For investigation of accommodation and presbyopia, the ciliary body and its dynamics were imaged with Optical Coherence Tomography (OCT) method. We used two OCT systems; a discretely-swept frequency-comb OCT with a center wavelength at 1.6µ and ultra-fast spectral domain OCT with a center wavelength at 1.3μm. Measurements of dynamical modification of the ciliary body were carried out with ranging in age from 22 to 79. The OCT images and movies represent the changes of the ciliary body in the relaxed state and accommodated state. Modification in the ciliary body with accommodation was more evident for the younger subject group from the results of 2D imaging. The time dependent 3D movies of ciliary body dynamics were observed for the first time using ultra-fast spectral domain OCT system. The time duration of ciliary body thickness change in relation to the accommodation was measured from the movies.
We have developed swept source optical coherence tomography (OCT) system with an optical comb swept source
system. The swept source system comprised of two super-structured grating distributed Bragg reflector lasers covering a
wavelength range from 1561-1693 nm. A method to scan these lasers to obtain an interference signal without stitching
noises, which are inherent in these lasers, and to connect two lasers without concatenation noise is explained. Method to
reduce optical aliasing noises in this optical comb swept laser OCT is explained and demonstrated based on the
characteristic of the optical aliasing noises in this particular OCT system. By reduction of those noises, a sensitivity of
124 dB was realized. The A-scan rate, resolution and depth range were 3.1 kHz, 16 μm (in air) and 12 mm, respectively.
Deep imaging penetration into tissue is demonstrated for two selected samples.
We describe a high-speed long-depth range optical frequency domain imaging (OFDI) system employing a long-coherence length tunable source and demonstrate dynamic full-range imaging of the anterior segment of the eye including from the cornea surface to the posterior capsule of the crystalline lens with a depth range of 12 mm without removing complex conjugate image ambiguity. The dependence of the whole anterior segment change on time following abrupt relaxation from the accommodated to the relaxed status
was measured for a healthy eye and that with an intraocular lens.
A large depth range is needed if optical coherence tomography (OCT) is to be used to observe multiple teeth
simultaneously. A discretely swept optical frequency domain imaging system with a 24-mm depth range was made by
using a superstructure-grating distributed Bragg reflector (SSG-DBR) laser as the light source and setting the frequencystep
interval to be 3.13 GHz (λ ≈ 0.026 nm). The swept wavelength range was 40 nm centered at 1580 nm, the resolution
was 29 μm, and the A-scan rate was 1.3 kHz. Application of the OCT system to a dental phantom was demonstrated.
We describe preliminary results of high-speed 2-dimensional Doppler OCT measurement using a unique optical
frequency domain imaging (OFDI) system. SSG-DBR laser is the light source from which wave number is swept
discretely over predetermined absolute values in equal wave number interval with constant output intensity.
Multi-sampling at each wave number enables us to reconstruct multiple images by 1 transversal scan, and the
2 dimensional flow image is reconstructed from the phase Doppler shift between 2 successive images. Maximum
detectable velocity is restricted by sampling rate, which is higher than A-scan flow has been carried out with this system adopting Kasai velocity estimator. The results predict
that the method is valid for stationary flow.
We describe a high-speed Fourier domain optical coherence tomography (OCT) using optical de-multiplexers for
spectral dispersion of interferograms. The optical de-multiplexer enables to separate 256 narrow spectral bands from a
broadband incident light in 25.0 GHz frequency interval centered at 192.2 THz (1559.8 nm) and allows simultaneous
detection of all the bands at the speed of DAQ. Using the optical de-multiplexers into a Fourier domain OCT system as
spectral analyzers, OCT imaging of 60,000,000 axial scans per second has been achieved. Using a resonant scanner for
lateral scan, 16 kHz frame rate, 1400 A-lines per frame, 3 mm depth range, 23 micron meter resolution OCT imaging has
been demonstrated.
We evaluate the image penetration depth of optical-frequency domain imaging into the biomedical tissue at longer wavelengths.
The light sources are fiber laser at the center wavelength of 1310 nm and at the center wavelength of 1550 nm. These sources provide frequency scan rate of up to 8 kHz over a wavelength range of 110 nm at 1310 nm with ~10 μm axial resolution and a wavelength range of 150 nm at 1550 nm with ~12 μm axial resolution. OCT tomograms of soft and hard tissues acquired at 1310 nm are compared to those obtained at 1550 nm.
We propose another window function used in production process of A-line by Fourier transform in optical frequency domain imaging. It is shown that cosine tapered window has an advantage over Gaussian window employed conventionally.
KEYWORDS: Optical coherence tomography, Data acquisition, Mirrors, Scanners, Tomography, Data transmission, Optical scanning, In vivo imaging, Biomedical optics, Light sources
We demonstrate a novel imaging technique for high-speed optical-frequency domain imaging (OFDI)with a discretely swept laser source. In this technique, one frame of OCT data can be acquired within a single frequency sweep. Tomographic images consisting of 1550 A-lines are obtained at 21 frames per second. The method is explained and experimental results are demonstrated.
The superstructured-grating distributed-Bragg-reflector laser is a small (shorter than 1 mm in length) and
relatively cheap swept source for optical-frequency-domain- reflectometry optical coherence tomography (OFDR-OCT),
which practically enables use of multiple sources in a single OCT system. Simultaneous scanning of
multiple sources over different wavelength regions and at different wavelength values in the same wavelength
region enable improvement of the resolution and scanning speed, respectively. Those improvements have been
demonstrated using C-band and L-band SSG-DBR sources.
We have been developing a unique discretely swept optical frequency domain imaging (OFDI) using superstructured-grating
distributed Bragg reflector (SSG-DBR) lasers. To increase resolution, four SSG-DBR lasers are being developed
to obtain spectral coverage of 160 nm in total. To increase speed of D-OFDI imaging, simultaneous scanning of multiple
sources with a parallel OFDI system and unique transversal scanning D-OFDI have been demonstrated. Introduction of
an optical amplifier can increase sensitivity beyond the conventional shot noise limit. A deep 12 mm depth range has
been demonstrated with the wavelength interval of 0.05 nm.
We measure an extracted tooth by OFDR-OCT. Three-dimensional reconstruction is performed against OCT images. Non-telecentric scanning is reproduced in three-dimensions and refractive image distortions are corrected by ray tracing.
Optical coherence tomography (OCT) system based on optical frequency-domain reflectometry (OFDR) has been developed using a superstructure-grating distributed Bragg reflector (SSG-DBR) laser, which can tune the wavelength from 1533 to 1574 nm stepwise with tuning speed of 10micro s per 0.1 nm step. Theoretical expressions of OCT imaging by the discretely swept OFDR-OCT system are described. OFDR-OCT images are demonstrated for a few biological tissues; an extracted canine, human skin, human nail, and anterior segment of enucleated porcine eye.
Recently, frequency-domain (FD) -optical-coherence-tomography (OCT) methods have been
investigated extensively as more efficient and sensitive system compared with
conventional time-domain (TD) -OCT.
Superstructure-grating-distributed-Bragg-reflector (SSG-DBR) lasers are particularly
suited for optical-frequency-domain-reflectometry (OFDR) -OCT with its wide wavelength tunability
and frequency agility.
We have made a discrete frequency OFDR-OCT system with an SSG-DBR laser,
which can tune the wavelength
from 1533 to 1574 nm with tuning speed of 10μs per 0.1 nm step.
The theoretical expression of the discrete frequency OFDR-OCT is given.
Utilizing near-transparent nature of enamel of teeth in the wavelength region of
the SSG-DBR laser and long object range of the OFDR-OCT, we have carried out
OCT measurements on teeth. Experimental
OCT imaging of a canine are reported here.
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