Cochlear implantation offers the potential to restore sensitive hearing in patients with severe to profound deafness. However, surgical placement of the electrode array within the cochlea can produce trauma to sensorineural components, particularly if the initial turn of the cochlea is not successfully navigated as the array is advanced. In this work, we present a robot-mounted common-path swept-source optical coherence tomography endoscopic platform for three-dimensional (3-D) optical coherence tomography (OCT) registration and preoperative surgical planning for cochlear implant surgery. The platform is composed of a common-path 600-μm diameter fiber optic rotary probe attached to a five degrees of freedom robot capable of 1 μm precision movement. The system is tested on a dry fixed ex vivo human temporal bone, and we demonstrate the feasibility of a 3-D OCT registration of the cochlea to accurately describe the spatial and angular profiles of the canal formed by the scala tympani into the first cochlear turn.
We describe a novel common-path optical coherence tomography (CP-OCT) fiber probe design using a sapphire ball
lens for cross-sectional imaging and sensing in retina vitrectomy surgery. Single mode Gaussian beam (TEM00) simulation was used to optimize lateral resolution and working distance (WD) of the common-path probe. A theoretical sensitivity model for CP-OCT was prosed to assess its optimal performance based an unbalanced photodetector configuration. Two probe designs with working distances (WD) 415μm and 1221μm and lateral resolution 11μm and 18μm, respectively were implemented with sensitivity up to 88dB. The designs are also fully compatible with conventional Michelson interferometer based OCT configurations. The reference plane of the probe, located at the distal beam exit interface of the single mode fiber (SMF), was encased within a 25-gauge hypodermic needle by the sapphire ball lens facilitates its applications in bloody and harsh environments. The performances of the fiber probe with 11μm of lateral resolution and 19μm of axial resolution were demonstrated by cross-sectional imaging of a cow cornea and retina in vitro with a 1310nm swept source OCT system. This probe was also attached to a piezoelectric motor for active compensation of physiological tremor for handheld retinal surgical tools.
We describe a novel dual-functional optical coherence tomography (OCT) system with both a fiber probe using a sapphire ball lens for cross-sectional imaging and sensing, and a 3-D bulk scanner for 3-D OCT imaging. A theoretical sensitivity model for Common Path (CP)-OCT was proposed to assess its optimal performance based on an unbalanced photodetector configuration. A probe design with working distances (WD) 415μm and lateral resolution 11 μm was implemented with sensitivity up to 88dB. To achieve high-speed data processing and real-time three-dimensional visualization, we use graphics processing unit (GPU) based real-time signal processing and visualization to boost the computing performance of swept source optical coherence tomography. Both the basal turn and facial nerve bundles inside the cadaveric human cochlea temporal bone can be clearly identified and 3D images can be rendered with the OCT system, which was integrated with a flexible robotic arm for robotically assisted microsurgery.
We describe a novel dual-functional optical coherence tomography (OCT) system with both a 3-D OCT real time
scanner and a fiber probe using a sapphire ball lens for imaging and sensing the critical structures of the temporal
bone. To prevent injury to facial nerve, 3-D visualization links anatomic landmarks to 3-D map of critical
intracochlear structures. We used a graphics processing unit to boost the computing and 3-D rendering performance
of swept source OCT. Both the intracochlear structures and facial nerve trunk of cadaveric human temporal bones
are clearly identified with 3-D OCT volumetric rendering.
KEYWORDS: Optical coherence tomography, In vivo imaging, Visualization, Arteries, 3D image processing, Real time imaging, Neck, Surgery, Ultrasonography, Diagnostics
Carotid endarterectomy is a common vascular surgical procedure which may help prevent patients’ risk of having a stroke. A high resolution real-time imaging technique that can detect the position and size of vascular plaques would provide great value to reduce the risk level and increase the surgical outcome. Optical coherence tomography (OCT), as a high resolution high speed noninvasive imaging technique, was evaluated in this study. Twenty-four 24-week old apolipoprotein E-deficient (ApoE-/-) mice were divided into three groups with 8 in each. One served as the control group fed with normal diet. One served as the study group fed with high-fat diet to induce atherosclerosis. The last served as the treatment group fed with both high-fat diet and medicine to treat atherosclerosis. Full-range, complex-conjugate-free spectral-domain OCT was used to image the mouse aorta near the neck area in-vivo with aorta exposed to the imaging head through surgical procedure. 2D and 3D images of the area of interest were presented real-time through graphics processing unit accelerated algorithm. In-situ imaging of all the mice after perfusion were performed again to validate the invivo detection result and to show potential capability of OCT if combined with surgical saline flush. Later all the imaged arteries were stained with H and E to perform histology analysis. Preliminary results confirmed the accuracy and fast imaging speed of OCT imaging technique in determining atherosclerosis.
Phase-sensitive adjuncts to optical coherence tomography (OCT) including Doppler and polarization-sensitive implementations allow for quantitative depth-resolved measurements of sample structure and dynamics including fluid flows and orientation of birefringent structures. The development of Fourier-domain OCT (FDOCT), particularly spectrometer-based spectral-domain systems with no moving parts (spectral-domain OCT or SDOCT), have greatly enhanced the phase stability of OCT systems particularly when implemented in a common-path geometry. The latter combination has given rise to a new class of nm-scale sensitive quantitative phase microscopies we have termed spectral domain phase microscopy. However, the phase information in all of these techniques suffers from a 2π ambiguity that limits resolvable pathlength differences to less than half the source center wavelength. This is problematic for situations such as cellular imaging, Doppler velocimetry, or polarization sensitive applications where it may be necessary to monitor sample profiles, displacements, phase differences, or refractive index variations which vary rapidly in space or time. A technique previously introduced in phase shifting interferometry uses phase information from multiple wavelengths to overcome this limitation. We show that by appropriate spectral windowing of the broadband light source already used in OCT, particularly by reshaping the source spectrum about two different center wavelengths, the resulting phase variation may be cast in terms of a much longer synthetic wavelength chosen to span the phase variation of interest. We show theoretically that the optimal choice of synthetic wavelength depends upon a tradeoff between the minimum resolvable phase and the length of unambiguous phase measurement. We demonstrate this technique using a broadband source centered at 790 nm by correctly reconstructing the phase profile from a phantom sample containing multiple 2π wrapping artifacts at the center wavelength and compare our result with atomic force microscopy.
Investigation of the autoregulatory mechanism of human retinal perfusion is conducted with a real-time spectral domain Doppler optical coherence tomography (SDOCT) system. Volumetric, time-sequential, and Doppler flow imaging are performed in the inferior arcade region on normal healthy subjects breathing normal room air and 100% oxygen. The real-time Doppler SDOCT system displays fully processed, high-resolution [512 (axial)×1000 (lateral) pixels] B scans at 17 frames/sec in volumetric and time-sequential imaging modes, and also displays fully processed overlaid color Doppler flow images comprising 512 (axial)×500 (lateral) pixels at 6 frames/sec. Data acquired following 5 min of 100% oxygen inhalation is compared with that acquired 5 min postinhalation for four healthy subjects. The average vessel constriction across the population is −16±26% after oxygen inhalation with a dilation of 36±54% after a return to room air. The flow decreases by −6±20% in response to oxygen and in turn increases by 21±28% as flow returns to normal in response to room air. These trends are in agreement with those previously reported using laser Doppler velocimetry to study retinal vessel autoregulation. Doppler flow repeatability data are presented to address the high standard deviations in the measurements.
The complex conjugate artifact intrinsic to spectral domain optical coherence tomography (SDOCT) complicates retinal image acquisition in patients with poor fixation or head control, imaging of vitreal and choroidal structures, and imaging of extended retinal pathologies. We demonstrate high speed complex conjugate artifact-resolved imaging of human retina using simple and inexpensive sinusoidal reference mirror modulation in combination with 4-step integrating-bucket acquisition and a quadrature projection reconstruction algorithm. The method uses a sinusoidal PZT driving signal to modulate the reference delay continuously during N integration buckets per modulation. The spectral interferometric signal measured by the CCD is phase shifted as a function of the amplitude and phase offset of the driving
signal. We show that the amplitude and phase can be optimized for DC and complex conjugate artifact
removal and minimal fringe washout. This method is illustrated experimentally using a four bucket phase
modulating signal and quadrature projection algorithm for complex conjugate suppression. DC
suppression of 53dB and complex conjugate suppression of 30dB is demonstrated for sets of four Ascans,
each acquired at 17kHz. Densely sampled (3000 A-scans/image, acquired at 1.46 images/sec) in
vivo complex conjugate artifact-resolved images of fovea and optic nerve-head acquired show complex
conjugate artifact suppression for most image reflections to the noise floor.
KEYWORDS: Image segmentation, Optical coherence tomography, 3D image processing, Eye, 3D acquisition, Visualization, Retina, 3D metrology, Data acquisition, 3D visualizations
The acquisition speed of current FD-OCT (Fourier Domain - Optical Coherence Tomography) instruments allows rapid
screening of three-dimensional (3D) volumes of human retinas in clinical settings. To take advantage of this ability
requires software used by physicians to be capable of displaying and accessing volumetric data as well as supporting
post processing in order to access important quantitative information such as thickness maps and segmented volumes.
We describe our clinical FD-OCT system used to acquire 3D data from the human retina over the macula and optic
nerve head. B-scans are registered to remove motion artifacts and post-processed with customized 3D visualization and
analysis software. Our analysis software includes standard 3D visualization techniques along with a machine learning
support vector machine (SVM) algorithm that allows a user to semi-automatically segment different retinal structures
and layers. Our program makes possible measurements of the retinal layer thickness as well as volumes of structures of
interest, despite the presence of noise and structural deformations associated with retinal pathology. Our software has
been tested successfully in clinical settings for its efficacy in assessing 3D retinal structures in healthy as well as
diseased cases. Our tool facilitates diagnosis and treatment monitoring of retinal diseases.
Adaptive Optics - Optical Coherence Tomography (AO-OCT) has demonstrated a promising improvement in lateral
resolution for retinal imaging compared to standard OCT. Recent developments in Fourier-domain OCT technology
allow AO-OCT instruments to acquire three-dimensional (3D) retinal structures with high speed and high "volumetric"
resolution (in all three dimensions). One of the most important factors (besides acquisition speed) that will determine the
true potential of this technique is its ability to achieve diffraction-limited lateral resolution (~3 μm) while operating in
the ultrahigh axial resolution range (~3 μm) offered by OCT. Theoretical studies have shown that the eye's chromatic
aberrations may drastically reduce volumetric resolution. This is a critical finding because for "standard" stand alone
ultrahigh OCT, increasing the spectral bandwidth of the light source improves axial resolution without compromising
lateral resolution. To study the effects of spectral bandwidth on AO-OCT systems for retinal imaging two different light
sources offering 6 and 3 μm axial resolution were tested. This comparison was based on both AO correcting system
performance as well as the quality of corresponding OCT images.
Adaptive optics-optical coherence tomography (AO-OCT) has the potential to improve lateral resolution for OCT retinal
imaging. Several reports have already described the successful combination of AO with a scanning confocal Fourier-domain
OCT instrument to permit real-time three-dimensional (3D) imaging with high resolution (in all three
dimensions). One of the key components that sets the performance limit of AO is the wavefront corrector. Several
different wavefront correctors have been used in AO-OCT systems so far. In this paper we compare two commercially
available wavefront correctors: an AOptix Bimorph deformable mirror (DM) and a Boston Micromachines Micro-
Electro Mechanical System (MEMS) DM (used for the first time in an AO-OCT system). To simplify the analysis, we
tested their performance for the correction of low-amplitude high-order aberrations (with minimal defocus and
astigmatism). Results were obtained with an AO-OCT instrument constructed at UC Davis that combines state-of-the-art
Fourier-domain OCT and an AO design to allow simultaneous testing of both mirrors without the need to modify the
optical system.
Investigation of the autoregulatory mechanism of human retinal perfusion was conducted with a novel real-time spectral domain Doppler optical coherence tomography (SDOCT) system. Volumetric, time-sequential, and Doppler flow imaging was performed in the superior arcade region on normal healthy subjects breathing normal room air and 100% oxygen. The real-time Doppler SDOCT system displays fully processed, high-resolution [512 (axial) x 1000 (lateral) pixels] B-scans at 17 frames/sec in volumetric and time-sequential imaging modes, and also displays fully processed overlaid color Doppler flow images comprising 512 (axial) x 500 (lateral) pixels at 6 frames/sec. OCT fundus images generated from volumetric datasets updated in real time (up to 2 fundus images/sec for 100 x 100 pixel volumes) were used to image and localize retinal vessels for time-sequential and Doppler flow analysis. In preliminary measurements, data acquired following 5 minutes of 100% oxygen inhalation was compared with that acquired 5 minutes post-inhalation. The same arterial segments examined at both time points exhibit constriction in vessel diameter under pure oxygen inhalation of up to 7% and reduction in peak flow velocity as great as 38%, both of which are in good agreement with previous laser Doppler velocimetry studies.
We have combined Fourier-domain optical coherence tomography (OCT) with a closed-loop Adaptive Optics (AO) system. The AO-OCT instrument has been used for in vivo retinal imaging. High-lateral resolution of our AO-OCT system allows visualization of the microscopic retinal structures not accessible by standard OCT instruments.
KEYWORDS: Optical coherence tomography, Image quality, In vivo imaging, Signal to noise ratio, Mirrors, Spectroscopy, Charge-coupled devices, Retina, Eye, Imaging systems
We built a Fourier domain optical coherence tomography (FD-OCT) system using a line scan CCD camera that allows real time data display and acquisition. This instrument is able to produce 2D B-scans as well as 3D data sets with human subjects in vivo in clinical settings. In this paper we analyze the influence of varying exposure times of the CCD detector on image quality. Sensitivity values derived from theoretical predictions have been compared with measurements (obtained with mirrors and neutral density filters placed in both interferometer arms). The results of these experiments, discussion about differences between sensitivity values, potential sources of discrepancies, and recommendations for optimal exposure times will be described in this paper. A short discussion of observed artifacts as well as possible ways to remove them is presented. The influence of relative retinal position with respect to reference mirror position will also be described.
We present a low-cost, high resolution, real-time Spectral Domain Optical Coherence Tomography (SDOCT) system optimized for rapid 3D imaging of the human retina in vivo. Using a source with an 841nm center wavelength and a FWHM bandwidth of 49nm, 6.67 second length bursts of 100 512 x 1000 pixel images were acquired with an integration time of 50 microseconds/line and a frame rate of 16 frames/sec. Three-dimensional data sets comprising up to 4.0mm x 1.2mm x 2.45mm retinal volumes were streamed to hard disk during this brief ocular fixation interval and post-processed to create 3D volumetric images of the optic nerve head and fovea.
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