Photoacoustic Neuroimaging - Perspectives on a Maturing Imaging Technique and its Applications in Neuroscience

A prominent goal of neuroscience is to improve our understanding of how brain structure and activity interact to produce perception, emotion, behavior, and cognition. The brain’s network activity is inherently organized in distinct spatiotemporal patterns that span scales from nanometer-sized synapses to meter-long nerve fibers and millisecond intervals between electrical signals to decades of memory storage. There is currently no single imaging method that alone can provide all the relevant information, but intelligent combinations of complementary techniques can be effective. Here, we thus present the latest advances in biomedical and biological engineering on photoacoustic neuroimaging in the context of complementary imaging techniques. A particular focus is placed on recent advances in whole-brain photoacoustic imaging in rodent models and its influential role in bridging the gap between fluorescence microscopy and more non-invasive techniques such as magnetic resonance imaging (MRI). We consider current strategies to address persistent challenges, particularly in developing molecular contrast agents, and conclude with an overview of potential future directions for photoacoustic neuroimaging to provide deeper insights into healthy and pathological brain processes

Single Cell Optical Imaging and Spectroscopy

In his 1665 treatise, Micrographia, Robert Hooke described the many observations he had made using a microscope, including compartment-like structures in cork samples that he termed “cells

Molecular Imaging of Inflammation - current and emerging technologies for diagnosis and treatment

Inflammation is a key factor in multiple diseases including primary immune-mediated inflammatory diseases e.g. rheumatoid arthritis but also, less obviously, in many other common conditions, e.g. cardiovascular disease and diabetes. Together, chronic inflammatory diseases contribute to the majority of global morbidity and mortality. However, our understanding of the underlying processes by which the immune response is activated and sustained is limited by a lack of cellular and molecular information obtained in situ. Molecular imaging is the visualization, detection and quantification of molecules in the body. The ability to reveal information on inflammatory biomarkers, pathways and cells can improve disease diagnosis, guide and monitor therapeutic intervention and identify new targets for research. The optimum molecular imaging modality will possess high sensitivity and high resolution and be capable of non-invasive quantitative imaging of multiple disease biomarkers while maintaining an acceptable safety profile. The mainstays of current clinical imaging are computed tomography (CT), magnetic resonance imaging (MRI), ultrasound (US) and nuclear imaging such as positron emission tomography (PET). However, none of these have yet progressed to routine clinical use in the molecular imaging of inflammation, therefore new approaches are required to meet this goal. This review sets out the respective merits and limitations of both established and emerging imaging modalities as clinically useful molecular imaging tools in addition to potential theranostic applications

Multimodal imaging to evaluate the distribution and fate of a mesenchymal stromal cell therapy.

Mesenchymal stromal cell (MSC) treatments have shown beneficial outcomes in preclinical models of various diseases, but limited therapeutic effects in clinical trials. This disparity in translation reflects the need to understand the mechanisms involved in the host’s response to therapy. Intravenous injection is the preferred delivery method in the clinics, but it has been observed that using this route leads to MSCs becoming entrapped in the lungs, making this organ an interesting study target. In this thesis, different imaging modalities to study the distribution and fate of administered MSCs in the lung were used. The first aim was to combine the sensitivity of bioluminescence imaging (BLI) with the ability of micro-computed tomography (micro-CT) to image lung tissue to track the cells in vivo. Then, to study the biodistribution of the MSCs in the lung microenvironment at single-cell resolution, an optical tissue clearing protocol was established. Finally, the effect of the MSCs on innate immune cells in the lung and their potential interactions were investigated. Human umbilical cord MSCs (hUC-MSCs) that had been labelled with the genetic reporter Firefly luciferase (FLuc), the fluorescent reporter tandem Tomato (tdTomato), or with gold nanorods were used. The hUC-MSCs were injected into the tail vein of mice, which were then imaged in vivo using BLI and micro-CT. After MSC injection, animals were culled, and the lungs collected and processed for confocal microscopy or flow cytometry. BLI revealed that following intravenous injection, the MSCs localized to the lungs hampering the ability of MSOT to image the MSCs within this organ. Using micro-CT, it was not possible to detect the MSCs, indicating that this method might lack sensitivity to image gold-labelled cells. Next, the CUBIC, a modified stabilized DISCO (s-DISCO) and ethyl cinnamate (ECi) optical tissue clearing protocols were compared to find a suitable method for studying the biodistribution of hUC-MSCs and their interactions with the mouse lung microenvironment. CUBIC was the only method that enabled direct imaging of tdTomato-expressing hUC-MSCs as the other methods quenched the fluorescence of the reporter. Moreover, CUBIC in combination with immunofluorescence allowed the interaction of the hUC-MSCs with cells in the host lung to be investigated. Particularly, it was observed that the hUC-MSCs appeared to be retained in the pulmonary microvasculature as they were not found in large blood vessels. Flow cytometric analysis showed that shortly after hUC-MSC IV injection, neutrophils, monocytes, and macrophages mobilized to the lung and participated in an inflammatory response. Twenty-four hours post cell infusion, the number of innate immune cells in the lungs decreased but a polarization toward an anti-inflammatory phenotype was observed. Moreover, immunofluorescent staining revealed that neutrophils were preferentially distributed in close vicinity to the hUC-MSCs, suggesting that their clearance within 24 h might involve efferocytosis. In summary, using a range of in vivo and ex vivo imaging techniques, it was shown that following intravenous injection into mice, hUC-MSCs appeared to accumulate in the pulmonary vessels and mostly died within 24 h. Within 2 h following administration, the hUC-MSCs caused an inflammatory response in the lung, leading to an increase in neutrophils and pro-inflammatory macrophages. However, by 24 h, neutrophils were at basal levels and there was an increase in anti-inflammatory macrophages. Although there are numerous reports indicating that MSCs polarise macrophage towards an anti-inflammatory phenotype, an interesting finding of this study was that the initial effect of hUC-MSCs on host immune cells was actually pro-inflammatory. This may provide some insight into the potential therapeutic mechanisms of MSCs

Molecular imaging of inflammation - Current and emerging technologies for diagnosis and treatment

Inflammation is a key factor in multiple diseases including primary immune-mediated inflammatory diseases e.g. rheumatoid arthritis but also, less obviously, in many other common conditions, e.g. cardiovascular disease and diabetes. Together, chronic inflammatory diseases contribute to the majority of global morbidity and mortality. However, our understanding of the underlying processes by which the immune response is activated and sustained is limited by a lack of cellular and molecular information obtained in situ. Molecular imaging is the visualization, detection and quantification of molecules in the body. The ability to reveal information on inflammatory biomarkers, pathways and cells can improve disease diagnosis, guide and monitor therapeutic intervention and identify new targets for research. The optimum molecular imaging modality will possess high sensitivity and high resolution and be capable of non-invasive quantitative imaging of multiple disease biomarkers while maintaining an acceptable safety profile. The mainstays of current clinical imaging are computed tomography (CT), magnetic resonance imaging (MRI), ultrasound (US) and nuclear imaging such as positron emission tomography (PET). However, none of these have yet progressed to routine clinical use in the molecular imaging of inflammation, therefore new approaches are required to meet this goal. This review sets out the respective merits and limitations of both established and emerging imaging modalities as clinically useful molecular imaging tools in addition to potential theranostic applications

Optical Properties and Application of Metallic Nanoparticles and their Assembled Superstructures.

This dissertation reports the development of novel targeted contrast agents based on gold nanorods (GNRs) and their application in imaging cancer cells, cardiovascular inflammatory diseases and drug delivery monitoring using photoacoustic imaging (PAI). The GNRs based contrast agents were imaged with high signal-to-noise ratio (~17) and excellent spatial resolution (~250 micron) with concentration down to 10pM in biological tissues. The inherent disadvantage of limited imaging depth (~5 mm from skin surface) in PAI due to strong attenuation of light in biological tissues restricts the monitoring of drug delivery in intra-articular connective tissues. A novel targeted optical and nuclear dual-modality contrast agent was successfully developed by radiolabeling GNRs with [125I] to monitor anti-rheumatic drug delivery. PAI and nuclear imaging in combination present the detailed distribution of GNRs conjugated anti-rheumatic agent in intra-articular connective tissues with concentration down to 10 pM and radioactive label of 5 microCi . Radiolabeled contrast agents were further conjugated with polyethylene glycol (PEG) to increase the in vivo circulation time and prevent rapid clearance through accumulation into liver. Addition of PEG molecules on the surface of contrast agent increased the in vivo circulation time from 4 minutes to over 4 hours allowing specific targeting by the contrast agent. Apart from application as a contrast agent, gold nanorods due to their anisotropic shape also form interesting building blocks for 3D superstructures with wide range of optical properties for applications in plasmonics, metamaterials and sensors. Under controlled evaporation monodisperse GNRs were self-assembled into micron sized three dimensional supercrystals. The highly organized supercrystals of GNRs with plasmonic antennae enhancement of electrical field have made possible the first real-time detection of prions (concentration down to 10^-10 M in complex biological media such as serum using surface enhanced raman scattering. CdTe nanoparticle-GNRs superstructures were made through biotin-streptavidin specific binding and investigated as potential gain materials for overcoming metallic losses in metamaterials through exciton-plasmon coupling. An extremely simple technique was developed to transfer gold nanorods from aqueous to organic medium, which allowed orientational ordering (order parameter of S~0.9) of low aspect ratio rods in dispersion through application of high electric fields.Ph.D.Chemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78935/1/agashish_1.pd

Application of Nanomaterials in Biomedical Imaging and Cancer Therapy

To mark the recent advances in nanomaterials and nanotechnology in biomedical imaging and cancer therapy, this book, entitled Application of Nanomaterials in Biomedical Imaging and Cancer Therapy includes a collection of important nanomaterial studies on medical imaging and therapy. The book covers recent works on hyperthermia, external beam radiotherapy, MRI-guided radiotherapy, immunotherapy, photothermal therapy, and photodynamic therapy, as well as medical imaging, including high-contrast and deep-tissue imaging, quantum sensing, super-resolution microscopy, and three-dimensional correlative light and electron microscopy. The significant research results and findings explored in this work are expected to help students, researchers and teachers working in the field of nanomaterials and nanotechnology in biomedical physics, to keep pace with the rapid development and the applications of nanomaterials in precise imaging and targeted therapy

Photoacoustics for Cardiovascular Applications

In the thesis entitled Photoacoustic imaging for Cardiovascular Applications, two cardiovascular diseases were tackled, namely atrial fibrillation and coronary atherosclerosis. An imaging algorithm was also devised to enhance imaging target super-localization. Photoacoustic imaging is an imaging modality which provides molecular information, based on optical absorption and subsequent thermoelastic expansion resulting in detectable pressure waves with common ultrasonic detectors. Capability of imaging tissue molecular changes was shown relevant to enable real-time monitoring of lesion formation in catheter-based ablation for atrial fibrillation as well as to assess lipid content of atherosclerotic plaques in an animal model in vivo. This thesis describes the development and design of the photoacoustic imaging system from instrumentation to realization in clinically translatable setups

Molecularly-Targeted Gold-Based Nanoparticles for Cancer Imaging and Near-Infrared Photothermal Therapy

This thesis advances the use of nanopartic1es as multifunctional agents for molecularly-targeted cancer imaging and photothermal therapy. Cancer mortality has remained relatively unchanged for several decades, indicating a significant need for improvements in care. Researchers are evaluating strategies incorporating nanopartic1es as exogenous energy absorbers to deliver heat capable of inducing cell death selectively to tumors, sparing normal tissue. Molecular targeting of nanopartic1es is predicted to improve photothermal therapy by enhancing tumor retention. This hypothesis is evaluated with two types of nanopartic1es. The nanopartic1es utilized, silica-gold nanoshells and gold-gold sulfide nanopartic1es, can convert light energy into heat to damage cancerous cells. For in vivo applications nanopartic1es are usually coated with poly(ethylene glycol) (PEG) to increase blood circulation time. Here, heterobifunctional PEG links nanopartic1es to targeting agents (antibodies and growth factors) to provide cell-specific binding. This approach is evaluated through a series of experiments. In vitro, antibody-coated nanopartic1es can bind breast carcinoma cells expressing the targeted receptor and act as contrast agents for multiphoton microscopy prior to inducing cell death via photoablation. Furthermore, antibody-coated nanopartic1es can bind tissue ex vivo at levels corresponding to receptor expression, suggesting they should bind their target even in the complex biological milieu. This is evaluated by comparing the accumulation of antibody-coated and PEG-coated nanoparticles in subcutaneous glioma tumors in mice. Contrary to expectations, antibody targeting did not yield more nanoparticles within tumors. Nevertheless, these studies established the sensitivity of glioma to photothermal therapy; mice treated with PEG-coated nanoshells experienced 57% complete tumor regression versus no regression in control mice. Subsequent experiments employed intracranial tumors to better mimic the clinical setting. These tumors are highly vascularized, so nanoparticles were addressed toward receptors abundantly expressed on tumor vessels using growth factors as a novel targeting strategy. Photothermal therapy with these vascular-targeted nanoparticles disrupted tumor vessels, leading to a 2.2-fold prolongation of median survival versus control mice. This work confirms that nanoparticle surface coating can affect biodistribution and therapeutic efficacy. With continued optimization of molecular targeting strategies, imaging and photothermal therapy mediated by nanoshells and gold-gold sulfide nanoparticles may offer an effective alternative to conventional cancer management