Optical Imaging Innovations for Atherosclerosis Research

Abstract

Abstract-Cardiovascular disease is the leading cause of death and morbidity worldwide. Improving vascular prevention and therapy based on a refined mechanistic pervasion of atherosclerosis as the underlying pathology could limit the effect of vascular disease in aging societies. During the past decades, microscopy has contributed greatly to a better understanding of vascular physiology and pathology by allowing imaging of living specimen with subcellular resolution and high specificity. An important advance has been accomplished through the application of multiphoton microscopy in the vascular domain, a technological development that enabled multidimensional and dynamic imaging deep into the cellular architecture of intact tissue under physiological conditions. To identify and validate new targets for treating atherosclerosis, novel imaging strategies with nanoscale resolution will be essential to visualize molecular processes in intracellular and extracellular compartments. This review will discuss the current use of 2-photon microscopy and will provide an overview and outlook on options for introducing nanoscopic optical imaging modalities in atherosclerosis research. as histology. 5 A method that enables TPLSM in ex vivo intact murine carotid arteries mounted and pressurized in perfusion chambers and where both intraluminal and extraluminal physiological conditions are maintained for prolonged time 6 has been used for studying of structural components of the intima, such as endothelial cell orientation and activation, 7 endothelial junction distribution, 8,9 and glycocalyx thickness. 10 TPLSM can also be used for studying the extracellular matrix proteins collagen and elastin, 2 key mechanical components present in these layers. Collagen can be visualized by second harmonic generation, 11 a nonlinear energy-conservative process based on the recombination of 2 near-infrared scattered photons into one with exactly half the wavelength. This phenomenon only occurs in dense noncentrosymmetric samples, such as fibered collagens and striated muscle myosin, and produces mainly forward scattered light in ≤200-μm thick specimens, whereas backward scattered photons are the major signal components at deeper locations in tissues. 12 This strategy has been used to characterize the collagen fiber network in the tunica adventitia and intima of mounted healthy and diseased arteries 7,13 and to evaluate plaque burden 14 and the thickness of the fibrous cap of atherosclerotic stable and unstable plaques in the human aorta. 15 Elastin is the most abundant extracellular matrix protein in the tunica media where it forms elastic laminae interspersed among smooth muscle cells. When illuminated with near-infrared light, it emits autofluorescent signals in a broad range of the visible spectrum, providing further useful insights into arterial structure and function. 15Nonstandard Abbreviations and Acronyms 3D3-dimensional STED stimulated emission depletion TPLSM 2-photon laser scanning microscopy Figure 1. A, Single photon vs. 2-photon...

Microstructure and mechanics of human resistance arteries

“…Only against this background can the functional significance of changes that occur with age (12), lifestyle (18), disease (34), and body location (11) be fully understood. These objectives can be realized using nonlinear microscopy (NLM), a technique that recently has been reviewed in the context of vascular disease (32) and employed in the characterization of static resistance arteries (6). …”

Cardiovascular bioimaging of nitric oxide: Achievements, challenges, and the future

“…The abilities to directly trap NO in tissues or blood and to proportionately amplify the reporter‐signal such as fluorescence will enhance the sensitivity and applicability of a sensor as a tool to monitor clinically relevant changes of NO. The application of the latest imaging modalities such as multiphoton microscopy and optical nanoscopy will be useful in atherosclerotic research, to further characterize the role of NO at different stages of plaque progression in blood vessels 136 . Preferred characteristics and the sequence of events in such a nanoscale imaging tool include: (1) reversible, specific binding of the sensor to NO, (2) stable binding for a desired short period, (3) production of a signal that is detectable using the existing imaging modalities, (4) the ability to facilitate monitoring of fluctuations of NO, and (5) excretion as nontoxic sensor‐NO complexes using the regular mechanisms of metabolism.…”

“…The application of the latest imaging modalities such as multiphoton microscopy and optical nanoscopy will be useful in atherosclerotic research, to further characterize the role of NO at different stages of plaque progression in blood vessels. 136 Preferred characteristics and the sequence of events in such a nanoscale imaging tool include: (1) reversible, specific binding of the sensor to NO, (2) stable binding for a desired short period, (3) production of a signal that is detectable using the existing imaging modalities,…”

Monitoring Endothelin-A Receptor Expression during the Progression of Atherosclerosis

“…However, especially when it comes to coronary artery imaging, the myocardial background limits its use [18]. During the last years, innovative molecular optical imaging methods like fluorescence-mediated tomography (FMT), fluorescence-reflection imaging (FRI) or multispectral-optoacoustic tomography (MSOT) were established, which can be used with the aid of fluorescent probes for the early and specific in vivo detection of molecular processes in the preclinical setting [19][20][21][22][23]. Optical imaging is based on the identification of near-infrared (NIR) fluorescent substances within the organism and offers comparative sensitivity and spatial resolution as nuclear imaging methods.…”