Thinning of the outer nuclear layer (ONL) is an important pathological feature and possible biomarker of age-related macular degeneration (AMD). The demarcation of the ONL and Henle’s fiber layer (HFL) is visually unattainable with standard optical coherence tomography (OCT) imaging. In this work, we built a volumetric directional OCT prototype which constitutes two optical scanners in the sample arm that synchronously scan the imaging beam on the pupil and retina. The imaging beam’s entry positions and incident angles on the pupil and retina respectively are precisely controlled and optimally maintained to generate sufficient contrast of the HFL over the entire macular volume.
An automated algorithm was developed for total retinal blood flow (TRBF) using 70-kHz spectral optical coherence tomography (OCT). The OCT was calibrated for the transformation from Doppler shift to speed based on a flow phantom. The TRBF scan pattern contained five repeated volume scans (2×2 mm) obtained in 3 s and centered on central retinal vessels in the optic disc. The TRBF was calculated using an en face Doppler technique. For each retinal vein, blood flow was measured at an optimal plane where the calculated flow was maximized. The TRBF was calculated by summing flow in all veins. The algorithm tracked vascular branching so that either root or branch veins are summed, but never both. The TRBF in five repeated volumes were averaged to reduce variation due to cardiac cycle pulsation. Finally, the TRBF was corrected for eye length variation. Twelve healthy eyes and 12 glaucomatous eyes were enrolled to test the algorithm. The TRBF was 45.4±6.7 μl/min for healthy control and 34.7±7.6 μl/min for glaucomatous participants (p-value=0.01). The intravisit repeatability was 8.6% for healthy controls and 8.4% for glaucoma participants. The proposed automated method provided repeatable TRBF measurement.
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.
The detection of early-stage keratoconus is one of the most important safety issues in screening candidates for corneal
refractive surgeries. We propose to use epithelial thickness maps to assist the diagnosis of keratoconus. The corneal
epithelial thickness in normal and keratoconic eyes was mapped with optical coherence tomography (OCT). A Fourier-domain
OCT system capable of acquiring 26,000 axial-scans per second was used. It has an axial resolution of 5μm in
cornea. A pachymetry scan pattern (8 radials, 1024 axial-scans each, 6mm diameter, repeat 3 times) centered at the pupil
center was used to image the cornea. The 3 repeated radial scans on each meridian were registered and averaged. Then
the anterior corneal, posterior corneal and epithelial boundaries were segmented automatically with a computer
algorithm by increased signal intensity at corresponding boundaries. The epithelial thickness map was generated by
interpolating epithelial thickness profile calculated from each meridian. Normal and keratoconic eyes (24 eyes each)
were scanned 3 times. The central epithelial thickness in normal eyes was thicker than those of keratoconic eyes (mean
difference 2.1 μm, t-test p=0.05). The epithelium was thinner superiorly than inferiorly in normal eyes (mean difference
-1.4±1.1μm, p<0.001) while thicker superiorly than inferiorly in keratoconic eyes (2.0±4.1 μm, p=0.02).
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.
A new image segmentation method was developed to detect macular retinal sub-layers boundary on newly-developed
Fourier-Domain Optical Coherence Tomography (FD-OCT) with macular grid scan pattern. The segmentation results
were used to create thickness map of macular ganglion cell complex (GCC), which contains the ganglion cell dendrites,
cell bodies and axons. Overall average and several pattern analysis parameters were defined on the GCC thickness map
and compared for the diagnosis of glaucoma. Intraclass correlation (ICC) is used to compare the reproducibility of the
parameters. Area under receiving operative characteristic curve (AROC) was calculated to compare the diagnostic
power. The result is also compared to the output of clinical time-domain OCT (TD-OCT). We found that GCC based
parameters had good repeatability and comparable diagnostic power with circumpapillary nerve fiber layer (cpNFL)
thickness. Parameters based on pattern analysis can increase the diagnostic power of GCC macular mapping.
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.
A template-based and semi-automatic volumetrics system--BrainVol is build to divide the any given patient brain to neo-cortical and sub-cortical regions. The standard region is given as standard ROI drawn on a standard brain volume. After normalization between the standard MR image and the patient MR image, the sub-cortical ROIs' boundary are refined based on gray matter. The neo-cortical ROIs are refined by sulcus information that is semi-automatically marked on the patient brain. Then the segmentation is applied to 4D PET image of same patient for calculation of TAC (Time Activity Curve) by co-registration between MR and PET.
It is difficult to automatically segment and classify tomograph images of actual patient's brain. Therefore, many interactive operations are performed. It is very time consuming and its precision is much depended on the user. In this paper, we combine a brain atlas and 3D fuzzy image segmentation into the image matching. It can not only find out the precise boundary of anatomic structure but also save time of the interactive operation. At first, the anatomic information of atlas is mapped into tomograph images of actual brain with a two step image matching method. Then, based on the mapping result, a 3D fuzzy structure mask is calculated. With the fuzzy information of anatomic structure, a new method of fuzzy clustering based on genetic algorithm is used to segment and classify the real brain image. There is only a minimum requirement of interaction in the whole process, including removing the skull and selecting some intrinsic point pairs.
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