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.
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.
Ocular blood flow measurement may have a number of potential applications that explore the relationship between blood flow in the eye and diseases such as: diabetic retinopathy, ocular artery obstruction, hypertensive retinopathy and Alzheimer's disease. Reliable and quantitative method for retinal blood flow estimation is still to be created. Doppler OCT is one of candidates for such a method, but suffers from a number of limitations. Recently we proposed a solution to one of the most prominent artefacts in Doppler OCT, which is the phase wrapping problem. This allows for precise recovery of velocity profile the Doppler OCT technique remains sensitive to temporal dependence of the result on the blood flow velocity changing with the pulse during the OCT measurement. In this report we explore this problem and show that the synchronization of the OCT measurement with heart beats only partially gives control over the acquired blood flows.
Madonna dei Fusi (‘Madonna of the Yarnwider’) is a spectacular example of Italian Renaissance painting, attributed to Leonardo da Vinci. The aim of this study is to give an account of past restoration procedures. The evidence of a former retouching campaign will be presented with cross-sectional images obtained non-invasively with Optical Coherence Tomography (OCT). Specifically, the locations of overpaintings/retouchings with respect to the original paint layer and secondary varnishes will be given. Additionally, the evidence of a former transfer of the pictorial layer to the new canvas support by detecting the presence of its structure incised into paint layer will be shown.
KEYWORDS: Optical coherence tomography, Visualization, Real time imaging, Data processing, Doppler tomography, Data acquisition, Graphics processing units, Cameras, 3D image processing, Doppler effect
In this report the application of graphics processing unit (GPU) programming for real-time 3D Fourier domain Optical Coherence Tomography (FdOCT) imaging with implementation of Doppler algorithms for visualization of the flows in capillary vessels is presented. Generally, the time of the data processing of the FdOCT data on the main processor of the computer (CPU) constitute a main limitation for real-time imaging. Employing additional algorithms, such as Doppler OCT analysis, makes this processing even more time consuming. Lately developed GPUs, which offers a very high computational power, give a solution to this problem. Taking advantages of them for massively parallel data processing, allow for real-time imaging in FdOCT. The presented software for structural and Doppler OCT allow for the whole processing with visualization of 2D data consisting of 2000 A-scans generated from 2048 pixels spectra with frame rate about 120 fps. The 3D imaging in the same mode of the volume data build of 220 × 100 A-scans is performed at a rate of about 8 frames per second. In this paper a software architecture, organization of the threads and optimization applied is shown. For illustration the screen shots recorded during real time imaging of the phantom (homogeneous water solution of Intralipid in glass capillary) and the human eye in-vivo is presented.
The authors present the application of graphics processing unit (GPU) programming for real-time three-dimensional (3-D) Fourier domain optical coherence tomography (FdOCT) imaging with implementation of flow visualization algorithms. One of the limitations of FdOCT is data processing time, which is generally longer than data acquisition time. Utilizing additional algorithms, such as Doppler analysis, further increases computation time. The general purpose computing on GPU (GPGPU) has been used successfully for structural OCT imaging, but real-time 3-D imaging of flows has so far not been presented. We have developed software for structural and Doppler OCT processing capable of visualization of two-dimensional (2-D) data (2000 A-scans, 2048 pixels per spectrum) with an image refresh rate higher than 120 Hz. The 3-D imaging of 100×100 A-scans data is performed at a rate of about 9 volumes per second. We describe the software architecture, organization of threads, and optimization. Screen shots recorded during real-time imaging of a flow phantom and the human eye are presented.
Optical coherence tomography (OCT) is a fast non-contact and non-invasive technique for examination of objects
consisting of transparent or semitransparent layers. Since it is a useful tool for inspection of Hinterglasmalerei paintings,
the aim of the experiment was to explore its feasibility for monitoring of the consolidation process, which plays the most
important role in the conservation treatment of such artefacts.
KEYWORDS: Data processing, Optical coherence tomography, Visualization, Data acquisition, Real time imaging, Graphics processing units, Imaging systems, Parallel processing, 3D acquisition, Image processing
In this contribution we describe a specialised data processing system for Spectral Optical Coherence Tomography (SOCT)
biomedical imaging which utilises massively parallel data processing on a low-cost, Graphics Processing Unit (GPU). One
of the most significant limitations of SOCT is the data processing time on the main processor of the computer (CPU),
which is generally longer than the data acquisition. Therefore, real-time imaging with acceptable quality is limited to a
small number of tomogram lines (A-scans). Recent progress in graphics cards technology gives a promising solution of
this problem. The newest graphics processing units allow not only for a very high speed three dimensional (3D)
rendering, but also for a general purpose parallel numerical calculations with efficiency higher than provided by the
CPU. The presented system utilizes CUDATM graphic card and allows for a very effective real time SOCT imaging. The
total imaging speed for 2D data consisting of 1200 A-scans is higher than refresh rate of a 120 Hz monitor. 3D rendering
of the volume data build of 10 000 A-scans is performed with frame rate of about 9 frames per second. These frame rates
include data transfer from a frame grabber to GPU, data processing and 3D rendering to the screen. The software
description includes data flow, parallel processing and organization of threads. For illustration we show real time high
resolution SOCT imaging of human skin and eye.
In this contribution a proof of concept for the alternate way of twofold increasing the axial resolution of Optical
Coherence Tomography systems is shown. On the contrary to expanding the bandwidth of the light source, the number
of passes of light between sample and the Michelson interferometer is increased. In two simplified novel configurations
of Spectral OCT devices designed for this research, the interferometer is equipped with polarization controlling elements
in order to force light to pass the distance from the beam splitter to the sample four times: during the first pass the initial
linear polarization of the probing beam is converted to the perpendicular one and on return to the interferometer
deflected by the polarization sensitive beam splitter towards the additional mirror reflecting it back to the sample. After
the second pass the state of polarization is changed again and restored to the initial one in order to interfere with the
reference beam. As a result in both set-ups optical paths difference between both arms of the Michelson interferometer is
twofold longer comparing to the standard system. This results in two times smaller axial calibration coefficient and
finally twofold increase of an effective axial resolution for the same coherence length of the light source. In the paper the
experimental evidences are given and limitations of the method discussed.
In this contribution we describe an apparatus for precise laser ablation of delicate layers, like varnish on pictures. This
specific case is very demanding. First of all any changes in colour of remaining varnish layer as well as underneath paint
layers are unacceptable. This effect may be induced photochemically or thermically. In the first case strong absorption of
the radiation used will eliminate its influence on underlying strata. The thermal effect is limited to so called heat affected
zone (HAZ). In addition to colour change, a mechanical damage caused by overheating of the structure adjacent to
ablated region should be considered also. All kinds of treads must be carefully eliminated in order to make laser ablation
of varnish commonly accepted alternative to chemical and/or mechanical treatments [1].
Since the varnish ablation process is obviously irreversible its effective monitoring is very important to make it safe and
trusted. As we showed previously [2-6] optical coherence tomography (OCT) originated from medicine diagnostic method
for examination and imaging of cross-sections of weakly absorbing objects can be used for this task. OCT utilises infrared
light for non-invasive structure examination and has been under consideration for the examining of objects of art since 2004
[7-10]. In this case the in-depth (axial) resolution is obtained by means of interference of light of high spatial (to ensure
sensitivity) and very low temporal coherence (to ensure high axial resolution). In practice, IR sources of bandwidths from
25 to 150 nm are utilised. Resolutions obtained range from 15 down to 2 μm in the media of refracting index equal 1.5.
In this contribution we expand application of OCT to space resolved determination of ablation rates, separately for every
point of examined area. Such data help in better understanding of the ablation process, fine tuning the laser and finally
permit increase of the safety of the ablation process.
Optical Coherence Tomography (OCT) is an interferometric method utilising light of low temporal coherence for noninvasive
structural imaging of objects weakly absorbing and scattering light. In this contribution, using various examples
of images of objects made of glass affected by the atmospheric corrosion and/or by crizzling, we demonstrate a software
developed in our laboratory specifically for 3D OCT imaging of samples with a fine structure. For this task we employed
the OpenGL platform (Open Graphics Library), an Application Programming Interface (API) for writing applications
dedicated to interactive 3D computer graphics. In our application we have utilized texture rendering with a modulation of
transparency and a colour as a function of elevation.
In this contribution preliminary studies on the application of Optical Coherence Tomography (OCT) to absolute depth
calibration of Laser Induced Breakdown Spectroscopy (LIBS) data in application to revealing stratigraphy of easel
paintings are presented. The procedure of in-situ monitoring of LIBS by means of OCT is described. Numerical method
developed for precise extraction of the depth of the LIBS ablation crater is explained. Results obtained with model
paintings are discussed.
In this contribution the application of Optical Coherence Tomography (OCT) for non-invasive structural imaging of easel paintings will be presented. Since the technique permits imaging semi-transparent layers accessible for infrared light, the varnish and glaze layers are usually under investigation. The major emphasis will be laid on application of OCT to resolving specific conservation problems, arising during the restoration process. The examples of imaging multilayer varnishes and subsequent alterations will be given and the application of these images for authentication of inscriptions will be discussed. Since the thickness of imaged layers may be directly measured with OCT in completely non-destructive, quick and convenient way as many times as necessary, the application of the technique to generation of varnish thickness maps will be presented.
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