OCT is a promising tool for performing fast and cheap noninvasive biopsies. High speed imaging helps to reduce motion artifacts that cause decreased sensitivity and resolution. Using a point scanning configuration one is ultimately limited in sensitivity. Therefore parallel configurations are a potentially attractive solution to further enhance the speed capabilities of future OCT systems. Even more, if full field configurations are employed one can exploit the intrinsic phase correlation over the field of view for digital wavefront correction techniques. Full field OCT has nevertheless limitations concerning the missing confocal gating. The sensitivity is decreased in the presence of specular reflexes from optical interfaces, furthermore light scattering cross talk between pixel causes additional signal degradation. A good compromise between parallel detection capabilities and confocal gating seems therefore line field OCT. We built a bench top line field system employing a frequency swept source enabling 2D/3D imaging at up to 200 kA-scans/s with an axial resolution of 8μm and a depth range of 3.53mm in air. To prevent specular reflexes reaching the line scan camera, an off axis configuration of the optical path together with spatial filters placed in conjugate planes of the system was used. Geometrical optics based digital refocusing through the full depth range was shown on a sample target containing FeO particles, on a biological sample and in vivo. Furthermore, we assessed the regime where line field has an advantage over point scanning OCT in terms of sensitivity.
In vascular plexuses perpendicular to the optical axis, traditional Doppler OCT (DOCT) is highly sensitive to the
Doppler angle, limiting its reproducibility and accuracy in clinical practice. A more stable approach is the dual-beam
bidirectional technique that probes the sample from two distinct illumination directions allowing reconstruction of the
true flow velocity and later the blood flow with knowledge of the vessel diameter. However the absolute velocity
calculation still requires the evaluation of the flow angle in the en face plane. Based on dual beam bidirectional DOCT
we suggest calculating the flow directly from an adequately chosen Doppler cross section and demonstrate that this
method is independent of the vessel angle. The principle is implemented with Swept Source OCT at 1060nm with
100,000 A-Scans/s. We confirm, with in vitro measurements of a perfused capillary and with a selected human retinal
artery, that this method employing two beams only is completely independent of any vessel orientation.
Traditional Doppler OCT is highly sensitive to motion artifacts due to the dependence on the Doppler angle. This limits its reproducibility in clinical practice. To overcome this limitation, we use a bidirectional technique with a novel rotating scanning scheme. The volume is probed simultaneously from two distinct illumination directions with variable controlled orientations, allowing reconstruction of the true flow velocity, independently of the vessel orientation. A Dove prism in the sample arm permits a rotation of the illumination directions that can be synchronized with the standard beam steering device. The principle is implemented with Swept Source OCT at 1060nm with 100,000 A-Scans/s. We apply the system to human retinal absolute blood velocity measurement by performing segment and circumpapillary time series scans around the optic nerve head. We also demonstrate microvasculature imaging by calculation of squared intensity differences between successive tomograms.
Retinal and choroidal vascular imaging is an important diagnostic benefit for ocular diseases such as age-related macular degeneration. The current gold standard for vessel visualization is fluorescence angiography. We present a potential non-invasive alternative to image blood vessels based on functional Fourier domain optical coherence tomography (OCT). For OCT to compete with the field of view and resolution of angiography while maintaining motion artifacts to a minimum, ultrahigh-speed imaging has to be introduced. We employ Fourier domain mode locking swept source technology that offers high quality imaging at an A-scan rate of up to 1.68 MHz. We present retinal angiogram over ∼ 48 deg acquired in a few seconds in a single recording without the need of image stitching. OCT at 1060 nm allows for high penetration in the choroid and efficient separate characterization of the retinal and choroidal vascularization.
We present an extended focus OCT system for dermatologic applications that maintains high lateral resolution over a
large depth range by using Bessel beam illumination. More, Bessel beams exhibit a self-reconstruction property that is
particularly useful to avoid shadowing from surface structures such as hairs. High lateral resolution and high-speed
measurement, thanks to a rapidly tuning swept source, allows not only for imaging of small skin structures in depth but
also for comprehensive visualization of the small capillary network within the human skin in-vivo. We use this
information for studying temporal vaso-responses to hypothermia. In contrast to other perfusion imaging methods such
as laser Doppler imaging (LDI), OCT gives specific access to vascular responses in different vascular beds in depth.
We introduce a swept source FDOCT imaging system that allows measuring simultaneously the reflected light and
scattered light (bright field) and the scattered light only (dark field) in two different channels through separate Gaussian
and Bessel detection. Specular reflections can then be used to obtain knowledge about the sample time evolution with
high SNR for phase analysis. Based on this configuration, we provide a proof-of principle study for resolving ultrasound
pulse trains with high temporal resolution on surfaces, which potentially provides a novel phase sensitive all optical
detection scheme for the combination of OCT with photoacoustic imaging.
We present a Bessel beam illumination FDOCT setup with FDML buffered swept source at 1300nm. An extended focus
is achieved due to the Bessel beam that preserves its lateral extend over a large depth range. Decoupling the illumination
from the Gaussian detection improves the sensitivity as compared to double passing the ring filter and enables dark field
imaging. Dark field imaging is useful to avoid strong reflexes from the sample's surface that adversely affect the
sensitivity due to the limited dynamic range of high-speed 8bit acquisition cards. Furthermore, Bessel beams exhibit a
self-reconstruction property that allows imaging even behind obstacles such as hairs on skin.
Densely sampled volumes of skin in-vivo with high lateral resolution are acquired at up to 440kHz A-Scan rate. In
addition the possibility of contrasting capillaries with high sensitivity is shown, using inter-B-scan speckle variance
analysis. High-speed imaging is of crucial importance for imaging small details since sample motion artifacts are
reduced and high sampling can be maintained while increasing the B-Scan rate.
We present a spectral domain refractive low coherence interferometry technique (SD-rLCI) using a novel extreme
broadband Super Continuum laser source equipped with a dual spectrometer system which is able to measure the
dispersion in the visual and near infrared range simultaneously. The setup was verified obtaining the second order
dispersion of distilled water. We will use this system for measuring the dispersion sensitivities of important tissue
substances in order to determine analyte concentrations within mixtures.
We present an extended focus FDOCT setup with FDML swept source centered at 1310nm. The illumination, preserving
its lateral extend over a large depth range thanks to the use of a Bessel beam, is decoupled from the Gaussian detection in
order to increase the global sensitivity. The efficient spatial separation enables dark-field imaging. In-vivo measurements
in the skin were performed to demonstrate the gain in lateral resolution while preserving the imaging depth. More, the
calculation of the speckle variance between B-Scans allows a clear visualization of the microvasculature.
Using refractive low coherence interferometry (rLCI) technique we determined the concentration of aqueous mixtures of
glucose and albumin. The method is based on second-order dispersion derived from spectral phase of time-domain
interferogram. A series of 9 mixtures with different concentration ratios in the range of 5mg/ml to 50mg/ml was
performed. The results show errors between prepared and measured concentration of a few percent up to 38%.
KEYWORDS: Eye, In vivo imaging, Distance measurement, Spectroscopy, Cornea, Signal detection, Signal to noise ratio, Mirrors, Optical coherence tomography, Beam splitters
We present a system for intraocular distance measurement of the human eye in vivo with high sensitivity. The instrument is based on Fourier domain low coherence interferometry (FD-LCI). State-of-the-art FD-LCI systems are capable to image a depth range of only a few mm, because the depth range is determined by the spectral resolution of the spectrometer. To measure larger distances (e.g. human eye length) we implemented two separate reference arms with different arm lengths into the interferometer. Each reference arm length corresponds to a different depth position within the sample (e.g. cornea and retina). Therefore two different depth sections, each with a depth range of a few mm can be imaged simultaneously. With the new system axial distances could be measured with a precision of 8&mgr;m. We demonstrate the performance of the instrument by measuring the axial eye length of 9 patients with cataract and compare our results with those obtained using the IOL Master (Carl Zeiss Meditec Inc.).
We present an Optical coherence tomography (OCT) system which records full tomograms of in vivo eye structure in parallel. A full tomogram of 256(x) x 512(z) pixels covering a sample region of 6.7mm x 3,8mm is recorded in only 1ms. A standard Superluminescent diode (SLD) is used which results a depth resolution of 17 mm. Since neither depth nor transverse scanning is necessary, the system allows capturing full tomograms with high acquisition speed and reduced motion artifacts. To the best of our knowledge we present the first in vivo tomogram obtained with full parallel FD OCT system. In order to study cross talk issues for parallel illumination the transversal resolution for a thermal light source is compared to that with an SLD.
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