The effectiveness of speckle reduction using traditional frame averaging technique was limited in ultrahigh speed optical
coherence tomography (OCT). As the motion between repeated frames was very small, the speckle pattern of the frames
might be identical. This problem could be solved by averaging frames acquired at slightly different locations. The
optimized scan range depended on the spot size of the laser beam, the smoothness of the boundary, and the homogeneity
of the tissue. In this study we presented a method to average frames obtained within a narrow range along the slow-axis.
A swept-source OCT with 100,000 Hz axial scan rate was used to scan the retina in vivo. A series of narrow raster scans
(0-50 micron along the slow axis) were evaluated. Each scan contained 20 image frames evenly distributed in the scan
range. The imaging frame rate was 417 HZ. Only frames with high correlation after rigid registration were used in
averaging. The result showed that the contrast-to-noise ratio (CNR) increased with the scan range. But the best edge
reservation was obtained with 15 micron scan range. Thus, for ultrahigh speed OCT systems, averaging frames from a
narrow band along the slow-axis could achieve better speckle reduction than traditional frame averaging techniques.
To improve the scan quality of Doppler Optical coherence tomography for blood flow measurement, we investigate how
to improve the Doppler signal for all vessels around optic disc. Doppler signal is depending on the Doppler angle, which
is defined as angle between OCT beams and normal direction vessel. In this examination, we test the effect of different
OCT beam direction on Doppler angles of all veins. We also test maximizing the Doppler angle by combining scans with
different OCT beams direction. Three criteria were used to evaluate the overall quality, average Doppler angle, the
percentage of vessels with Doppler angle larger than the optimize value, the percentage of vessel with Coefficient
variance of Doppler angle less than the optimize value. The result showed that the best protocol is to maximize the
Doppler angle from one scan with OCT beam through supranasal portion of pupil and other scan with OCT beam
through infranasal portion of pupil.
The measurement of ocular blood flow is important in studying the pathophysiology and treatment of
several leading causes of blindness. A pilot study was performed to evaluate the total retinal blood flow in
glaucoma patient using Fourier domain optical coherence tomography. For normal people, the measured total
retinal flow was between 40.8 and 60.2 μl/minute. We found that eyes with glaucoma had decreased retinal
blood flow and average flow veocity, while the venous cross sectional areas were essentially the same as
normal. The decrease in blood flow was highly correlated with the severity of visual field loss.
We present in vivo human retinal blood flow investigation using Fourier domain optical coherence tomography. A pilot study was performed to evaluate the total retinal blood flow in glaucoma patients and normal subjects. For normal people, the measured total retinal flow was between 40.8 and 52.9 μl/minute. The measured venous flow for glaucoma patients was from 23.6 to 43.11 μl/minute. The retinal flow of glaucoma patients was lower than that of normal subjects. Retinal blood flow was highly correlated with visual field parameters in glaucoma patients.
We present in vivo human total retinal blood flow measurements using Doppler Fourier domain optical coherence tomography (OCT). The scan pattern consisted of two concentric circles around the optic nerve head, transecting all retinal branch arteries and veins. The relative positions of each blood vessel in the two OCT conic cross sections were measured and used to determine the angle between the OCT beam and the vessel. The measured angle and the Doppler shift profile were used to compute blood flow in the blood vessel. The flows in the branch veins was summed to give the total retinal blood flow at one time point. Each measurement of total retinal blood flow was completed within 2 s and averaged. The total retinal venous flow was measured in one eye each of two volunteers. The results were 52.90±2.75 and 45.23±3.18 µl/min, respectively. Volumetric flow rate positively correlated with vessel diameter. This new technique may be useful in the diagnosis and treatment of optic nerve and retinal diseases that are associated with poor blood flow, such as glaucoma and diabetic retinopathy.
The measurement of ocular blood flow is important in studying the pathophysiology and treatment of several
leading causes of blindness. We present a method for in vivo human retinal flow measurement using Fourier domain
optical coherence tomography. A double circular scanning pattern was used to scan the blood vessels around the optic
nerve head 8 times over 2 seconds. The venous flow totaled 36.13 μl/min in the right eye of a volunteer. The flow
difference was observed before and after breath holding. The fast flow measurement method did not require any
assumption on the flow profile over time or space.
There is considerable interest in new methods for the assessment of retinal blood flow for the diagnosis of eye diseases. We present in vivo normal human volumetric retinal flow measurement using Fourier domain Doppler optical coherence tomography. We used a dual-plane scanning pattern to determine the angle between the blood flow and the scanning beam in order to measure total flow velocity. Volumetric flow in each blood vessel around the optic nerve head was integrated in one cardiac cycle in each measurement. Measurements were performed in the right eye of one human subject. The measured venous flow velocity ranged from 16.26 mm/s to 29.7 mm/s. The arterial flow velocity ranged from 38.35 mm/s to 51.13 mm/s. The total retinal venous and arterial flow both added up to approximately 54 µl/min. We believe this is the first demonstration of total retinal blood flow measurement using the OCT technique.
We present a low-cost, high resolution, real-time Spectral Domain Optical Coherence Tomography (SDOCT) system optimized for rapid 3D imaging of the human retina in vivo. Using a source with an 841nm center wavelength and a FWHM bandwidth of 49nm, 6.67 second length bursts of 100 512 x 1000 pixel images were acquired with an integration time of 50 microseconds/line and a frame rate of 16 frames/sec. Three-dimensional data sets comprising up to 4.0mm x 1.2mm x 2.45mm retinal volumes were streamed to hard disk during this brief ocular fixation interval and post-processed to create 3D volumetric images of the optic nerve head and fovea.
A high-resolution Second Harmonic Optical Coherence Tomography (SH-OCT) system is demonstrated using a spectrum broadened femtosecond Ti:sapphire laser. An axial resolution of 4.2 μm at the second harmonic wave center wavelength of 400 nm has been achieved. Because the SH-OCT system uses the second harmonic generation signals that strongly depend on the orientation, polarization and local symmetry properties of chiral molecules, this technique provides unique contrast enhancement to conventional optical coherence tomography. The system is applied to image biological tissues like the rat-tail tendon. Images of highly organized collagen fibrils in the rat-tail tendon have been demonstrated.
Wideband light generation from a single mode optical fiber was investigated. Investigation showed that spectral structure of light broadened by self-phase modulation was not sensitive to fluctuations of the input pulse energy, and its intensity noise was much lower than that of contimuum light from a microstructure fiber. The spectral width of a femtosecond input laser pulse was successfully broadened by a factor of eleven, and a longitudinal resolution of OCT was improved from 35 to 3.7 μm. The system empoyed a dynamic focusing tracking method to maintain high lateral resolution over a large imaging depth.
We present a phase-resolved optical Doppler tomography (ODT) sys tem at 1310 nm using frequency domain method. Frequency domain phase-resolved ODT potentially allows for an increased longitudinal imaging range, signal-to-noise ratio and imaging acquisition rates, which can dramatically increase the measurable velocity dynamic range. A detailed derivation of phase-resolved frequency domain ODT and a measurement of flow through micro channel are presented. This technique can be used to quantify flow in integrated microfluidic devices in which complex three-dimensional structures and a wide velocity range are present.
We describe a phase-resolved polarization sensitive optical coherence tomography system that can obtain the Stokes vectors, polarization diversity intensity, and birefringence images of rat-tail tendon and muscle. The Stokes vectors were obtained by processing the analytical interference fringe signals from two perpendicular polarization-detection channels for the same reference polarization state. From the four Stokes vectors, the birefringence image, which is insensitive to orientation of the optical axis in the sample, and the polarization diversity intensity image, in which speckle noise is greatly reduced, were obtained. The birefringence changes in the rat muscle caused by freezing were investigated using phase-resolved polarization sensitive optical coherence tomography. It was found that freezing degrades birefringence in rat muscle.
We developed an ultrahigh resolution optical coherence tomographic system utilizing broadband continuum generation from a photonic crystal fiber for high axial resolution. Longitudinal resolution of 1.3 μm has been achieved in a biological tissue by use of continuum light from 800 - 1400 nm as the light source. The system employed a dynamic focusing tracking method to maintain high lateral resolution over a large imaging depth. Subcellular imging is demonstrated.
We describe power optical Doppler tomography (ODT) imaging in phase-resolved optical coherence tomography (OCT) capable of providing the precise location of blood flow in human skin. The power Doppler signal is the squared amplitude of the Doppler signal. By properly setting the intensity threshold and priority displaying Doppler power in phase-resolved OCT, we obtained a Doppler power tomography image of the blood flow in human skin. Power Doppler tomography uses only the amplitude information, so it is not susceptible to aliasing and Doppler flow angle and provides more accurate and smooth imaging of the location of the blood vessels in human skin than Doppler velocimetry. We also modified the phase-resolved algorithm we published before and used it to do Doppler tomography and M-mode Doppler imaging. The dynamic of blood flow in chick chorioallantoic membrane (CAM) was studied using M-mode Doppler imaging.
We developed a optical coherence tomographic (OCT) system that utilized broadband continuum generation from a crystal fiber for high axial resolution. Longitudinal resolution of 3 micrometers has been achieved in free space with continuum light from 780 to 1400nm as light source. The system employed a dynamic focusing tracking method to get high lateral resolution. Ultrahigh resolution imaging in onion was demonstrated.
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.