast echo imaging is performed, individual “speckles” of contrast can be often observed in the interrogated tissues. These white foci may represent the images of individual micron-sized bubbles. This implies exceptional detection sensitivity of ultrasound imaging with contrast agents. The capability of echo imaging to detect individual microbubbles is important for the quantification of the amount of bubbles in the tissues, determination of microvascular volume and targeted microbubble imaging. In order to test the ability of ultrasound imaging to detect individual microbubbles, dilute dispersions of microbubbles were prepared and evaluated by ultrasound imaging in vitro.

Targeting and ultrasound imaging of microbubble-based contrast agents.

Preparation and characterization of targeted microbubbles (ultrasound contrast agents) is described. Specific ligands were attached to the microbubble shell, and ligand-coated microbubbles were selectively attached to various targets, using either an avidin-biotin model system or an antigen-antibody system for targeting to live activated endothelial cells. Firm attachment of microbubbles to the target was achieved. Forces necessary to detach microbubbles from the target were estimated to exceed dozens of pN. Microbubbles were bound to the target even in the rapidly moving stream of the aqueous medium. Down to 20 ng of the ultrasound contrast material on the target surface could be detected by the ultrasound imaging with a commercial medical imaging system. At high bubble density on the target surface, strong ultrasound image attenuation was observed.

Direct video-microscopic observation of the dynamic effects of medical ultrasound on ultrasound contrast microspheres.

RATIONALE AND OBJECTIVES Ultrasound can cause destruction of microbubble contrast agents used to enhance medical ultrasound imaging. This study sought to characterize the dynamics of this interaction by direct visual observation of microbubbles during insonification in vitro by a medical ultrasound imaging system. METHODS Video microscopy was used to observe air-filled sonicated albumin microspheres adsorbed to a solid support during insonation. RESULTS Deflation was not observed at lowest transmit power settings. At higher intensities, gas left the microparticle gradually, apparently dissolving into the surrounding medium. Deflation was slower for higher microsphere surface densities. Intermittent ultrasound imaging (0.5 Hz refresh rate) caused slower deflation than continuous imaging (33 Hz). CONCLUSIONS Higher concentrations of microbubbles, lower ultrasound transmit power settings, and intermittent imaging each can reduce the rate of destruction of microspheres resulting from medical ultrasound insonation.

Destruction of contrast agent microbubbles in the ultrasound field: the fate of the microbubble shell and the importance of the bubble gas content.

Disappearance of ultrasound (US) contrast agents (gasfilled microbubbles) after contrast agent administration in the bloodstream occurs by way of several mechanisms. First, microbubbles are filtered and captured by various organs, including uptake by Kupffer cells in the liver (1,2). Second, gas diffuses from the microbubble core and dissolves in the surrounding medium, leaving the nonechogenic shell behind (3). The third process is the most rapid and important for the practice of diagnostic imaging by US. It is the destruction of microbubbles by the acoustic field of the US medical imaging system. It has been shown that the rate of microbubble destruction in the ultrasound field depends on the ultrasound frequency and pressure (4–7). During imaging, the microbubble contrast agent can be destroyed by a single pulse of the ultrasound, if the ultrasound mechanical index (MI) value is high enough (7,8). This phenomenon has been applied successfully for the imaging of tissue perfusion and perfusion defects (8,9). Thus, the mechanisms of microbubble contrast agent disappearance in the ultrasound field are important and need to be investigated in detail. We have previously reported a microbubble destruction/microscopy study performed with an air-filled microbubble agent, sonicated human serum albumin (Albunex; Mallinckrodt, St Louis, Mo) (10). More recent contrast agents filled with insoluble fluorinated gases, such as Optison (Mallinckrodt), demonstrate extended in vivo circulation and stability (11). It is of interest to evaluate the stability of these microbubbles in the field of the US medical imager. The nature of the gas and the gas exchange may play an important role in the bubble destruction. Here, we describe video microscopic studies performed in vitro for immobilized microbubbles during their insonification. Fluorescence microscopy was used to evaluate the behavior of microbubble shells during the destruction of microbubbles.

Inhaled gases affect the ultrasound contrast produced by albunex® in anesthetized dogs

In anesthetized animals maintained with isoflurane using 100% oxygen as a carrier gas, Albunex (Molecular Biosystems, Inc., San Diego, Calif.) produced no ultrasound contrast in the left ventricle after intravenous administration. The current study tested the hypothesis that the inhalation of gas mixtures with increased concentrations of oxygen decreased the quality and duration of Albunex-induced contrast. Albunex (0.22 mL/kg) was injected intravenously into anesthetized dogs (n = 9) breathing compressed air, oxygen, mixtures of oxygen and nitrogen, or combinations of oxygen and nitrous oxide. Albunex produced ultrasound contrast of shorter duration and decreased quality during the inhalation of gas mixtures containing increased amounts of oxygen. In the presence of inhaled gas mixtures containing nitrous oxide, Albunex produced no contrast in the left ventricle, regardless of the oxygen content. These data indicate that the inhalation of gas mixtures containing smaller amounts of nitrogen, compared with air, decreased the ability of Albunex to cause ultrasound contrast in the heart after intravenous administration.

Cardiovascular effects caused by rapid administration of gadoversetamide injection in anesthetized dogs.

Wible JH, Galen KP, Wojdyla J. Cardiovascular effects caused by rapid administration of gadoversetamide injection in anesthetized dogs. Invest Radiol 2001;36:292–298. rationale and objectives. This study assessed the cardiovascular effects of gadoversetamide and other gadolinium chelates administered at high rates of injection. methods.Anesthetized beagles were instrumented to record the electrocardiogram and to measure arterial blood pressure. In part 1, each animal was injected with gadoversetamide at rates of 1.0, 3.0, and 10 mL/s. In part 2, each animal was injected with gadoversetamide, gadopentetate dimeglumine, gadodiamide, and gadoteridol at a dose of 0.6 mmol/kg delivered at a rate of 3.0 mL/s. results.Intravenous administration of gadoversetamide caused transient decreases in both heart rate and blood pressure. The rate of injection did not affect the magnitude of the heart rate or blood pressure changes. Administration of gadoversetamide, gadopentetate dimeglumine, and gadodiamide elicited equivalent changes in cardiovascular function. Injection of gadoteridol caused a similar degree of hypotension, but the changes lasted longer. conclusions.Rapid administration of gadoversetamide caused no potentiation in cardiovascular changes. Our data support the initiation of a clinical trial to demonstrate the safety of rapidly administering gadoversetamide with the use of a power injector.

Neurotoxicity of non-ionic X-ray contrast media after intracisternal administration in rats

The neurotoxicity of an X-ray contrast medium appears inversely related to the hydrophilicity of the agent. To further test this hypothesis, four non-ionic X-ray contrast agents, differing in hydrophilicity, (ioversol, iopromide, iohexol and iopamidol) were injected into the cisternal magna of ether-anesthetized rats. Iopromide demonstrated an acute median lethal dose of 122 mg I/kg. Other signs of toxicity included convulsions, apnea, dyspnea and hypoactivity. In contrast, ioversol, iohexol and iopamidol caused no deaths when administered intracisternally, up to a dose of 1000 mg I/kg. Animals treated with these nonionic agents displayed signs of convulsions, apnea, dyspnea, chewing and hypoactivity. Iopromide possesses a hydrophilicity (e.g., water to octanol partition coefficient) approximately 8.5 times smaller than ioversol, 4.6 times smaller than iohexol and 2.3 times smaller than iopamidol. These data support the hypothesis that tri-iodinated X-ray contrast materials with smaller degrees of hydrophilicity produce greater toxicity to the central nervous system.

EFFECTS OF INHALED GASES ON THE ULTRASOUND CONTRAST PRODUCED BY MICROSPHERES CONTAINING AIR OR PERFLUOROPROPANE IN ANESTHETIZED DOGS

RATIONALE AND OBJECTIVES Inhaled gas mixtures with increased amounts of oxygen cause air containing ultrasound contrast agents to lose efficacy faster than during the inhalation of air. The authors hypothesized that contrast materials containing relatively insoluble gases would decrease the effects of inhaled gases on the ultrasound contrast. METHODS Anesthetized dogs were ventilated with compressed air and different oxygen/nitrogen gas mixtures. Video densitometric analysis was performed on end diastolic ultrasound images of the heart after administration of Albunex (air-filled microspheres) or Optison (perfluoropropane-filled microspheres). RESULTS Increased concentrations of oxygen caused no change in the contrast intensity produced by Optison in the left ventricular chamber. In the myocardium, however, increases in oxygen caused Optison to produce significantly less enhancement of the myocardial tissue. CONCLUSIONS The use of perfluoropropane within albumin microspheres prevented the effects of inhaled gas mixtures on contrast produced within the left ventricular chamber. In the myocardium, increased concentrations of oxygen in the inhaled gas mixtures reduce contrast intensity.

Abstract 4400: Anti-tumor activity of liposomal docetaxel prodrug MNK-010 on PC3 human prostate xenografts in mice

The anti-mitotic taxanes are one of the most important families of anticancer drugs that have broad anti-tumor activity and are widely used for a variety of human cancer types. However, the taxanes are limited by a number of serious pharmacological and toxicological effects, including dose limiting myelosuppression, neurotoxicity and serious hypersensitivity reactions. We are developing a unique delivery system for docetaxel, comprised of a PEGylated liposomal nanoparticle containing a prodrug of docetaxel to improve solubility, tolerability and increase efficacy through improved pharmacokinetics and biodistribution. In this study we evaluated the antitumor activity of MNK-010 on the growth of established human PC3 xenografts in male immunodeficient mice. This study tested the hypothesis that MNK-010 can provide greater efficacy than Taxotere (docetaxel) at equivalent maximum tolerated doses (MTD) in mice implanted with human PC3 tumor cells. Male nude mice bearing PC3 human prostate xenografts were given two or four intravenous (IV) doses of MNK-010, Taxotere or saline. Dosing intervals were twenty-one days for two cycles or every four days for four cycles. The doses of Taxotere and MNK-010 were based on maximum tolerated dose (MTD) or highest dose tested for a given dose interval. Tumor volume was measured twice per week using the Biopticon tumor imaging system and tumor volume data was analyzed to determine tumor growth delay and partial tumor regression. Survival analysis was conducted and median survival time determined. MNK-010 significantly (p Citation Format: Richard M. Fitch, Jolette K. Wojdyla, James A. Blackledge, William D. McGhee. Anti-tumor activity of liposomal docetaxel prodrug MNK-010 on PC3 human prostate xenografts in mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4400. doi:10.1158/1538-7445.AM2015-4400