ABSTRACT: Color Doppler optical coherence tomography (CDOCT) is capable of precise velocity mapping in turbid media. Previous CDOCT systems based on the short-time Fourier transform have been limited to maximum flow velocities of the order of tens of millimeters per second. We describe a technique, based on interference signal demodulation at multiple frequencies, to extend the physiological relevance of CDOCT by increasing the dynamic range of measurable velocities to hundreds of millimeters per second. The physiologically important parameter of shear rate is also derived from CDOCT measurements. The measured flow-velocity profiles and shear-rate distributions correlate very well with theoretical predictions. The multiple demodulation technique, therefore, may be useful to monitor blood flow in vivo and to identify regions with high and low shear rates.
Optics Letters 12/1999; 24(22):1584-6. · 3.40 Impact Factor
ABSTRACT: Current laser treatment for vascular disorders such as port wine stains can have incomplete or unacceptable results. A customized treatment strategy based on knowledge of the patient's blood vessel structure may effect an improved clinical outcome.
We tested the feasibility of using color Doppler optical coherence tomography (OCT) and image processing techniques to locate, measure and reconstruct cutaneous blood vessels in rat and hamster skin. OCT is a recent, potentially noninvasive technique for imaging subsurface tissue structures with micrometer scale resolution.
Blood vessels were identified in a series of cross-sectional images, then a three-dimensional reconstruction was made. Parameters that can affect optimum laser treatment parameters, such as average blood vessel depth and luminal diameter, were found from the images.
This study shows that color Doppler OCT is a potential tool for improving laser treatment of vascular disorders.
Dermatology 02/1999; 198(4):355-61. · 2.05 Impact Factor
ABSTRACT: Color Doppler optical coherence tomography (CDOCT) is a recent innovation that allows spatially localized flow-velocity mapping simultaneously with microstructural imaging. We present a theoretical model for velocity-image formation in CDOCT. The proportionality between the heterodyne detector current Doppler power spectrum in CDOCT and the optical source power spectrum is established. We show that stochastic modifications of the Doppler spectrum by fluctuating scatterer distributions in the flow field give rise to unavoidable velocity-estimation inaccuracies as well as to a fundamental trade-off between image-acquisition rate and velocity precision. Novel algorithms that permit high-fidelity depth-resolved measurements of velocities in turbid media are also reported.
Optics Letters 08/1998; 23(13):1057-9. · 3.40 Impact Factor
ABSTRACT: Optical coherence tomography (OCT) is a novel technique for noninvasive cross-sectional imaging with high spatial resolution (10 to 20 microm). OCT is similar to B-mode ultrasound except that it uses infrared light rather than ultrasound. We studied OCT imaging of the gastrointestinal (GI) tract in vitro to analyze the potential of this technique for endoscopic applications.
Human gastrointestinal tissues harvested from surgical resection and autopsy specimens were used. Specimens were imaged within 5 hours of resection or snap frozen in liquid nitrogen. After imaging, OCT scan locations were carefully marked using dye microinjections, fixed, and prepared for routine histologic processing. OCT images were then compared and correlated with the histologic sections.
OCT images demonstrated clear delineation of the mucosa and submucosa in most specimens. Furthermore, microscopic structures such as crypts, blood vessels, or esophageal glands in the submucosa and lymphatic nodules were observed.
The resolution of OCT images of GI wall is sufficient to delineate the microscopic structure of the mucosa and submucosa. Potentially, OCT would allow in vivo imaging at endoscopy of the microstructure of the mucosa and submucosa. This would be particularly useful in the detection and staging of small lesions such as early stage cancers.
Gastrointestinal Endoscopy 07/1998; 47(6):515-23. · 4.88 Impact Factor
ABSTRACT: Color Doppler optical coherence tomography (CDOCT) is an
innovative extension of optical coherence tomography. CDOCT permits
spatially localized blood flow velocity mapping simultaneous with
microstructural imaging of living tissue. In CDOCT, longitudinal
velocity profiles are estimated by measuring Doppler shifts in localized
backscattered light spectra. Velocity images are built up from adjacent
axial velocity profiles, which are color coded for velocity magnitude
and direction as performed in color Doppler ultrasound. CDOCT could
potentially be used for retinal perfusion analysis for diagnosing
macular diseases and optimizing treatments of vascular disorders. CDOCT
uses an optical heterodyne detection technique based on scanning white
light interferometry. Therefore the detector current carrier frequency
is the same as the resultant Doppler shift in the received light given
by the difference of the Doppler shifts due to the reference mirror
velocity and moving scatterers in the sample. The width of the detector
current power spectrum is proportional to the product of the net Doppler
shift and the light source spectrum width. Light backscattered from a
turbid specimen generates a speckle pattern consisting of the sum of
partial reflections from many randomly distributed scatterers. As a
result, the detector current spectrum measured in CDOCT maybe strongly
frequency dependent and is modulated by a postulated transfer function,
which encodes information regarding scattering sites
Lasers and Electro-Optics, 1998. CLEO 98. Technical Digest. Summaries of papers presented at the Conference on; 06/1998
ABSTRACT: We describe a novel optical system for bidirectional color Doppler imaging of flow in biological tissues with micrometer-scale resolution and demonstrate its use for in vivo imaging of blood flow in an animal model. Our technique, color Doppler optical coherence tomography (CDOCT), performs spatially localized optical Doppler velocimetry by use of scanning low-coherence interferometry. CDOCT is an extension of optical coherence tomography (OCT), employing coherent signal-acquisition electronics and joint time-frequency analysis algorithms to perform flow imaging simultaneous with conventional OCT imaging. Cross-sectional maps of blood flow velocity with <50-microm spatial resolution and <0.6-mm/s velocity precision were obtained through intact skin in living hamster subdermal tissue. This technology has several potential medical applications.
Optics Letters 09/1997; 22(18):1439-41. · 3.40 Impact Factor
ABSTRACT: A linear shift invariant system model describing coherent
light-specimen interactions in optical coherence tomography is
presented. Based on this model, an iterative deconvolution algorithm is
demonstrated for enhancing the sharpness of optical coherence
tomographic images of biological structures
Electronics Letters 08/1997; · 0.96 Impact Factor
ABSTRACT: Optical coherence tomography (OCT) and optical coherence
microscopy (OCM) are novel techniques for noninvasive biomedical imaging
based on low-coherence interferometry. OCT achieves high-spatial
resolution (<30 μm in three dimensions) and high dynamic range
(>100 dB) in a fiber-optically integrated system which is suitable
for application in minimally invasive diagnostics, including endoscopy.
The technique of OCM combines the depth-ranging capability of OCT with
the micron-scale resolution imaging capability of confocal microscopy to
extend the available imaging depth of confocal microscopy up to several
hundred micrometers deep in highly scattering tissues. The theoretical
and technical bases for OCT and OCM imaging are described. Example OCT
images are provided in gastrointestinal (GI) tissues to illustrate
contrast between histological layers of the GI mucosa and
differentiation of the mucosa from submucosa. Example OCM images
revealing cellular-level microstructure up to several hundred
micrometers deep in GI tissue are presented for the first time. The
potential applications of OCT and OCM imaging in clinical diagnostic
medicine are discussed
IEEE Journal of Selected Topics in Quantum Electronics 01/1997; · 3.78 Impact Factor
ABSTRACT: Summary form only given. Implementations of OCT, which take advantage of the spectral bandwidth of low coherence sources for tissue spectroscopy, have not yet been reported. We describe a novel technique for depth-resolved coherent backscatter spectroscopy, which is an extension of OCT technology. Our system incorporates an OCT scanner illuminated by a superluminescent diode (SLD) at 1.3-/spl mu/m center wavelength. In the low-coherence interferometer, a scanning reference mirror generates the temporal cross-correlation function of light reflected from the reference mirror, and that backscattered from the sample arm target. A separate helium-neon interferometer is utilized for digital correction of artifacts in the low-coherence interferometer output due to nonlinearities in the reference arm retroreflector stage velocity. The low-coherence interferometric signal is digitally demodulated and filtered to obtain the complete complex envelope of the interferometric signal, which is required for the spectroscopic technique. Using this system, low-coherence interferograms with accurate sampling intervals and high dynamic range (>98 dB) are acquired.
Lasers and Electro-Optics, 1996. CLEO '96., Summaries of papers presented at the Conference on; 07/1996
ABSTRACT: Optical coherence tomography (OCT) is a novel method for
non-invasive sub-surface imaging of biological tissue micro-structure.
OCT is based on low-coherence interferometry. OCT achieves high spatial
resolution (~15 μm in three dimensions) and high sensitivity
(<-100 dB) in a fiber-optically integrated system which is suitable
for application in minimally invasive diagnostics, including endoscopy.
The authors present in vitro cross-sectional OCT images obtained
non-invasively in gastrointestinal (GI) tissues to illustrate contrast
between histological layers of the GI mucosa and differentiation of the
mucosa from submucosa. The authors also present a novel technique,
termed color Doppler OCT (CDOCT) which is an extension of OCT for
performing spatially localized optical Doppler velocimetry. The authors
demonstrate micron-scale resolution tomographic imaging of
bi-directional blood flow in sub-surface vessels in living tissue using
CDOCT. Both OCT and CDOCT have several potential medical applications
Engineering in Medicine and Biology Society, 1997. Proceedings of the 19th Annual International Conference of the IEEE;