High-speed Spectral-domain Optical Coherence Tomography Research Articles

Evaluation of choriocapillaris with high-speed spectral-domain optical coherence tomography angiography and image averaging

To study the capabilities of high-speed spectral-domain optical coherence tomography angiography (SD-OCTA) with image averaging in the evaluation of choriocapillaries in healthy individuals and patients with central serous chorioretinopathy (CSC). All participants underwent OCTA examination on the SOLIX tomograph (Optovue, USA) using quadruplicate 3×3 mm scan with image averaging. Image analysis was performed in 9-µm custom slab with Phansalkar auto local threshold algorithm and calculation of flow voids larger than 5000 µm2 and 10 000 µm2. The optimal slab depth was determined in healthy eyes by consecutive analysis of the slabs with a 3-µm shift from zero position to 33 µm below Bruch's membrane. The study included 18 eyes of 18 healthy volunteers (40.4±6.0 years old) and 18 fellow eyes of 18 unilateral CSC patients (37.4±10.7 years old). The slab 12 µm below the Bruch's membrane showed the minimal number of flow voids (23.1±7.0 of >5000 µm2 voids per scan) and was chosen for further analysis. The number of flow voids of >5000 µm2 in healthy paired eyes of CSC patients was statistically significantly higher than in the eyes of healthy individuals (32.7±10.7 and 25.3±8.1 voids/scan, respectively; p=0.022). The number of flow voids of >10000 µm2 was also statistically significantly higher in CSC eyes compared to healthy eyes (5.6±3.3 and 3.5±1.9 voids/scan, respectively; p=0.045). There was no statistically significant difference in total area of the voids between the eyes of healthy individuals and CSC patients (96406.1±3924.5 µm2 and 95395.7 ± 3615.1 µm2, respectively; p=0.42). The optimal settings for choriocapillaris imaging on the SOLIX tomograph include 9-µm slab 9 to 18 µm below the Bruch's membrane. Using a 9-µm slab 12 µm below the Bruch's membrane, a substantial difference was found in choriocapillaris perfusion between eyes of healthy individuals and CSC patients.

Contrast Enhanced Subsurface Fingerprint Detection Using High-Speed Optical Coherence Tomography

Spectral-domain optical coherence tomography (SD-OCT) has been demonstrated to be a viable tool in forensic science for fingerprint detection, yet it still suffers from certain practical issues, e.g., the limited scanning speed and low image contrast. In this letter, we report a high-speed SD-OCT together with an image contrast enhancement mechanism for reliable subsurface fingerprint detection. The constructed SD-OCT system achieves a scanning rate up to 60k A-lines/s, and thus, both 3D volumetric images, reaching up to 20 mm $\times 20$ mm $\times 1.2$ mm, and en face internal fingerprint furrow pattern images could be obtained. Based upon the analyses of the papillary layer anatomical structures, the contrast enhancement technique not only suppresses image artifacts, but also is effective in detecting fingerprint spoofing. Experiments on healthy subjects have also been conducted to verify the system imaging capability and the effectiveness of the contrast-enhancement technique.

Scalable wide-field optical coherence tomography-based angiography for in vivo imaging applications.

Recent advances in optical coherence tomography (OCT)-based angiography have demonstrated a variety of biomedical applications in the diagnosis and therapeutic monitoring of diseases with vascular involvement. While promising, its imaging field of view (FOV) is however still limited (typically less than 9 mm2), which somehow slows down its clinical acceptance. In this paper, we report a high-speed spectral-domain OCT operating at 1310 nm to enable wide FOV up to 750 mm2. Using optical microangiography (OMAG) algorithm, we are able to map vascular networks within living biological tissues. Thanks to 2,048 pixel-array line scan InGaAs camera operating at 147 kHz scan rate, the system delivers a ranging depth of ~7.5 mm and provides wide-field OCT-based angiography at a single data acquisition. We implement two imaging modes (i.e., wide-field mode and high-resolution mode) in the OCT system, which gives highly scalable FOV with flexible lateral resolution. We demonstrate scalable wide-field vascular imaging for multiple finger nail beds in human and whole brain in mice with skull left intact at a single 3D scan, promising new opportunities for wide-field OCT-based angiography for many clinical applications.

Measurement of wall strain in embryonic chick heart by spectral domain optical coherence tomography

During cardiac development, the growth, remodeling and morphogenesis of embryonic hearts are closely linked to hemodynamic forces. An understanding of the interaction mechanism between hemodynamic forces and heart development is important for the early diagnosis and treatment of various congenital defects. The myocardial wall strain (MWS) in embryonic heart is a critical parameter for quantifying the mechanical properties of cardiac tissues. Here, we focus on the radial strain which is defined as the change of the myocardial wall thickness. An effective measurement of MWS is conductive to studies of embryonic heart development. Chick embryo is a popular animal model used for studing the cardiac development due to the similarity of cardiac development between the human heart and the chick heart at early developmental stages and its easy access. Although various imaging methods have been proposed, there still remain significant challenges to imaging of early stage chick embryo heart because it is small in size and beats fast. Optical coherence tomography (OCT) is a non-contact three-dimensional imaging modality with high spatial and temporal resolution which has been widely used for imaging the biological tissue. In this paper, we describe a method to measure in vivo MWS of chicken embryonic hearts with a high speed spectral domain OCT(SDOCT) system worked at 1310 nm. We perform four-dimensional (4D) (x, y, z, t) scanning on the outflow tract (OFT) of chick embryonic hearts in a non-gated way. The transient states of the OFT are extracted from the 4D data by using the beating synchronization algorithm. The OFT center line can be achieved by image processing. Assuming that the blood flow is parallel to the center line in the blood vessel, we calculate the Doppler angle of blood flow from the OFT center line. In a certain OFT cross-section, the OFT myocardial wall (inner and external borders) is segmented from the OCT images with a semi-automatic boundary-detection algorithm. Then, the myocardial wall thickness is calculated from the Doppler angle, area and sum of inner and external radii of the segmented myocardial wall. The radial strain is obtained by calculating the myocardial wall thickness variation. Previous methods calculated the myocardial wall thickness by directly subtracting inner and external radii. The measured result may be deteriorated by insufficient resolution of the system since the myocardial wall of OFT is very thin. The present method can solve this problem by calculating the thickness through using the sum of the radii instead of the subtraction. The experimental results on embryonic chick hearts demonstrate that the proposed method can measure the MWS of OFT along arbitrary orientation and it is a useful tool for studying the biomechanical characteristics of embryonic hearts.

Optically deviated focusing method based high-speed SD-OCT for in vivo retinal clinical applications

The aim of this study is to provide accurately focused, high-resolution in vivo human retinal depth images using an optically deviated focusing method with spectral-domain optical coherence tomography (SD-OCT) system. The proposed method was applied to increase the retinal diagnosing speed of patients with various values of retinal distances (i.e., the distance between the crystalline eye lens and the retina). The increased diagnosing speed was facilitated through an optical modification in the OCT sample arm configuration. Moreover, the optical path length matching process was compensated using the proposed optically deviated focusing method. The developed system was mounted on a bench-top cradle to overcome the motion artifacts. Further, we demonstrated the capability of the system by carrying out in vivo retinal imaging experiments. The clinical trials confirmed that the system was effective in diagnosing normal and abnormal retinal layers as several retinal abnormalities were identified using non-averaged single-shot OCT images, which demonstrate the feasibility of the method for clinical applications.

In vivo assessment of wall strain in embryonic chick heart by spectral domain optical coherence tomography.

The ability to measure in vivo wall strain in embryonic hearts is important for fully understanding the mechanisms of cardiac development. Optical coherence tomography (OCT) is a powerful tool for the three-dimensional imaging of complex myocardial activities in early-stage embryonic hearts with high spatial and temporal resolutions. We describe a method to analyze periodic deformations of myocardial walls and evaluate in vivo myocardial wall strains with a high-speed spectral domain OCT system. We perform four-dimensional scanning on the outflow tract (OFT) of chick embryonic hearts and determine a special cross-section in which the OFT can be approximated as an annulus by analyzing Doppler blood-flow velocities. For each image acquired at the special cross-section, the annular myocardial wall is segmented with a semiautomatic boundary-detection algorithm, and the fluctuation myocardial wall thickness is calculated from the area and mean circumference of the myocardial wall. The experimental results shown with the embryonic chick hearts demonstrate that the proposed method is a useful tool for studying the biomechanical characteristics of embryonic hearts.

In vivo OCT microangiography of rodent iris.

We report on the functional optical coherence tomography (OCT) imaging of iris tissue morphology and microcirculation in living small animals. Anterior segments of healthy mouse and rat eyes are imaged with high-speed spectral domain OCT (SD-OCT) utilizing ultrahigh sensitive optical microangiography (UHS-OMAG) imaging protocol. 3D iris microvasculature is produced by the use of an algorithm that calculates absolute differences between the amplitudes of the OCT interframes. We demonstrate that the UHS-OMAG is capable of delineating iris microvascular beds in the mouse and rat with capillary-level resolution. Furthermore, the fast imaging speed enables dynamic imaging of iris micro-vascular response during drug-induced pupil dilation. We believe that this OCT angiographic approach has a great potential for in situ and in vivo monitoring of the microcirculation within iris tissue beds in rodent disease models that have microvascular involvement.

Imaging the eye fundus with real-time en-face spectral domain optical coherence tomography

Real-time display of processed en-face spectral domain optical coherence tomography (SD-OCT) images is important for diagnosis. However, due to many steps of data processing requirements, such as Fast Fourier transformation (FFT), data re-sampling, spectral shaping, apodization, zero padding, followed by software cut of the 3D volume acquired to produce an en-face slice, conventional high-speed SD-OCT cannot render an en-face OCT image in real time. Recently we demonstrated a Master/Slave (MS)-OCT method that is highly parallelizable, as it provides reflectivity values of points at depth within an A-scan in parallel. This allows direct production of en-face images. In addition, the MS-OCT method does not require data linearization, which further simplifies the processing. The computation in our previous paper was however time consuming. In this paper we present an optimized algorithm that can be used to provide en-face MS-OCT images much quicker. Using such an algorithm we demonstrate around 10 times faster production of sets of en-face OCT images than previously obtained as well as simultaneous real-time display of up to 4 en-face OCT images of 200 × 200 pixels(2) from the fovea and the optic nerve of a volunteer. We also demonstrate 3D and B-scan OCT images obtained from sets of MS-OCT C-scans, i.e. with no FFT and no intermediate step of generation of A-scans.

High Speed SD-OCT System Using GPU Accelerated Mode for in vivo Human Eye Imaging

We developed an SD-OCT (Spectral Domain-Optical Coherence Tomography) system which uses a GPU (Graphics Processing Unit) for processing. The image size from the SD-OCT system is 1024 × 512 and the speed is 110 frame/sec in real-time. K-domain linearization, FFT (Fast Fourier Transform), and log scaling were included in the GPU processing. The signal processing speed was about 62 ms using a CPU (Central Processing Unit) and 1.6 ms using a GPU, which is 39 times faster. We performed an in-vivo retinal scan, and reconstructed a 3D visualization based on C-scan images. As a result, there were minimal motion artifacts and we confirmed that tomograms of blood vessels, the optic nerve, and the optic disk are clearly identified. According to the results of this study, this SD-OCT can be applied to real-time 3D display technology, particularly auxiliary instruments for eye operations in ophthalmology.

Non-destructive analysis of tablet coatings with optical coherence tomography

Optical coherence tomography (OCT) is a non-invasive analysis technique allowing fast and high-quality cross-sectional imaging of scattering media. OCT is based on the physical phenomenon of low coherence interferometry and is thus well suited to image layered structures. In this paper, high-speed spectral domain OCT was used for the characterization of pharmaceutical tablet coatings, sampled at different stages of an industrial drum spray coating process, comprising tablets with a coating thickness ranging from uncoated to a target coating thickness of about 70 μm. In addition to the OCT investigation of layer thickness and homogeneity, tablet weight gain and tablet diameters were determined on a single-tablet level. Scanning electron microscopy (SEM) was applied for referencing the coating thickness obtained with OCT. We demonstrated that OCT allows rapid evaluation of coating properties, such as thickness and homogeneity independently from variations of the tablet core. In contrast to indirect methods, deviations observed with OCT can be related directly to the coating properties. Furthermore, for an extended morphological coating characterization, three dimensional images were reconstructed. Pending further developments, the high axial resolution and fast data acquisition rate of OCT has the potential for highly accurate, fast and low-cost coating control during and after manufacturing.

High-speed spectral domain optical coherence tomography using non-uniform fast Fourier transform

The useful imaging range in spectral domain optical coherence tomography (SD-OCT) is often limited by the depth dependent sensitivity fall-off. Processing SD-OCT data with the non-uniform fast Fourier transform (NFFT) can improve the sensitivity fall-off at maximum depth by greater than 5dB concurrently with a 30 fold decrease in processing time compared to the fast Fourier transform with cubic spline interpolation method. NFFT can also improve local signal to noise ratio (SNR) and reduce image artifacts introduced in post-processing. Combined with parallel processing, NFFT is shown to have the ability to process up to 90k A-lines per second. High-speed SD-OCT imaging is demonstrated at camera-limited 100 frames per second on an ex-vivo squid eye.

3.01] 3-D intraoperative imaging combining an operating microscope with optical coherence tomography (OCT)

Objective Optical coherence tomography (OCT) allows non-contact/non-invasive analysis of tissues with a penetration depth of 2–3 mm reaching a spatial resolution of approximately 4–15 μm. This resolution is compatible with the resolution of modern operation microscopes. Aim of this work was to provide a three-dimensional (3D) intraoperative visualization of tissue structures. Material and methods A high-speed spectral domain OCT (a modified version of the Ganymed, Thorlabs HL) was adapted to a motorized operation microscope (HR 1000, Moller-Wedel). Via a specially designed two axis-scanner, the 840 nm OCT was adapted directly to a camera port of the operation microscope. Group velocity dispersion of the microscope optics was compensated successfully to provide bandwidth-limited depth resolution. Together with a step motor-controlled reference arm, an automatic control of the working distance (232–290 mm), the scan field (4–24 mm) and the position of the OCT focus within the sample is possible. Results The system allows a 3-D visualization of OCT imaged during the surgical procedure. The OCT images were provide to the surgeon via a special video ocular in the surgical microscope. This new device was tested successfully in a preclinical setting with different ENT tissues to evaluate the principle. Conclusion It may be used during brain tumor surgery, tumor surgery of the vocal cords, the placement of cochlear transplants or during bone surgery in the middle ear.

Linear-wavenumber spectrometer for high-speed spectral-domain optical coherence tomography

An equidistant (in the wavenumber) spectrometer based on a diffraction grating, a compensation prism, and a CCD linear array is developed and implemented for spectral-domain optical coherence tomography. A criterion is introduced for estimating the level of residual nonequidistance. This criterion allows one to determine the threshold compensation level necessary for obtaining the spectrally limited spatial resolution. The method is tested in spectral-domain optical coherent tomography systems at wavelengths of 1270 and 830 nm.

Optical coherence angiography

Noninvasive angiography is demonstrated for the in vivo human eye. Three-dimensional flow imaging has been performed with high-speed spectral-domain optical coherence tomography. Sample motion is compensated by two algorithms. Axial motion between adjacent A-lines within one OCT image is compensated by the Doppler shift due to bulk sample motion. Axial displacements between neighboring images are compensated by a correlation-based algorithm. Three-dimensional vasculature of ocular vessels has been visualized. By integrating volume sets of flow images, two-dimensional images of blood vessels are obtained. Retinal and choroidal blood vessel images are simultaneously obtained by separating the volume set into retinal part and choroidal parts. These are corresponding to fluorescein angiogram and indocyanine angiogram.

Simultaneous acquisition of sectional and fundus ophthalmic images with spectral-domain optical coherence tomography

A high-speed spectral-domain optical coherence tomography (OCT) system was built to image the human retina in vivo. A fundus image similar to the intensity image produced by a scanning laser ophthalmoscope (SLO) was generated from the same spectra that were used for generating the OCT sectional images immediately after the spectra were collected. This function offers perfect spatial registration between the sectional OCT images and the fundus image, which is desired in ophthalmology for monitoring data quality, locating pathology, and increasing reproducibility. This function also offers a practical way to detect eye movements that occur during the acquisition of the OCT image. The system was successfully applied to imaging human retina in vivo.

High-speed spectral-domain optical coherence tomography at 13 μm wavelength

We demonstrate a high-speed spectral domain optical coherence tomography (SD-OCT) system capable of acquiring individual axial scans in 24.4 micros at a rate of 19,000 axial scans per second, using an InGaAs line scan camera and broadband light source centered at 1.31microm. Sensitivity of >105 dB over a 2-mm depth range was obtained with a free-space axial resolution of 12-14 microm, in agreement with our signal-to-noise ratio predictions. Images of human tissue obtained in vivo with SD-OCT show similar penetration depths to those obtained with state-of-the-art time domain OCT despite the ten-fold higher image acquisition speed. These results demonstrate the potential of 1.3 microm SD-OCT for high-speed and high-sensitivity imaging in patients.