Radiofrequency ablation (RFA) is widely used for the eradication of dysplasia and the treatment of early stage esophageal carcinoma in patients with Barrett’s esophagus (BE). However, there are several factors, such as variation of BE epithelium (EP) thickness among individual patients and varying RFA catheter-tissue contact, which may compromise RFA efficacy. We used a high-speed optical coherence tomography (OCT) system to identify and monitor changes in the esophageal tissue architecture from RFA. Two different OCT imaging/RFA application protocols were performed using an ex vivo swine esophagus model: (1) post-RFA volumetric OCT imaging for quantitative analysis of the coagulum formation using RFA applications with different energy settings, and (2) M-mode OCT imaging for monitoring the dynamics of tissue architectural changes in real time during RFA application. Post-RFA volumetric OCT measurements showed an increase in the coagulum thickness with respect to the increasing RFA energies. Using a subset of the specimens, OCT measurements of coagulum and coagulum + residual EP thickness were shown to agree with histology, which accounted for specimen shrinkage during histological processing. In addition, we demonstrated the feasibility of OCT for real-time visualization of the architectural changes during RFA application with different energy settings. Results suggest feasibility of using OCT for RFA treatment planning and guidance.
In the last 2 years, the field of micro-electro-mechanical systems tunable vertical cavity surface-emitting lasers (MEMS-VCSELs)
has seen dramatic improvements in laser tuning range and tuning speed, along with expansion into unexplored
wavelength bands, enabling new applications. This paper describes the design and performance of high-speed ultra-broad
tuning range 1050nm and 1310nm MEMS-VCSELs for medical imaging and spectroscopy. Key results include
achievement of the first MEMS-VCSELs at 1050nm and 1310nm, with 100nm tuning demonstrated at 1050nm and
150nm tuning at shown at 1310nm. The latter result represents the widest tuning range of any MEMS-VCSEL at any
wavelength. Wide tuning range has been achieved in conjunction with high-speed wavelength scanning at rates beyond 1
MHz. These advances, coupled with recent demonstrations of very long MEMS-VCSEL dynamic coherence length,
have enabled advancements in both swept source optical coherence tomography (SS-OCT) and gas spectroscopy.
VCSEL-based SS-OCT at 1050nm has enabled human eye imaging from the anterior eye through retinal and choroid
layers using a single instrument for the first time. VCSEL-based SS-OCT at 1310nm has enabled real-time 3-D SS-OCT
imaging of large tissue volumes in endoscopic settings. The long coherence length of the VCSEL has also enabled, for
the first time, meter-scale SS-OCT applicable to industrial metrology. With respect to gas spectroscopy, narrow dynamic
line-width has allowed accurate high-speed measurement of multiple water vapor and HF absorption lines in the 1310nm
wavelength range, useful in gas thermometry of dynamic combustion engines.
Recent advances in swept-source / Fourier domain optical coherence tomography (SS-OCT) technology enable in vivo ultrahigh speed imaging, offering a promising technique for four-dimensional (4-D) imaging of the eye. Using an ultrahigh speed tunable vertical cavity surface emitting laser (VCSEL) light source based SS-OCT prototype system, we performed imaging of human eye dynamics in four different imaging modes: 1) Pupillary reaction to light at 200,000 axial scans per second and 9 μm resolution in tissue. 2) Anterior eye focusing dynamics at 100,000 axial scans per second and 9 μm resolution in tissue. 3) Tear film break up at 50,000 axial scans per second and 19 μm resolution in tissue. 4) Retinal blood flow at 800,000 axial scans per second and 12 μm resolution in tissue. The combination of tunable ultrahigh speeds and long coherence length of the VCSEL along with the outstanding roll-off performance of SS-OCT makes this technology an ideal tool for time-resolved volumetric imaging of the eye. Visualization and quantitative analysis of 4-D OCT data can potentially provide insight to functional and structural changes in the eye during disease progression. Ultrahigh speed imaging using SS-OCT promises to enable novel 4-D visualization of realtime dynamic processes of the human eye. Furthermore, this non-invasive imaging technology is a promising tool for research to characterize and understand a variety of visual functions.
The effectiveness of speckle reduction using traditional frame averaging technique was limited in ultrahigh speed optical
coherence tomography (OCT). As the motion between repeated frames was very small, the speckle pattern of the frames
might be identical. This problem could be solved by averaging frames acquired at slightly different locations. The
optimized scan range depended on the spot size of the laser beam, the smoothness of the boundary, and the homogeneity
of the tissue. In this study we presented a method to average frames obtained within a narrow range along the slow-axis.
A swept-source OCT with 100,000 Hz axial scan rate was used to scan the retina in vivo. A series of narrow raster scans
(0-50 micron along the slow axis) were evaluated. Each scan contained 20 image frames evenly distributed in the scan
range. The imaging frame rate was 417 HZ. Only frames with high correlation after rigid registration were used in
averaging. The result showed that the contrast-to-noise ratio (CNR) increased with the scan range. But the best edge
reservation was obtained with 15 micron scan range. Thus, for ultrahigh speed OCT systems, averaging frames from a
narrow band along the slow-axis could achieve better speckle reduction than traditional frame averaging techniques.
We developed a piezoelectric transducer (PZT) based miniature catheter with an outer diameter of 3 mm for
ultrahigh speed endoscopic optical coherence tomography (OCT) using Fourier domain modelocked (FDML)
laser at a 480 kHz axial scan rate. The miniaturized PZT bender actuates a fiber to provide high scanning
speed. The side-viewing probe can be pulled back for a long distance to acquire three-dimensional (3D)
dataset covering a large area on the specimen. Operating with a high speed data acquisition (DAQ) system,
OCT imaging with 6.5 mm imaging range, 10 μm axial resolution, 20 μm lateral resolution, and frame rate of
480 frames per second (fps) is demonstrated.
Doppler OCT is a functional extension of OCT that provides information on flow in biological tissues. We present a
novel approach for total retinal blood flow assessment using ultrahigh speed Doppler OCT. A swept source / Fourier
domain OCT system at 1050 nm was used for 3D imaging of the human retina. The high axial scan rate of 200 kHz
allowed measuring the high flow velocities in the central retinal vessels. By analyzing en-face images extracted from 3D
Doppler data sets, absolute flow for single vessels as well as total retinal blood flow can be measured using a simple and
robust protocol.
We performed OCT imaging of the rat retina at 70,000 axial scans per second with ~3 μm axial resolution. Three-dimensional OCT (3D-OCT) data sets of the rat retina were acquired. The high speed and high density data sets enable improved en face visualization by reducing eye motion artifacts and improve Doppler OCT measurements. Minimal motion artifacts were visible and the OCT fundus images offer more precise registration of individual OCT images to retinal fundus features. Projection OCT fundus images show
features such as the nerve fiber layer, retinal capillary networks and choroidal vasculature. Doppler OCT images and quantitative measurements show pulsatility in retinal blood vessels. Doppler OCT provides noninvasive in vivo quantitative measurements of retinal blood flow properties and may benefit studies of diseases such as glaucoma and diabetic retinopathy. Ultrahigh speed imaging using ultrahigh resolution spectral / Fourier domain OCT promises to enable novel protocols for measuring small animal retinal
structure and retinal blood flow. This non-invasive imaging technology is a promising tool for monitoring disease progression in rat and mouse models to assess ocular disease pathogenesis and response to treatment.
The performance and imaging characteristics of ultrahigh speed ophthalmic optical coherence tomography (OCT) are investigated. In vivo imaging results are obtained at 850nm and 1050nm using different configurations of spectral and swept source / Fourier domain OCT. A spectral / Fourier domain instrument using a high speed
CMOS linescan camera with SLD light source centered at 850nm achieves speeds of ~91,000 axial scans per second with ~3μm axial resolution in tissue. A spectral / Fourier domain instrument using an InGaAs linescan camera with SLD light source centered at 1050nm achieves ~47,000 axial scans per second with ~7μm resolution in tissue. A swept source instrument using a novel wavelength swept laser light source centered at 1050nm achieves 100,000
axial scans per second. Retinal diseases seen in the clinical setting are imaged using the 91kHz 850nm CMOS camera and 47kHz 1050nm InGaAs camera based instruments to investigate the combined effects of varying speed, axial resolution, center wavelength, and instrument sensitivity on image quality. The novel 1050nm swept
source / Fourier domain instrument using a recently developed commercially available short cavity laser source images at 100,000 axial scans per second and is demonstrated in the normal retina. The dense 3D volumetric data sets obtained with ultrahigh speed OCT promise to improve reproducibility of quantitative measurements,
enabling early diagnosis as well as more sensitive assessment of disease progression and response to therapy.
Ultrahigh speed Spectral/Fourier domain ophthalmic OCT imaging at 70,000-312,500 axial scans per second is
demonstrated using a high speed CMOS camera at 800 nm. Comparative imaging results of the fovea illustrate the
performance tradeoffs between different imaging speeds and spectrometer configurations. Dense 3D volumetric
acquisitions show minimal motion artifacts when acquired at 250,000 axial scans per second. The porous structure of the
lamina cribrosa is shown in en face images extracted from a dense volumetric acquisition of the optical nerve head
acquired at 106, 382 axial scans per second. Rapid repeated volume imaging (4D-OCT) shows blood flow in retinal
capillaries. Boundaries of the capillary network are enhanced by motion contrast. 3D volumetric data acquired at 49,000
axial scans per second using an InGaAs camera at 1050 nm is compared to volumetric data acquired at 101, 010 axial
scans per second using a CMOS camera at 800nm. Averaging of adjacent cross sectional scans in the volume is shown to
increase contrast in the images and reduce speckle. The enhanced penetration of the 1050 nm compared to the 800 nm
OCT imaging system is shown. Dense 2D/3D data sets and 4D-OCT repeated volume imaging promise alternative
methods for diagnosis and monitoring of disease.
Ultrahigh speed spectral / Fourier domain optical coherence tomography (OCT) imaging using a CMOS line scan camera with acquisition rates of 70,000 - 312,500 axial scans per second is investigated. Several design configurations are presented to illustrate trade-offs between acquisition speed, sensitivity, resolution and sensitivity roll-off performance. We demonstrate: extended imaging range and improved sensitivity roll-off at 70,000 axial scans per second , high speed and ultrahigh resolution imaging at 106,382 axial scans per second, and ultrahigh speed imaging at 250,000-312,500 axial scans per second. Each configuration is characterized through optical testing and the trade-offs demonstrated with in vivo imaging of the fovea and optic disk in the human retina. OCT fundus images constructed from 3D-OCT data acquired at 250,000 axial scans per second have no noticeable discontinuity of retinal features and show that there are minimal motion artifacts. The fine structures of the lamina cribrosa can be seen. Long cross sectional scans are acquired at 70,000 axial scans per second for imaging large areas of the retina, including the fovea and optic disk. Rapid repeated imaging of a small volume (4D-OCT) enables time resolved visualization of the capillary network surrounding the INL and may show individual red blood cells. The results of this study suggest that high speed CMOS cameras can achieve a significant improvement in performance for ophthalmic imaging. This promises to have a powerful impact in clinical applications by improving early diagnosis, reproducibility of measurements and enabling more sensitive assessment of disease progression or response to therapy.
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