We demonstrate in-vivo functional imaging of the human retina with Fourier domain optical
coherence tomography employing frequency encoding of an excitation pattern. The
principle is based on projecting a modulated rectangular pattern across the foveal region and
acquiring a time series of B-Scans at the same vertical position across the pattern. The idea is
to modulate the excitation with a frequency that is distinct from the heartbeat and irregular
motion artifacts. Fourier analysis of the time series at each transverse position in the B-scan
series allows assessing the retinal response as change in the FDOCT reflectivity signal exactly
at the pattern modulation frequency. We observe a change in retinal reflectivity within the
region of the outer segment photoreceptor layer exactly at the pattern modulation
frequency.
Resonant Doppler Fourier Domain Optical Coherence Tomography is a functional imaging modality for quantifying fast
tissue flow. The method profits from the effect of interference fringe blurring in spectrometer-based FDOCT in the
presence of sample motion. If the reference path length is changed in resonance with the Doppler frequency of the
sample flow the signals of resting structures will be suppressed whereas the signals of blood flow are enhanced. This
allows for an easy extraction of vascularization structure. 3D images of blood vessels at the human optic nerve head are
obtained with high axial resolution of 8 μm in air and an imaging speed of 17.400 depth profiles per second. An electro-optic
modulator allows controlled reference phase shifting during camera integration. A differential approach is
presented for the quantification of fast flows that are un-accessible via standard phase sensitive Doppler analysis. Flow
velocity analysis extracts only the axial component which is dependent on the orientation of the vessel with respect to the
optical axis. 3D information of the segmented vessel structure is readily used to obtain the flow velocity vectors along
the individual vessels and to calculate the true angle-corrected flow speed.
KEYWORDS: Blood circulation, Doppler tomography, Signal attenuation, Optical coherence tomography, Doppler effect, Cameras, 3D image processing, Reconstruction algorithms, Image segmentation, Signal to noise ratio
Resonant Doppler Fourier domain optical coherence tomography (FDOCT) is a functional imaging tool for extracting tissue flow. The method is based on the effect of interference fringe blurring in spectrometer-based FDOCT, where the path difference between structure and reference changes during camera integration. If the reference path length is changed in resonance with the Doppler frequency of the sample flow, the signals of resting structures will be suppressed, whereas the signals of blood flow are enhanced. This allows for an easy extraction of vascularization structure. Conventional flow velocity analysis extracts only the axial flow component, which strongly depends on the orientation of the vessel with respect to the incident light. We introduce an algorithm to extract the vessel geometry within the 3-D data volume. The algorithm calculates the angular correction according to the local gradients of the vessel orientations. We apply the algorithm on a measured 3-D resonant Doppler dataset. For validation of the reproducibility, we compare two independently obtained 3-D flow maps of the same volunteer and region.
Fourier Domain OCT proved to be an outstanding tool for measuring 3D retinal structures with
high sensitivity, resolution, and speed. We extended the FDOCT concept towards functional
imaging by analyzing the spectroscopic tissue properties, polarization contrast and Doppler
velocity imaging. Differential spectral contrast FDOCT allows optical staining of retinal
tomograms and to contrast tissue of high pigmentation such as the retinal pigment epithelium
(RPE). The latter shows strong correlation if compared to polarization sensitive OCT images.
First implementations of Doppler FDOCT systems demonstrated the capability of measuring in-vivo
retinal blood flow profiles and pulsatility. We developed a new concept of Doppler FDOCT
that allows measuring also large flow velocities typically close to the optic nerve head. Studies of
retinal perfusion based on Laser Doppler Flowmetry (LDF) demonstrated the high sensitivity of
blood flow to external stimuli. We performed first experiments of studying retinal perfusion in
response to flicker stimulation. An increase in vessel diameter by 11% and of flow velocity by
49% was measured. We believe that a multi-modal functional imaging concept is of high value
for an accurate and early diagnosis and understanding of retinal pathologies and pathogenesis.
KEYWORDS: Doppler effect, Blood circulation, Skin, Imaging systems, 3D metrology, 3D image processing, In vivo imaging, Tissue optics, Wound healing, Digital micromirror devices
We present a combination of topography measurements based on digital fringe projection and blood flow imaging based on Laser Doppler Imaging (LDI). Both techniques are optical, non-contact and high-speed whole-field methods well suited for in-vivo measurements on the skin. Laser Doppler perfusion imaging is an interferometric technique used for visualization of two-dimensional (2D) maps of blood flow. Typically the measured sample has a surface with a specific 3D relief. In many cases the sample relief can be of importance for correct interpretation of the obtained perfusion data. We combined the topography and the blood flow data obtained from the same object. The structural information provided by the topography is completed by the functional images provided by LDI.
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