Parallel frequency-domain optical coherence tomography scatter-mode imaging of the hamster cheek pouch using a thermal light source.

We use a parallel frequency-domain optical coherence tomography (FDOCT) system to generate a scatter-mode image of the hamster cheek pouch epithelium. To our knowledge, this is the first optical coherence tomography (OCT) image of a biological sample obtained using a thermal light source in the frequency domain. The system employs an imaging spectrometer to acquire depth-resolved profiles from adjacent spatial points without the need for any scanning. To enable this imaging modality, we have considered that signals originating from multiple depths combine in a different manner in FDOCT compared to time-domain optical coherence tomography (TDOCT). Because a multicomponent FDOCT signal is a coherent sum, it is necessary to limit the number of modes that contribute to the detected signal. Conversely, multicomponent TDOCT signals can be represented as incoherent sums, where increasing the number of modes improves the signal.

Instrumentation for multi-modal spectroscopic diagnosis of epithelial dysplasia.

Reflectance and fluorescence spectroscopies have shown great promise for early detection of epithelial dysplasia. We have developed a clinical reflectance spectrofluorimeter for multimodal spectroscopic diagnosis of epithelial dysplasia. This clinical instrument, the FastEEM, collects white light reflectance and fluorescence excitation-emission matrices (EEM's) within a fraction of a second. In this paper we describe the FastEEM instrumentation, designed for collection of multi-modal spectroscopic data. We illustrate its performance using tissue phantoms with well defined optical properties and biochemicals of known fluorescence properties. In addition, we discuss our plans to develop a system that combines a multi-spectral imaging device for wide area surveillance with this contact probe device.

Path-length-resolved dynamic light scattering: modeling the transition from single to diffusive scattering.

Dynamic light-scattering spectroscopy is used to study Brownian motion within highly scattering samples. The fluctuations of the light field that is backscattered by a suspension of polystyrene microspheres are measured as power spectra by use of low-coherence interferometry to obtain path-length resolution. The data are modeled as the sum of contributions to the detected light weighted by a Poisson probability for the number of events that each component has experienced. By analyzing the broadening of the power spectra as a function of the path length for various sizes of particles, we determine the contribution of multiple scattering to the detected signal as a function of scattering anisotropy.

Measurement of the anomalous phase velocity of ballistic light in a random medium by use of a novel interferometer.

Ballistic light, i.e., radiation that propagates undeflected through a turbid medium, undergoes a small change in phase velocity and exhibits unusual dispersion because of its wave nature. We use a novel highly sensitive differential phase optical interferometer to study these previously unmeasurable phenomena. We find that ballistic propagation can be classified into three regimes based on the wavelength-to-size ratio. In the regime in which the scatterer size is comparable with the wavelength, there is an anomalous phase-velocity increase as a result of adding scatterers of higher refractive index. We also observe an anomaly in the relative phase velocity, where red light is slowed more than blue light even though the added scatterers are made of material with normal dispersion.

Measurement of angular distributions by use of low-coherence interferometry for light-scattering spectroscopy.

We present a novel interferometer for measuring angular distributions of backscattered light. The new system exploits a low-coherence source in a modified Michelson interferometer to provide depth resolution, as in optical coherence tomography, but includes an imaging system that permits the angle of the reference field to be varied in the detector plane by simple translation of an optical element. We employ this system to examine the angular distribution of light scattered by polystyrene microspheres. The measured data indicate that size information can be recovered from angular-scattering distributions and that the coherence length of the source influences the applicability of Mie theory.

Phase-dispersion optical tomography.

We report on phase-dispersion optical tomography, a new imaging technique based on phase measurements using low-coherence interferometry. The technique simultaneously probes the target with fundamental and second-harmonic light and interferometrically measures the relative phase shift of the backscattered light fields. This phase change can arise either from reflection at an interface within a sample or from bulk refraction. We show that this highly sensitive (~5 degrees ) phase technique can complement optical coherence tomography, which measures electric field amplitude, by revealing otherwise undetectable dispersive variations in the sample.

Phase-referenced interferometer with subwavelength and subhertz sensitivity applied to the study of cell membrane dynamics.

We report a highly sensitive means of measuring cellular dynamics with a novel interferometer that can measure motional phase changes. The system is based on a modified Michelson interferometer with a composite laser beam of 1550-nm low-coherence light and 775-nm CW light. The sample is prepared on a coverslip that is highly reflective at 775 nm. By referencing the heterodyne phase of the 1550-nm light reflected from the sample to that of the 775-nm light reflected from the coverslip, small motions in the sample are detected, and motional artifacts from vibrations in the interferometer are completely eliminated. We demonstrate that the system is sensitive to motions as small as 3.6 nm and velocities as small as 1 nm/s. Using the instrument, we study transient volume changes of a few (approximately three) cells in a monolayer immersed in weakly hypotonic and hypertonic solutions.

Time-resolved phase-space distributions for light backscattered from a disordered medium.

We demonstrate time-resolved measurement of optical phase-space distributions as a new probe for investigating the propagation of light in disordered media. Phase-space techniques measure the joint transverse position and momentum distribution of the scattered light, and are sensitive to the spatially varying phase and amplitude of the field. Using this method we investigate light backscattered from a random medium. The measurements indicate that the weakly localized component is a phase conjugate of the incident light field. A new model of backscatter, based on Wigner phase-space distributions, elucidates the spatial and angular behavior of the localized and unlocalized components.

Feasibility of field-based light scattering spectroscopy.

Light scattering spectroscopy (LSS) is a new technique capable of accurately measuring the features of nuclei and other cellular organelles in situ. We present the considerations required to implement and interpret field-based detection in LSS, where the scattered electric field is detected interferometrically, and demonstrate that the technique is experimentally feasible. A theoretical formalism for modeling field-based LSS signals based on Mie scattering is presented. Phase-front uniformity is shown to play an important and novel role. Results of heterodyne experiments with polystyrene microspheres that localize LSS signals to a region about 30 microns in axial extent are reported. In addition, differences between field-based LSS and the earlier intensity-based LSS are discussed.

Interferometric phase-dispersion microscopy.

We describe a new scanning microscopy technique, phase-dispersion microscopy (PDM). The technique is based on measuring the phase difference between the fundamental and the second-harmonic light in a novel interferometer. PDM is highly sensitive to subtle refractive-index differences that are due to dispersion (differential optical path sensitivity, 5 nm). We apply PDM to measure minute amounts of DNA in solution and to study biological tissue sections. We demonstrate that PDM performs better than conventional phase-contrast microscopy in imaging dispersive and weakly scattering samples.

Optical phase-space distributions for low-coherence light.

Using a novel heterodyne technique, we measure optical phase-space distributions in momentum and position for low-coherence light. Quantitative information is obtained simultaneously about the longitudinal and the transverse coherence properties as well as the wave-front curvature of the light field. This method can be used to monitor these optical parameters directly for signal fields scattered from samples of interest, for tomographic imaging.

Heterodyne measurement of Wigner distributions for classical optical fields.

We demonstrate a two-window heterodyne method for measuring the x-p cross correlation, ??(*)(x)? (p)?, of an optical field ? for transverse position x and transverse momentum p. This scheme permits independent control of the x and p resolution. A simple linear transform of the x-p correlation function yields the Wigner phase-space distribution. This technique is useful for both coherent and low-coherence light sources and may permit new biological imaging techniques based on transverse coherence measurement with time gating. We point out an interesting analogy between x-p correlation measurements for classical-wave and quantum fields.

Characterizing the Coherence of Broadband Sources using Optical Phase Space Contours.

Advances in optical coherence tomography (OCT) rely on the availability of broadband light that is spatially coherent. We present a technique to characterize coherence properties of broadband light using optical phase-space contours in transverse momentum and position. We demonstrate that these contour plots can be directly measured by a simple heterodyne imaging scheme possessing high dynamic range (130 dB) and 0.1 fW sensitivity (for mW input beams). These phase space distributions are shown to yield quantitative information on the longitudinal and transverse coherence and the wavefront curvature of the light beam. We apply this technique to characterize the light emitted by a novel high-power extended-bandwidth superluminescent diode (SLD) recently developed at the David Sarnoff Research Center. Its performance is compared to that of standard commercially available SLDs. © 1999 Society of Photo-Optical Instrumentation Engineers.

Measurement of smoothed Wigner phase-space distributions for small-angle scattering in a turbid medium.

We study Wigner phase-space distributions W (x, p) in position (x) and momentum (p) for light undergoing multiple small-angle scattering in a turbid medium. Smoothed Wigner phase-space distributions are measured by using a heterodyne technique that achieves position and momentum resolution determined by the width and the diffraction angle of the local oscillator beam. The sample consists of 5.7-micron-radius polystyrene spheres suspended in a water-glycerol mixture. The momentum distribution of the transmitted light is found to contain a ballistic peak, a narrow diffractive pedestal, and a broad background. The narrow diffractive pedestal is found to decay more slowly than the ballistic peak as the concentration of scatterers is increased. The data are in excellent agreement with a simple theoretical model that explains the behavior of the narrow pedestal by including multiple diffractive scattering and treating large-angle scattering as a loss.

Optical heterodyne imaging and Wigner phase space distributions.

We demonstrate that optical heterodyne imaging directly measures smoothed Wigner phase space distributions. This method may be broadly applicable to fundamental studies of light propagation and tomographic imaging. Basic physical properties of Wigner distributions are illustrated by experimental measurements.

Two unusual presentations of müllerian adenosarcoma: case reports, literature review, and treatment considerations.

Müllerian adenosarcomas of the uterus usually present as pedunculated endometrial masses in postmenopausal women with vaginal bleeding. Extraendometrial variants (originating in the ovary, adnexa, or myometrium) are much less common, and they tend to present at a more advanced stage due to their location. The sarcomatous portion of müllerian adenosarcoma can vary from low grade to very high grade and the clinical behavior of the tumors can be indolent or aggressive. We present two cases, one of which originated in the adnexa and the other in an apparent focus of uterine adenomyosis. These cases illustrate the difficulty of correct diagnosis and treatment.

Retrospective study of tapered, smooth post systems in place for 10 years or more.

A total of 211 consecutive patients of a restorative dentist who received full-mouth radiographs between October 1988 and March 1989 were screened for teeth treated endodontically at least 10 years earlier. In all, 51 patients had 138 teeth treated and restored by the authors. All involved teeth were restored with tapered smooth posts, cores with complete or 7/8 cast ferrules, and an onlay or cast precious metal crown (with or without veneering). No posts, splints, or bridges were loose, and only one crown was loose. There were nine failures in 138 teeth (6.5%)--three restorative, two endodontic, two root fractures, and two periodontal. When tapered smooth posts are used properly, retentive problems do not occur.

Cancer patient accessions into clinical trials: a pilot investigation into some patient and physician determinants of entry.

This study investigated the external validity (or generalizability of results) of randomized clinical trials in cancer. Tao ECOG lung cancer chemotherapy protocols active in the early 1970s were studied using a case-control design. All lung cancer patients of the four specified cell types resident in Monroe County during the ECOG study period were identified from the Rochester Regional Tumor Registry. All of the patients entered into either protocol ("ECOG cases") and a random sample of the nonprotocol cases were examined by medical records review. Thirty-seven percent of the nonprotocol cases were determined to have been eligible for either of the two ECOG protocols, but not entered ("eligible controls"). A comparison of the ECOG cases (n = 65) and the eligible controls (n = 109) revealed that (1) ECOG cases were more likely than eligible controls to have been diagnosed at a hospital which participated in the University of Rochester Cancer Center's medical oncology program; (2) ECOG cases were of higher occupational status than eligible controls; (3) duration from diagnosis to protocol entry for ECOG cases was longer than duration from diagnosis to earliest date of eligibility for eligible controls. The implications of these findings for the conduct of cancer clinical trials are discussed.