[show abstract][hide abstract] ABSTRACT: We describe a novel microscopy technique for quantitative phase-contrast imaging of a transparent specimen. The technique is based on depth-resolved phase information provided by common path spectral-domain optical coherence tomography and can measure minute phase variations caused by changes in refractive index and thickness inside the specimen. We demonstrate subnanometer level path-length sensitivity and present images obtained on reflection from a known phase object and human epithelial cheek cells.
[show abstract][hide abstract] ABSTRACT: Accurate evaluation of the depth of injury in burn victims is of considerable practical value to the surgeon, both for initial determination of resuscitation fluid requirements, and in deciding whether excision and closure of the wound is necessary. Currently, burn depth is most accurately evaluated by visual inspection, though decisions concerning treatment may not be possible for a number of days post-injury. As part of our ongoing efforts to provide an objective, quantitative method for burn depth determination, we present here the results of a study using polarization-sensitive optical coherence tomography (PS-OCT) to detect and measure thermally induced changes in collagen birefringence in skin excised from burn patients. We find that PS-OCT is capable of imaging and quantifying significantly reduced birefringence in burned human skin.
[show abstract][hide abstract] ABSTRACT: We present phase resolved digital signal processing techniques for Optical Coherence Tomography to correct for the non Gaussian shape of source spectra and for Group Delay Dispersion (GDD). A broadband source centered at 820 nm was synthesized by combining the spectra of two superluminescent diodes to improve axial image resolution in an optical coherence tomography (OCT) system. Spectral shaping was used to reduce the side lobes (ringing) in the axial point spread function due to the non-Gaussian shape of the spectra. Images of onion cells taken with each individual source and the combined sources, respectively, show the improved resolution and quality enhancement in a turbid biological sample. An OCT system operating at 1310 nm was used to demonstrate that the broadening effect of group delay dispersion (GDD) on the coherence function could be eliminated completely by introducing a quadratic phase shift in the Fourier domain of the interferometric signal. The technique is demonstrated by images of human skin grafts with group delay dispersion mismatch between sample and reference arm before and after digital processing.
[show abstract][hide abstract] ABSTRACT: Glaucoma causes irreversible damage to nerves in the retinal nerve fiber layer. A technique that could measure both the condition and thickness of the retinal nerve fiber layer (RNFL) would be very useful for the early detection and treatment of glaucoma. Polarization Sensitive Optical Coherence Tomography (PS-OCT) is a modality that measures the depth resolved optical birefringence of biological tissue. Since damage to the nerve fiber layer could decrease its birefringence, PS-OCT has the potential to enhance specificity in determining RNFL thickness and integrity in OCT images. In order to measure the RNFL birefringence on humans in vivo, a fiber-based PS-OCT set-up was built with which quasi real time images of the human retina were made. Preliminary measurements on a healthy retina show that the birefringence of the RNFL around the optic nerve head was equal to 34+/- 3 degree(s)/100 micrometers . In conclusion, to our knowledge, we present the first depth resolved birefringence measurements of the human RNFL in vivo.
[show abstract][hide abstract] ABSTRACT: Optical coherence tomography (OCT) was used to obtain cross sectional images of the internal structure of the cochlea in guinea pigs following sacrifice. The 1310 nm source (bandwidth (lambda) equals75 nm) allowed a penetration depth of approximately 1.5 mm. Cross-sectional images (1.87 x 2.00 mm, 10 x 10 micrometers /pixel) were acquired at a frame rate of 1 Hz. Access to the middle ear space was obtained by removing the mastoid bulla. Imaging was performed in situ and also in ex vivo temporal bones. The scala vestibuli, scala media, scala tympani, modiolus and all four and a half turns of the cochlea were identified. These images demonstrate the potential value of OCT for use in determining the internal structures of the cochlea with near-microscopic resolution and at near-real time frame rates.
[show abstract][hide abstract] ABSTRACT: Burn depth determination is a critical factor in the treatment of thermal injury. We have developed a technique, polarization sensitive optical coherence tomography (PS- OCT), to assess burn depth non-invasively. Thermal injury denatures collagen in human skin. PS-OCT is able to measure the resulting reduction in collagen birefringence using depth resolved changes in the polarization of light propagated and reflected from the sample. In a previous study, we used a free space PS-OCT system at 850 nm to image in vivo the skin of rats burned for various amounts of time. Using a high-speed system at 1.3 micrometers has the advantages of greater depth penetration and reduction of motion artifacts due to breathing and small movements of the animal. Stokes vectors were calculated for each point in the scans and the relative birefringence was determined using different incident polarization states. Birefringence was correlated with actual burn depth determined by histological analysis. Our results show a marked difference between normal tissue and even the slightest burn, and a consistent trend for various degrees of burns.
[show abstract][hide abstract] ABSTRACT: In optical coherence tomography (OCT), mapping the polarization state of
the reflected light provides additional information about tissue
structure and prevents polarization induced image artifacts. As OCT is
increasingly used with subjects in vivo, demands on the imaging system
and data acquisition rates increase. We present a fiber- based, rapid
scanning, polarization-sensitive OCT system capable of acquiring image
data at the rate of 20K pixel/s. To achieve high scan rates, a
rapid-scanning optical delay line generates a reference arm group delay
while a waveguide-based phase modulator generates a suitable, stable
carrier frequency for the detection electronics. Group delays up to 4.5
mm are obtained at frequencies approaching 1 kHz. The group delay and
carrier frequency are independently controllable, which has the
advantage that either the lateral or the axial scan direction may be
chosen as the fast axis. Tomographic images corresponding to the
intensity and polarization components of the Stokes vector describing
the back scattered light are obtained by analyzing the interference
signals from two orthogonally polarized channels in the detection arm
for each of four polarization states incident on the sample.
Polarization images of human skin taken in vivo are shown.
[show abstract][hide abstract] ABSTRACT: Optical coherence tomography (OCT) was used to image the internal structure of a rat cochlea. Immediately following sacrifice, the temporal bone of a SPrague-Dawley rat was harvested. Axial OCT cross sectional images were obtained with a spatial resolution of 10-15 micrometers . The osseous borders of the lateral membranous labyrinth overlying the cochlea and the scala vestibuli, media, and tympani which were well demarcated by the modiolus, Reissner's and the basilar membranes were clearly identified. OCT can be used to image internal structures in the cochlea without violating the osseous labyrinth, and may potentially be used to diagnose inner ear pathology in vivo in both animal and human subjects.