A numerical deconvolution method that cancels the blurring due to lateral defocus in line field Fourier domain optical coherence tomography (LF-FDOCT) using imaging optics is proposed. This method employs an inverse filter designed from the point spread function (PSF) that is calculated by Fresnel diffraction. The inverse filter can eliminate the lateral defocus, and consequently, the out-of-focus lateral resolution can be improved to a level comparable with the in-focus resolution over the entire axial measurement range. In this paper, we describe the process of calculating the PSF and the inverse filter designed from it in LF-FDOCT. The effect of deconvolution is also schematically discussed and estimated. A knife-edge method also verifies the effect of in-focus resolution experimentally.
KEYWORDS: Optical coherence tomography, Deconvolution, Image segmentation, Point spread functions, Resolution enhancement technologies, Super resolution, Signal detection, In vivo imaging, Eye, Infrared imaging
A method of lateral superresolution for Fourier domain optical coherence tomography is presented. This method consists of intentional defocus and its numerical compensation using a spatial frequency- phase filter. The designing process of the phase filter is described, and the superresolution effect is discussed theoretically. Experimental results of a knife-edge test prove that the frequency filter enhances the lateral resolution better than a diffraction-limited resolution. This method is applied to the investigation of an in vivo human iris and shows the effect of the cancellation of defocus.
KEYWORDS: Optical coherence tomography, Cameras, In vivo imaging, 3D acquisition, Spectroscopy, 3D image processing, Tissues, Camera shutters, Tomography, Visualization
A high-speed line-field Fourier-domain optical coherence tomography system has been developed. Tomographic images consisting of 656 A-lines are obtained at 121 frames per second. It is corresponding to 79,400 A-line/s. Three-dimensional volume sets consist of 256 OCT images are measured within 2.1 seconds. The sensitivity of this system is 79.5 dB. A biological tissue measurement is demonstrated with human nail fold in vivo. The three-dimensional nail fold structure is visualized.
We demonstrate 3-D optical coherence tomography using only 1-D mechanical scanning. This system uses the principle of Fourier domain optical coherence tomography for depth resolution, 1-D imaging for lateral vertical resolution, and mechanical scanning by a galvanometer for lateral horizontal resolution. An in vivo human fingerpad is investigated in three dimensions with an image size of 480 points (vertical) × 300 points (horizontal) × 1024 points (depth), which corresponds to 2.1×1.4×1.3 mm. The acquisition time for a single cross section is 1 ms and that for a single volume is 10 s. The system sensitivity is 75.6 dB at a probe beam power of 1.1 mW.
A method of lateral superresolution for Fourier domain optical
coherence tomography is presented.
This method consists of intentional defocus and its numerical
compensation using a spatial frequency- phase filter.
The designing process of the phase filter is described, and
the superresolution effect is discussed theoretically.
Experimental results of knife-edge test prove that
the frequency filter enhances the lateral resolution better than
a trans-form limited resolution.
Standard high-speed Fourier domain optical coherence tomography
(FD-OCT) and a modified version of FD-OCT; a line-field FD-OCT
(LF-FDOCT) are demonstrated.
LF-FDOCT is using the principle of FD-OCT for its depth resolution and
a one-dimensional imaging optics for its one-dimensional lateral
resolution.
A mechanical C-scan drived by a galvano scanner is introduced into the
FD-FDOCT, which shows a cross sectional OCT image without any
mechanical scanning.
The improved version of FD-OCT visualizes the three-dimensional
structure of a sample with only one-dimensional scanning.
Both standard FD-OCT and LF-FDOCT are applied to dermatological
applications and visualize the inner structure of an in vivo
human fingerpad.
High speed complex full-range Fourier domain optical coherence tomography (FD-OCT) is demonstrated. In this FD-OCT phase modulation of a reference beam (M-scan) and transversal scanning (B-scan) are performed simultaneously. Because of this simultaneous BM-scan, this FD-OCT requires only a single A-scan for each single transversal position. The Fourier transform method is applied along the direction of the B-scan to reconstruct complex spectra, and the complex spectra compose a full-range OCT image. A simple but slow version of this FD-OCT visualizes the cross-section of a plastic plate. A modified fast version of this FD-OCT investigates a sweat duct in a finger pad in vivo, and visualizes it with 100 ms acquisition time.
A conventional Fourier-domain optical coherence tomography(FD-OCT) is improved to a line-field FD-OCT. The line-field FD-OCT is a conventional FD-OCT in its vertical axis, and a one-dimensional(1-D) imaging system in its lateral axis. Hence, depth and lateral information, which provide a 2-D OCT image, are simultaneously detected without any mechanical scan. Using an additional 1-D mechanical scan, which is realized by a galvano mirror in our system, a 3-D volume can be measured. Because the dimensions of mechanical scan are decreased compared with conventional FD-OCT, this system is capable of faster measurement.
A novel optical scheme for a full range Fourier domain optical coherence tomography (FD-OCT) is presented. This method avoids a mechanical scan for phase-shifting (mechanical M-scan) which enables a full range FD-OCT. A tilting reference wavefront is used to make variable phase offset of spectral interferometric fringes. Several spectral fringes are detected by a two dimensional CCD camera simultaneously. One axis of the CCD camera is occupied with the optical spectral axis, and the other axis is employed for phase offset variation. A few spectral fringes are extracted and used for phase-shifting algorithm. The principle of this system is confirmed with a plane mirror sample.
We will present a new version of the polarization sensitive spectrally interfrometric optical coherence tomography which uses one broadband light source and two measurements to determine the Mueller images of a biomedical sample. This system uses phase information of the OCT images. The SI-OCT enables direct measurement of the phase-information of OCT images without complex signal processing method.
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