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Neuroinflammation can cause cognitive deficits, and preexisting neuroinflammation is observed frequently in the clinic after trauma, surgery, and infection. Patients with preexisting neuroinflammation often need further medical treatment under general anesthesia. However, the effects of postconditioning with general anesthetics on preexisting neuroinflammation have not been determined. In this study, adult rats were posttreated with sevoflurane or propofol after intracerebroventricular administration of lipopolysaccharide. The effects of sevoflurane or propofol postconditioning on neuroinflammation-induced recognition memory deficits were detected. Our results found that postconditioning with sevoflurane but not propofol reversed the selective spatial recognition memory impairment induced by neuroinflammation, and these differential effects did not appear to be associated with the similar anti-neuroinflammatory responses of general anesthetics. However, postconditioning with propofol induced a selective long-lasting upregulation of extrasynaptic NR2B-containing N-methyl-D-aspartate receptors in the dorsal hippocampus, which downregulated the cAMP response element-binding signaling pathway and impaired spatial recognition memory. Additionally, the NR2B antagonists memantine and Ro25-6981 reversed this neurotoxicity induced by propofol postconditioning. Taken together, these results indicate that under preexisting neuroinflammation, postconditioning with sevoflurane can provide reliable neuroprotection by attenuating lipopolysaccharide-induced neuroinflammation, apoptosis, and neuronal loss and eventually improving spatial recognition deficits. However, although posttreatment with propofol also has the same anti-neuroinflammatory effects, the neurotoxicity caused by propofol postconditioning following neuroinflammation warrants further consideration.

C-X-C chemokine receptor type 4 (CXCR4) is an alpha-chemokine receptor specific for stromal cell-derived factor 1 (SDF-1 also called CXCL12). The antagonist of CXCR4 can mobilize CD34+ cells and hematopoietic stem cells from bone marrow within several hours, and it has an efficacy on diabetes ulcer through acting on the SDF-1/CXCR4 axis. In this study, we investigated for the first time whether the antagonist of CXCR4 (Plerixafor/AMD3100) delivered on acellular dermal matrix (ADM) may accelerate diabetes-impaired wound healing. ADM scaffolds were fabricated from nondiabetic mouse skin through decellularization processing and incorporated with AMD3100 to construct ADM-AMD3100 scaffold. Full-thickness cutaneous wound in streptozotocin (STZ)-induced diabetic mice were treated with ADM, AMD3100, or ADM-AMD3100. 21 days after treatment, wound closure in ADM-AMD3100-treated mice was more complete than ADM group and AMD3100 group, and it was accompanied by thicker collagen formation. Correspondingly, diabetic mice treated with ADM-AMD3100 demonstrated prominent neovascularization (higher capillary density and vascular smooth muscle actin), which were accompanied by up-regulated mRNA levels of SDF-1 and enhanced migration of CXCR4 in the granulation tissue. Our results demonstrate that ADM scaffold provide perfect niche for loading AMD3100 and ADM-AMD3100 is a promising method for diabetic wound healing mainly by increasing expression of SDF-1 and enhancing migration of CXCR4-positive cells.

Convenient methods for rapidly evaluating wound healing could help clinicians to select effective treatment measures for patients within an appropriate time frame. In this study, we explored the use of second-harmonic generation (SHG) combined with optical coherence tomography (OCT) to monitor the healing state of wounds, including the macro-morphology and optical signal characteristics of regenerated tissue. Wounds were imaged and monitored using OCT and SHG on healing days 3, 5, 7, 14, 21, and 28. The accumulation and maturation of newly formed collagen during the healing process was detected using SHG in real time. Additionally, changes in the OCT signal and attenuation coefficient in wounds before and after trauma were measured using the single-scattering OCT model. The wound closure percentage, the SHG intensity of collagen, and the attenuation coefficient of the wounds were analyzed using correlation analysis, which produced correlation coefficients of R12 = 0.944, R22 = 0.9776, and R32 = 0.9354, respectively. In theory, it is feasible to replace the wound closure percentage with the SHG intensity of collagen and the attenuation coefficient to evaluate wound healing. The OCT and SHG combination could be used to diagnose wound healing in real time.

Ketamine can induce neurotoxicity after exposures to the developing brain. To investigate whether ketamine at subanesthetic dosage or its environmental condition can cause long-term cognitive dysfunction after multiple exposures in male or female neonatal rats, postnatal day 5 (P5)-day-old Sprague-Dawley rats were randomized into three groups: ketamine group, vehicle group, and control group (no disturbance). Learning and memory abilities from P60 to P65 and immunofluorescence tests for myelin basic protein (MBP) in gray matter on P65 were conducted. The results showed that in female rats, the path length on day 1 in ketamine group and on days 1 and 2 in vehicle group was longer than that in control (P0.05). The mean density of MBP in the medial prefrontal cortex (mPFC) was significantly increased in vehicle and ketamine groups compared with that in control (P0.05). In male rats, there were no significant differences in path length among the groups, and the density of MBP in the mPFC and hippocampus in vehicle or ketamine group was not different from that in control (P>0.05). Pearson’s correlation analysis showed that there was a positive correlation between MBP density in the mPFC and path length in adult female rats (r=0.753, P

Propofol can induce acute neuronal apoptosis, neuronal loss or long-term cognitive impairment when exposed in neonatal rodents, but the mechanisms by which propofol induces developmental neurotoxicity are unclear. Recent studies have demonstrated that propofol can increase the TNF-α level in the developing brain, but there is a lack of direct evidence to show whether TNF-α is partially or fully involved in propofol-induced neurotoxicity. The present study shows that propofol exposure in neonatal rats induces an increase of TNF-α in the cerebral spinal fluid, hippocampus and prefrontal cortex (PFC). Etanercept, a TNF-α inhibitor, prevents propofol-induced short- or long-term neuronal apoptosis, neuronal loss, synaptic loss and long-term cognitive impairment. Furthermore, mTNF-α (precursor of TNF-α) expression in microglia cells is increased after propofol anaesthesia in either the hippocampus or PFC, but mTNF-α expression in neurons is only increased in the PFC. These findings suggest that TNF-α may mediate propofol-induced developmental neurotoxicity, and etanercept can provide neural protection. Microglia are the main cellular source of TNF-α after propofol exposure, while the synthesis of TNF-α in neurons is brain-region selective.

In fetal skin, there is a process of scarless repair that does not exist in adults. The characteristics of the fetal skin extracellular matrix (ECM) are presumed to play a pivotal role for this scarless wound healing. The use of an acellular dermal matrix (ADM) with certain specific characteristics of the skin ECM thus is implied to have impact on skin repair and regeneration and the alteration of ADM properties may allow for the development of an effective intervention for scarless wound healing. In this study, two types of ADM from skin ECM were adopted to explore the potential to achieve scarless wound healing in adult mice. We transplanted this matrix onto the 10-week-old full-thickness cutaneous wound mice model. The ADM derived from the ECM of 1-day-old mouse skin (ADM-1D) was chosen to approximate certain characteristics of fetal skin while the ADM from the ECM of 20-week-old mouse skin (ADM-20W) provided a control with characteristics of mature skin. Second-harmonic generation (SHG) microscopic imaging was performed to dynamically demonstrate the collagen reconstruction process in the new born dermis during primary wound healing. The outcome of healing on day 21 was evaluated. Compared to ADM-20W, ADM-1D provided a more favorable influence on the re-establishment of the epidermis as well as collagen density, orientation and stiffness in the new born dermis, to a degree approaching normal uninjured adult dermal tissue. A remarkable difference in biomechanical stiffness is present between ADM-1D and ADM-20W, which might be one of the crucial determinants for potential adult scarless wound healing.

Propofol can induce acute neuronal apoptosis or long-term cognitive dysfunction when exposed at early age in rodents, but it is unclear how the neurotoxicity including neuronal apoptosis and synaptic loss will change in a dynamic manner with brain development after multiple or single exposure of propofol, and the role of neuronal apoptosis and synaptic loss in propofol-induced long-term cognitive impairment needs to be elucidated. In this study, we investigated dynamic changes of neuronal apoptosis, neuronal density, synaptic density in hippocampal CA1 region and the prelimbic cortex (PrL), and long-term cognitive function after multiple or single exposure of propofol in neonatal rats. Results showed that single exposure of propofol only induced great neuronal apoptosis and deficit at postnatal day 9(P9); while multiple exposures of propofol could induce significant neuronal apoptosis, neuronal deficit and synaptic loss at P9, P14, P21, or P35 compared with intact, and spatial learning and memory impairment from P36 to P41. Results suggest that single exposure of propofol only induces transient neuronal apoptosis and deficit, while multiple exposures of propofol induce persistent neuronal apoptosis, neuronal deficit, synaptic loss, and long-term cognitive impairment. Furthermore, persistent neuronal deficit and disturbances in synapse formation but not transient neuronal apoptosis may contribute to long-term cognitive impairment.

In this study, we report permeability coefficients of 30% glucose diffusion by the optical coherence tomography signal slope (OCTSS) method in four kinds of human lung tissue in vitro: normal lung tissue, benign granulomatosis lung tissue, squamous cell carcinoma and adenocarcinoma tumor. To quantify the permeability coefficient of the agent, the monitored region was 80 μm thickness at a tissue depth of ca 230 μm from the surface. The permeability coefficients of 30% glucose from 10 independent experiments were averaged and found to be (1.35 ± 0.13) × 10(-5) cm s(-1) from the normal lung tissue, (1.78 ± 0.21) × 10(-5) cm s(-1) from the benign granulomatosis lung tissue, (2.88 ± 0.19) × 10(-5) cm s(-1) from the adenocarcinoma tumor and (3.53 ± 0.25) × 10(-5) cm s(-1) from the squamous cell carcinoma, respectively. It could be clearly seen that the permeability coefficients of 30% glucose increase ca 32%, 113% and 162% in the benign granulomatosis, adenocarcinoma tumor and squamous cell carcinoma of human lung tissue compared with that from the normal lung tissue, respectively. Therefore, we inferred from this pilot study that the OCT imaging is a feasible method to distinguish normal and cancer lung tissue.

Significantly effective therapies need to be developed for chronic nonhealing diabetic wounds. In this work, the topical transplantation of mesenchymal stem cell (MSC) seeded on an acellular dermal matrix (ADM) scaffold is proposed as a novel therapeutic strategy for diabetic cutaneous wound healing. GFP-labeled MSCs were cocultured with an ADM scaffold that was decellularized from normal mouse skin. These cultures were subsequently transplanted as a whole into the full-thickness cutaneous wound site in streptozotocin-induced diabetic mice. Wounds treated with MSC-ADM demonstrated an increased percentage of wound closure. The treatment of MSC-ADM also greatly increased angiogenesis and rapidly completed the reepithelialization of newly formed skin on diabetic mice. More importantly, multiphoton microscopy was used for the intravital and dynamic monitoring of collagen type I (Col-I) fibers synthesis via second harmonic generation imaging. The synthesis of Col-I fibers during diabetic wound healing is of great significance for revealing wound repair mechanisms. In addition, the activity of GFP-labeled MSCs during wound healing was simultaneously traced via two-photon excitation fluorescence imaging. Our research offers a novel advanced nonlinear optical imaging method for monitoring the diabetic wound healing process while the ADM and MSCs interact in situ. Schematic of dynamic imaging of ADM scaffolds seeded with mesenchymal stem cells in diabetic wound healing using multiphoton microscopy. PMT, photo-multiplier tube.

Second-harmonic generation (SHG) microscopy is a recently developed nonlinear optical imaging modality for imaging tissue structures with submicron resolution and is a potent tool for visualizing pathological effects of diseases. In this letter, we present our investigation on the influence of van Gieson's (VG) alcoholic picrofuchsin staining on SHG in type I collagen (from tendon-rich C57BL/6). Multi-channel imaging and spectra analysis show that the strong SHG signal produced in fresh collagen type I fiber has been greatly suppressed after VG staining, which indicates that staining may induce the structural or characteristic changes of SHG-dependent crystal formed by collagen constituents, such as glycine, proline, and hydroxyproline.

This chapter covers the basic principles that are used in Monte Carlo simulation for investigation into microscopy imaging through tissue media. Section 3.1 summarizes the basic formula in a conventional Monte Carlo simulation process. The implementation of this method in reflection and transmission optical microscopes is given in Sect. 3.2. The effect of the polarization states and pulsed illumination of a beam are described in Sects. 3.3 and 3.4. Sections 3.5–3.8 are dedicated to dealing with the various features of turbid media including the effect of the boundary, scatterer size, and aggregation . In Sects. 3.9 and 3.10, Monte Carlo simulation methods for multi-photon fluorescence and coherent imaging processes are discussed.

As has been discussed in the previous chapter, the trade-off between image resolution and signal level plays a crucial role in determining the efficiency of optical gating methods under single-photon (1p) fluorescence imaging. Another important development in fluorescence imaging is the two-photon (2p) scanning fluorescence microscopy because of its advantages over 1p scanning fluorescence optical microscopy (Denk et al. Science 248:73–76, 1990; Schilders and Gu Appl Opt 38:720–722, 1999; Guo et al. Appl Opt 36:968–970, 1997). First, 2p excitation is a nonlinear process and therefore the fluorescence intensity is directly proportional to the square of the excitation intensity. Due to this quadratic dependence, the 2p imaging technique provides a pinpoint excitation/detection method at a deep position within thick samples. Second, if an infrared laser beam is employed for 2p excitation, 2p fluorescence microscopy offers access to ultraviolet (UV) excitation without using UV lasers, and reduces Rayleigh scattering appreciably, provided that the size of scatterers in tissue is smaller than the illumination wavelength. According to these properties of 2p excitation, it has been claimed that 2p excitation results in a deeper penetration depth than 1p excitation (Denk et al. Science 248:73–76, 1990; Guo et al. Appl Opt 36:968–970, 1997). The trade-off between image resolution and signal level for 2p fluorescence imaging is discussed in Sect. 8.1, which determines the penetration depth. The effects of various parameters on 2p fluorescence imaging are discussed in Sect. 8.2. Section 8.3 discusses the Monte Carlo simulation of 2p fluorescence imaging through various complex modeling structures. Section 8.4 presents the comparison of 1p and 2p imaging with three-photon (3p) imaging through skin and human cortex media.

The angle-gating mechanism discussed is Chap. 5 is one possible method of suppressing scattered photons in imaging through turbid media. However, the limitation of the angle-gating mechanism is that it requires a significant proportion of unscattered photons to be available for detection. Thus, as the scattering event increases the signal-to-noise ratio of the detected images is substantially reduced. To solve this problem, a polarization-gating method can be adopted. This chapter is dedicated to the experimental and theoretical understanding of the polarization-gating mechanisms in an optical microscope (Schilders et al. Appl Opt 37:4300,1998; Schilders et al. Opt Commun 157:238, 1998; Gan et al. J Opt Soc Am A 16:2177, 1999). Section 6.1 discusses the principles of polarization-gating. The performance of the polarization-gating mechanisms on image quality for different sized scatterers is experimentally presented for a reflection optical microscope in Sect. 6.2. With the use of the Monte Carlo simulation model, the polarization-gating performance in reflection and transmission optical microscopes is investigated in Sects. 6.3 and 6.4, respectively. Finally, the effective point spread function together with image resolution and signal level in a transmission optical microscope is presented in Sect. 6.5.

The gating methods discussed in Chaps. 5 and 6 are based on the use of different optical devices or elements. Fluorescence-gating is based on the fact the wavelength of the fluorescence signal, which comes from a specific part within a turbid medium, is different from that of the excitation and the scattered signal if scattering is elastic. Therefore, selecting fluorescence signal is an effective way of removing the effect of multiple scattering in a turbid medium. In this chapter, single-photon (1p) excited fluorescence microscopy through turbid media is studied, in which, one incident photon is absorbed to excite an electron to an excited state (Pawley, Handbook of biological confocal microscopy. Plenum, New York, 1995; Gu, Principles of three-dimensional imaging in confocal microscopes. World Scientific, Singapore, 1996). We will focus the Monte Carlo simulation in this chapter, while experimental investigation will be given in Chap. 8 together with comparisons with two-photon (2p) and three-photon (3p) fluorescence microscopy. In Sect. 7.1, we define resolution and signal level since these two parameters are critical for imaging through a thick turbid medium. In Sects. 7.2 and 7.3, we study the image quality in a single-layer homogeneous and inhomogeneous turbid media, respectively. Double-layer turbid media in which a fluorescent object is embedded is investigated in Sect. 7.4. The effect of spherical scattering aggregates on the focusing of an objective through a turbid medium is presented in Sect. 7.5.

The key element in an optical microscope is an objective. As a result, an object embedded in a turbid medium is illuminated by a focused beam of angles of convergence determined by the numerical aperture of the objective. Consequently, scattered and unscattered photons are mixed in a range of angles when they leave a turbid medium. In this chapter, an angle-gating mechanism for separating scattered and unscattered photons, achieved by the utilization of polarized annular objectives in the illumination and collection beam paths of microscopic imaging systems, are presented. The principle of angle-gating together with the confirmation by Monte Carlo simulation is described in Sect. 5.1. The performance of annular objectives in transmission and reflection optical microscopes is presented in Sects. 5.2 and 5.3, respectively. In Sect. 5.4, a general issue regarding imaging resolution in turbid media is discussed.

We report on the measurement of second-harmonic signals from hyperplastic parenchyma and stroma in malignant human prostate tissue under femtosecond pulsed illumination in the wavelength range from 730 to 870 nm. In particular, the relationship of the second-harmonic generation to the excitation wavelength is measured. The result in these two regions behaves considerably differently and thus provides a possible indicator for identifying tissue components and malignancy.

Image formation in multiphoton fluorescence microscopy through double-layer turbid tissue media is investigated using Monte Carlo simulation. With the help of the concept of the effective point spread function, the relationship of image resolution and signal level to the thickness and scattering properties of the double-layer turbid media under single-, two-, and three-photon excitation is revealed. Results show that for a double-layer turbid medium of a given thickness, small particles in the top layer result in a quicker degradation of signal level than large particles in the top layer. This model is then applied to study the penetration depth of multiphoton fluorescence microscopy through human skin tissue which exhibits a layered structure. It is predicated that using 3p excitation leads to a signal level up to two orders of magnitude higher than that under 2p excitation, while diffraction-limited image resolution can be maintained for skin tissue of thickness up to 500 μm.

Following our established theoretical model to deal with the second-harmonic generation (SHG) excited by a linearly polarized focused beam in type I collagen, in this paper, we further quantitatively characterize the differences between SHG emissions in type I collagen excited by collimated and focused beams. The effects of the linear polarization angle (α) and the fibril polarity characterized by the hyperpolarizability ratio ρ on SHG emission has been compared under collimated and focused beam excitation, respectively. In particular, SHG emission components along the i axis \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\left( {I_{2\omega {,}i} } \right)$\end{document} (i = x,y,z), the induced SHG emission deviation angle γij, and the detected SHG signals (I2ω,ij) in the ij plane by rotating the applied polarizer angle φij have been investigated (i = x, x, y; j = y, z, z). Results show that under our simulation model, SHG emission in the xy plane, such as I2ω,x ,I2ω,y ,γxy and I2ω,xy varying as polarization angle (α) under collimated and focused light, presents no significant difference. The reverse of the fibril polarity has induced great impact on I2ω,x ,γxy and I2ω,xy in both collimated and focused light. I2ω,x and γxy show similarity, but I2ω,xy at α = 30° demonstrates a slight difference in focused light to that in collimated light. Under focused light, the reverse of fibril polarity causes obvious changes of the collected SHG intensity I2ω,xz and I2ω,yz at a special polarization angle α = 60° and γxz, γyz along α.

In biological tissue, the relative strongly SHG (second-harmonic Generation) will be shown in the collagen and the cell membrane with dye molecules under the irradiation of laser. The SHG has a broad prospect in detecting and imaging of the biological tissue for its non-phototoxicity and non-photobleaching. In biological tissue, not only the SHG intensity and emission angle will have more obvious change, but also the spectrum of the SHG will be subject to certain changes when the temperature in the outside world and its structure got a obviously change. According to Kuzyk and Kruhlak's dipole-free sum-over-states theory which gives a introduction for the nonlinear susceptibilities, the relationship between hyperpolarizability of biological tissue, environment temperature and biological tissue's structure is shown in mathematics. In the conditions of control the temperature in experiments, the biological tissue's structure shift can be detected by analyze the SHG spectrum of biological. Also diverse biological tissues' differences in structure can be demonstrated in the spectrum. The change of SHG spectrum for the same biological tissue with environment temperature is discussed. Therefore, SHG spectroscopy analysis provides a new technology for the process of biological tissue lesions. Beside, this research gives a theory results provided by environment temperature which give an explanation for experiment result.

We establish, for the first time, a simulation model for deal- ing with the second-harmonic signals under a microscope through a tissue-like turbid medium, based on the Monte Carlo method. With this model, the angle-resolved distribution and the signal level of second-harmonic light through a slab of the turbid medium are dem- onstrated and the effects of the thickness d of the turbid medium, the numerical aperture NA of the objective as well as the size of the scatterers forming the turbid medium are explored. Simulation results reveal that the use of a small objective NA results in a narrow angle distribution but strong second-harmonic signals. A turbid medium consisting of large scattering particles has a strong influence on the angle distribution and the signal level , which results in a low pen- etration limit for second-harmonic signals made up of ballistic pho- tons. It is approximately 30 m in our situation. © 2006 Society of Photo

Penetration depth is investigated in terms of the performance of transverse image resolution and signal level in human cortex under single-, two-, and three-photon fluorescence microscopy. Simulation results show that, in a double-layer human cortex structure consisting of gray and white matter media, the signal level is strongly affected by the existence of the white matter medium under three-photon excitation. Compared with three-photon excitation, two-photon excitation keeps a better signal level and sacrifices a slight degradation in image resolution. In a thick gray matter medium, a penetration depth of 1500 microm with a near-diffraction-limited resolution is obtainable under three-photon excitation. It is also demonstrated that the numerical aperture has a slight influence on image resolution and signal level under two- and three-photon excitation because of the nonlinear nature in the excitation process.

Diffuse Photon Density Waves (DPDW) is new concept and principle, which takes advantage of the difference of absorption and scattering coefficients of different tissues to study the law of photon density fluctuation during a modulated light traveling through the tissues, thus to explore the structure and function of tissues. With the combination of image reconstruction technology, we can directly `visualize' the tissues. As a non- invasive exam, it has highly extensive applied prospect in medical field and brain cognition study. In this paper, the behavior of DPDW traveling through simulated breast tissue is tentatively examined. Under various conditions, we observed the characteristics of DPDW. We observed the reasonability of the distribution of sources and detectors, the factors that influence the distortion of DPDW. Simulation results could be used as a good theoretical guideline for experiments.

In this paper, a theoretical model to reveal the second-harmonic generation (SHG) from the crystallized collagen fibre, that is, the collagen is highly organized by a bundle of closely packed thin fibrils excited by tightly focused linearly polarized beams, has been established. With this model, we first theoretically demonstrate the phenomenon of the coexisting of forward (F) and backward (B) second-harmonic emissions in a specific SHG medium. The ratio of forward-to-backward (F/B) SHG is dependent on the constituted SHG medium by a particular collagen fibril diameter d1 as well as the structural order (m,l) of collagen fibre.

A theoretical model that deals with SHG from crystallized type I collagen fiber formed by a bundle of fibrils is established. By introducing a density distribution function of dipoles within fibrils assembly into the dipole theory and combining with structural order (m,l) parameters revealed by quasi-phase-matching (QPM) theory, our established theoretical model comprehensively characterizes both biophysical features of collagen dipoles and the crystalline characteristics of collagen fiber. This new model quantitatively reveals the 3-D distribution of second-harmonic generation (SHG) emission angle (θ,ϕ) in accordance with the emission power. Results show that fibrils diameter d1 and structural order m, which describes the structural characteristics of collagen fiber along the incident light propagation direction has significant influence on backward/forward SHG emission. The decrease of fibrils diameter d1 induces an increase of the peak SHG emission angle θmax .A sd1 decreases to a threshold value, in our case it is around d1 = 150 nm when (m,l) = (1,0), θmax > 90 deg, indicating that backward SHG emission appears. The SHG may have two symmetrical emission distribution lobes or may have only one or two unsymmetrical emission lobes with unequal emission power, depending on the functional area of (m,l) on d1. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.3596174)

Quasiphase matching (QPM) is a widely used theory in crystal to analyze the character of second-harmonic generation (SHG) emitted from it. Based on the structural features of collagen type I, where the constituted fibrils in collagen function as a crystal which has the structure of two-dimensional (2D) quasicrystalline, in this paper, we use the QPM theory on collagen for SHG emission direction study under the excitation of laser light through a microscope. The effects of numerical aperture NA, as well as the structural parameters, such as QPM order (m,l) and collagen period a=d1+d2 associated with the fibrils diameter (d1), packing density and interfibrils structure (d2), etc., on SHG emission angle φ have been investigated. Our theoretical results show that collagen period a has threshold effect on φ to present forward or backward SHG emission and NA has minor influence on this threshold value a. Collagen period of a has more significant influence on SHG emission angle φ when a is smaller than the thres...

A theoretical model is established for dealing with second-harmonic generation (SHG) in type I collagen excited by linearly polarized light focused by a microscope. With this model, the effects of the polarization angle alpha, numerical aperture (NA), as well as the ratio of hyperpolarizability rho=beta(xxx)beta(xyy) on SHG emission have been investigated. Simulation results reveal that SHG emission power changes periodically as alpha. The use of lower NA leads to weaker SHG emission but is more concentrated in two closer lobes, whereas more distributed emission in two detached lobes appear at higher NA. As the introduction of polarization direction, which is not along with the fiber axis (alpha not equal0 deg), one more element beta(xyy) is valid in our case than beta(xxx) alone, while their ratio rho plays a very important role for collagen features characterization. SHG emission with rho shows complicated modality that SHG emission is different at different alpha and not symmetric at +/-rho except at alpha=0 deg, suggesting the important impact of polarization working on rho for SHG emission. Our theoretical simulation results provide useful clues for experimental study of microscopic SHG emission in collagen excited by linearly polarized beam.

An effective Mie-scattering model is developed to deal with the scattering property of a spherical fractal aggregate consisting of scattering particles. In this model the scattered field of a scattering particle is given by the classical Mie-scattering theory. On the basis of the Monte Carlo simulation method, we determine the physical parameters of a scattering aggregate, the scattering efficiency Q, and the anisotropy value g, as well as their dependence on the size and the effective mean-free-path length of a scattering aggregate. Accordingly, photon migration through a microscope objective focused into a turbid medium including scattering aggregates is simulated to understand the effect of complex tissue on image quality.

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.

Second-harmonic signals were measured from hyperplastic parenchyma and stroma in malignant human prostate tissue under femtosecond pulsed illumination at different excitation wavelengths. The dependence of the second-harmonic generation on the excitation wavelength provides a possible indicator for recognising tissue components and malignancy.