We demonstrate intensity-based optical coherence tomography (OCT) angiography using the squared difference of two sequential frames with bulk-tissue-motion (BTM) correction. This motion correction was performed by minimization of the sum of the pixel values using axial- and lateral-pixel–shifted structural OCT images. We extract the BTM-corrected image from a total of 25 calculated OCT angiographic images. Image processing was accelerated by a graphics processing unit (GPU) with many stream processors to optimize the parallel processing procedure. The GPU processing rate was faster than that of a line scan camera (46.9 kHz). Our OCT system provides the means of displaying structural OCT images and BTM-corrected OCT angiographic images in real time.
The author presents a graphics processing unit (GPU) programming for real-time Fourier domain optical coherence tomography (FD-OCT) with fixed-pattern noise removal by subtracting mean and median. In general, the fixed-pattern noise can be removed by the averaged spectrum from the many spectra of an actual measurement. However, a mean-spectrum results in artifacts as residual lateral lines caused by a small number of high-reflective points on a sample surface. These artifacts can be eliminated from OCT images by using medians instead of means. However, median calculations that are based on a sorting algorithm can generate a large amount of computation time. With the developed GPU programming, highly reflective surface regions were obtained by calculating the standard deviation of the Fourier transformed data in the lateral direction. The medians and means were then subtracted at the observed regions and other regions, such as backgrounds. When the median calculation was less than 256 positions out of a total 512 depths in an OCT image with 1024 A-lines, the GPU processing rate was faster than that of the line scan camera (46.9 kHz). Therefore, processed OCT images can be displayed in real-time using partial medians.
We developed the ultra high-speed processing of FD-OCT images using a low-cost graphics processing unit (GPU)
with many stream processors to realize highly parallel processing. The processing line rates of half range FD-OCT
and full range FD-OCT were 1.34 MHz and 0.70 MHz for a spectral interference image of 1024 FFT size x 2048
lateral A-scans, respectively. A display rate of 22.5 frames per second for processed full range images was
achieved in our OCT system using an InGaAs line scan camera operated at 47 kHz.
We demonstrate speckle reduction based on angular compounding using parallel-detection spectral-domain optical coherence tomography (OCT). An ultrahigh-speed two-dimensional complementary metal-oxide semiconductor camera acquired angular and spectral interference fringes (128×1024 pixels) simultaneously at 15,000 frames/s for a single lateral point. A signal-to-noise ratio improvement of 8 dB was achieved for imaging human skin in vivo by averaging 121 angle-resolved OCT images.
We demonstrated a real-time display of processed OCT images using a linear-in-wavenumber (linear-k) spectrometer
and a graphics processing unit (GPU). We used the linear-k spectrometer with optimal combination of a diffractive
grating with 1200 lines/mm and a F2 equilateral prism in the 840 nm spectral region, to avoid calculating the re-sampling
process. The calculations of the FFT (fast Fourier transform) were accelerated by the low cost GPU with many stream
processors, which realized highly parallel processing. A display rate of 27.9 frames per second for processed images
(2048 FFT size × 1000 lateral A-scans) was achieved in our OCT system using a line scan CCD camera operated at 27.9
kHz.
Fourier domain optical coherence tomography (FD-OCT) requires resampling of spectrally resolved depth information from wavelength to wave number, and the subsequent application of the inverse Fourier transform. The display rates of OCT images are much slower than the image acquisition rates due to processing speed limitations on most computers. We demonstrate a real-time display of processed OCT images using a linear-in-wave-number (linear-k) spectrometer and a graphics processing unit (GPU). We use the linear-k spectrometer with the combination of a diffractive grating with 1200 lines/mm and a F2 equilateral prism in the 840-nm spectral region to avoid calculating the resampling process. The calculations of the fast Fourier transform (FFT) are accelerated by the GPU with many stream processors, which realizes highly parallel processing. A display rate of 27.9 frames/sec for processed images (2048 FFT size×1000 lateral A-scans) is achieved in our OCT system using a line scan CCD camera operated at 27.9 kHz.
We demonstrate a compact single-shot full-field optical coherence tomography (OCT) system for obtaining real-time
high-resolution depth resolved en-face OCT images from weakly scattering specimens. The experimental setup is based
on a Linnik type polarization Michelson interferometer and a four-channel compact polarization phase stepper optics.
The four-channel phase-stepper optics comprise of a dual channel beam splitter, a Wollaston prism and a pair of wave
plate for simultaneously capturing four quadratually phase-stepped images on a single CCD. The interferometer is
illuminated using a SLD source with a central wavelength of 842 nm and a bandwidth of 16.2 nm, yielding an axial
resolution of 19.8 μm. Using a 10 × (0.25-NA) microscope objective and a CCD camera with 400 × 400 pixels, the
system covers an area of 225 μm × 225 μm with a transverse resolution of 4.4 μm. The en-face OCT images of an onion
is measured with an exposure time of 7ms and a frame rate of 28 fps.
We demonstrate axial-lateral parallel time-domain optical coherence tomography using an optical zoom lens and highorder diffracted lights at 830 nm to adjust imaging range. Our 2-D CCD camera (640 x 480 pixels, 207fps) measured a depth-resolved interference image using diffracted light as the reference beam and a linear illumination beam without any scan. The lateral range can be varied continuously from 6.4 to 1.6 mm by increasing the magnification of optical zoom lens. The axial range can be adjusted discretely from 1st to 7th orders because we used a diffraction grating with 300 lines/mm in a 830 nm wavelength region.
We developed axial-lateral parallel time domain optical coherence tomography (OCT) with an ultrahigh-speed
complementary metal oxide semiconductor (CMOS) camera. A cylindrical lens is inserted in the signal arm to
illuminate the sample with a linear beam that can be moved horizontally by a galvano scanner. A reflective grating is
installed in the Littrow configuration so that first-order diffracted light propagates backward along the incoming path at
the reference beam to obtain a continuous delay. The backscattered light from the sample and the diffracted light from
the grating are imaged onto a CMOS camera (512 × 512 pixels, 17 × 17 &mgr;m pixels, 10 bit resolution, frame rate 3000
fps) using an achromatic imaging lens. The camera obtains a depth-resolved interference image using diffracted light
as the reference beam and a linear illumination beam without axial and vertical scans. We can obtain the OCT images
(512 × 512 pixels) at 1,500 fps by calculating two sequential images. To create a 3-D image, the linear probe beam
was scanned at 3 Hz to obtain volume data. 500 interference images per scan (corresponding to 250 OCT images
through calculations from two sequential images) created a 3-D dataset of 512 × 250 × 512 pixels. The experimental
sensitivity was approximately 76 dB after 2 × 2-pixel binning. The system was successfully used to image the human
finger in vivo.
We demonstrated that a synthesized light source (SLS) consisting of two low coherence light sources is capable of enhancing spatial resolution in optical coherence tomography (OCT). The axial resolution of OCT is given by the half of coherence length of the light source. We fabricated an SLS with a coherence length of 2.3 μm and the side lobe intensity of 29% under the intensity ratio of LED 1: LED 2 = 1: 0.4 by combining two light sources, LED 1 with a central wavelength of 700 nm and spectral bandwidth of 100 nm, and LED 2 of 898 nm and 85 nm. The coherence length of 2.3 μm is 56% of the shorter coherence length in two LED's, therefore the axial resolution is 1.2 μm.
Optical tomography and imaging techniques using coherence domain methods are widely studied for biomedical applications. Most optical tomographic images are reconstructed using the intensities of transmitted or reflected lights. In highly scattering media such as biological tissues, the exponential attenuation of the coherence-gated transmitted light beyond an optical thickness of 20 scattering mean free paths is small when compared to attenuation in a relatively transparent media. Tomographic image reconstruction of optical thicker scattering media using the intensity of emergent photons results in images of low resolution and contrast. Here, we report transillumination optical computed tomography (CT) of highly scattering media using the laser spectral linewidth broadening, instead of the transmitted light intensity. We demonstrate that quantitative scattering linewidth broadening CT images. Our method could provide novel information on biomedical applications of thick tissues, where the differences in the scattering coefficients or dynamic properties can not be quantitatively determined from the images reconstructed with the intensity of transmitted light.
In this research, we propose an algebraic reconstruction method suitable for the coherent detection imaging (CDI) based transillumination laser CT. When imaging highly scattering media such as tissues, the laser CT does not obey a simple absorption model, i.e., the Radon transform, because of the surface effects that arise due to refractive index mismatch at the object boundary. The surface effects degrade the reconstructed images quality. To compensate for the surface effects. However, a stable solution can not be obtained from the expression, since the equation system is always an underdetermined one. The constraint from the quantitative relationship between projections is considered to obtain the stable solution. The constraint ins based on the properties of CT and Gaussian beam. Accordingly, our reconstruction results in a least squares problem with a constraint. The problem is solved via the conjugate gradient method, whose convergence rate is relatively high. We demonstrate the effectiveness by applying the proposed method to experimental data acquired from a physical phantom.
Optical tomography for biomedical target is an evolving research area with emerging potential applications. In transillumination optical tomography, the filtered back projection (FBP) method is generally used for image reconstruction and the images represent a distribution of the optical attenuation coefficient. However, in practical optical imaging systems, refractive index mismatch at boundaries, such as the tissue surface, strongly affects optical attenuation. The surface effects are not constant even at the same part of the sample at different incident angles. Therefore, the surface effects introduce artifacts that obscure the internal structure and functional information in the laser CT images reconstructed by the FBP method. In this paper, we propose a simple correction method that could minimize the surface effects in laser CT images. The experiments were performed with the coherent detection imaging system based on the optical heterodyne detection technique. Experimentally determined attenuation coefficient corresponding to different incident angles was used to correct the surface effects. Improved target structures were demonstrated in the reconstructed laser CT images. Our correction method for laser CT image reconstruction is quite effective for visualizing internal structures with small variations in attenuation coefficients that would otherwise be masked by the dominant surface attenuation.
This paper considers the interior problem of CT reconstruction in which outer data are deficient in each projection. It is effective to this problem to restrict the parameters, i.e., the pixels, to be estimated to the region in which an object exists. We investigate this problem using the minimum description length principle proposed by Rissanen which is the amount of information required to describe a model based on information theory. Reconstruction algorithm and the data structure for this model to reduce amounts of calculation and memory are proposed. Finally, its effectiveness is shown by simulation.
We describe a new system of fluorescent x-ray computed tomography applied to image nonradioactive contrast materials in vivo. The system operates on the basis of computed tomography (CT) of the first generation. The experiment was also simulated using the Monte Carlo method. The research was carried out at the BLNE-5A bending-magnet beam line of the Tristan Accumulation Ring in Kek, Japan. An acrylic cylindrical phantom containing five paraxial channels of 5 and 4 mm diameters was imaged. The channels were filled with a diluted iodine-based contrast material, with iodine concentrations of 2 mg/ml and 500 (mu) g/ml. Spectra obtained with the system's high purity germanium (HPGe) detector separated clearly the K(alpha ) and K(beta 1) x-ray fluorescent lines, and the Compton scattering. CT images were reconstructed from projections generated by integrating the counts in these spectral lines. The method had adequate sensitivity and detection power, as shown by the experiment and predicted by the simulations, to show the iodine content of the phantom channels, which corresponded to 1 and 4 (mu) g iodine content per pixel in the reconstructed images.
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