Three-dimensional autofluorescence spectroscopy of rat skeletal muscle tissue under two-photon excitation

Analysis of muscle tissue in vivo using fiber-optic autofluorescence and diffuse reflectance spectroscopy

SIGNIFICANCE

Current methods for analyzing pathological muscle tissue are time consuming and rarely quantitative, and they involve invasive biopsies. Faster and less invasive diagnosis of muscle disease may be achievable using marker-free in vivo optical sensing methods.

AIM

It was speculated that changes in the biochemical composition and structure of muscle associated with pathology could be measured quantitatively using visible wavelength optical spectroscopy techniques enabling automated classification.

APPROACH

A fiber-optic autofluorescence (AF) and diffuse reflectance (DR) spectroscopy device was manufactured. The device and data processing techniques based on principal component analysis were validated using in situ measurements on healthy skeletal and cardiac muscle. These methods were then applied to two mouse models of genetic muscle disease: a type 1 neurofibromatosis (NF1) limb-mesenchyme knockout (Nf1Prx1  -  /  -  ) and a muscular dystrophy mouse (mdx).

RESULTS

Healthy skeletal and cardiac muscle specimens were separable using AF and DR with receiver operator curve areas (ROC-AUC) of >0.79. AF and DR analyses showed optically separable changes in Nf1Prx1  -  /  -   quadriceps muscle (ROC-AUC >0.97) with no differences detected in the heart (ROC-AUC <0.67), which does not undergo gene deletion in this model. Changes in AF spectra in mdx muscle were seen between the 3 week and 10 week time points (ROC-AUC = 0.96) and were not seen in the wild-type controls (ROC-AUC = 0.58).

CONCLUSION

These findings support the utility of in vivo fiber-optic AF and DR spectroscopy for the assessment of muscle tissue. This report highlights that there is considerable scope to develop this marker-free optical technology for preclinical muscle research and for diagnostic assessment of clinical myopathies and dystrophies.

Multimodal nonlinear microscopy of head and neck carcinoma - toward surgery assisting frozen section analysis

BACKGROUND

Treatment of early cancer stages is deeply connected to a good prognosis, a moderate reduction of the quality of life, and comparably low treatment costs.

METHODS

Head and neck squamous cell carcinomas were investigated using the multimodal combination of coherent anti-Stokes Raman scattering (CARS), two-photon excited fluorescence (TPEF), and second-harmonic generation (SHG) microscopy.

RESULTS

An increased median TPEF to CARS contrast was found comparing cancerous and healthy squamous epithelium with a p value of 1.8·10(-10) . A following comprehensive image analysis was able to predict the diagnosis of imaged tissue sections with an overall accuracy of 90% for a 4-class model.

CONCLUSION

Nonlinear multimodal imaging is verified objectively as a valuable diagnostic tool that complements conventional staining protocols and can serve as filter in future clinical routine reducing the pathologist's workload. © 2016 Wiley Periodicals, Inc. Head Neck 38: First-1552, 2016.

Fibre-optic nonlinear optical microscopy and endoscopy

Nonlinear optical microscopy has been an indispensable laboratory tool of high-resolution imaging in thick tissue and live animals. Rapid developments of fibre-optic components in terms of growing functionality and decreasing size provide enormous opportunities for innovations in nonlinear optical microscopy. Fibre-based nonlinear optical endoscopy is the sole instrumentation to permit the cellular imaging within hollow tissue tracts or solid organs that are inaccessible to a conventional optical microscope. This article reviews the current development of fibre-optic nonlinear optical microscopy and endoscopy, which includes crucial technologies for miniaturized nonlinear optical microscopy and their embodiments of endoscopic systems. A particular attention is given to several classes of photonic crystal fibres that have been applied to nonlinear optical microscopy due to their unique properties for ultrashort pulse delivery and signal collection. Furthermore, fibre-optic nonlinear optical imaging systems can be classified into portable microscopes suitable for imaging behaving animals, rigid endoscopes that allow for deep tissue imaging with minimally invasive manners, and flexible endoscopes enabling imaging of internal organs. Fibre-optic nonlinear optical endoscopy is coming of age and a paradigm shift leading to optical microscope tools for early cancer detection and minimally invasive surgery.

Two-photon 3-D mapping of ex vivo human skin endogenous fluorescence species based on fluorescence emission spectra

Spectral resolved tissue imaging has a broad range of biomedical applications such as the minimally invasive diagnosis of diseases and the study of wound healing and tissue engineering processes. Two-photon microscopy imaging of endogenous fluorescence has been shown to be a powerful method for the quantification of tissue structure and biochemistry. While two-photon excited autofluorescence is observed ubiquitously, the identities and distributions of endogenous fluorophores have not been completely characterized in most tissues. We develop an image-guided spectral analysis method to analyze the distribution of fluorophores in human skin from 3-D resolved two-photon images. We identify five factors that contribute to most of the luminescence signals from human skin. Luminescence species identified include tryptophan, NAD(P)H, melanin, and elastin, which are autofluorescent, and collagen that contributes to a second harmonic signal.

Three- and four-photon absorption of a multiphoton absorbing fluorescent probe

High-order multiphoton excitation processes are becoming a reality for fluorescence imaging and phototherapy treatment because they afford minimization of scattered light losses and a reduction of unwanted linear absorption in the living organism transparency window, making them less susceptible to photodamage, while improving the irradiation penetration depth and spatial resolution. We report the four-photon-excited fluorescence emission of (7-benzothiazol-2-yl-9,-didecylfluoren-2-yl)diphenylamine in hexane and its four-photon absorption cross section sigma4' = 8.1 x 10(-109) cm8 s3 photon(-3) for the transition S0 --> S1 when excited at 1600 nm with a tunable optical parametric generator (OPG) pumped by picosecond laser pulses. When pumped at 1200 nm, three-photon absorption was observed, corresponding to the same transition.

Imaging coronary artery microstructure using second-harmonic and two-photon fluorescence microscopy

The microstructural basis for the mechanical properties of blood vessels has not been directly determined because of the lack of a nondestructive method that yields a three-dimensional view of these vascular wall constituents. Here, we demonstrate that multiphoton microscopy can be used to visualize the microstructural basis of blood vessel mechanical properties, by combining mechanical testing (distension) of excised porcine coronary arteries with simultaneous two-photon excited fluorescence and second-harmonic generation microscopy. Our results show that second-harmonic generation signals derived from collagen can be spectrally isolated from elastin and smooth muscle cell two-photon fluorescence. Two-photon fluorescence signals can be further characterized by emission maxima at 495 nm and 520 nm, corresponding to elastin and cellular contributions, respectively. Two-dimensional reconstructions of spectrally fused images permit high-resolution visualization of collagen and elastin fibrils and smooth muscle cells from intima to adventitia. These structural features are confirmed by coregistration of multiphoton microscopy images with conventional histology. Significant changes in mean fibril thickness and overall wall dimension were observed when comparing no load (zero transmural pressure) and zero-stress conditions to 30 and 180 mmHg distension pressures. Overall, these data suggest that multiphoton microscopy is a highly sensitive and promising technique for studying the morphometric properties of the microstructure of the blood vessel wall.

Monte Carlo simulation of multiphoton fluorescence microscopic imaging through inhomogeneous tissuelike turbid media

Image resolution and signal level in fluorescence microscopy through inhomogeneous turbid media consisting of scatterers of multiple sizes under single- (1p), two- (2p), and three-photon (3p) excitation have been investigated based on a modified Monte Carlo model. The effects of the size distribution and the concentration distribution of scattering particles are explored. Simulation results reveal that the size and the concentration distribution both have an impact on image formation in media consisting of small particles and that 3p excitation has the most significant impact. In media with scatterers of a large size, both size and concentration distributions lead to a slight effect. Image formation in a mixed medium containing small and large scattering particles is more affected by the large particles.

Single molecule fluorescence and force microscopy

The investigation of biomolecules has entered a new age since the development of methodologies capable of studies at the level of single molecules. In biology, most molecules show a complex dynamical behavior, with individual motions and transitions between different states occurring highly correlated in space and time within an arrangement of various elements. Recent advances in the development of new microscopy techniques with sensitivity at the single molecule have gained access to essentially new types of information obtainable from imaging biomolecular samples. These methodologies are described here in terms of their applicability to the in vivo detection and visualization of molecular processes on surfaces, membranes, and cells. First examples of single molecule microscopy on cell membranes revealed new basic insight into the lateral organization of the plasma membrane, providing the captivating perspective of an ultra-sensitive methodology as a general tool to study local processes and heterogeneities in living cells.

Three-dimensional localisation of fluorescence resonance energy transfer in living cells under two-photon excitation

Three-dimensional (3-D) imaging of fluorescence resonance energy transfer (FRET) in human cells under two-photon excitation was demonstrated in this study. A sample was prepared by expressing a donor and an acceptor in living cells and using an antibody to secure the proximity of contact between the donor and the acceptor. The quenching of fluorescence emission of a donor in the double-labelled cells indicates the presence of FRET that occurred in these living cells. Because of the quadratic relation of the excitation power, 3-D localisation of FRET becomes possible.

Effect of handling and fixation processes on fluorescence spectroscopy of mouse skeletal muscles under two-photon excitation

We investigated the effects of handling and fixation processes on the two-photon fluorescence spectroscopy of endogenous fluorophors in mouse skeletal muscle. The skeletal muscle was handled in one of two ways: either sectioned without storage or sectioned following storage in a freezer. The two-photon fluorescence spectra measured for different storage or fixation periods show a differential among those samples that were stored in water or were fixed either in formalin or methanol. The spectroscopic results indicate that formalin was the least disruptive fixative, having only a weak effect on the two-photon fluorescence spectroscopy of muscle tissue, whereas methanol had a significant influence on one of the autofluorescence peaks. The two handling processes yielded similar spectral information, indicating no different effects between them.

Spatial distribution of single-photon and two-photon fluorescence light in scattering media: Monte Carlo simulation

Three-dimensional fluorescence spatial distributions under single-photon and two-photon excitation within a turbid medium are studied with Monte Carlo simulation. It is demonstrated that two-photon excitation has an advantage of producing much less fluorescence light outside the focal region compared with single-photon excitation. With the increase of the concentration of scattering particles in a turbid medium, the position of the maximum fluorescence intensity point shifts from the geometric focal region toward the medium surface. Further studies show that the optical sectioning property of two-photon fluorescence microscopy is degraded in thick turbid media or when the numerical aperture of an objective becomes low.

Single molecule microscopy of biomembranes (review)

Recent advances in the development of new microscopy techniques with a sensitivity of a single molecule have gained access to essentially new types of information obtainable from imaging biomolecular samples. These methodologies are analysed here in terms of their applicability to the in vivo visualization of cellular processes on the molecular scale, in particular of processes in cell membranes. First examples of single molecule microscopy on cell membranes revealed new basic insight into the lateral organization of the plasma membrane, providing the captivating perspective of an ultrasensitive methodology as a general tool to study local processes and heterogeneities in living cells.