It is a well established fact that detection of multiply scattered light causes image quality degradation in optical microscopy. In this study experimental and computational methods were employed to examine the effect of multiply scattered light detection on the image contrast, resolution and image penetration depth of optical coherence microscopy (OCM) in turbid media. Dynamic low coherence interferometry (DLCI), a method sensitive to changes in the photon momentum transfer resulting from scattering, was used to study the OCM background light rejection ability in homogeneous turbid media and to determine the optical depths at which single scattered, multiply scattered and diffuse light constitute the dominant components of the measured intensity. OCM resolution measurements performed at various optical depths in scattering media revealed correlation between loss of OCM spatial resolution and spectrum linewidth broadening (DLCI) resulting from detection of multiply scattered light. The data from the resolution measurements was used to determine the dependence of image contrast, resolution and penetration depth on the optical properties of the turbid background and the instrument imaging geometry. In addition, a Monte Carlo model was designed to examine the contribution of background light (light that does not carry any information about the imaged object and multiply scattered while traversing the turbid layer above) to loss of OCM image quality. The results from this study contribute to our understanding of the practical limits to OCM imaging in turbid media.

We report results on the problem of OCT spatial resolution degradation with depth due to tissue scattering of super- broadband probing light. Analytical and numerical theoretical models of the OCT signal are discussed. Experiments were also carried out with turbid phantoms. Results suggest that OCT spatial resolution degrades rather fast and comes to an asymptotic form at the depth of few photon scattering lengths independently of the initial coherence duration of the OCT source of light. In certain cases it imposes a burden for the application of super broadband sources of the probing light.

An OCT system is built around a confocal optical receiver by adding a reference beam to the beam returned from the target tissue to the photodetector. The amount of light collected by the OCT receiver (both signal and background signal) depends on the parameters of the confocal receiver. We are interested in a configuration that allows the simultaneous display of the confocal signal and the OCT signal, which requires a separate confocal channel in the system. In this case, the S/N performance is different in the two channels and depends on the optical configuration used. The paper discusses the noise sources in the two channels. S/N ratios are numerically evaluated for cases of experimental interest. As far as the penetration depth in OCT is concerned, a value of 20 optical depths was considered achievable in previous reports if only the shot noise was considered. We correct this value by taking into account the excess photon noise and the limitations imposed by the safety power limits. Multiple scattering determines an increase in noise via the excess photon noise term.

Coherent sidelobes of a source can severely degrade OCT image quality by introducing false targets if no targets are present at the sidelobe locations. Sidelobes can also add constructively or destructively to the targets that are present at the sidelobe locations. This constructive or destructive interference will result in cancellation of the true targets or display of incorrect echo amplitudes of the targets. We introduce the use of CLEAN, a nonlinear deconvolution algorithm, to cancel coherent sidelobes in OCT images of extracted human teeth. The results show that CLEAN can reduce the coherent artifacts to the noise background, sharpen the air-enamel and enamel-dentin interfaces and improve the image contrast.

A modified Michelson interferometer is used to measure path- length resolved angular distributions of light backscattered by turbid media. The path length resolution is obtained by exploiting the coherence properties of a broadband source. The angular distribution is mapped out using a simple optical system to scan the angle at which the reference field intersects the detector plane. Angular scattering distributions can be compared to Mie theory to determine the size and refractive index of spherical scatterers. Initial studies utilizing this system demonstrate the potential of low coherence interferometry for obtaining structural information using angular distributions.

We developed a novel optical coherence tomographic (OCT) system which utilized broadband continuum generation for high axial resolution and a high numeric-aperture (N.A.) Objective for high lateral resolution (<5 micrometers ). The optimal focusing point was dynamically compensated during axial scanning so that it can be kept at the same position as the point that has an equal optical path length as that in the reference arm. This gives us uniform focusing size (<5 mum) at different depths. A new self-adaptive fast Fourier transform (FFT) algorithm was developed to digitally demodulate the interference fringes. The system employed a four-channel detector array for speckle reduction that significantly improved the image's signal-to-noise ratio.

We demonstrate ultrahigh resolution optical coherence tomography using the continuum generation in an air-silica microstructure fiber. A broadband OCT system was developed, supporting a bandwidth of 370 nm at 1.3 micrometers center wavelength. We achieved longitudinal resolutions of 2.5 micrometers in air, or ~2 micrometers in tissue. This is to our knowledge with the highest longitudinal OCT resolution demonstrated at this wavelength range and the first application of this new light source for OCT. We will also describe the application of this technique for imaging biological tissue in vivo.

Many biological objects have a poor contrast in microscopy when they are imaged on the basis of the intensity of transmitted and reflected light. For pure phase objects the differential phase contrast technique increases the contrast of the images. We combined the differential phase contrast technique with optical coherence tomography. Our setup is based on a Michelson interferometer with a polarization sensitive detection unit. We scan the sample with two orthogonally polarized beams, which are separated by a distance of 17.5 micrometers . The full interferometric signal of each object beam is recorded by a separate detector. We calculate the phase functions of the interferometric signal through analytic continuation by use of the Hilbert transformation. Subtracting the two phase functions we get the phase difference between the object beams. Now we can derive the path length difference of the object beams at a certain depth in the object where the light was backscattered. The method is independent of variations in the backscattering coefficient, which was a problem in an earlier version of our setup. To investigate the performance of the technique we measured pure phase objects in the nm range. Differential phase measurements through scattering test samples quantified the influence of scattering on the phase measurement. First images of cell structures are presented.

Optical coherence tomography (OCT) is an emerging technology capable of imaging tissue architectural morphology at micron scale resolution . OCT was first developed to image the relatively transparent suctures in the eye 2,3 and later applied extensively in highly scattering tissues for moiphologic and functional imaging with unprecedented resolution 48 Real-time, in vivo imaging and ultrahigh (1 tm) resolution imaging have also been demonstrated. A variety of applications of OCT imaging have been made possible by designing novel OCT delivery/collection probes. Examples include a forward imaging hand-held probe for assessing tissue during open field surgery 11,12 and a transverse scanning OCT endoscope/catheter for imaging hollow organs such as the gastrointestinal tract and cardiovascular system 1318 oT applications have been limited to the surfaces or lumina of organ systems because the penetration depth of OCT is 2-3 mm and also because high transverse resolution is only achievable within a short confocal length. To date, it has not been possible to image structures inside solid tissues or organs. However, there are many clinical scenarios where high resolution internal imaging of solid tissues is required. One such application of OCT is to image pathology and guide biopsy in solid tissues. Other applications include optical imaging where excisional biopsy is hazardous, and surgical guidance such as in cryosurgery or interstitial photodvnmic therapy.

We describe our phase-sensitive interferometry technique implemented as phase dispersion microscopy (PDM)/optical tomography (PDOT). The technique is based on measuring the phase difference between fundamental and second harmonic low coherence light in a novel interferometer. We attain high sensitivity to subtle refractive index differences due to dispersion with a differential optical path sensitivity of 5 nm. Using PDM, we show that ballistic light in a turbid medium undergoes a phase velocity change that is dependent on scatterer size. We demonstrate that the microscopy technique performs better than a conventional phase contrast microscope in imaging dispersive and weakly scattering samples. The tomographic implementation of the technique (PDOT) can complement Optical Coherence Tomography (OCT) by providing phase information about the scanned object.

We demonstrate a wavelength multiplexed low coherence interferometer that detects and demodulates four subbands of the source spectrum in parallel. By introducing dispersion into one of the interferometer arms we obtain a wavelength dependent measurement depth in the object. We analyze the influence of the dispersion on the signals and demonstrate simultaneous Doppler measurements of dynamic flow at three different positions within a tube. The method can be used to remove false Doppler signals caused by an unsteady object and therefore has potential in blood flow monitoring.

Very recently, we proposed and demonstrated a novel optical reflection tomography along the geometrical thickness, reflecting a real cross-sectional structure of an object. This technique is based on simultaneous measurement of refractive index n and thickness t of a sample using the combination of a low coherence interferometer and confocal optics. The interferometer provides optical coherence tomography (OCT) of the dimension of the optical thickness (=n x t) along the optical axis, while the confocal optics gives us another type of reflection tomography, having the thickness dimension of nearly t/n along the optical axis. This tomography can be called confocal reflection tomography (CRT) and has not yet been demonstrated, to our knowledge. Simple image processing of OCT and CRT results in desired reflection tomographic image, showing 2D refractive index distribution along the geometrical thickness. In this paper, we present the validity of our proposed method using the concave glass plate as well as the application for in vivo measurement of biological tissue.

Quantitative phase measurements by optical coherence tomography and low coherence interferometry are restricted by the well known 2(pi) ambiguity to path length differences smaller than +/- (lambda) /2. We present a method that can overcome this ambiguity. We introduce a slight imbalance of dispersive material between the reference and sample arms of the interferometer. Thereby, short and long wavelengths of the source spectrum are separated within the signature of the interferometric signal. This causes a varying phase slope within the signal. To measure phase differences between two adjacent beams traversing a sample, the total interferometric signal of the two beams is recorded. The phase difference is calculated by subtracting the phase values obtained for both recorded signals. Without dispersive effects, the phase difference is constant across the coherence envelope. With the dispersive effect, the phase difference varies (because of the varying phase slopes) as a function of position within the interferometric signal. The slope of the phase difference between the two signals is proportional to the optical path difference, without 2(pi) ambiguity.

We demonstrate a low cost, high-speed scanning delay line using a Herriott cell cavity and electromagnetic actuation. Path length scanning at 2 kHz repetition rate is demonstrated for real time OCT imaging.

The concept of refractive index matching used for the enhancement of optical penetration depth of the whole blood is discussed on the basis of in vitro studies using optical coherence tomography technique. It was found that blood optical clearing is defined not only by refractive index matching effect, but also by changes of RBC size and their aggregation ability when chemicals are added. Chemical agents studied include glycerol, propylene glycol, trazograph, and dextrans. For the hyperosmotic agents, the application of 6.5% glycerol into twice diluted blood reduces the total attenuation coefficient from 4.2/mm to 2.0/mm, and correspondingly increases the optical penetration at 820 nm up to 117%. Similar effects of increase in transmittance and decrease in light scattering are also demonstrated by various molecular detrans with the light penetration enhancement within a range between 52.1% and 150.5%. We also demonstrate that the use of biocompatible agents could enhance in-depth imaging of the human esophagus and stomach tissues.

We demonstrate the use of phase-shifting interferometry in OCT to determine the optical phase and fringe visibility within the coherence envelope. Phase-shifting algorithms provide both the optical phase and visibility from a series of intensity measurements corresponding to controlled phase shifts. In addition to providing phase information which supplements the visibility or envelope data which is traditionally obtained in OCT, this technique will provide an independent, highly sensitive measurement of the coherence envelope which may be used for a precise determination of the source power spectrum.

The spatial resolution of the retinal images cannot approach a diffraction limit due to the high-order aberrations of the human eye. We present a technique, which allows restoring fine details on the retinal images using information about OTF (optical transfer function) of the eye obtained by the Shack-Hartman wavefront sensor. The precision of wavefront measurements greatly enhanced by reference source scanning on the retina. A closed loop adaptive system based on the bimorph mirror suppresses low-order aberrations. The residual errors are removed by the image deconvolution. The finite depth of retina layers of the human eye significantly reduce resolution of color retinal images as far as it introduces additional defocusing depending on the wave- length of the reflecting light. We present a novel technique of color retinal image deconvolution. The key feature of the algorithm is in use of information on retina structure. This permits calculating of optical transfer functions for each of the retina layers. Significant improvement of image quality was obtained. The processing time was about a few dozens of seconds for contemporary PC computers and image size 2000*2000 pixels.

We present optical coherence quantitation technique to monitor the redox state of mitochondria enzyme Cytochrome oxidase (CytOx) in bone tissue by the use of optical coherence tomography (OCT) system. Superluminescent diode (SLD) with its peak emission wavelength ((lambda) = 820nm) on the absorption band of oxidized form of CytOx was used in the experiments. The reflectance returning from the liquid phantoms (naphthol green B with intralipid) and bone tissue specimens (periosteum of calvaria from newborn rats) as a function of penetration depth was used to quantify the absorption changes of the sample. Absorption coefficients of naphthol green B were accurately quantified by the linear relationship between attenuation coefficients from the slopes of the reflected signals and naphthol green B concentration. The results show that the attenuation coefficient decreases in periosteums as CytOx is reduced by sodium dithionite, demonstrating the feasibility of this method to quantify the redox state of tissues studied. A 70% +/- 7% (n=4) reduction of attenuation coefficients in periosteums was clearly observed with redox change of CytOx after 5 min reduction. In addition, the results demonstrate that the OCT system is also capable of imaging the calvaria tomographically with a resolution at 9 microns, which could only be previously obtained by the conventional excisional biopsy.

During the last years Optical Coherence Tomography could proof its value as a precise and non-invasive tool for providing morphologic information about biological tissue. Nevertheless there is also a demand for obtaining functional tissue parameters like for instance oxygen saturation of blood. Such information can be accessed by spectroscopic tissue analysis. It is shown how Fourier Domain Optical Coherence Tomography (FDOCT) can serve as a tool for the assessment of spectroscopic object properties. In order to show the feasibility of this method, absorption measurements of a RG830 filter glass plate and of a dye in a glass cuvette are presented.

The feasibility of Optical Coherence Tomography to determine the oxygenation of whole blood was investigated on porcine blood samples. Our experimental data show a sensitivity in the OCT spectral content to changes in oxygenation that qualitatively correspond to expectations based on the absorption spectra of oxidized and reduced hemoglobin, using a broadband source operating at the isobestic wavelength of 800 nm.

Besides morphological images created by optical coherence tomography (OCT), another inherent physical parameter is evaluated in skin tissue under in vivo conditions. Refractive indices may support tissue characterization for research and diagnostic purposes in cosmetics/pharmacy and medicine, respectively. To accomplish refractive index evaluation, the sample arm of our OCT setup has been arranged to minimize mechanical adjustment and yet accommodate a wide parameter range at the entire penetration depth of up to 1 mm. A simple algorithm for local mapping has been derived. Refractive index maps have been measured locally in skin of stratum corneum, epidermis and upper parts of the dermis. Dry and moist skin areas have been observed by refractive index evaluation.

We have developed a fiber-based polarization-sensitive optical coherence tomography (PS-OCT) system using non- polarization-maintaining fiber and a single detector, in which the polarization-sensitive components are implemented entirely in bulk optics in the sample arm.

In this paper a few speckle techniques is discussed from the point of view of their application for medical diagnosis in dermatology and ophthalmology using monitoring of tissue structure and blood microcirculation. The basic principles of proposed techniques and corresponding hard and software descriptions are presented. Results of model (tissue phantoms), in vitro and in vivo measurements for the human eye tissues and skin are discussed.

Color Doppler optical coherence tomography (CDOCT) is a method for noninvasive cross-sectional imaging of blood flow in vivo. In previous implementations, velocity estimates were obtained by measuring the frequency shift of discrete depth-resolved backscatter spectra, resulting in a velocity resolution on the order of 1 mm/s. We present a novel processing method that detects Doppler shifts calculated across sequential axial scans, enabling ultrahigh velocity resolution (~1 micron/s) flow measurement in scattering media. This method of sequential scan processing was calibrated with a moving mirror mounted on a precision motorized translator. Latex microspheres suspended in deuterium oxide were used as a highly scattering test phantom. Laminar flow profiles down to ~15 micron/s centerline velocity (0.02 cc/hr) were observed with a sensitivity of 1.2 micron/s. Finally, vessels on the order of 10 microns in diameter were imaged in living human skin, with a relative frequency sensitivity less than 4 x 10^-5. To our knowledge, these results are the lowest velocities ever measured with CDOCT.

Apoptosis is the effector of regulated cell death and plays a role in many physiologic and pathologic processes. It is characterized by a highly regulated condensation and fragmentation of the cell nucleus, a large scatterer, and breakup of the entire cell into vesicles, (apoptotic bodies) containing cell organelles and fragments of the nucleus. A two-fold increase in attenuation coefficient ((mu) ) is observed in cell culture after chemical induction of apoptosis. An identical increase in scattering is observed in a tissue culture of porcine carotid artery, in which apoptosis is induced by balloon dilation. These observations are theoretically supported by calculations based on MIE theory. The preliminary results of this study indicate that the apoptotic process may be detected using OCT due to an increase in scattering by the typical disintegration of cellular material. The described increase in scattering may also be detected by other optical techniques.

Many studies have been performed which compare ex-vivo OCT imaging to histopathology in a wide range of tissues and organ systems. While some tissues, such as arterial pathology or cartilage, are relatively stable post mortem, others, such as epithelial tissues, exhibit rapid degradation. It is important to preserve these tissues with minimal changes in morphology relative to their in vivo state in order to enable meaningful ex vivo OCT imaging studies. In this paper, we investigate the differences between in vivo and ex vivo OCT imaging and the effect of different tissue preservation solutions on tissue degradation and image quality. Ultrahigh resolution OCT imaging was preformed using a Ti:Al₂O₃ light source with 2 micrometers axial and 5 micrometers transverse resolution, using the hamster cheek pouch as a model for epithelial tissue. Tissue preservation solutions examined included: low temperature saline, room temperature saline, phosphate buffered sucrose, University of Wisconsin solution, and 10% formalin. Results of in vivo versus ex vivo ultrahigh resolution OCT imaging indicate that changes in optical properties and image degradation occur on a rapid time scale (in minutes) for all preservation solutions except formalin.

Optical-thermal models that can accurately predict temperature rise and damage in blood vessels and surrounding tissue may be used to improve the treatment of vascular disorders. Verification of these models has been hampered by the lack of time- and depth-resolved experimental data. In vitro and in vivo studies were performed to visualize laser irradiation of blood in cuvettes or cutaneous (hamster dorsal skin flap) blood vessels. Two optical coherence tomography systems, one operating at 400 a-scans per second and the other at 4-30 frames per second, were used. For the in vitro study, a frequency doubled Nd:YAG laser was used (532 nm, 10 ms pulse duration, 2 mm spot size, 10 J/cm² radiant exposure). In vivo, an Argon laser was employed (all lines, 0.1-2.0 s pulse duration, 0.1-1.0 mm spot size, 100- 400 mW power. Video microscopy images were compared to predictions of temperature rise and damage using Monte Carlo and finite difference techniques. In general, predicted damage agreed with actual blood, blood vessel, and surrounding tissue coagulation seen in images. However, limitations of current optical-thermal models were identified, such as the inability to model the dynamic changes in blood optical properties and vessel diameters that were seen in the optical coherence tomography images.

Using state of the art laser technology, third generation ophthalmologic optical coherence tomography (OCT) has been developed which enables ultrahigh resolution, non-invasive in vivo imaging of retinal morphology with an unprecedented axial resolution of 3 micrometers . This represents a quantum leap in performance over the 10-15 micrometers resolution currently available in ophthalmic OCT systems and, to our knowledge, is the highest resolution in vivo ophthalmologic imaging achieved to date. This resolution enables optical biopsy, i.e. the in vivo visualization of intraretinal architectural morphology which had previously only been possible with histopathology. Image processing and segmentation techniques are demonstrated for automatic identification and quantification of retinal morphology. Ultrahigh resolution ophthalmic OCT has the potential to enhance the sensitivity and specificity for early diagnosis of several ocular diseases, e.g. glaucoma, which requires precise imaging and measurement of retinal nerve fiber layer thickness, as well as improve monitoring of disease progression and efficacy of therapy.

Color Doppler optical coherence tomography (CDOCT), also called Optical Doppler Tomography) is a noninvasive optical imaging technique, which allows for micron-scale physiological flow mapping simultaneous with morphological OCT imaging. Current systems for real-time endoscopic optical coherence tomography (EOCT) would be enhanced by the capability to visualize sub-surface blood flow for applications in early cancer diagnosis and the management of bleeding ulcers. Unfortunately, previous implementations of CDOCT have either been sufficiently computationally expensive (employing Fourier or Hilbert transform techniques) to rule out real-time imaging of flow, or have been restricted to imaging of excessively high flow velocities when used in real time. We have developed a novel Doppler OCT signal-processing strategy capable of imaging physiological flow rates in real time. This strategy employs cross-correlation processing of sequential A-scans in an EOCT image, as opposed to autocorrelation processing as described previously. To measure Doppler shifts in the kHz range using this technique, it was necessary to stabilize the EOCT interferometer center frequency, eliminate parasitic phase noise, and to construct a digital cross correlation unit able to correlate signals of megahertz bandwidth by a fixed lag of up to a few ms. The performance of the color Doppler OCT system was demonstrated in a flow phantom, demonstrating a minimum detectable flow velocity of ~0.8 mm/s at a data acquisition rate of 8 images/second (with 480 A-scans/image) using a handheld probe. Dynamic flow as well as using it freehanded was shown. Flow was also detectable in a phantom in combination with a clinical usable endoscopic probe.

Conventional endoscopy is limited to imaging macroscopic views of tissue. The British Columbia Cancer Research Center, in collaboration with Digital Optical Imaging Corp., is developing a fiber-bundle based microendoscopy system to enable in vivo confocal imaging of cells and tissue structure through the biopsy channel of an endoscope, hypodermic needle, or catheter. The feasibility of imaging individual cells and tissue architecture will be presented using both reflectance and tissue auto-fluorescence modes of imaging. The system consists of a coherent fiber bundle, low-magnification high-NA objective lens, Digital Micromirror Device^TM(DMD), light source, and CCD camera. The novel approach is the precise control and manipulation of light flow into and out of individual optical fibers. This control is achieved by employing a DMD to illuminate and detect light from selected fibers such that only the core of each fiber is illuminated or detected. The objective of the research is to develop a low-cost, clinically viable microendoscopy system for a range of detection, diagnostic, localization and differentiation uses associated with cancer and pre-cancerous conditions. Currently, multi-wavelength reflectance confocal images with 1 micrometers lateral resolution and 1.6 micrometers axial resolution have been achieved using a 0.95 mm bundle with 30,000 fibers.

Over the past three decades extensive studies have been performed on the structural and mechanical properties of Achilles tendon trying to explain its mechanical proprieties and trying to realize more precise mathematical model trough constitutive equations. Among the various mechanical parameters, deformation-load and stress-strain curves give first mechanical parameters of interest, but also the vibrational behavior of tendon may be of interest, in particular for in-vivo applications. The present paper describes how in vitro tensile experiments can be performed, taking also into account the need to simulate physiological condition of Achilles tendon, approaching thus some opened problems in the design of the experimental set-up. A new system for measuring tendon vibrations by non-contact techniques under specific deformation-load conditions is presented. In the first step preliminary simple elongation tests are made in order to characterize the tissue extracting the mainly mechanical parameters: load-deformation and stress-strain curves. Then, an experimental vibration study is made at each tension level evaluating the free oscillations caused by a small hammer. Modification of first resonance frequency as function of load or strain is reported. The underlying idea is to establish a measurement procedure to perform the mechanical characterization of tendons by extracting parameters, as the resonance frequency, achievable also during in-vivo investigation.

In the paper lymph flow in microvessels by two methods in norm and under influence of vasoactive drugs: N-nitro-L- Arginine (L-NNA, 10^-4M and dimethyl sufoxide (DMSO, 30%) was studied. We measured absolute linear flow velocity by microscopic method and parameter proportional to velocity (M₁) using the speckle-interferometry. Also other parameters of lymph and blood microcirculation were measured. The lymph flow differs from blood flow. The average flow velocity for the lymphatics is more than for the blood microvessels. The negative correlation between blood flow velocity and diameter of vessel absents in lymphatics. The phase contractions contribute to the lymph flow. The M₁ in contracting lymphatics are of the same values in different vessels. But the non-contracting microvessels has very varying indexes of M₁. Probably the wall movements during phasic contractions led to the change of speckle signals. The action of vasoactive drugs (L-NNA and DMSO) stimulates the lymph flow and phasic activity in microvessels of rat mesentery. The effects of L-NNA and DMSO on diameters are different. The constriction of microvessels prevailed at the DMSO application. The dilatation dominated at the L-NNA action.

We report experimentally how the wavelength dependence affects the OCT imaging contrast and depth by the use of normal human and animal tissues in vitro. Two systems, using the light sources with central wavelengths at 820nm and 1310nm, respectively, were set-up and used in present work to study the light penetrating and imaging contrast dependence on wavelength. The tissue specimens used were colonic and stomach mucosa. The results confirmed that the longer wavelength suffers less scattering and absorption, thus penetrating deeper into the tissue, but pays a penalty of reduced imaging contrast. In general, both imaging depth as well as tissue contrast is determined by tissue absorption, scattering properties and the refractive indices in microscopic and macroscopic scale, which vary with wavelength. Thus, the choice of wavelengths used in the OCT system should be careful in terms of optimizing imaging depth, imaging contrast as well as differentiation between different tissue morphologies.

Two instruments are now available for high depth resolution imaging of the retina. A scanning laser ophthalmoscope is a confocal instruments which can achieve no more than 0.3 mm depth resolution. A longitudinal OCT instrument uses a superluminescent diode which determines a depth resolution better than 20 microns. There is a gap in depth resolution between the two technologies. Therefore, different OCT configurations and low coherence sources are investigated to produce a choice of depth resolutions, and to cover the gap between the old confocal technology and the new OCT imaging method. We show that an instrument with adjustable depth resolution is especially useful for the en-face OCT technology. Such an instrument can bring additional benefits to the investigation process, where different requirements must be met. For instance, a poor depth resolution is required in the process of positioning the patient's eye prior to investigation. A good depth resolution is however necessary when imaging small details inside the eye. The utility of the OCT en-face imaging with adjustable coherence length for diagnostic is illustrated by images taken from the eye of a volunteer. Images with a similar aspect to those produced by a scanning laser ophthalmoscope can now be obtained in real time using the OCT principle.

We propose a new method of photon transport to analyze the imaging properties of focused light in highly scattering media. The Monte Carlo based photon transport model is modified to a semi-complete quantum mechanical realization that incorporates probability amplitudes on the path of the unscattered photons. This approach incorporates a phase term on the propagating photons that allows a diffraction- limited analysis on the three-dimensional photon distribution. The interaction between the photons and the lens are treated in the macroscopic level where the lens is considered as a phase transformer that delays the photons by the amount proportional to the thickness of the lens at each embarkation point. When a photon deviates form its original path due to scattering, the probability amplitude of the photon is no longer considered and the intensity of scattered light is calculated similar to the method proposed by Flock. The total intensity is derived by the sum of the unscattered light and the scattered intensity. The 3D point spread functions of objective lenses that are commonly used for microscopic imaging of thick biological samples are presented. Degradation of the 3D PSF is analyzed when the focal plane is at some distance below the surface of th medium with known optical properties.

In this study, a noninvasive laser Doppler measurement method based on the self-mixing effect of a diode laser was used to measure baroreflex regulation, which is manifest in the blood pressure signal as a 0.1 Hz sinusoidal variation. The laser Doppler measurement system was used to measure the movement of the right radial artery of ten volunteers. Variation in blood pressure caused by the baroreflex affects the elastic properties of the arterial wall. When diastolic blood pressure increases, the elasticity of the arterial wall decreases, causing the wall to lose some of its movability. This decreased elasticity reveals itself in the Doppler signal such that when the blood pressure increases, the Doppler frequency decreases and vice versa. The results show, that the laser Doppler method can be used to measure baroreflex regulation. Finally, baroreflex regulation in the Doppler signal is approximately in the inverse phase with respect to variation in diastolic blood pressure.

We report further the capability of OCT to delineate the microstructures beneath the colonic tissue surface, and to discriminate the normal tissues form the diseased ones. The OCT system operating at central wavelength at 820 nm was used which has measured axial resolution of 12 microns in free space and transversal resolution at 16 microns. The tissue specimens were obtained form the patient in the theater, who diagnosed as bearing colonic cancer and underwent conventional operations in the Hospital, and imaged with the OCT within 0.5-1 hour of removal. More than 10 patients were studied. The result of this study indicates that the important clinical layers and features with depth down to 1~2.0 mm of the colonic mucosa could be clearly delineated with the OCT imaging, and their thickness correlates well with the histology. The OCT images are also able to differentiate the normal colonic mucosa from the diseased ones. In conclusion, OCT is capable of high- resolution in situ imaging of colonic microstructures, without the need for excisional biopsy.