Staying Coherent After Kent： From Optical Communications to Biomedical Optics

In this paper, an overview of author＇s research is presented, commencing at the University of Kent under Prof. David A. Jackson. Early research in short optical pulses and fiber-optic delay-line digital correlators led to optical communications research in code-division multiple access networking. This research was based on broadband incoherent light, and this theme continued with research into spectrum-sliced wavelength-division multiplexing. In shifting from photonics research to biomedical optics and biophotonics in the late 1990s, the emphasis on exploiting broadband light continued with research in optical coherence tomography, amongst other topics. In addition to the research outcomes, how these outcomes were attained is described, including mention of the exceptional contributions of many of my colleagues.

Biomedical optical properties of color light and near-infrared fuorescence separated-merged imager

Objective:We study the biomedical optical properties of the color light and near-infrared fluorescence separated-merged imager.Materials and Methods:The color light and near infrared fuorescence separated merged imager can iluninate the visible light and the near infrared light of 760±10 nm,receiving the reflected light and 835±10 nm near-infrared fuorescence,and display the color,fuorescence and merge inage.ICG solution of different concentration,including standing time,was allocated to study the best inaging condition in vitro,and the depth of fuorescence penetration was studied with 5%agarose gel;the imaging characteristics of the imager was studied using SD rat;and then the SLNs tracing in 4 cases of penile carcinoma was performed.Results:When the concentration of ICG is 13.11 pumol/L,the fuorescence intensity and the merge imnage are the best.The maximun depth of fluorescence imaging is 9 mm in 5%agarose gel,while the bone has the greatest influence on it.The SLNs tracing shows that the imager can locate the SLNs in vitro,to achieve perioperative navigation during biopsy.Conclusion:There are many factors that affect the imaging effect,but the imaging effect of the imager meets the requirement of vision in a wide range,and can effectively trace the SLNs in perioperative period.

Numerical model for evaluating the speckle activity and characteristics of bone tissue under the biospeckle laser system

This paper discusses and studies the composition and characteristics of biospeckle on the surface of bone tissues.We used a laser speckle device to capture biospeckle patterns from fresh pig bone tissue.Traditional speckle activity metrics were used to measure the speckle activity of ex vivo bone tissue over time.Both Gaussian and Lorentzian correlation functions were used to char-acterize the ordered and disordered motion of the bone surface,together with volume scattering,to construct the model.Using the established mathematical model of the spatio-temporal evo-lution of the biospeckle pattern,it is possible to account for the presence of volume scattering from the biospeckle of bones,quantify the ordered or disordered motions in the biological speckle activity at the current time,and assess the ability of laser speckle correlation technique to determine biological activity.

FRACTAL NATURE OF LIGHT SCATTERING IN TISSUES

Light scattering by a tissue has a wavelength dependence that depends on the size distribution of scatterers in the tissue.By measuring the wavelength dependence of scattering,one can deduce changes in the nanoscale architecture of cells and tissues.This report discusses the connection between nanoscale architecture and measurable light scattering.The significance of this work is to develop label-free optical imaging that describes tissue structure,to complement the absorption,fluorescence,and Raman scattering spectra that describe the chemical constituents of a tissue.

Degradation of multiphoton signal and resolution when focusing through a planar interface with index mismatch:Analytical approximation and numerical investigation

Multiphoton microscopy(MPM)is an invaluable tool for visualizing subelllar structures in biomedical and life sdences.High-numerical-aperture(NA)immersion objective lenses are used to deliver excitation light to focus inside the biological tissue.The refractive index of tissue is commonly different from that of the immersion medium,which introduces spherical aberration,leading to signal and resolution degradation as imaging depth increases.However,the explicit dependence of this index mismatch induced aberration on the involved physical parameters is not dlear,espeially its dependence on index mismatch.Here,from the vectorial equations for fo-cusing through a planar interface bet ween materials of mismatched refractive indices,we derive an approximate analytical expression for the spherical aberration.The analytical expression explicitly reveals the dependence of spherical aberration on index mismatch,imaging depth and excitation wavelength,from which we can expect the following qualitative behaviors:(1)Mul-tiphoton sigmal and resolution degradation is less for longer excitation wavelength,(2)a longer wavelength tolerates a higher index mismatch,(3)a longer wavelength tolerates a larger imaging depth and(4)both signal and resohution degradations show the same dependence om imaging depth,regardless of NA or immersion on the condition that the integration angle is the same.Detailed numerical simulation results agree quite well with the above expectations based on the analytical approximation.These theoretical results suggest the use of long excitation wavelength to better suppress index mismatch.induced sigmal and resolution degradation in deep-tssue MPM.

Features of structure of external layer of murine hair at different stages of malignant tumor development

In the paper,the results of experimental investigations on the diferences of wool structure ofhealthy mice and mice with malignant tumor(s)are represented.It is shown that destruction ofwool structure happens during pathology development.Quantity of cells of external wool layerand their thickness decrease when the tumor capsule enlarges.Difference is seen even when thetumor is small.The obtained results can be used to improve optical techniques of biomedicaldiagnostics of cancer diseases.

POWER OF DUAL-WAVELENGTH APPROACHES IN STUDYING PHYSIOLOGICAL AND FUNCTIONAL CHANGES OF INTACT HEART AND IN VIVO BRAIN

Since the dual-wavelength spectrophotometer was developed,it has been widely used for studying biological samples and applied to extensive investigations of the electron transport in respiration and redox cofactors,redox state,metabolic control,and the generation of reactive oxygen species in mitochondria.Here,we discuss some extension of dual-wavelength approaches in our research to study the physiological and functional changes in intact hearts and in vivo brain.Specifically,we aimed at(1)making nonratiometricfluorescent indicator become ratiometricfluorescence function for investigation of Ca^(2+) dynamics in live tissue;(2)eliminating the effects of physiological changes on measurement of intracellular calcium;(3)permitting simultaneous imaging of multiple physiological parameters.The animal models of the perfused heart and transiently ischemic insult of brain are used to validate these approaches for physiological applications.

Towards in vivo photoacoustic human imaging:Shining a new light on clinical diagnostics

Multiscale visualization of human anatomical structures is revolutionizing clinical diagnosis and treatment.As one of the most promising clinical diagnostic techniques,photoacoustic imaging(PAI),or optoacoustic imaging,bridges the spatial-resolution gap between pure optical and ultrasonic imaging techniques,by the modes of optical illumination and acoustic detection.PAI can non-invasively capture multiple optical contrasts from the endogenous agents such as oxygenated/deoxygenated hemoglobin,lipid and melanin or a variety of exogenous specific biomarkers to reveal anatomy,function,and molecular for biological tissues in vivo,showing significant potential in clinical diagnostics.In 2001,the worldwide first clinical prototype of the photoacoustic system was used to screen breast cancer in vivo,which opened the prelude to photoacoustic clinical diagnostics.Over the past two decades,PAI has achieved monumental discoveries and applications in human imaging.Progress towards preclinical/clinical applications includes breast,skin,lymphatics,bowel,thyroid,ovarian,prostate,and brain imaging,etc.,and there is no doubt that PAI is opening new avenues to realize early diagnosis and precise treatment of human diseases.In this review,the breakthrough researches and key applications of photoacoustic human imaging in vivo are emphatically summarized,which demonstrates the technical superiorities and emerging applications of photoacoustic human imaging in clinical diagnostics,providing clinical translational orientations for the photoacoustic community and clinicians.The perspectives on potential improvements of photoacoustic human imaging are finally highlighted.

Automated superpixels-based identification and mosaicking of cone photoreceptor cells for adaptive optics scanning laser ophthalmoscope

An automated superpixels identification/mosaicking method is presented for the analysis of cone photoreceptor cells with the use of adaptive optics scanning laser ophthalmoscope(AO-SLO) images. This is an image oversegmentation method used for the identification and mosaicking of cone photoreceptor cells in AO-SLO images.It includes image denoising, estimation of the cone photoreceptor cell number, superpixels segmentation, merging of superpixels, and final identification and mosaicking processing steps. The effectiveness of the presented method was confirmed based on its comparison with a manual method in terms of precision, recall, and F1-score of 77.3%, 95.2%, and 85.3%, respectively.

Extraction of Target Fluorescence Signal from In Vivo Background Signal Using Image Subtraction Algorithm

Challenges remain in fluorescence reflectance imaging (FRI) in in vivo experiments, since the target fluorescence signal is often contaminated by the high level of background signal originated from autofluorescence and leakage of excitation light. In this paper, we propose an image subtraction algorithm based on two images acquired using two excitation filters with different spectral regions. One in vivo experiment with a mouse locally injected with fluorescein isothiocyanate (FITC) was conducted to calculate the subtraction coefficient used in our studies and to validate the subtraction result when the exact position of the target fluorescence signal was known. Another in vivo experiment employing a nude mouse implanted with green fluorescent protein (GFP)—expressing colon tumor was conducted to demonstrate the performance of the employed method to extract target fluorescence signal when the exact position of the target fluorescence signal was unknown. The subtraction results show that this image subtraction algorithm can effectively extract the target fluorescence signal and quantitative analysis results demonstrate that the target-to-background ratio (TBR) can be significantly improved by 33.5 times after background signal subtraction.