archives@tulane.edu / Photoacoustic imaging functions via two foundations: light delivery and acoustic signal reception. In order for acoustic signal to be received and processed into an image, photons must first penetrate the tissue. However, biological media highly attenuates light, and the maximum imaging depth for photoacoustic images lies between 2-3 centimeters. Thus, models and simulations are integral to approach this problem, and they can be used to easily change imaging parameters and simulate various conditions. This study used a MATLAB Monte Carlo simulation algorithm to model and simulate a homogeneous placental tissue sample. The simulated data was compared to experimental ex vivo placental images taken under identical conditions of the simulation. These two data sets were used to gauge the simulation’s accuracy to predicting fluence trends in tissue, and the results were then applied to a heterogeneous tissue model simulating in vivo placental imaging. It was found that to maximize fluence in the placenta during in vivo imaging, 808 nm and 950 nm both offer different benefits to maximize fluence in the placenta. This simulation toolbox can be used to determine which experimental setup can maximize fluence in photoacoustic images, resulting in high-quality, high-contrast images. / 1 / Adam Kolkin

Molecular photoacoustic imaging is an exciting new field that promises to visualize molecular indicators of disease. The objective of this dissertation is to progress molecular imaging by providing a photoacoustic microscopy platform to better validate in vivo molecular photoacoustic imaging, diagnose disease, and study fundamental photoacoustic processes. Initially, a custom photoacoustic microscope was developed to provide high-sensitivity and high-resolution of both endogenous and exogenous contrast agents in thin cell or tissue samples. After characterization, the photoacoustc microscope was first used to image the hemoglobin distribution in the spleen and liver. The photoacoustic microscope was then used to image nanoparticles in injured and diseased cell and tissues samples. These images can be used for in vivo photoacoustic image validation or, independently, as a diagnostic tool for disease. To enhance the utility of photoacoustic microscopy, a quantitation technique was developed for nanoparticles in cells and tissues. Quantitative photoacoustic imaging has the potential to replace mass spectrometry and histology for a wide array of molecular imaging and targeting studies. Finally, photoacoustic microscopy was used to study the nonlinear dependence of the photoacoustic pressure with laser fluence of nanoparticle-loaded cells. New discoveries about the nonlinear dependence with nanoparticle concentration and cell type are presented. These new discoveries may provide the framework for a new type of photoacoustic imaging with contrast that is cell-type specific. Overall, the work described in this dissertation can be used to improve diagnosis and accelerate clinical translation of new and emerging molecular imaging techniques. / text

Regenerative medicine is an interdisciplinary field which has advanced with the use of biotechnologies related to biomaterials, growth factors, and stem cells to replace or restore damaged cells, tissues, and organs. Among various therapeutic approaches, cell-based therapy is most challenging and exciting for both scientists and clinicians pursuing regenerative medicine. Specifically, stem cells, including mesenchymal stem cells and adipose-derived stem cells, are promising candidate cell types for cell-based therapy because they can differentiate into multiple cell types for tissue regeneration and stimulate other cells through neovascularization or paracrine signaling. Also, for effective treatment using stem cells, the tissue engineered constructs, such as bioactive degradable scaffolds, that provide the physical and chemical cues to guide their differentiation are incorporated with stem cells before implantation. Also, it was previously demonstrated that tissue-engineered matrices can promote tubulogenesis and differentiation of stem cells to vascular cell phenotypes. Hence, during tissue regeneration after stem cell therapy, there are numerous factors that need to be monitored. As a result, imaging-based stem cell tracking is essential to evaluate the distribution of stem cells as well as to monitor proliferation, differentiation, and interaction with the microenvironment. Therefore, there is a need for a stem cell imaging technique that is not only noninvasive, sensitive, and easy to operate, but also capable of quantitatively assessing stem cell behaviors in the long term with high spatial resolution. Therefore, the overall goal of this research is to demonstrate a novel imaging method capable of continuous in vitro assessment of stem cells as prepared with tissue engineered constructs and noninvasive longitudinal in vivo monitoring of stem cell behaviors and tissue regeneration after stem cell implantation. In order to accomplish this, gold nanoparticles are demonstrated as photoacoustic imaging contrasts to label stem cells. In addition, ultrasound and photoacoustic imaging was utilized to monitor stem cells and neovascularization in the injured rat tissue. Therefore, using these methods, tissue regeneration can be promoted and noninvasively monitored, resulting in a better understanding of the tissue repair mechanisms following tissue injury. / text

Cancer has been one of main causes of human deaths for many years. Early detection of cancer is essential to provide definitive treatment. Among many cancer treatment methods, nanoparticle-mediated photothermal therapy is considered as one of the promising cancer treatment methods because of its non-invasiveness and cancer-specific therapy. Ultrasound and photoacoustic imaging can be utilized for both cancer detection and photothermal therapy guidance. Ultrasound elasticity imaging can detect cancer using tissue elastic properties. Once cancer is diagnosed, spectroscopic photoacoustic imaging can be used to monitor nanoparticle delivery before photothermal therapy. When nanoparticles are well accumulated at the tumor, ultrasound and photoacoustic-based thermal imaging can be utilized for estimating temperature distribution during photothermal therapy to guide therapeutic procedure. In this dissertation, ultrasound beamforming, elasticity imaging, and spectroscopic photoacoustic imaging methods were developed to improve cancer detection and therapy guidance. Firstly, a display pixel based synthetic aperture focusing method was developed to fundamentally improve ultrasound image qualities. Secondly, an autocorrelation based sub-pixel displacement estimation method was developed to enhance signal-to-noise ratio of elasticity images. The developed elasticity imaging method was utilized to clinically evaluate the feasibility of using ultrasound elasticity imaging for prostate cancer detection. Lastly, a minimum mean square error based spectral separation method was developed to robustly utilize spectroscopic photoacoustic imaging. The developed spectroscopic photoacoustic imaging method was utilized to demonstrate ultrasound and photoacoustic image-guided photothermal cancer therapy using in-vivo tumor-bearing mouse models. The results of these studies suggest that ultrasound and photoacoustic imaging can assist both cancer detection and therapy guidance. / text

Ces travaux de thèse sont motivés par le développement de techniques d’imagerie alternatives pour le diagnostic précoce du cancer du sein. Parmi celles-ci, l’imagerie photoacoustique couple potentiellement les avantages de deux modalités d’imagerie non-invasives, à savoir la quantification de contrastes physiologiques du fait de l’excitation optique et la haute résolution du fait d’un sondage acoustique.Le but de ces travaux est de proposer une modélisation multiondes du phénomène photoacoustique, et d’incorporer ce modèle dans un algorithme de reconstruction efficace pour résoudre le problème inverse. Celui-ci se rapporte à la reconstruction de cartes de propriétés physiques (optique et/ou acoustiques) de l’intérieur du sein. La Méthode des Eléments Finis (MEF) a été retenue pour résoudre l’équation de propagation optique. Pour la résolution de l’équation de propagation acoustique, une méthode semi-analytique, basée sur des calculs par transformées de Fourier (méthod k-space), a été choisie. Pour la résolution du problème inverse, deux approches ont été étudiées : i) un sondage passif, permettant de remonter à la distribution de pression initiale, à l’aide de la méthode de retournement temporel ; ii) un sondage actif, où l’on interroge le milieu sélectivement sous différentes excitations, permettant de remonter quantitativement aux propriétés optiques du milieu. On appelle cette dernière approche Tomographie PhotoAcoustique Quantitative (TPAQ). Une étude spécifique sur le protocole d’illumination/détection a été conduite, prenant également en compte les contraintes expérimentales. / The present work was motivated by the development of alternative imaging techniques for breast cancer early diagnosis, that is photoacoustic imaging, which potentially couples the merits of optical imaging and ultrasound imaging, that is high optical functional contrasts brought by optical probing and high spatial resolution by ultrasound detection. Our work aims at modeling the photoacoustic multiwave phenomenon and incorporate it in an efficient reconstruction algorithm to solve the inverse problem. The inverse problem consists in the recovery of interior maps of physical properties of the breast. The forward model couples optical and acoustic propagations. The Finite Element Method (FEM) was chosen for solving the optical propagation equation, while a semi-analytical method based on Fourier transforms calculations (k-space method) was preferred for solving the acoustic propagation equation. For the inverse model, time reversal method was adopted to reconstruct the initial pressure distribution, an active approach of the inverse problem was also achieved, which decoupled the optical properties from measured photoacoustic pressure, this approach is called quantitative photoacoustic tomography (QPAT), in this approach, illumination/detection protocol was studied, and the experimental set up is also take into consideration. In the last step, photoacoustic pressure measurements obtained from experiment and simulation are studied and compared.

Photoacoustic (PA) Imaging is an emerging biomedical imaging modality based on the laser-generated ultrasound. The method has unique advantages in providing microvessel structure visualization, neuroimaging, and functional imaging provided by its physical principle. Photoacoustic microscopy (PAM) is one of the PA imaging instruments which provides high resolution and contrast imaging of a near-field target. Relying on the acoustic focusing, Acoustic-resolution PAM (AR-PAM) is capable of reaching a sub-centimeter of penetration depth with sub-millimeter resolution and is optimized for tissue samples and small animals. However, the state-of-art AR-PAMs are large in size and expensive in cost, which hinders its democratization. There are previous researches conducted on reducing the cost by introducing a low-cost optical source or ultrasound acquisition device. Few research has investigated the possibility of modification on actuator design. The total system cost should be further reduced by substituting the translation stage while maintaining the imaging quality. In this research, a delta configuration actuation is introduced to the AR-PAM. The delta-configuration actuation adapted from a low-cost off-the-shelf 3D printer has been implemented in the design. An economical PAM system that integrates the combination of hardware and software enhancement is designed and tested in this research. With the software approach, advanced beamforming methods such as Delay-and-Sum with Coherence Factor (DAS+CF) and Delay-Multiply-and-Sum (DMAS) algorithms are applied to obtaining the high-resolution PA image through 3D reconstruction. The preliminary phantom study demonstrated the applicability of low-cost delta configuration actuators for AR-PAM imaging. The simulation study shows the beamforming algorithms has capability to remove the device precision error and increasing the tolerance. The research suggests that the 3D reconstruction algorithms significantly improve the resolution and contrast of the image quality.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22460号 / 工博第4721号 / 新制||工||1737(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 近藤 輝幸, 教授 大江 浩一, 教授 中村 正治 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23215号 / 工博第4859号 / 新制||工||1758(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 大江 浩一, 教授 近藤 輝幸, 教授 深澤 愛子 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21684号 / 医博第4490号 / 新制||医||1036(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 松田 道行, 教授 松田 秀一, 教授 椛島 健治 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Small molecule organic dyes with absorption and emission in the near infrared region (NIR) attracted much attention for various applications such as dye sensitized solar cells, fluorescent guided surgery, stimuli responsive bioimaging and photodynamic therapy. Dyes with high absorption and emission in the NIR region are beneficial for stimuli responsive bioimaging due to the deeper penetration of NIR light, less cell damage, high resolution, and low background autofluorescence from biomolecules. Of the many small molecule dyes, xanthene-based dyes exhibit outstanding photophysical properties and good stimuli response for use in bioimaging applications. However, absorption and emission of the xanthene dyes lie in the visible region, which limit their applications in cellular imaging. Many of the NIR dyes have very poor fluorescence; consequently, an alternative approach to fluorescent imaging is photoacoustic imaging that uses sound waves to generate pictures of deep tissues. In this dissertation, we discuss the utility of xanthene based NIR dyes as photoacoustic imaging contrast agents for multiplex imaging and deep tissue nitric oxide sensing in the drug-induced liver injury. Chapter I discuss the fundamentals of fluorescence and photoacoustic imaging, background of the xanthene dyes and other fluorescent dyes, and the design strategies to develop NIR xanthene-based dyes. Chapter II is based on our approach to the design and synthesis of NIR xanthene-based dyes by C-H bond functionalization, with the first example being Rhodindolizine, which absorb and emits in NIR II or short-wave infrared (SWIR) region. In chapter III, we describe the design and synthesis of thienylpiperidine xanthene-based NIR and shortwave-infrared (SWIR) dyes for the photoacoustic imaging. One dye in particular (XanthCR-880) boasts a strong PA signal at 880 nm with good biological compatibility and photostability, yields multiplexed imaging with an aza-BODIPY reference dye, and is detected at a depth of 4 cm. In chapter IV, we report a series of SWIR dyes based on a dibenzazepine donor conjugated to thiophene (SCR-1, SCR-4), thienothiophene (SCR-2, SCR-5), and bithiophene (SCR-3, SCR-6). We leverage the fact that SCR-1 undergoes a bathochromic shift when aggregated to develop a ratiometric nanoparticle for nitric oxide (NO) (rNP-NO). rNP-NO was used to successfully perform in vivo studies to visualize pathological levels of nitric oxide in a drug-induced liver injury model via deep tissue SWIR photoacoustic (PA) imaging. Chapter V describes another series of xanthene-based dyes with a thiophene ᴫ spacer and several different donors. UV-Vis absorption studies were performed after converting the dyes to the opened form with trifluoracetic acid. These novel XanthCR-TD dyes exhibit absorption maxima in NIR I region from 700 - 900 nm.