Mechanical delay line has been used in the Michelson interferometer to see the geometry and internal structure of objects. This method has to change the optical path length of a reference arm to match with that of a sample arm. However, its reference mirror must be continuously moved for depth scans, it requires a long time because it is limited by mechanical movement speed. We proposed and demonstrated an high speed optical delay line using two phase modulators in optical coherence tomography for axial scanning. Experimental setup is consist of pulse laser source (center wavelength 1304nm, pulse width 30ps, repetition rate 10GHz), two phase modulators and dispersive shifted fiber. As experimental results, the system has high scanning speed of 120km/s and a high repetition rate of 10MHz were achieved.

A novel instrument for real-time in vivo measurement of blood composition is presented. Two optical technologies are combined in this instrument: spectral domain low coherence interferometry (SD-LCI) and retinal tracking. Retinal tracking is used to stabilize the LCI beam on vessels. SD-LCI is used to get depth-reflectivity profiles within the vessels. Multiple signals are rapidly acquired, averaged and processed. Differences in the slopes of the depth reflectivity profiles for different subjects correspond to the difference in the scattering coefficient, which is proportional to the concentration of red blood cells per cubic mm of blood (hematocrit). Preliminary measurements on several healthy volunteers show a good correlation with the normal range of the hematocrit.

We describe the design and performance of a new full-field high-speed laser Doppler imaging system developed for mapping and monitoring of blood flow in biological tissue. The total imaging time for 256x256 pixels region of interest is 1.2 seconds. An integrating CMOS image sensor is utilized to detect Doppler signal in a plurality of points simultaneously on the sample illuminated by a divergent laser beam of a uniform intensity profile. The integrating property of the detector improves the signal-to-noise ratio of the measurement, which results in high-quality flow-images provided by the system. The new technique is real-time, non-invasive and the instrument is easy to use. The wide range of applications is one of the major challenges for a future application of the imager. High-resolution high-speed laser Doppler perfusion imaging is a promising optical technique for diagnostic and assessing the treatment effect of the diseases such as e.g. atherosclerosis, psoriasis, diabetes, skin cancer, allergies, peripheral vascular diseases, skin irritancy and wound healing. We present some biological applications of the new imager and discuss the perspectives for the future implementations of the imager for clinical and physiological applications.

The objective of this paper is to perform a comprehensive experimental and numerical analysis of the short pulse laser interaction with tissue medium with the goal of tumor / cancer diagnostics. For short pulse laser source, the shape of output signal is a function of the optical properties of the medium and hence the scattered temporal optical signal helps in understanding of the medium characteristics. Initially experiments are performed on tissue phantoms imbedded with inhomogeneities in order to optimize the time-resolved optical detection scheme. Both the temporal and the spatial profiles of the scattered reflected and transmitted optical signals are compared with the numerical modeling results obtained by solving the transient radiative transport equation using the discrete ordinates technique. Next experiments are performed on in vitro rat tissue samples to characterize the interaction of light with skin layers and to validate the time varying optical signatures with the numerical model. The numerical modeling results and the experimental measurements are in excellent agreement for the different parameters studied in this paper. The final step is to perform in vivo imaging of anaesthetized rats with tumor-promoting agents injected inside skin tissues in order to demonstrate the feasibility of the technique in detecting tumors in animal model.

The vibrational modes corresponding to protein tertiary structural motion lay in the far infrared or terahertz frequency range. These collective large scale motions depend on global structure and thus will necessarily be perturbed by ligand binding events. We discuss the use of terahertz dielectric spectroscopy to measure these vibrational modes and the sensitivity of the technique to changes in protein conformation, oxidation state and environment. A challenge of applying this sensitivity as a spectroscopic assay for ligand binding is the sensitivity of the technique to both bulk water and water bound to the protein. This sensitivity can entirely obscure the signal from the protein or protein-ligand complex itself, thus necessitating sophisticated sample preparation making the technique impractical for industrial applications. We discuss methods to overcome this background and demonstrate how terahertz spectroscopy can be used to quickly assay protein binding for proteomics and pharmaceutical research.

Time-domain Terahertz (THz) spectroscopy and imaging is currently evaluated as a novel tool for medical imaging and diagnostics. The application of THz-pulse imaging of human skin tissues and related cancers has been demonstrated recently in-vitro and in-vivo. With this in mind, we present a time-domain THz-transmission study of artificial skin. The skin samples consist of a monolayer of porous matrix of fibers of cross-linked bovine tendon collagen and a glycosaminoglycan (chondroitin-6-sulfate) that is manufactured with a controlled porosity and defined degradation rate. Another set of samples consists of the collagen monolayer covered with a silicone layer. We have measured the THz-transmission and determined the index of refraction and absorption of our samples between 0.1 and 3 THz for various states of hydration in distilled water and saline solutions. The transmission of the THz-radiation through the artificial skin samples is modeled by electromagnetic wave theory. Moreover, the THz-optical properties of the artificial skin layers are compared to the THz-optical properties of freshly excised human skin samples. Based on this comparison the potential use of artificial skin samples as photo-medical phantoms for human skin is discussed.

A new type of cell-cultivation system based on laser processing has been developed for the on-chip cultivation of living cells. We introduce a "laser cell-chip", on which migration of cells, such as stem cells, tumor cells or immunocompetent cells, can be observed. A sheet prepared from epoxy resin was processed by KrF excimer laser (248 nm, 1.6 J/cm²) for preparation of microgrooved surfaces with various groove width, spacing, and depth. A laser cell-chip can make kinetic studies of cell migration depending on the concentration gradient of a chemoattractant. In this study, megakaryocytes were used for the migration on a groove of laser cell-chip by the concentration gradient of the stromal cell derived factor 1 (SDF-1/CXCL12). SDF-1/CXCL12 plays an important and unique role in the regulation of stem/progenitor cell trafficking. A megakaryocyte was migrated on a groove of laser cell-chip depending on the optical concentration gradient of SDF-1/CXCL12. Since SDF-1/CXCL12-induced migration of mature megakaryocyte was known to increase the platelet production in the bone marrow extravascular space, the diagnosis of cell migration on laser cell-chip could provide a new strategy to potentially reconstitute hematopoiesis and avoid life-threatening hemorrhage after myelosuppression or bone marrow failure.

We describe a compact computational spectroscopy platform optimized for molecular recognition using metal nanoparticle assays. The objective is motivated by the urgent need for low-cost, portable and high-throughput sensors for point-of-care (POC) clinical diagnostics. Nanoparticle based sensing has been successfully demonstrated for diagnosis and monitoring of infectious diseases, drug discovery, proteomics, and biological agent detection. Molecular binding on the nanoparticle surface is transuded into an optical signal by modification of the nanoparticle extinction spectrum (via a shift in Localized Surface Plasmon Resonance) or by modification of the molecular scattering spectrum (via Surface Enhanced Raman Scattering). Translating a nanoparticle -based molecular recognition system into a functional miniature hand-held biosensor requires spectrometer designs optimized to large area nanoparticle assays and integrated spectral filtering to improve the signal specificity. Large population sampling with small population sensitivity is essential to highly sensitive nanoparticle assay analysis. We describe a multimodal multiplex spectroscopy (MMS) platform that samples the spectral response of up to 10⁶ populations of 10-100 nanoparticles in parallel. The advantages of MMS approach include: extremely high signal throughput due to its large aperture and high resolution with small form factor. We will demonstrate a nanoparticle biosensor platform based on MMS. Ultimately, a fully integrated functional miniature nanoparticle based biosensor for real time disease diagnosis in whole blood assays can be realized.

Diffuse optical tomography (DOT) using diffuse light, red or near-infrared (NIR) light, is in an attempt to image the interior of human tissues such as breasts, arms, etc. In the current design of our NIR tomography imaging system, the system uses a single rotating source/detector scanning device associated with an image reconstruction scheme. The device can dramatically save source- and detection-fiber-bundles, and offer promising measured radiance reflecting the optical properties of the test phantoms. Both source and detector can rotate on command with any pre-defined angles controlled by the computer. Additionally, an image reconstruction algorithm applied to the tomography scanning device in the DC domain is also implemented. The ability and performance of this image reconstruction algorithm are discussed and presented. Results reveal that inclusion (tumor) positions can be well defined and the spatial resolution is beyond 1:16, inclusion to background.

We demonstrate a new endoscope system for laparoscopic surgery that provides two different views simultaneously. One is a 'wide view' and the other is an 'enlarged view' derived from the wide view with an optical image-shifting mechanism. By using this endoscope, surgeons can observe a surgical area as an enlarged view without moving or rotating the endoscope. Moreover, the wide view is useful for examining the outside of a surgical area. They can move the enlarged view within the area of the wide view by using the image-shifting mechanism. This system consists of a rigid scope and a 'zoom unit.' The rigid scope includes a set of optical lenses for the wide view angle (120 degrees) and light-guide fibers built in for illumination. These fibers are connected to a light source directly. The zoom unit includes imaging optical elements and two CCD cameras. In the zoom unit, an image provided by the rigid scope is divided into two ways by a half-mirror. One image is captured by the first CCD camera with relay lenses for a wide view. The other passes through a Porro prism (II), which is used to shift the enlarged view vertically and horizontally, and zoom lenses with a three variable power. Then, the image is captured by the second CCD camera for an enlarged view. A working distance between the tip of the rigid scope and the surface of viscera is 100mm that is sufficient for surgical operation.

The overall objective this work is the development of a miniaturized fluorescence spectroscopy analyzer realized via microfabrication technology. Previously, we reported a MEMS micro grating actuated by a piezoelectric cantilever. For such device to be used in a spectroscopic system, optical characterization of the grating's efficiency and the system's stray light are required. We report here the characterization of the grating cantilever with a MEMS micro lens with the intention of fitting into a packaged micro spectroscopic system. This packaging is accomplished by multi-wafer (silicon) bonding of strategically aligned crystalline planes in order to form the basic geometry of a miniaturized spectroscopy setup. One of these crystalline planes, <111> of silicon, is used as a mirror for folding and compacting the optics at the specific angle of 54.74° (with wafer plane normal). The packaging, microlens, and grating cantilever are position in the designed geometry to accept a self-aligned fiber input from a flash lamp source. The microlens component is presented with beam profilometry of its focusing at a focal length of 7.7 mm. The diffraction is interrogated by a monochromator for quantifying the above said characteristics. The relative efficiency of the grating was 40-70% in the 400-600 nm range. Together these characterized components define the geometry and performance of our micro fluorescence spectroscopy system.

Past studies have demonstrated that combined fluorescence and diffuse reflectance spectroscopy can successfully discriminate between normal, tumor core, and tumor margin tissues in the brain. To achieve efficient surgical resection guidance with optical biopsy, probe-based spectroscopy must be extended to spectral imaging to spatially demarcate the tumor margins. This paper describes the design and testing of a combined fluorescence and diffuse reflectance imaging system which uses liquid-crystal tunable filter technology. Experiments were conducted to quantitatively determine its linearity, field of view, spatial and spectral resolution, and wavelength sensitivity. For functional testing, spectral images were acquired from tissue phantoms, mouse brain in vitro, and rat brain cortex in vivo. The spectral imaging system is characterized by measured intensities which are linear with sample emission intensity and integration time, a one-inch field of view for a seven-inch object distance, spectral resolution which is linear with wavelength, spatial resolution which is pixel-limited, and sensitivity functions which provide a guide for the distribution of total image integration time between wavelengths. Functional testing demonstrated good spatial and spectral constrast between brain tissue types, the capability to acquire adequate fluorescence and diffuse reflectance intensities within a one-minute imaging timeframe, and the importance of hemostasis to acquired signal strengths and imaging speed.

The Mueller matrix is an elegant mathematical method to fully characterize the polarization properties of an object. If the Mueller matrix of an optical element is known as well as the polarization of an incident beam (and its Stokes vector) then the polarization state of the beam exiting the optical element can be uniquely determined. Over the last thirty years, several polarimeters have been proposed for reconstructing the Mueller matrix of any optical element through a set of measurements. One the most successful polarimeters is the dual rotating retarder polarimeter (DRR), invented by Azzam in 1978. This system is composed of two polarizer and retarder pairs, and is able to reconstruct the Mueller matrix of an object inserted in between the two polarizing pairs via an angular modulation of the retarders. Chenault et al. in 1992 suggested that the Mueller matrix of a sample inserted in a DRR polarimeter could be calculated multiplying the pseudo-inverse of a data reduction matrix by the measurements vector. The pseudo-inverse of the data reduction matrix is calculated with a least-square approach. This method is now of common usage in the scientific community. In this paper we will show that the reconstruction of the Mueller matrix can be done with higher accuracy using singular value decomposition of the data reduction equation. Our method suggests that a vast range of retardations for the retarders of a DRR obtaining identical results and not only the 127° one as recently suggested by few authors.

Collagen, the most abundant protein in the body, may provide invaluable clinical information of many major disorders due to its birefringence. Assessing collagen birefringence with polarization sensitive optical coherence tomography (PSOCT) could improve characterization of in vivo tissue pathology. Beyond detecting collagen organization, the information potentially gained from PSOCT include collagen type, form vs. intrinsic birefringence, the local environment, collagen angle, and the presence of multiple birefringence materials. In this work, we applied fast Fourier transform (FFT) analysis to both the mathematical model and in vitro bovine meniscus for improved PS-OCT data analysis. The FFT analysis yielded information on tissue composition in addition to identify the presence of organized collagen. PS-OCT images of Helistat^(R) phantoms (collagen type I) were also analyzed with the ultimate goal of improved tissue characterization. This study could advance the insights gained from PS-OCT images beyond simply determining the presence or absence of birefringence.

Even minute alterations in a cell's intracellular scaffolds, i.e. the cytoskeleton, which organize a cell, result in significant changes in a cell's elastic strength since the cytoskeletal mechanics nonlinearly amplify these alterations. Light has been used to observe cells since Leeuwenhoek's times and novel techniques in optical microscopy are frequently developed in biological physics. In contrast, with the optical stretcher we use the forces caused by light described by Maxwell's surface tensor to feel cells. Thus, the stretcher exemplifies the other type of biophotonic devices that do not image but manipulate cells. The optical stretcher uses optical surface forces to stretch cells between two opposing laser beams, while optical gradient forces, which are used in optical tweezers, play a minor role and only contribute to a stable trapping configuration. The combination of the optical stretcher's sensitivity and high throughput capacity make a cell's "optical stretchiness" an extremely precise parameter to distinguish different cell types. This avoids the use of expensive, often unspecific molecular cell markers. This technique applies particularly well to cells with dissimilar degrees of differentiation, as a cell's maturation correlates with an increase in cytoskeletal strength. Because malignant cells gradually dedifferentiate during the progression of cancer, the optical stretcher should allow, the direct staging from early dysplasia to metastasis of a tumor sample obtained by MRI-guided fine needle aspirations or cytobrushes. With two prototypes of a microfluidic optical stretcher at our hands, we prepare preclinical trials to study its potential in resolving breast tumors' progression towards metastasis. Since the optical stretcher represents a basic technology for cell recognition and sorting, an abundance of further biomedical applications can be envisioned.

An advanced hyper-spectral imaging (HSI) system has been developed for use in medical diagnostics. One such diagnostic, esophageal cancer is diagnosed currently through biopsy and subsequent pathology. The end goal of this research is to develop an optical-based technique to assist or replace biopsy. In this paper, we demonstrate an instrument that has the capability to optically diagnose cancer in laboratory mice. We have developed a real-time HSI system based on state-of-the-art liquid crystal tunable filter (LCTF) technology coupled to an endoscope. This unique HSI technology is being developed to obtain spatially resolved images of the slight differences in luminescent properties of normal versus tumorous tissues. In this report, an in-vivo mouse study is shown. A predictive measure of cancer for the mice studied is developed and shown. It is hoped that the results of this study will lead to advances in the optical diagnosis of esophageal cancer in humans.

We describe a new noninvasive microscopic near infrared reflectance hyperspectral imaging method for visualizing, in vivo, spatially distributed contributions of oxyhemoglobin perfusing the microvasculature within dermal tissue. Microscopic images of the dermis are acquired, generating a series of spectroscopic images formatted as a function of wavelength consisting of one spectral and two spatial dimensions; a hyperspectral image data cube. The data thus collected can be considered as a series of spatially resolved spectra. For data collection, images are acquired by a system consisting of a near infrared liquid crystal tunable filter (LCTF) and a Focal plane array detector (FPA) integrated with a microscope. The LCTF is continuously tunable over a useful near infrared spectral range (650-950 nm) with an average full width at half-height bandwidth of 6.78 nm. To provide high quantum efficiency without etaloning we utilized a back-illumination FPA with deep -depletion technology. A 30W halogen light source illuminates a dermal tissue area of approximately 18 mm in diameter. Reflected light from the dermal tissue is first passed through the microscope, the LCTF, and then imaged onto the FPA. The acquired hyperspectral data is deconvoluted using a multivariate least squares approach that requires at least two reference spectra, oxy- and deoxyhemoglobin. The resulting images are gray scale encoded to directly represent the varying spatial distributions of oxyhemoglobin contribution. As a proof of principle example, we examined a clinical model of vascular occlusion and reperfusion.

Pathogenic bacterial contamination in food products is costly to the public and to industry. Traditional methods for detection and identification of major food-borne pathogens such as Listeria monocytogenes typically take 3-7 days. Herein, the use of optical scattering for rapid detection, characterization, and identification of bacteria is proposed. Scatter patterns produced by the colonies are recognized without the need to use any specific model of light scattering on biological material. A classification system was developed to characterize and identify the scatter patterns obtained from colonies of various species of Listeria. The proposed classification algorithm is based on Zernike moment invariants (features) calculated from the scatter images. It has also been demonstrated that even a simplest approach to multivariate analysis utilizing principal component analysis paired with clustering or linear discriminant analysis can be successfully used to discriminate and classify feature vectors computed from the bacterial scatter patterns.

Bio- and chemi-luminescent based biochemical sensors are being developed in a multi-well single use format for multi-analyte applications employing a single step, disposable, easy to use and interpret ChemChip. We briefly review and summarize earlier and ongoing work. We also argue for far more, rather than less or limited, chemical data in all areas, and particularly in education, health, and medicine.

A centrifugal-based microfluidic device¹ was built with lyophilized bioluminescent reagents for measuring multiple metabolites from a sample of less than 15 μL. Microfluidic channels, reaction wells, and valves were cut in adhesive vinyl film using a knife plotter with features down to 30 μm and transferred to metalized polycarbonate compact disks (CDs). The fabrication method was simple enough to test over 100 prototypes within a few months. It also allowed enzymes to be packaged in microchannels without exposure to heat or chemicals. The valves were rendered hydrophobic using liquid phase deposition. Microchannels were patterned using soft lithography to make them hydrophilic. Reagents and calibration standards were deposited and lyophilized in different wells before being covered with another adhesive film. Sample delivery was controlled by a modified CD ROM. The CD was capable of distributing 200 nL sample aliquots to 36 channels, each with a different set of reagents that mixed with the sample before initiating the luminescent reactions. Reflection of light from the metalized layer and lens configuration allowed for 20% of the available light to be collected from each channel. ATP was detected down to 0.1 μM. Creatinine, glucose, and galactose were also measured in micro and milliMolar ranges. Other optical-based analytical assays can easily be incorporated into the device design. The minimal sample size needed and expandability of the device make it easier to simultaneously measure a variety of clinically relevant analytes in point-of-care settings.

Microarray analysis has become increasingly complex due to the growing size of arrays. In this work we explore the effects that temperature and SNP, mismatch, concentration have on the dynamic range of detection in a two component system. A finite element software is used to simulate the mass transport of DNA through a microfluidic chamber to the sensing surface where hybridization of DNA is modeled using the corresponding kinetic equation. We compare the theoretical maximum dynamic range with those from simulations when the match target is 90% of its equilibrium value. Results show that even though the maximum dyamic range decreases as temperature increases the observed dynamic range at 90% match equilibrium grows.

Personalized medicine is an emerging field in which clinical diagnostics information about a patient's genotype or phenotype is used to optimize his/her pharmacotherapy. This article evaluates whether planar waveguide fluorescent sensors are suitable for determining such information from patient testing in point-of-care (POC) settings. The model system was Long QT Syndrome, a congenital disease associated with single nucleotide polymorphisms (SNPs) in genes encoding for cardiac ion channels. Three different SNP assay formats were examined: DNA/DNA hybridization, DNA/PNA hybridization (PNA: "peptide nucleic acid"), and single base extension (SBEX). Although DNA/DNA hybridization produced a strong intensity-time response for both wildtype and SNP analytes in a 5-min assay at 32°C, their hybridization rates differed by only 32.7%, which was insufficient for clinical decision-making. Much better differentiation of the two rates was observed at 53°C, where the wildtype's hybridization rate was two-thirds of its maximum value, while that of the SNP was essentially zero. Such all-or-nothing resolution would be adequate for clinical decision-making; however, the elevated temperature and precise temperature control would be hard to achieve in a POC setting. Results from DNA/PNA hybridization studies were more promising. Nearly 20-fold discrimination between wildtype and SNP hybridization rates was observed in a 5-min assay at 30°C, although the low ionic strength conditions required necessitated a de-salting step between sample preparation and SNP detection. SBEX was the most promising of the three, determining the absolute identity of the suspected polymorphism in a 5-min assay at 40°C.

In recent years, using the capsule endoscope to inspect the pathological change of digestive system and intestine had a great break-through on the medical engineering. However, there are some problems needs to overcome. One is that, the field of view was not wide enough, and the other is that the image quality was not enough well. The drawbacks made medical professionals to examine digestive diseases unclearly and ambiguously. In order to solve these problems, the paper designed a novel miniature lenses which has a wide angle of field of view and a good quality of imaging. The lenses employed in the capsule endoscope consisted of a piece of plastic aspherical lens and a piece of glass lens and compacted in the 9.8mm (W) *9.8mm (L) *10.7mm (H) size. Taking the white LED light source and the 10μm pixel size of 256*256 CMOS sensor under considerations, the field of view of the lenses could be achieved to 86 degrees, and the MTF to 37% at 50lp/mm of space frequency. The experimental data proves that the design is consistent with the finished prototype.

Reduced deformability of red blood cells (RBCs) may play an important role on the pathogenesis of chronic vascular complications of diabetes mellitus. However, available techniques for measuring RBC deformability often require washing process after each measurement, which is not optimal for day-to-day clinical use at point of care. The objectives of the present study are to develop a device and to delineate the correlation of impaired RBC deformability with diabetic nephropathy. We developed a disposable ektacytometry to measure RBC deformability, which adopted a laser diffraction technique and slit rheometry. The essential features of this design are its simplicity (ease of operation and no moving parts) and a disposable element which is in contact with the blood sample. We studied adult diabetic patients divided into three groups according to diabetic complications. Group I comprised 57 diabetic patients with normal renal function. Group II comprised 26 diabetic patients with chronic renal failure (CRF). Group III consisted of 30 diabetic subjects with end-stage renal disease (ESRD) on hemodialysis. According to the renal function for the diabetic groups, matched non-diabetic groups were served as control. We found substantially impaired red blood cell deformability in those with normal renal function (group I) compared to non-diabetic control (P = 0.0005). As renal function decreases, an increased impairment in RBC deformability was found. Diabetic patients with chronic renal failure (group II) when compared to non-diabetic controls (CRF) had an apparently greater impairment in RBC deformability (P = 0.07). The non-diabetic cohort (CRF), on the other hand, manifested significant impairment in red blood cell deformability compared to healthy control (P = 0.0001). The newly developed slit ektacytometer can measure the RBC deformability with ease and accuracy. In addition, progressive impairment in cell deformability is associated with renal function loss in all patients regardless of the presence or absence of diabetes. In diabetic patients, early impairment in RBC deformability appears in patients with normal renal function.

Infiltration of medications during infusion therapy results in complications ranging from erythema and pain to tissue necrosis requiring amputation. Infiltration occurs from improper insertion of the cannula, separation of the cannula from the vein, penetration of the vein by the cannula during movement, and response of the vein to the medication. At present, visual inspection by the clinical staff is the primary means for detecting intravenous (IV) infiltration. An optical sensor was developed to monitor the needle insertion site for signs of IV infiltration. Initial studies on simulated and induced infiltrations on a swine model validated the feasibility of the methodology. The presence of IV infiltration was confirmed by visual inspection of the infusion site and/or absence of blood return in the IV line. Potential sources of error due to illumination changes, motion artifacts, and edema were also investigated. A comparison of the performance of the optical device and blinded expert observers showed that the optical sensor has higher sensitivity and specificity, and shorter detection time than the expert observers. An improved model of the infiltration monitoring device was developed and evaluated in a clinical study on induced infiltrations of healthy adult volunteers. The performance of the device was compared with the observation of a blinded expert observer. The results show that the rates of detection of infiltrations are 98% and 82% for the optical sensor and the observer, respectively. The sensitivity and specificity of the optical sensor are 0.97 and 0.98, respectively.

A fluorescence spectroscopy system combining depth- and time-resolved measurements is developed to investigate the layered fluorescence temporal characteristics of epithelial tissue. It is found that esophageal tissue structure can be resolved well by means of the autofluorescence time-resolved decay process with 375-, 405- and 435- nm excitation. The decay of the autofluorescence signals can be accurately fitted with a dual-exponential function consisting of a short lifetime (0.4 ~ 0.6 ns) and a long lifetime (3 ~ 4 ns) components. The short lifetime component dominates the decay of normal epithelial fluorescence while the decay of the signals from keratinized epithelium and stroma are mainly determined by the long lifetime component. The ratio of the amplitudes of two components provides the information of fine structure of epithelial tissue. This study demonstrates that the combined depth- and time-resolved measurements can potentially provide accurate information for the diagnosis of tissue pathology.