Academic literature on the topic 'Photoacoustic methodologies'

For combining optical and ultrasonic imaging methodologies, photoacoustic imaging (PAI) is the most important and successful hybrid technique, which has greatly contributed to biomedical research and applications. Its theoretical background is based on the photoacoustic effect, whereby a modulated or pulsed light is emitted into tissue, which selectively absorbs the optical energy of the light at optical wavelengths. This energy produces a fast thermal expansion in the illuminated tissue, generating pressure waves (or photoacoustic waves) that can be detected by ultrasonic transducers. Research has shown that optical absorption spectroscopy offers high optical sensitivity and contrast for ingredient determination, for example, while ultrasound has demonstrated good spatial resolution in biomedical imaging. Photoacoustic imaging combines these advantages, i.e., high contrast through optical absorption and high spatial resolution due to the low scattering of ultrasound in tissue. In this review, we focus on advances made in PAI in the last five years and present categories and key devices used in PAI techniques. In particular, we highlight the continuously increasing imaging depth achieved by PAI, particularly when using exogenous reagents. Finally, we discuss the potential of combining PAI with other imaging techniques.

Abstract. A wide range of globally significant biomass fuels were burned during the fourth Fire Lab at Missoula Experiment (FLAME-4). A multi-channel photoacoustic absorption spectrometer (PAS) measured dry absorption at 405, 532, and 660 nm and thermally denuded (250 °C) absorption at 405 and 660 nm. Absorption coefficients were broken into contributions from black carbon (BC), brown carbon (BrC), and lensing following three different methodologies, with one extreme being a method that assumes the thermal denuder effectively removes organics and the other extreme being a method based on the assumption that black carbon (BC) has an Ångström exponent of unity. The methodologies employed provide ranges of potential importance of BrC to absorption but, on average, there was a difference of a factor of 2 in the ratio of the fraction of absorption attributable to BrC estimated by the two methods. BrC absorption at shorter visible wavelengths is of equal or greater importance to that of BC, with maximum contributions of up to 92 % of total aerosol absorption at 405 nm and up to 58 % of total absorption at 532 nm. Lensing is estimated to contribute a maximum of 30 % of total absorption, but typically contributes much less than this. Absorption enhancements and the estimated fraction of absorption from BrC show good correlation with the elemental-carbon-to-organic-carbon ratio (EC ∕ OC) of emitted aerosols and weaker correlation with the modified combustion efficiency (MCE). Previous studies have shown that BrC grows darker (larger imaginary refractive index) as the ratio of black to organic aerosol (OA) mass increases. This study is consistent with those findings but also demonstrates that the fraction of total absorption attributable to BrC shows the opposite trend: increasing as the organic fraction of aerosol emissions increases and the EC ∕ OC ratio decreases.

AbstractPhotoacoustic sensing and imaging techniques have experienced tremendous research progress, ranging from fundamental physics and methodologies to various biomedical and clinical applications in recent years. However, the state-of-art photoacoustic systems still suffer from high cost and bulky size, which hinders their potential applications for low-cost and portable diagnostics. In this paper, we propose the design for a palm-size photoacoustic sensor prototype. The design’s lower cost and smaller size would allow it to be used for portable photoacoustic sensing applications like oxygen saturation and temperature. By converting the high-frequency photoacoustic pulse signal to low-frequency photoacoustic DC signal through a rectifier circuit, the proposed photoacoustic receiver could potentially reduce the cost and device size efficiently, compared with the conventional highspeed data acquisition card interfaced with computer solutions. Preliminary testing is demonstrated to show its feasibility for photoacoustic sensing applications.

ABSTRACTWe report, for the first time, the application of the photoacoustic spectroscopy for monitoring the optical absorption spectra in aquatic lirium (Eichhornia Crassipes), before and after it was exposed to ultrasonic irradiations. We obtained a decrease in the amplitude of the bands of the chlorophylls a and b for the irradiated samples with ultrasound of 17 kHz and 1.5 mW/cm2 of power density, and therefore, damage in the centers producing the photosynthesis, due to the irradiation. These results show the utility of the ultrasonic irradiation, as well as, of the photosynthesis monitoring by means of the photoacoustic technique, for the elaboration and establishment of methodologies in the control of this aquatic plant, whose propagation causes many consequences extremely unfavorable for the environment, as well as for the diverse human activities that are developed in the bodies of water in the tropical and sub-tropical regions of the world.

AbstractWith the advent of stem cell therapy for spinal cord injuries, stroke, burns, macular degeneration, heart diseases, diabetes, rheumatoid arthritis and osteoarthritis; the need to track the survival, migration pathways, spatial destination and differentiation of transplanted stem cells in a clinical setting has gained increased relevance. Indeed, getting regulatory approval to use these therapies in the clinic depends on biodistribution studies. Although optoacoustic imaging (OAI) or photoacoustic imaging can detect functional information of cell activities in real-time, the selection and application of suitable contrast agents is essential to achieve optimal sensitivity and contrast for sensing at clinically relevant depths and can even provide information about molecular activity. This review explores OAI methodologies in conjunction with the specific application of exogenous contrast agents in comparison to other imaging modalities and describes the properties of exogenous contrast agents for quantitative and qualitative monitoring of stem cells. Specific characteristics such as biocompatibility, the absorption coefficient, and surface functionalization are compared and how the labelling efficiency translates to both short and long-term visualization of mesenchymal stem cells is explored. An overview of novel properties of recently developed optoacoustic contrast agents and their capability to detect disease and recovery progression in clinical settings is provided which includes newly developed exogenous contrast agents to monitor stem cells in real-time for multimodal sensing.

Recent advances in medical imaging include integrating photoacoustic and optoacoustic techniques with conventional imaging modalities. The developments in the latter have led to the use of optics combined with the conventional ultrasound technique for imaging intravascular tissues and applied to different areas of the human body. Conventional ultrasound is a skin contact-based method used for imaging. It does not expose patients to harmful radiation compared to other techniques such as Computerised Tomography (CT) and Magnetic Resonance Imaging (MRI) scans. On the other hand, optical Ultrasound (OpUS) provides a new way of viewing internal organs of the human body by using skin and an eye-safe laser range. OpUS is mostly used for binary measurements since they do not require to be resolved at a much higher resolution but can be used to check for intravascular imaging. Various signal processing techniques and reconstruction methodologies exist for Photo-Acoustic Imaging, and their applicability in bioimaging is explored in this paper.

Abstract Photoacoustic (PA) imaging is a novel, rapidly expanding diagnostic technique, which has been predominately developed in the context of contemporary biomedical research studies. In this review, we demonstrate how PA technologies can break through the barriers of biomedicine to find innovative applications in cultural heritage (CH) diagnostics and laser cleaning monitoring. Having over three orders of magnitude higher transmission through strongly scattering media, compared to light in the visible and near infrared, PA signals offer substantially improved detection sensitivity, providing optical absorption contrast at high spatial resolution. This unique combination of features is employed for establishing novel diagnostic methodologies aiming to uncover well-hidden features and provide structural information in multi-layered CH objects such as paintings and documents. Finally, we demonstrate that the PA effect can be successfully utilized for the reliable monitoring of laser cleaning interventions on stonework, allowing for a safe and well-controlled cleaning procedure which will safeguard CH objects’ original surfaces. Simplicity of implementation, effectiveness and low-cost features provided by the developed diagnostic and monitoring systems, highlight the rich potential of emerging PA technologies in CH studies and offer exciting possibilities for future implementations.

Dissertação de Mestrado em Química apresentada à Faculdade de Ciências e Tecnologia
A membrana biológica é uma estrutura complexa através da qual alguns fenómenos importantes acontecem e, por isso, as suas propriedades têm sido alvo de estudo ao longo dos anos. O objetivo do presente trabalho é avaliar a permeabilidade e fusão de vesículas através de várias metodologias.Na literatura é reportado que as ondas fotoacústicas (PA) aumentam a eficiência de absorção de fármacos por aplicação transdérmica. Nesta dissertação tentou-se avaliar qual o mecanismo responsável e se envolve a perturbação da bicamada lipídica.Para isso, estudo de permeabilidade foram feitos através da cinética de libertação de uma molécula fluorescente (fluoresceína). Tentou-se sintetizar um derivado de maior peso molecular, obtendo produtos que requerem ainda passos de purificação. De forma a continuar o trabalho, escolheu-se utilizar a FITC-dextran (fluoresceína isotiocianato-dextran) pelo seu elevado peso molecular e foi encapsulada em vesículas unilamelares gigantes (GUVs) para realizar estudos preliminares de permeabilidade.O protocolo de produção de GUVs assistido por polyvinil álcool (PVA) foi adaptado da literatura. Amostras de GUVs foram submetidas a diferentes testes de estabilidade de forma a otimizar condições para a aplicação de ondas fotoacústicas.O efeito das ondas PA na fusão entre vesículas também foi averiguado, pois a entrega de fármacos via fusão de uma vesícula portadora com uma célula é muito versátil e permite a entrega de fármacos tanto polares como apolares.Foram produzidas vesículas unilamelares grandes (LUVs) para avaliar a fusão entre vesículas, que foi feito calculando a eficiência de transferência de energia (EET) através da transferência de energia por ressonância de Förster (FRET). A EET foi obtida por medições de fluorescência em estado estacionário e resolvida por tempo. Para promover a fusão entre as vesículas, a composição lipídica foi diversificada e duas metodologias para a obtenção da EET foram adotadas: mistura de LUVs com diferentes sondas e aplicação de ciclos de Freeze and Thaw; e utilizando diferentes percentagens de LUVs formados com as duas sondas. Neste estudo o par de sondas fluorescentes escolhido foi 7-nitro-2-1,3-benzoxadiazol-4-yl (NBD) e lissamina-rhodamina B sulfonil. Os LUVs foram também caracterizados por dispersão dinâmica de luz (DLS) e pelo seu potencial zeta.
The biological membrane is a complex structure through which important phenomena take part and its properties have been studied over the years. The aim of the present study is to evaluate the permeability and vesicle fusion by several methodologies. It has previously been reported that photoacoustic (PA) waves increase the absorption efficiency of drugs through transdermal application. With this thesis it was intended to evaluate what is the mechanism responsible and if it involves perturbation of the lipid bilayer. For that, permeability studies were done by assessing the kinetics of release of a fluorescent probe (fluorescein). The synthesis of a derivative with higher molecular weight was attempted, resulting in products that needed further purification. So, in order to pursue the work, FITC-dextran (fluorescein isothiocyanate-dextran) was chosen for its high molecular weight and preliminary permeability studies were done by encapsulation in Giants Unilamellar Vesicles (GUVs). The protocol of GUV formation was adapted from literature using polyvinyl alcohol (PVA) assisted method. GUVs samples were subjected to different stability tests to optimize conditions for the application of PA waves. The effect of PA waves in fusion between vesicles was also evaluated because the delivery of drugs via fusion of a drug carrier vesicle with a receiving vesicle is very versatile and allows both polar and apolar drugs to be delivered. LUVs were produced to assess fusion between vesicles, which was done by calculating the Efficiency of Energy Transfer (EET) from Förster Resonance Energy Transfer (FRET). EET was evaluated from steady-state and time-resolved fluorescence measurements. To promote fusion between vesicles the lipid composition was modified and two methodologies for obtaining the EET values were adopted: mixing LUVs with different probes and applying Freeze and Thaw cycles; and using different percentages of LUVs with both probes. In this work, the donor-acceptor pair chosen was NBD and Lissamine Rhodamine B sulfonyl. The LUVs were also characterized by Dynamic Light Scattering (DLS) and zeta potential.

Studio sull'applicabilità di tecniche ottiche lineari e nonlineari e metodi fotoacustici innovativi per l'analisi non invasiva (composizionale, strutturale e morfologica) di opere d'arte e per il monitoraggio di operazioni di restauro

“Any chemical species, which under ambient conditions (i.e., a temperature around 25°C, and a pressure close to 1 atm) will, for a combination of kinetic and thermodynamic reasons, decay on a timescale ranging from microseconds, or even nanoseconds, to a few minutes” can be classified as a short-lived compound. According to this definition, suggested by Almond, it is clear that the experimental methods described in previous chapters can only be used to study the thermochemistry of long-lived substances. The technique that we address here, known as photoacoustic calorimetry (PAC) or laser-induced optoacoustic calorimetry (LIOAC), is suitable for investigating the energetics of molecules with lifetimes smaller than about 1μs. It relies on the photoacoustic effect, which was discovered by Bell more than 100 years ago. With the assistance of Tainter, he was able to “devise a method of producing sounds by the action of an intermittent beam of light” and conclude that the method “can be adapted to solids, liquids, and gases”. Figure 13.1 shows a photophone, “an apparatus for the production of sound by light,” used by Bell to investigate the photoacoustic effect. The controversy around the origin of this phenomenon was settled by Bell himself and by Lord Rayleigh; their views were rather close to our present understanding: When a light pulse is absorbed by a substance, a given amount of heat is deposited, producing a local thermal expansion; this thermal expansion propagates through the medium, generating sound waves. The basic theory of the photoacoustic effect was described by Tam and Patel and some of its applications were presented in a review by Braslavsky and Heibel. The first use of PAC to determine enthalpies of chemical reactions was reported by the groups of Peters and Braslavsky. The same groups have also played an important role in developing the methodologies to extract those thermodynamic data from the experimentally measured quantities. In the ensuing discussion, we closely follow a publication where the use of the photoacoustic calorimety technique as a thermochemical tool was examined. Consider the elementary design of a photoacoustic calorimeter, shown in figure 13.3. The cell contains the sample, which is, for instance, a dilute solution of a photoreactive species.