The recent increase in survival rates of most cancers is due to early detection greatly aided by medical imaging modalities. Combined ultrasound and photoacoustic imaging provide both morphological and functional/molecular information which can help to detect and diagnose cancer in its earliest stages. However, both modalities can benefit from the use of contrast agents. The objective of this thesis was to design, synthesize, and test a nano-sized, dual contrast agent for combined ultrasound and photoacoustic imaging named Photoacoustic nanoDroplets. This agent consists of liquid perfluorocarbon nanodroplets with encapsulated plasmonic nanoparticles. These dual contrast agents utilize optically triggered vaporization for photoacoustic signal generation, providing significantly higher signal amplitude than that from the traditionally used mechanism, thermal expansion. Upon pulsed laser irradiation, liquid perfluorocarbon undergoes a liquid-to-gas phase transition generating giant photoacoustic transients from these dwarf nanoparticles. Once triggered, the gaseous phase provides ultrasound contrast enhancement. Demonstrated in this work are the design, synthesis, characterization, and testing of Photoacoustic nanoDroplets in phantom and animal studies, and preliminary work into adapting these agents into targeted, drug delivery vehicles for simultaneous detection, diagnosis, and treatment of diseases. / text

Microbubble contrast agents for ultrasound are widely used in numerous medical applications, both diagnostic and therapeutic. Due to their size, similar to that of red blood cells, microbubbles are able to traverse the entire vascular bed, enabling their utilization for applications such as tumour diagnosis. Vaporizable submicron droplets of liquid perfluoro- carbon potentially represent a new generation of extravascular contrast agents for ultrasound. Droplets of a few hundred nanometers in diameter have the ability to extravasate selectively in regions of tumour growth while staying intravascular in healthy tissues. Upon extravasation, these droplets may be vaporized with ultrasound and converted into gas bubbles. In this thesis we argue that vaporized submicron perfluorocarbon droplets possess the necessary stability and acoustic characteristics to be potentially applicable as a new gener- ation of extravascular ultrasound contrast agents. We examine, separately, the ultrasound conditions necessary for vaporization of the droplets into microbubbles, the size and stability of these bubbles following vaporization, on timescales ranging from nanoseconds to minutes, and the bubbles’ acoustic response to incident diagnostic ultrasound. We show that submicron droplets may be vaporized into bubbles of a few microns in diameter using single ultrasound pulse within the diagnostic range. The efficiency of conversion is shown to be on the order of at least 10% of the exposed droplets converting into stable microbubbles. The bubbles are shown to be stabilized by the original coating material encapsulating the droplet precursors, and be stable for at least minutes following vaporization. Finally, vaporized droplets are shown to be echogenic, with acoustic characteristics comparable to these of the commercially available ultrasound contrast agents. The results presented here show that vaporized droplets possess the necessary stability properties and echogenicity required for successful application as contrast agents, suggesting potential for their future translation into clinical practice.

Microbubble contrast agents for ultrasound are widely used in numerous medical applications, both diagnostic and therapeutic. Due to their size, similar to that of red blood cells, microbubbles are able to traverse the entire vascular bed, enabling their utilization for applications such as tumour diagnosis. Vaporizable submicron droplets of liquid perfluoro- carbon potentially represent a new generation of extravascular contrast agents for ultrasound. Droplets of a few hundred nanometers in diameter have the ability to extravasate selectively in regions of tumour growth while staying intravascular in healthy tissues. Upon extravasation, these droplets may be vaporized with ultrasound and converted into gas bubbles. In this thesis we argue that vaporized submicron perfluorocarbon droplets possess the necessary stability and acoustic characteristics to be potentially applicable as a new gener- ation of extravascular ultrasound contrast agents. We examine, separately, the ultrasound conditions necessary for vaporization of the droplets into microbubbles, the size and stability of these bubbles following vaporization, on timescales ranging from nanoseconds to minutes, and the bubbles’ acoustic response to incident diagnostic ultrasound. We show that submicron droplets may be vaporized into bubbles of a few microns in diameter using single ultrasound pulse within the diagnostic range. The efficiency of conversion is shown to be on the order of at least 10% of the exposed droplets converting into stable microbubbles. The bubbles are shown to be stabilized by the original coating material encapsulating the droplet precursors, and be stable for at least minutes following vaporization. Finally, vaporized droplets are shown to be echogenic, with acoustic characteristics comparable to these of the commercially available ultrasound contrast agents. The results presented here show that vaporized droplets possess the necessary stability properties and echogenicity required for successful application as contrast agents, suggesting potential for their future translation into clinical practice.

Inhaled drug delivery is currently the gold standard for treating many respiratory diseases. However, improved treatments are needed for lung diseases like Cystic Fibrosis (CF) and Acute Respiratory Distress Syndrome (ARDS), where mucus or fluid build-up in the lung limits ventilation and, thus, delivery of inhaled drugs. Delivery is most needed in the diseased or damaged regions of the lung, but if an area is not ventilated, inhaled drug will simply not reach it. To overcome this, this research proposes delivering drugs to the lungs within a perfluorocarbon (PFC) liquid. The lungs will be filled with a reverse emulsion containing a disperse phase of aqueous drugs within the bulk PFC and then ventilated. The PFC functions as both a respiratory medium, providing gas exchange, and as a delivery vehicle, providing a more uniform deposition of drugs. After treatment, the highly volatile PFCs are exhaled, returning the patient to normal respiration. This technique improves upon current therapies as follows. First, drugs are delivered directly to where they are needed, yielding higher concentrations in the lung and lower systemic concentrations. Second, PFCs are ideal for washing out lung exudate and mucus. The low surface tension and high density of PFC allows it to easily penetrate plugged or collapsed alveoli, detach infected mucus from the airway walls, and force these fluids to the top of the lungs where they can then be removed via suction. Mucus and exudate removal should allow drugs to penetrate previously plugged airways during emulsion delivery and subsequent treatment with inhaled therapies. Thus, drug delivery via emulsion would be used as a pre-treatment to enhance inhaled or systemic drug therapy. Third, PFC’s anti-inflammatory properties help return to normal lung function. This research examines two applications of this technology: delivery of antibiotics to combat respiratory infections (antibacterial perfluorocarbon ventilation, APV) or delivery of growth factors to enhance alveolar repair (perfluorocarbon emulsions for alveolar repair, PEAR). This work represents an in-depth analysis of the emulsions used during APV and PEAR. Initial efforts evaluated emulsion efficacy under in vitro setting that better simulated lung in vivo antibiotic delivery. The subsequent studies utilized an in vivo rat model of bacterial respiratory infection to validate the effects of emulsion on pharmacokinetics and to assess APVs potential treatment benefits. Lastly, in vitro methods of cellular response assessed the utility of delivering growth factors in PEAR. Significant advancements were made in optimizing the emulsion as a viable means of pulmonary drug delivery. Final efforts resulted in a promising emulsion formulation that overcame the quick transport of tobramycin away from the lung and successfully reduced pulmonary bacterial load in vivo. In vitro applications of PEAR showed the emulsions posed a significant barrier to the availability and, thus, the biological effect of lysophosphatidic acid growth factors. Further in vivo work is required to improve APV’s efficacy over conventional treatments and to determine PEAR’s feasibility and efficacy in promoting lung repair.

No description available.

Diffusion of gas molecules dissolved in the liquid bulk is the problem that is rarely addressed experimentally, mainly due to a difficulty in sensing the presence of dissolved gas and quantifying its concentration. Approaches which are typically used to overcome the problem include either indirect methods (e.g. based on the gas dissolution kinetics [1]), or newly developed complicated sensing techniques [2].

(English) Perfluorocarbons (PFC) are hydrocarbons in which some or all of the hydrogen atoms are replaced with fluorine. PFC have a very high capacity for dissolving oxygen. They are chemically and biologically inert. The most successful clinical application of PFC is the "two-layer method" for pancreas preservation before islet isolation. The two-layer organ preservation method (TLM) is based on oxygenated perfluorocarbon overlaid with University of Wisconsin (UW) solution. In experiment it has been successfully used for heart and intestine transplantation. We tested whether this technique would prevent tissue damage and improve results of kidney, pancreas and islets of Langerhans transplantation with prolonged ischemia time in an experimental model of syngenic rats. In kidney and islets of Langerhanse transplantation model we used TLM preservation method. In pancreas transplantation model we used perfluorohexyloctane (PFH) as a new generation of less lipophilic PFC. 1. Kidneys were stored for 24 hours either in UW solution (n = 16), with TLM (n = 16) or transplanted immediately (control group, n = 12). In half of the animals, survival was observed and in the other animals grafts were procured for semiquantitative histological scoring and TUNEL apoptosis assessment 24 h after transplantation....

The use of ultrasound contrast agents increases the information available for reconstruction during ultrasound imaging. Previously studied microbubbles, consisting of a gas core, are subject to limitations such as a short lifetime and a large size. Droplets with a liquid perfluorocarbon core that is stabilized by cellulose nanofibers eliminate these drawbacks, but require further investigation. By studying the frequency-dependent attenuation profile of the cellulose nanofiber coated perfluorocarbon droplets within an ultrasound field, information about the droplets as oscillators can be retrieved, enabling characterization of their physical properties. In this study, the frequency-dependent attenuation profile was experimentally acquired and compared between two concentrations, using flat transducers covering the frequency range of 1-15 MHz. The data collected in the time domain was processed and transformed into the frequency domain and the attenuation was calculated across the entire frequency range. Among the frequencies studied, the attenuation increases with frequency and covers the range of approximately 0.25-8.3 dB/cm and 0.01-3.3 dB/cm at the concentrations of 50 million droplets/ml and 10 million droplets/ml respectively. The attenuation reaches a minimum at 3 MHz within the highest concentration, compared to 4.43 MHz within the lowest. The increase of the attenuation with frequency is explained by the droplets not exhibiting large oscillations within the range covered. It is probable that the droplets do exhibit oscillations, due to a viscosity lower than that of water, but a resonance frequency is not found within the spectrum studied. This could be explained by a shell elasticity or a small droplet radius placing the resonance frequency outside of the spectrum studied, or high levels of damping broadening the resonance peak. Localizing the resonance frequency would enable characterization of these physical properties of the cellulose nanofiber shell as well as the perfluorocarbon liquid core of the droplets. The increase of the attenuation with frequency demonstrates that the droplets do not produce a maximized amount of scattering at a specific frequency within the range studied, which is observed among other oscillating particles implemented as ultrasound contrast agents. The attenuation is, however, larger than that of blood across all frequencies except for those among which the attenuation reaches its minimum. Potential errors that are affecting the results include droplet vaporization, the formation of flocs after the mechanical agitation has ceased, the experimental setup, the settings on the pulse generator, the sensitivity of the transducers and the processing code.

Today, microbubbles are one of the most commonly used ultrasound contrast agents, since their high compressibility results in a strongly scattered signal. Despite this advantage, microbubbles experience limitations by the decreased stability and large diameter. The cellulose nanofiber (CNF) stabilized perfluoropentane (PFC5) droplets have the possibility of eliminating these drawbacks. In order to examine the droplet behavior and scattering ability when exposed to ultrasound, the acoustic response of the droplets is studied and compared with that of microbubbles (MBs). Therefore, this thesis aims to design an experimental set-up and a processing method to determine the phase velocity, bulk modulus and compressibility of the CNF-coated PFC5 droplets. The experimental study of the acoustic characterization uses pulse-echo spectroscopy with an aluminum reflector and seven flat transducers covering the frequency range 0.7 to 14.1 MHz. By using fast Fourier transform, while accounting for the 2πn ambiguity, the phase velocity profiles are obtained. The dispersions within this frequency spectrum are 1391-1487 m/s and 1387-1488 m/s for the concentrations 10 ∙ 106 and 50 ∙ 106 droplets/ml, respectively. These profiles display an increasing phase velocity with frequency and a slight increase in dispersion with concentration. These results agree with theory and studies examining the phase velocity of MBs. The bulk modulus presents values between 3-4 GPa, while the compressibility is 2.7 − 3.2 ∙ 10-10 𝑃𝑎-1 within the frequency range studied. Compared to water and certain MBs, both possessing a lower bulk modulus, the droplets are less compressible. To conclude, the droplets have similar phase velocity profiles with the same dependencies on frequency and concentration as MBs, resulting in similar behavior of these droplets when exposed to ultrasound. Hence, affecting the wave similarly to MBs in terms of spreading. The droplet are, however, not as compressible. This most likely affects their oscillation and they, hence, might not have equally beneficial scattering ability. This could reduce their utilization as contrast agents. Some of the potential error sources present during the laboratory work and the development of the post-processing code were not achieving perfect optimization of the transducer alignment, vaporization of the droplets resulting in reduced concentration, possible diffraction, not optimal processing of data and inadequate correction for 2πn ambiguity.

No description available.