We report the existence of polarization memory effect (PME) in optical coherence tomography and investigate its potential applications in dental imaging. We performed the study in three steps. First, microsphere scattering phantoms of different sizes were imaged in order to validate experimental results with PME theory. Both linearly and circularly polarized light were used to probe the samples. Second, healthy tooth samples were scanned and polarization memory effect was identified in dentin. In this step, specific verification and signal processing were performed to rule out possible image interpretation by birefringence effect. Third, we evaluated dentin demineralization with PME. Results show polarization memory can be useful to characterize this dynamic mineralization process for early caries detection and rehabilitation.
A fiber optical coherence tomography (OCT) probe is used for three dimensional dental imaging. The probe has a
lightweight miniaturized design with a size of a pen to facilitate clinic in vivo diagnostics. The probe is interfaced with a
swept-source / Fourier domain optical coherence tomography at 20K axial scanning rate. The tooth samples were
scanned from occlusal, buccal, lingual, mesial, and distal orientations. Three dimensional imaging covers tooth surface
area up to 10 mm x 10 mm with a depth about 5 mm, where a majority of caries affection occurs. OCT image provides
better resolution and contrast compared to gold standard dental radiography (X-ray). In particular, the technology is well
suited for occlusal caries detection. This is complementary to X-ray as occlusal caries affection is difficult to be detected
due to the X-ray projectile scan geometry. The 3D topology of occlusal surface as well as the dentin-enamel junction
(DEJ) surface inside the tooth can be visualized. The lesion area appears with much stronger back scattering signal
intensity.
We performed OCT imaging of the rat retina at 70,000 axial scans per second with ~3 μm axial resolution. Three-dimensional OCT (3D-OCT) data sets of the rat retina were acquired. The high speed and high density data sets enable improved en face visualization by reducing eye motion artifacts and improve Doppler OCT measurements. Minimal motion artifacts were visible and the OCT fundus images offer more precise registration of individual OCT images to retinal fundus features. Projection OCT fundus images show
features such as the nerve fiber layer, retinal capillary networks and choroidal vasculature. Doppler OCT images and quantitative measurements show pulsatility in retinal blood vessels. Doppler OCT provides noninvasive in vivo quantitative measurements of retinal blood flow properties and may benefit studies of diseases such as glaucoma and diabetic retinopathy. Ultrahigh speed imaging using ultrahigh resolution spectral / Fourier domain OCT promises to enable novel protocols for measuring small animal retinal
structure and retinal blood flow. This non-invasive imaging technology is a promising tool for monitoring disease progression in rat and mouse models to assess ocular disease pathogenesis and response to treatment.
Ultrahigh speed Spectral/Fourier domain ophthalmic OCT imaging at 70,000-312,500 axial scans per second is
demonstrated using a high speed CMOS camera at 800 nm. Comparative imaging results of the fovea illustrate the
performance tradeoffs between different imaging speeds and spectrometer configurations. Dense 3D volumetric
acquisitions show minimal motion artifacts when acquired at 250,000 axial scans per second. The porous structure of the
lamina cribrosa is shown in en face images extracted from a dense volumetric acquisition of the optical nerve head
acquired at 106, 382 axial scans per second. Rapid repeated volume imaging (4D-OCT) shows blood flow in retinal
capillaries. Boundaries of the capillary network are enhanced by motion contrast. 3D volumetric data acquired at 49,000
axial scans per second using an InGaAs camera at 1050 nm is compared to volumetric data acquired at 101, 010 axial
scans per second using a CMOS camera at 800nm. Averaging of adjacent cross sectional scans in the volume is shown to
increase contrast in the images and reduce speckle. The enhanced penetration of the 1050 nm compared to the 800 nm
OCT imaging system is shown. Dense 2D/3D data sets and 4D-OCT repeated volume imaging promise alternative
methods for diagnosis and monitoring of disease.
To compare the optical properties of the human retina, 3-D volumetric images of the same eye are acquired with two nearly identical optical coherence tomography (OCT) systems at center wavelengths of 845 and 1060 nm using optical frequency domain imaging (OFDI). To characterize the contrast of individual tissue layers in the retina at these two wavelengths, the 3-D volumetric data sets are carefully spatially matched. The relative scattering intensities from different layers such as the nerve fiber, photoreceptor, pigment epithelium, and choroid are measured and a quantitative comparison is presented. OCT retinal imaging at 1060 nm is found to have a significantly better depth penetration but a reduced contrast between the retinal nerve fiber, the ganglion cell, and the inner plexiform layers compared to the OCT retinal imaging at 845 nm.
Ultrahigh speed spectral / Fourier domain optical coherence tomography (OCT) imaging using a CMOS line scan camera with acquisition rates of 70,000 - 312,500 axial scans per second is investigated. Several design configurations are presented to illustrate trade-offs between acquisition speed, sensitivity, resolution and sensitivity roll-off performance. We demonstrate: extended imaging range and improved sensitivity roll-off at 70,000 axial scans per second , high speed and ultrahigh resolution imaging at 106,382 axial scans per second, and ultrahigh speed imaging at 250,000-312,500 axial scans per second. Each configuration is characterized through optical testing and the trade-offs demonstrated with in vivo imaging of the fovea and optic disk in the human retina. OCT fundus images constructed from 3D-OCT data acquired at 250,000 axial scans per second have no noticeable discontinuity of retinal features and show that there are minimal motion artifacts. The fine structures of the lamina cribrosa can be seen. Long cross sectional scans are acquired at 70,000 axial scans per second for imaging large areas of the retina, including the fovea and optic disk. Rapid repeated imaging of a small volume (4D-OCT) enables time resolved visualization of the capillary network surrounding the INL and may show individual red blood cells. The results of this study suggest that high speed CMOS cameras can achieve a significant improvement in performance for ophthalmic imaging. This promises to have a powerful impact in clinical applications by improving early diagnosis, reproducibility of measurements and enabling more sensitive assessment of disease progression or response to therapy.
KEYWORDS: Data acquisition, Sensors, Signal detection, Signal to noise ratio, Fiber couplers, Biomedical optics, Optical coherence tomography, Mirrors, Signal processing, Laser sources
Balanced detection is required to suppress relative intensity noise (RIN) in optical frequency domain imaging (OFDI). Because a 50/50 fiber coupler does not provide a 50% splitting ratio over the full sweeping wavelength, balanced detection by the coupler's differential output with a balanced receiver is not perfect. We have designed a new balancing scheme that detects two outputs of 50/50 coupler separately and corrects the spectral deviation in the digital domain. A better balanced detection scheme has been designed in this work. In stead of detecting the hardware balanced signal from the 50/50 fiber coupler, we digitize the two channel fringe signal independently and perform the signal balancing in the poset process. The new software based balancing significantly improves the RIN suppression. Afterward, a systematic noise analysis has been performed on the 1050nm OFDI system. The results demonstrate a RIN suppression of 33dB by spectrally corrected balanced detection, which is 11dB more that regular balanced detection.
We report the existence of polarization memory effect in the polarization-sensitive
optical coherence tomography (PS-OCT). Linear and circular polarized light was
used in the sample arm and two spherical micro-sphere solutions were used as scattering
phantoms. We further showed that this polarization effect can be clinically useful for the
characterization of some real tissue properties such as tooth dentin.
KEYWORDS: Filtering (signal processing), Signal to noise ratio, Doppler tomography, Optical coherence tomography, Digital filtering, Signal processing, Detection and tracking algorithms, Linear filtering, Electronic filtering, Optical tracking
Optical Doppler tomography is a valuable functional extension of optical coherence tomography (OCT) that can be used to study subsurface blood flows of biological tissues. We propose a novel frequency estimation technique that uses an adaptive notch filter (ANF) to track the depth-resolved Doppler frequency. This new technique is a minimal-parameter filter and works in the time domain without the need of Fourier transformation. Therefore, the algorithm has a computationally efficient structure that may be well suited for implementation in real-time ODT systems. Our simulations and imaging results also demonstrate that this filter has good performance in terms of noise robustness and estimation accuracy compared with existing estimation algorithms.
We evaluate the performance of our novel hybrid optical coherence tomography (OCT) and scintillating probe, demonstrate simultaneous OCT imaging and scintillating detection, and validate the system using an atherosclerotic rabbit model. Preliminary data obtained from the rabbit model suggest that our prototype positron probe detects local uptake of fluorodeoxyglucose (FDG) labeled with 18F positron (beta) radionuclide emitter, and the high-uptake regions correlate with sites of injury and extensive atherosclerosis areas. Preliminary data also suggest that coregistered high-resolution OCT images provide imaging of detailed plaque microstructures, which cannot be resolved by positron detection.
Angiogenesis in advanced breast cancers is highly distorted and heterogeneous. Non-invasive imaging that can monitor angiogenesis may be invaluable for assessing tumor response to treatment. By combining ultrasound and near infrared optical imaging, a reliable new technique has emerged for predicting tumor angiogenesis within the breast.
We designed a polarization-sensitive optical coherence tomography (PS-OCT) system to study the tissue polarization properties. The system has a dual-configuration scheme with the capability of easily switching the state of probing beam in the sample arm between linear polarization (LP) and circular polarization (CP). This setup will give four sets of 2-D tomographic data for each sample measurement, thus reveal more polarization information embedded in the biological tissue than a standard two-channel CP-configured PS-OCT system. The imaging results of LPCP-OCT for dentin and enamel of tooth samples are compared and discussed.
KEYWORDS: Digital signal processing, Signal processing, Image processing, Optical filters, Filtering (signal processing), Doppler effect, Electronic filtering, Signal detection, Doppler tomography, Data acquisition
We present a real-time data-processing and display unit based on a custom-designed digital signal processor (DSP) module for imaging tissue structure and Doppler blood flow. The DSP module is incorporated into a conventional optical coherence tomography system. We also demonstrate the flexibility of embedding advanced Doppler processing algorithms in the DSP module. Two advanced velocity estimation algorithms previously introduced by us are incorporated in this DSP module. Experiments on Intralipid flow demonstrate that a pulsatile flow of several hundred pulses per minute can be faithfully captured in M-scan mode by this DSP system. In vivo imaging of a rat's abdominal blood flow is also presented.
KEYWORDS: Digital signal processing, Signal processing, Image processing, Data acquisition, Signal detection, MATLAB, Blood circulation, Data processing, Electronic filtering, Doppler tomography
Clinical application of ODT requires real-time data acquisition and signal processing. In this paper, we present a real-time signal processing ODT unit based on a custom designed digital signal processor (DSP) module. The DSP is incorporated into a conventional ODT system using a grating-based scanning optical delay line. The newly developed flow velocity algorithms are integrated into the DSP and real-time data processing can be readily achieved.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.