We have developed methods which allow us to analyze images obtained with high resolution scanning laser ophthalmoscope (SLO). Registered retinal vessels can be extracted and quantified using image processing methods. Obtained data can be further analyzed for calculations of vessel morphological parameters.
We have developed a high resolution scanning laser ophthalmoscope optimized for imaging the morphology and dynamics of the retinal vessels. The system has flexible control over the imaging field of view allowing for easy navigation on the retina and selection of the desired vessel for high magnification imaging. We have also developed image processing methods that allow for extraction and quantification of vessel walls and lumen that serve for calculation of various morphological parameters.
We present a novel platform for eye tracking showing high speed and accuracy in a wide range of realizable visual tasks. The optical setup consists of the scanning laser ophthalmoscope, the actual tracker (the FreezEye Tracker), and a visual projector for task presentation. The MEMS-based tracker scans the retina with a framerate of 1.24 kHz, providing high angular and temporal resolution. Advanced algorithms allow for precise reconstruction of the eye trajectory covering the range of movements from small microsaccades to high amplitude saccades. The high quality of the generated data provides an abundance of data potentially useful for diagnostic purposes.
Neurodegenerative diseases, such as multiple sclerosis (MS), negatively impact the aging global population. MS damage various parts of the central nervous system, leading to various eye-movement abnormalities. We have built a retinal FreezEye Tracker (FET) to measure a wide dynamic range of eye movements of up to 10 degrees with an ultrahigh temporal and spatial resolution during visual tasks, including fixations, experiments with saccades, and smooth pursuit. To compare, we performed the same experiments with pupil tracker EyeLink 1000. The amplitudes of detected saccades are similar in both devices, but FET provides high-resolution details on eye trajectory during fixation periods.
Constructing an image acquired by a non-uniform scanning pattern is a difficult task. The main challenges are:(1) resampling technique (2) discrepancy between demanded (dictated by control signal) and actually performed, empirical scanning path. Here, we show how to calibrate the scanning path of MEMS scanner using Galvanometric Scanner and to what extent the time of acquisition impacts the resulting image.
The eye motion is broadly considered as a valuable source of information in the fields related to psychology, neuroscience and neurology. Therefore, quantitative characterization of eye tracker data is an important task. Saccades are sigmoidal, ballistic movements that in particular deserve more attention due to their complex shape and natural diversity. We have developed the high accuracy model of saccades and microsaccades of mean absolute error equal to 0.0104 degree on average. We present the methodology for extraction of saccadic features using this model and show the potential of the method in biometric experiments.
We demonstrate a novel label-free OCT method allowing optical detection and differentiation of moving micro-objects,
such as blood cells. In this study we use phase-sensitive Fd-OCT/OCM system with broadband light source (axial
resolution: 3 μm in tissue and lateral resolution 4−8 μm) and fluidic sample setup. The novel part of this method is that
the optical identification is based on optical signal coming from optically uniform scattering media localized beneath the
flowing/moving objects and not from the objects itself. This signal reveals as an enhancement in speckle pattern
on intensity images and non-zero phase change on phase images (phase-change). Statistical parameters of such signals
depend on the features of the object, like its size, shape, internal structure, etc. In order to demonstrate the effectiveness
and reliability of proposed method, we performed an experiment to differentiate erythrocytes from leukocytes. Obtained
OCT cross-sectional images present signal enhancement in the scattering base, both on intensity and phase-change
images. This modulation signals, corresponding to erythrocytes and leukocytes, are significantly different and could be
easily distinguished qualitatively. Statistical parameters used for the analysis also represent satisfactory separation
to distinguish between different kinds of cells. Above-mentioned results of differentiation are presented in this paper.
KEYWORDS: Optical coherence tomography, Signal detection, Tissue optics, Blood, In vivo imaging, Mirrors, Sensors, Signal to noise ratio, Fourier transforms, Doppler tomography
Recently rapid development of ultrahigh speed optical coherence tomography (OCT) instruments have been observed.
This imaging modality enables performing cross-sectional in vivo imaging of biological samples with speeds of more
than 100,000,000 axial scans per second. This progress has been achieved by the introduction of Fourier domain
detection techniques to OCT instruments. High-speed imaging capabilities lifts the primary limitation of early OCT
technology by giving access to in vivo 3-D volumetric reconstructions in large scales within reasonable time constraints.
New perspectives for existing OCT applications has been added by creating new instrumentation including the functional
imaging. The latter shows a potential to differentiate tissue pathologies via metabolic properties or functional responses.
We present an application of the Joint Spectral and Time domain OCT (STdOCT) method for detection of wide range of
flows in the retinal vessels. We utilized spectral/Fourier domain OCT (SOCT) technique for development of scan
protocols for Doppler signal analysis. We performed retinal imaging in normal eyes using ultrahigh speed (200 000 axial
scans/s) SOCT instrument with a CMOS camera. Various raster scan protocols were implemented for investigation of
blood flow in the retina. Data analysis was performed using the method of joint Spectral and Time domain OCT
(STdOCT). Detection of blood flow velocities ranging from several tens of mm/s to a fraction of mm/s was possible with
scanning methods allowing for appropriate selection of time intervals between data taken for Doppler OCT analysis.
Axial blood flow velocity measurement was possible in retinal vessels. Doppler OCT signal can be utilized as a contrast
mechanism for visualization of retinal capillaries.
We present a simple and efficient numerical technique for segmentation retinal and choroidal blood
vasculature with bulk motion correction in functional Doppler Spectral Optical Coherence Tomography
(Doppler SOCT). The technique uses local variance of velocity tomogram which is higher in the areas of
the tomogram with internal flow. The resulting variance map reveals the position of vessels. This can be
used either for vessel segmentation purposes or for masking the vessels on velocity tomograms. The
remaining velocity information is connected only with static structure velocity offset. As only Fourier
transformations are used in calculations the algorithm removes the bulk motion from velocity tomograms
and provides images of segmented vessels with speed of 80 000 lines/s. The algorithm is shown to work
with velocity tomograms obtained by joint Spectral and Time domain OCT (STdOCT).
In this paper we report that optical inhomogeneity of flowing fluid has influence on Doppler OCT measurement.
Additional Doppler signal from scattering steady medium below blood vessels is visible. To investigate this
phenomenon, the experiments with different scattering mediums and different well controlled experimental
configurations were carried out. Imaging was performed using SOCT instrument with CCD camera, and joint Spectral
and Time domain OCT method was used during data analysis.
We show that recently developed joint Spectral and Time Optical Coherence Tomography data analysis
scheme combined with oscillatory change of optical path difference allows for simultaneous complex
ambiguity removal and quantitative flow velocity estimation. Full range structural tomograms as well as
velocity distributions of Intralipid solution in glass capillaries are presented.
We propose a modified method of acquisition and analysis of Spectral Optical Coherence Tomography (SOCT)
data to provide information about flow velocities in three dimensions. Joint Spectral and Time domain Optical
Coherence Tomography (joint STdOCT) enables flow velocity assessment and segmentation of flows. STdOCT
method is based on direct detection of Doppler shift that arises in time during the measurement. New scanning
protocols and analysis tools are proposed to create velocity distribution maps of the retina and to segment and
visualize 3D flows. STdOCT segmentation is more sensitive than methods based on phase measurements and
calculations are more straightforward than other techniques, which require more complex experimental setup and
more sophisticated numerical tools. We also discuss parameters, which improve the flow based segmentation
procedure with special attention paid to the problem of broadening of flow velocity distribution.
In this submission we demonstrate a new application of the joint Spectral and Time domain Optical Coherence
Tomography (STdOCT) technique for segmenting and measuring the retinal blood flow velocity in three
dimensions. The method is based on direct detection of Doppler shift that arises in time during the measurement.
New scanning protocols and analysis tools are proposed to create velocity distribution maps of the retina and to
segment and visualize 3D vasculature of human eye in-vivo. STdOCT segmentation is more sensitive than methods
based on phase measurements and calculations are more straightforward than other techniques, which require more
complex experimental setup and more sophisticated numerical tools. The usage of ultra-fast line scan camera allows
to broaden the axial velocity range up to ±24mm/s, thus all high flows in human retina can be registered.
In this contribution we propose a new method of acquisition and analysis of Spectral Optical Coherence Tomography
data to obtain information about depth dependent extinction in the scattering media. In joint Spectral and Time domain
OCT a set of Spectral Optical Coherence Tomography fringes is acquired in time increments. An axial component of the
flow velocity vector is accurately estimated from Doppler beating signal. Additional filtering and averaging of spatial-temporal
data allows for effective reduction of the speckle noise and enables reconstructing the envelope of spectral
fringes corresponding to the chosen depth. In this way the depth and wavelength dependent attenuation of light can be
determined in scattering media. In this contribution we demonstrate the proof of concept of spectroscopic OCT analysis
performed in scattering media and we discuss its potential for in-vivo functional imaging of the human retina.
We propose a new method of acquisition and analysis of Spectral Optical Coherence Tomography data. The method acquires a set of SOCT spectral fringes as a function of time. The Fourier analysis of such data allows for investigation of various functional aspects of analyzed tissue. We show that Doppler flow information of a sample can be easily evaluated from such data. We also compare the velocity estimates obtained with our method with these found via traditional phase-resolved procedure.
We propose a new technique of measuring and analysis of OCT signals: joint Spectral and Time domain Optical
Coherence Tomography (STdOCT). This technique is based on a multiple spectral interferogram registration in time
increments. The analysis of a single spectral interferogram provides an axial structure of a sample. The analysis of
signals registered in time enables velocity estimation of moving sample. The method is applied to biomedical imaging, in
particular to in vivo measurements of retinal blood circulation. The velocity estimations obtained with joint STdOCT are
compared with the ones obtained by known, phase-resolved OCT. In contrast to the phase-resolved technique,
STdOCT correctly reproduces parabolic shape of the flow velocity distribution despite decreasing signal-to-noise ratio
(SNR).
We propose a new method of flow velocity estimation by analysis of time dependent beating signal using Spectral
Optical Coherence Tomography. The oscillatory beating signal is caused by the Doppler shift of light reflected back
from a mobile object measured in the interferometric set-up. This signal provides information about the velocity of the
movable object. Measurements in model systems prove the method to give accurate results. Additional in vivo
measurements of blood flow in the retinal vessels show potential applicability of this method in the field of biomedical
imaging.
We present a computationally efficient, semiautomated method for analysis of posterior retinal layers in three-dimensional (3-D) images obtained by spectral optical coherence tomography (SOCT). The method consists of two steps: segmentation of posterior retinal layers and analysis of their thickness and distance from an outer retinal contour (ORC), which is introduced to approximate the normal position of external interface of the healthy retinal pigment epithelium (RPE). The algorithm is shown to effectively segment posterior retina by classifying every pixel in the SOCT tomogram using the similarity of its surroundings to a reference set of model pixels from user-selected area(s). Operator intervention is required to assess the quality of segmentation. Thickness and distance maps from the segmented layers and their analysis are presented for healthy and pathological retinas.
Purpose: To show potential of Spectral Optical Coherence Tomography system for high resolution, cross-sectional
and three-dimensional imaging of eye surface pathologies. Methods:
High-speed spectral OCT prototype instrument with 4.5 &mgr;m axial resolution was designed and constructed
for clinical use. Measurements of anterior segment of human eye have been performed in ophthalmology clinic on 86
patients suffering various eye surface disorders including corneal dystrophies, corneal scars, conjunctival folds,
keratoconus, bullus keratopathy, filtration blebs and other post-operative changes. Additionally, examinations of
contact lens fit on 97 healthy corneas have been performed up to date. Results:
High quality, high resolution cross-sectional images and three-dimensional reconstructions of cornea,
conjunctiva and sclera of pathologic eyes together with examples of numerical analysis including segmentation of
fluid in filtration blebs, scars and deposits are shown. Quantitative analysis of contact lens fit is demonstrated.
Novel Fourier domain OCT method and instrumentation using Optical Frequency Comb (OFC) is demonstrated.
This technique can overcome some limitations of Spectral OCT and Optical Frequency domain Imaging (Swept
Source OCT) and enables ultrahigh resolution imaging in 800 nm range. In the novel method external OFC generator
placed after the broad band light source is used. We will demonstrate preliminary data showing the general
performance, advantages and limitations of the Fourier domain OCT method using Optical Frequency Comb
generator based on Fabry-Perot interferometer (F-P). High quality, high resolution cross-sectional images of
biological samples obtained with the presented technique are shown.
The overview of the Spectral Optical Coherence Tomography an alternative method to more popular Time domain modality
is given. Examples from medical practice utilizing high resolution, ultra fast SOCT device are presented.
The aim of this article is to demonstrate an application of Spectral Optical Coherence Tomography SOCT for visualization of the anterior segment of the human eye. A SOCT system with an axial resolution of 4-6 μm and a lateral one of 10 μm provides tomograms composed of 3000 - 5000 A-scans when a total acquisition time of 100-250 ms is used to acquire tomograms. The quality of the images is adequate for detailed evaluation of the corneal structure and contact lens fit. Erosion of the epithelium, scars and lesions may be precisely localized. The design, shape and edge position of the contact lens, as well as other fitting relationships between the lens and the ocular surface, may be accurately assessed. The information provided by SOCT may be helpful in diagnosis, evaluation and documentation of corneal pathologies and contact lens complications.
In this contribution we demonstrate comparison between two high speed Spectral OCT instruments with different axial and identical transverse resolutions used for imaging of various retinal pathologies. Cross-sectional OCT images of higher axial resolution enable improved visualization of small focal lesions in the retina, which can be missed in standard resolution OCT measurements. Optimal parameters of SOCT clinical systems are discussed. We compare cross-sectional images of selected clinical cases of advanced retinal pathologies obtained with both instrument.
Spectral Optical Coherence Tomography is a new modality to be introduced in ophthalmology. It introduces several improvements such as real-time and 3-dimensional imaging, and possibility of tomographic films, due to high speed of imaging offered by the method. For the same reason -- 2-dimensional cross-sectional images now can be performed with higher sampling density, which increase the signal-to-noise ratio. We analyze advantages and possible problems which may arise with the high speed imaging.
In this study we show clinical application of Spectral Optical Coherence Tomography (SOCT), which enables operation with 40 times higher speed than commercial Stratus OCT instrument. Using high speed SOCT instrument it is possible to collect more information and increase the quality of reconstructed cross-sectional retinal images. Two generations of compact and portable clinical SOCT instruments were constructed in Medical Physics Group at Nicolaus Copernicus University in Poland. The first SOCT instrument is a low-cost system operating with standard, 12 micrometer axial resolution and the second is high resolution system using combined superluminescent diodes light source, which enables imaging with 4.8 micrometer axial resolution. Both instruments have worked in Ophthalmology Clinic of Collegium Medicum in Bydgoszcz. During the study we have examined 44 patients with different pathologies of the retina including: Central Serous Chorioretinopathy (CSC), Choroidal Neovascularization (CNV), Pigment Epithelial Detachment (PED), Macular Hole, Epiretinal Membrane, Outer Retinal Infarction etc. All these pathologies were first diagnosed by classical methods (like fundus camera imaging and angiography) and then examined with the aid of SOCT system. In this contribution we present examples of SOCT cross-sectional retinal imaging of pathologic eyes measured with standard resolution. We also compare cross-sectional images of pathology obtained by standard and high resolution systems.
Spectral Optical Coherence Tomography system was used to perform clinical examinations of the human eye. Images of different pathologies were obtained with the aid of a high speed standard resolution instrument. High speed allows performing scanning with high sampling density. We show that high density lateral scanning together with standard resolution is sufficient to obtain good quality cross sectional images which enable detecting such details of the eye anatomy like the external limiting membrane.
Complex Spectral domain Optical Coherence Tomography (CSdOCT) produces images free of parasitic mirror component which results in twofold extension of the measurement range. Complete removal of this component requires exact knowledge of the introduced phase shifts, what is usually difficult to achieve. Presented method effectively removes the mirror image, even without the knowledge of the phases. The method is applicable to any variation of CSdOCT. The 'mirror image-free' tomograms of human anterior chamber in-vivo obtained with the aid of this approach are shown.
Fourier Domain Optical Coherene Tomography (FD OCT) is a high speed imaging modality with increased sensitivity as compared to standard time domain (TD) OCT. The higher sensitivity is especially important, if strongly scattering tissue such as blood is investigated. Recently it could be shown that retinal blood flow can be assessed in-vivo by high speed FD OCT. However the detection bandwidth of color Doppler (CD) FDOCT is strongly limited due to blurring of the detected interference fringes during exposure. This leads to a loss of sensitivity for detection of fast changes in tissue. Using a moving mirror as a reference one can effectively increase the detection bandwidth for CD FDOCT and perform perfusion sectioning. The modality is called resonant CD FDOCT imaging. The principle of the method is presented and experimentally verified.
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