We conducted a first-in-human study using a fluorescent slurry comprised of 10 ml Methylene Blue (50 mg dissolved in water) and 10 ml Agave nectar. Preliminary data from the first patient indicates that at 20 minutes Barrett's Esophagus (esophageal pre-cancer) can be discriminated from normal tissue with a target-to-background ratio of 1.96 and an effect size > 5 (Cohen's D). We further show a dose modification pathway to high-TBR imaging shortly after swallowing the slurry.
A component used to extend the depth of field for compact endoscopic OCT probes is the mirror tunnel. BeamLab software, which uses the beam propagation method, was used to simulate the mirror tunnel probes and quantify depth of field extension and lateral resolution. Considering the exit face of the mirror tunnel as an extended object decouples the physical operation of the mirror tunnel from the focusing optics, which reduces the optimization parameter space. Lateral resolution performance was found to depend heavily on the metric chosen, with strong side lobes reducing image contrast; hence, the optimization merit function should be carefully chosen.
Eosiophilic esophagitis (EoE) is an inflammatory disease of the esophagus, with long-term EoE causing fibrotic and hypertrophic restructuring of the sub-epithelial wall. We have developed a polarization-sensitive micro-optical coherence tomography (PS-µOCT) imaging device for its characterization. This device was used to quantify collagen at 15 sites on each of 5 swine esophagi, with results compared to histology. A linear mixed model with random intercept showed significant agreement between OCT and histology (slope = 0.41, 95% CI [0.22, 0.60], t(67) = 4.30, p = 5.8 x 10-5). This validates our technology and will allow longitudinal assessment of patient response to drug and diet, without endoscopic biopsy.
We introduce two multimodal extensions of our optical coherence tomography (OCT) based tethered capsule endomicroscopy (TCE) platform, tailored towards an enhanced clinical applicability for upper gastrointestinal tract imaging. The first extension presented – white light (RGB)-OCT-based TCE – provides both, true-color visualization of the tissue surface and depth-resolved sub-surface OCT imaging, co-registered in time and space. The second extension presented – fluorescence (FL)-OCT-based TCE – enables the addition of tissue specific molecular contrast. We present compact, modular, easily portable, plug-and-play system designs for both extensions, as well as imaging results in swine esophagus, in vivo.
KEYWORDS: Optical coherence tomography, Luminescence, Imaging systems, Tissues, Process control, Near infrared, Visualization, Standards development, Lens design, Control systems
We present our next generation clinical dual-modality OCT and near infrared autofluorescence/fluorescence (NIRAF/NIRF) imaging platform. This platform allows combined tissue microstructure visualization (OCT) and obtaining molecular information either by intrinsic tissue near infrared autofluorescence (NIRAF) or by exogenous near infrared fluorescence contrast agents (NIRF). Components of this platform, OCT-NIRAF/NIRF imaging system, rotary junction and catheters, were developed using an industry standard design control processes to enable quality clinical translation. We have identified sources of image degradation in dual-modality catheter-based imaging (e.g. core-cladding crosstalk in OCT, background noise in fluorescence) and present methods to mitigate their effects. We also show catheter fabrication and validation, as well as automated fluorescence sensitivity and distance calibration methods that ensure robust and repeatable system performance.
Spontaneous retinal venous pulsations (SRVP) describe rhythmic caliber oscillations of one or multiple major retinal veins at the site of the optic nerve head (ONH). This phenomenon is reported to possibly enable non-invasive intracranial pressure (ICP) assessment besides its potential significance for major ocular diseases such as glaucoma or diabetic retinopathy. In this work, we illustrate the advantages of optical coherence tomography (OCT) imaging for investigation of SRVP. Using conventional intensity based OCT as well as the functional extension Doppler OCT (DOCT), the pulsatile changes in venous vessel caliber are analyzed qualitatively and quantitatively. Single-channel and double-channel line scanning protocols of our time-encoded multi-channel OCT prototype are employed to investigate venous caliber oscillations as well as venous flow pulsatility in the eyes of healthy volunteers. A comparison to recordings of scanning laser ophthalmoscopy – a standard en-face imaging modality for evaluation of SRVP – is provided, emphasizing the advantages of tomographic image acquisition. To the best of our knowledge, this is the first quantitative time-resolved investigation of SRVP and associated retinal perfusion characteristics using OCT.
Investigations on retinal vasculature and blood flow are of interest for understanding and diagnostics of numerous ocular diseases. Conventional OCT systems use various scan patterns like linear B-scans, circular scans around the optic nerve head, or raster scans for 3D data acquisition. However, for some studies it is preferable to have customized scan patterns that can, e.g., follow the trace of an arbitrary linear structure in the retina, such as a vessel. In this work, we present an OCT instrument with an integrated retinal tracker that allows repeated scans along an arbitrary trace, whereby ocular motions are corrected by the retinal tracker. The setup comprises an OCT system and a line scanning laser ophthalmoscope (LSLO). The OCT subsystem operates at a center wavelength of 860 nm, with a bandwidth of 60 nm and an A-scan rate of 70kHz. The LSLO system operates at 790 nm and at a frame rate of 60 Hz. This system was used for reflectivity and Doppler imaging along retinal vessels. In a first step, the vessel is manually marked on the LSLO image. Then, repeated scans along the vessel trace are performed (2048 A-scans per scan along trace, up to 500 scans along the trace). The intensity images show a clear delineation of the vessel walls, the phase difference (Doppler) tomograms allow for a time-resolved analysis of blood flow along the vessel over the cardiac cycle.
Polarization-sensitive optical coherence tomography (PS-OCT) enables noninvasive, high-resolution imaging of tissue polarization properties. In the anterior segments of human eyes, PS-OCT allows the visualization of birefringent and depolarizing structures. We present the use of PS-OCT for imaging the murine anterior eye. Using a spectral domain PS-OCT setup operating in the 840-nm regime, we performed in vivo volumetric imaging in anesthetized C57BL/6 mice. The polarization properties of murine anterior eye structures largely replicated those known from human PS-OCT imagery, suggesting that the mouse eye may also serve as a model system under polarization contrast. However, dissimilarities were found in the depolarizing structure of the iris which, as we confirmed in postmortem histological sections, were caused by anatomical differences between both species. In addition to the imaging of tissues in the anterior chamber and the iridocorneal angle, we demonstrate longitudinal PS-OCT imaging of the murine anterior segment during mydriasis as well as birefringence imaging of corneal pathology in an aged mouse.
KEYWORDS: Optical coherence tomography, Endoscopy, Endoscopes, Signal detection, In vivo imaging, Mirrors, GRIN lenses, Tissues, Image quality, Imaging systems
We demonstrate in vivo endoscopic optical coherence tomography (OCT) imaging in the forward direction using a flexible fiber bundle (FB). In comparison to current conventional forward-looking probe schemes, our approach simplifies the endoscope design by avoiding the integration of any beam steering components in the distal probe end due to two-dimensional scanning of a focused light beam over the proximal FB surface. We describe the challenges that arise when OCT imaging with an FB is performed, such as multimoding or cross coupling. The performance of different FBs varying in parameters, such as numerical aperture, core size, core structure, and flexibility, was consequently compared, and image quality degrading artifacts were described in detail. Based on our findings, we propose an optimal FB design for endoscopic OCT imaging.
We introduce the approach of variable time encoding for multichannel optical coherence tomography (OCT). High-speed fiber optical switches are applied for sequential sample arm switching to enable quasisimultaneous image acquisition from three different orientation angles. In comparison with previous multichannel OCT (using simultaneous sample illumination), time-encoded multichannel OCT has no need for division of illumination power among the respective channels to satisfy laser safety requirements. Especially for ophthalmic applications—in particular retinal imaging, which the presented prototype was developed for—this advantage strongly influences image quality through an enhanced sensitivity. Nevertheless, time encoding comes at the cost of a decrease in imaging speed due to sequential channel illumination. For the typical multichannel OCT modality Doppler OCT, this results in a reduction of the maximum unambiguously determinable Doppler velocity. However, we demonstrate that this drawback can be overcome by adaptation of the illumination channel switching scheme. Thus, a re-extension of the maximum unambiguously determinable Doppler frequency to the full A-scan rate of the tunable light source is presented. The performance of the technique is demonstrated by flow phantom experiments and measurements of retinal blood flow in the eyes of healthy human volunteers.
Adaptive Optics (AO) retinal imaging is revealing microscopic structures of the eye in a non-invasive way. Due to anisoplanatism, conventional AO systems are efficient on small 1°x1° field of view (FoV). We present a lens-based AO scanning laser ophthalmoscope (SLO) set-up with 2 deformable mirrors (DM), providing high-resolution retinal imaging on a 4°x4° FoV, for an eye pupil diameter of 7 mm. The first DM is in a pupil plane and is driven using a Shack-Hartmann (SH). The second DM is conjugated to a plane located 0.7 mm in front of the retina, to correct for aberrations varying within the FoV. Its shape is optimized using sensorless AO technique.
The performance of this set-up was characterized in-vivo by measuring the eyes of four healthy volunteers. The obtained image quality was satisfactory and uniform over the entire FoV. Foveal cones could be resolved and no image distortion was detected. Furthermore, a 10°x10° FoV image was acquired at the fovea of one volunteer, by stitching 9 images recorded at different eccentricities. Finally, different layers of the retina were imaged. In addition to the photoreceptors mosaic, small capillaries and nerve fibers were clearly identified.
The presented AO-SLO instrument provides high-resolution images of the retina on a relatively large FoV in reasonable time. With 2 DMs, one SH and no guide star, the system stays quite simple. The imaging performance of the set-up was validated on 4 healthy volunteers and we are currently imaging patients with different eye diseases.
A sequential multi-channel OCT prototype featuring high-speed fiber optical switches to enable inter A-scan (A-scan rate: 100 kHz) sample arm switching was developed and human retinal image data is presented.
A few-mode fiber based detection for OCT systems is presented. The capability of few-mode fibers for delivering light through different fiber paths enables the application of these fibers for angular scattering tissue character- ization. Since the optical path lengths traveled in the fiber change between the fiber modes, the OCT image information will be reconstructed at different depth positions, separating the directly backscattered light from the light scattered at other angles. Using the proposed method, the relation between the angle of reflection from the sample and the respective modal intensity distribution was investigated. The system was demonstrated for imaging ex-vivo brain tissue samples of patients with Alzheimer’s disease.
Adaptive optics (AO) is essential in order to visualize small structures such as cone and rod photoreceptors in the living human retina in vivo. By combining AO with optical coherence tomography (OCT) the axial resolution in the images can be further improved. OCT provides access to the phase of the light returning from the retina which allows a measurement of subtle length changes in the nanometer range. These occur for example during the renewal process of cone outer segments. We present an approach for measuring very small length changes using an extended AO scanning laser ophthalmoscope (SLO)/ OCT instrument. By adding a second OCT interferometer that shares the same sample arm as the first interferometer, phase sensitive measurements can be performed in the en-face imaging plane. Frame averaging decreases phase noise which greatly improves the precision in the measurement of associated length changes.
A novel approach for investigation of human retinal and choroidal blood flow by the means of multi-channel swept
source Doppler optical coherence tomography (SS-D-OCT) system is being developed. We present preliminary in vitro
measurement results for quantification of the 3D velocity vector of scatterers in a flow phantom. The absolute flow
velocity of moving scatterers can be obtained without prior knowledge of flow orientation. In contrast to previous
spectral domain (SD-) D-OCT investigations, that already proved the three-channel D-OCT approach to be suitable for
in vivo retinal blood flow evaluation, this current work aims for a similar functional approach by means of a differing
technique. To the best of our knowledge, this is the first three-channel D-OCT setup featuring a wavelength tunable laser
source. Furthermore, we present a modification of our setup allowing a reduction of the former three active illumination
channels to one active illumination channel and two passive channels, which only probe the illuminated sample. This
joint aperture (JA) approach provides the advantage of not having to divide beam power among three beams to meet
corresponding laser safety limits. The in vitro measurement results regarding the flow phantom show good agreement
between theoretically calculated and experimentally obtained flow velocity values.
We present a three beam optical Doppler tomography (ODT) technique suitable for 3-D velocity and flow measurements to evaluate total retinal blood circulation from and to the optic nerve head (ONH). The system consists of three independent ODT channels. Superluminescent diodes with a central wavelength of 840 nm and a spectral bandwidth of 50 nm were used. The sources are coupled to collimators resting in a specially designed mount to ensure a well-defined beam geometry, necessary for the full reconstruction of the three dimensional velocity vector. The reconstruction works without prior knowledge on the vessel geometry, which is normally required for ODT systems with less than three beams. The beams share a common bulk optics Michelson interferometer, while the detection comprises three identical spectrometers with a line scan rate of 50 kHz. 20 eyes of healthy volunteers were imaged with the 3 beam ODT, employing a circular scan pattern around the ONH. The mean total blood flow was calculated for arteries (47.1 ± 2.4 μl/min (mean ± SD)) and veins (47.1 ± 2.7 μl/min μl/min) independently. The two results showed no significant difference (paired t-test, p < 0.96), rendering both equally reliable for total flow measurements. Furthermore the reproducibility of the method was evaluated for the total flow and flow, velocities within each individual vessel of 6 eyes. The average variation for total flow measurements is sufficiently low to detect deviations of ~ 6% indicating high precision of the proposed method.
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