Full-field Optical Coherence Tomography Research Articles

Crosstalk rejection in parallel optical coherence tomography using spatially incoherent illumination with partially coherent sources

The continuing improvement of high-speed area-scan cameras has made possible the construction of parallel optical coherence tomography (OCT) systems that are competitive with the fastest demonstrated swept-source OCT systems. Unfortunately, when imaging through turbid media using a partially coherent source, parallel OCT suffers resolution loss from coherent multiple scattering, a phenomenon known as crosstalk. We demonstrate the use of a full-field OCT system employing multimode fiber in the illumination arm to reduce the spatial coherence of a partially coherent source. By reducing the spatial coherence area below the system's lateral resolution, we create a spatial coherence gate that rejects these multiply scattered photons. We quantify the image quality and resolution improvement of this method by comparing images of a USAF test chart acquired beneath turbid phantoms using both coherent and incoherent illumination and computing the resulting modulation transfer functions. We demonstrate the feasibility of this method for imaging biological specimens by imaging a Drosophila melanogaster sample.

Multilayered scattering reference mirror for full field optical coherence tomography with application to cell profiling

A multilayered scattering structure is proposed and demonstrated as a reference mirror for use with full field optical coherence tomography (FF-OCT) to increase contrast of tissue imaging and provide compensation. Common-path FF-OCT systems were built demonstrating high resolution cell profiling. The use of this mirror with frequency domain FF-OCT allows 3D images in real time.

Motion artifact suppression in full-field optical coherence tomography

Significant motion artifacts limit the performance of conventional full-field optical coherence tomography (FF-OCT) for in-vivo imaging. We present a theoretical and experimental study of those limitations. A new FF-OCT system suppressing most of artifacts due to sample motions is demonstrated using instantaneous phase shifting with nonpolarizing optics and pulsed illumination. The experimental setup is based on a Linnik-type interferometer illuminated by the superluminescence emission from a Ti:Al(2)O(3) waveguide crystal. En face tomographic images are calculated as a combination of two phase-opposed interferometric images acquired simultaneously by two CCD cameras placed at both outputs of the interferometer, with a spatial resolution of 0.8 microm x 1.6 microm (axial x transverse) and a detection sensitivity of approximately 60 dB.

Full-field optical coherence tomography by achromatic phase shifting with a rotatinghalf-wave plate

An achromatic phase shifter with a rotating half-wave plate (HWP) and a full-field opticalcoherence tomography (FF-OCT) system based on it are presented. The novelconfiguration of this phase shifter in the FF-OCT system can achromaticallyprovide a phase shift of eight times the rotation angle of the HWP. The theoreticalcalculation of the phase shift and numerical analysis of the phase shift error,as well as the amplitude ratio, are conducted by means of Jones matrices. Theactual phase shift has also been measured to confirm the validity of the ‘8θ phase shift—HWProtation angle θ’ relation. The coherent image of a mirror has been obtained by using the Hariharanalgorithm to verify the phase shifter’s feasibility. Using traditional phase shiftingalgorithms, en-face images of a coin have been measured at different depths to illustrate thetomographic capability of this FF-OCT system. In comparison with other current systems,our design has several advantages, and high-resolution high-speed FF-OCT imaging can beenvisioned. The phase shifter can be used for common path setups and is verysuitable for implementing the phase shifting of a broad-spectrum light source.

Full-field optical coherence tomography for the rapid estimation of epidermal thickness: study of patients with diabetes mellitus type 1

Changes in morphology of the skin are an important factor that can affect non-invasive measurements performed through this organ, in particular for glucose monitoring in e.g. patients with diabetes mellitus. A characterization technique for non-contact in vivo profiling of the superficial skin layers can be beneficial for evaluation of the performance of such measurement systems. We applied a full-field optical coherence tomography (OCT) system followed by the fully automatic processing for this task. With the developed procedure, non-invasive quantification of the skin morphology can be performed within a few minutes. The dorsal skin of the upper arm of 22 patients with Type 1 Diabetes Mellitus was investigated with an OCT system and with a commercially available dermatological laser scanning confocal microscope (CM) as a reference method. The estimates of epidermal thickness from OCT were compared with the results of expert-assisted analysis of confocal images. The highest correlation with the CM measurements has been obtained for the distance from the entrance peak to the first minimum of the OCT reflection profile (). In this specific patient group, we have observed a statistically significant correlation of the subjects' body mass index with the distance from the entrance peak to the dermal reflection peak in the OCT profile (p = 0.010). Furthermore, the same OCT parameter is negatively correlated with age with marginal statistical significance (p = 0.062). At the same time, no relation of diabetes-related parameters (duration of disease and concentration of glycated haemoglobin) to the skin morphology observed with the OCT and CM was found.

Structural and optical properties of wood and wood finishes studied using optical coherence tomography: application to an 18th century Italian violin

Optical coherence tomography (OCT) is especially attractive for the study of cultural heritage artifacts because it is noninvasive and nondestructive. We have developed an original full-field time-domain OCT system dedicated to the investigation of varnished and painted artifacts: an interferometric Mirau objective allows one to perform the scan without moving the works of art. The axial and transverse high resolution (respectively, 1.5 and 1 microm) are well adapted to the detection of the investigated structures (pigment grains, wood fibers, etc.). The illumination spectrum is in the visible range (centered at 630 nm, 150 nm wide) to potentially allow us to perform spectroscopic OCT on pigment particles. The examination of wood samples coated with a traditional finish, demonstrates the ability of the system to detect particles, characterize layers thickness, and image the three-dimensional wood structures below the varnishes. OCT has finally been applied to study in situ the coated wood surface of an 18th century Italian violin and provides important information for its conservation treatment.

Single-shot holography for depth resolved three dimensional imaging

We introduce a method for depth-resolved photorefractive holographic imaging with potentially extremely short acquisition time for a complete three dimensional (3D) image. By combining the advantages of full-field frequency-domain optical coherence tomography with those of photorefractive holography our concept is capable of obtaining 3D information with only one single shot. We describe the operation principle of our concept and give a first experimental proof of principle.

Coherence Effects in Applications of Frequency and Time Domain Full Field Optical Coherence Tomography to Optical Metrology

Coherence Effects in Applications of Frequency and Time Domain Full Field Optical Coherence Tomography to Optical Metrology

Defocus test and defocus correction in full-field optical coherence tomography

We report experimental evidence and correction of defocus in full-field optical coherence tomography of biological samples owing to mismatch of the refractive index of biological tissues and water. Via a metric based on the image quality, we demonstrate that we are able to compensate this index-induced defocus and to recover a sharp image in depth.

Resolution Enhancement for Tomographical Images of a Full-Field OCT System

In this paper a new method is proposed to enhance the resolution of tomographical images of a full-field optical coherence tomography (OCT) system without improving the bandwidth of light source. Theoretic study and simulation indicate that the method improves the system resolution and quality of retrieved tomographic images for the multilayer in- formation carrier. Experiment results are also given in support of the proposed method.

Recent Optical Coherence Tomography Imaging of Vitreomacular Disorders

Optical coherence tomography (OCT) has become a ubiquitous and invaluable tool in the retinal clinic as it provides the examiner with a 2D cross-section of the retina; newer machines are also able to reconstruct 3D images. The greater detail afforded by OCT scanning enhances diagnostic capabilities and advances vitreoretinal research. It has proved very useful in surgical planning and provides fine anatomical retinal detail, which can aid post-operative prognostication in certain vitreoretinal disorders. OCT operates on the same physical principles as an ultrasound scan, except it uses light as the carrier signal. First-generation OCTs are capable of resolutions only between 10 and 20μm. Second-generation OCTs improved this to 5–6μm. We await the commercial availability of third-generation and full-field OCTs, which yield resolutions as low as 1–3μm.

Development of full-field optical coherence tomography system

A full-field optical coherence tomography system using an achromatic phase shifter based on a rotating half-wave plate to implement phase shifting is developed. The phase shifter can achromatically introduce phase shift of eight times the rotating angle of the half-wave plate, and can rapidly provide various phase shifts for various algorithms. Real phase shift is measured and the result demonstrates that the system gives a phase shift of eight times the rotating angle of the half-wave plate, showing the achromatic phase shifter model is correct. Imaging experiment results of a mirror using Hariharan algorithm show that the system has high phase shift precision. A coin as the sample is imaged to demonstrate the performance of the system.

In vivo imaging of dynamic biological specimen by real-time single-shot full-field optical coherence tomography

We demonstrate the feasibility of a compact single-shot full-field time domain optical coherence tomography (OCT) for imaging dynamic biological sample in real-time. The system is based on a Linnik type polarization Michelson interferometer and a four-quadrature phase-stepper optics, which can simultaneously capture four quadraturely phase-stepped interferograms on a single CCD. Using a superluminescent diode as light source with center wavelength of 842nm and spectral width of 16.2nm, the system yields an axial resolution of 19.8μm, and covers a field of view of 280×320μm2 (220×250 pixels) with a transverse resolution of 4.4μm by using a 10× microscope objective (0.3NA). Three-dimensional OCT images of biological samples such as an onion slice and a diaptomus were obtained without any image averaging or pixel binning. In addition, in vivo depth resolved dynamic imaging was demonstrated to show the beating internal structure of a diaptomus with a fame rate of 5fps.

Simultaneous dual-band ultra-high resolution full-field optical coherence tomography

Ultrahigh-resolution full-field optical coherence tomography (FF-OCT) is demonstrated in the 800 nm and 1200 nm wavelength regions simultaneously using a Silicon-based (Si) CCD camera and an Indium Gallium Arsenide (InGaAs) camera as area detectors and a halogen lamp as illumination source. The FF-OCT setup is optimized to support the two broad spectral bands in parallel, achieving a detection sensitivity of approximately 90 dB and a micrometer-scale resolution in the three directions. Images of ex vivo biological tissues are presented (rabbit trachea and Xenopus laevis tadpole) with an increase in penetration depth at 1200 nm. A color image representation is applied to fuse both images and enhance spectroscopic property visualization.

Large Area Full-Field Optical Coherence Tomography and its Applications

Large Area Full-Field Optical Coherence Tomography and its Applications

Image restoration method based on Hilbert transform for full-field optical coherence tomography

A full-field optical coherence tomography (FF-OCT) system utilizing a simple but novel image restoration method suitable for a high-speed system is demonstrated. An en-face image is retrieved from only two phase-shifted interference fringe images through using the mathematical Hilbert transform. With a thermal light source, a high-resolution FF-OCT system having axial and transverse resolutions of 1 and 2.2 microm, respectively, was implemented. The feasibility of the proposed scheme is confirmed by presenting the obtained en-face images of biological samples such as a piece of garlic and a gold beetle. The proposed method is robust to the error in the amount of the phase shift and does not leave residual fringes. The use of just two interference images and the strong immunity to phase errors provide great advantages in the imaging speed and the system design flexibility of a high-speed high-resolution FF-OCT system.

Full-Field Optical Coherence Tomography Based on Hilbert Transform

Novel image restoration technique suitable for parallel detection in full-field optical coherence tomography (FF-OCT) is introduced. An en-face information of a sample can be demodulated from only two phase-modulated interference images with simple mathematical Hilbert transform process. With the proposed method, a FF-OCT was implemented and its feasibility was verified by taking tomographic images of a biological sample; the wing of the spilota plagicollis fairmaire ex vivo. The system shows the image resolutions of 1.0 µm for the axial direction and 2.2 µm for the lateral direction.

High-Resolution Imaging of Ophthalmic Tissues Using Full-Field Optical Coherence Tomography

High-Resolution Imaging of Ophthalmic Tissues Using Full-Field Optical Coherence Tomography

In vivo video-rate cellular-level full-field optical coherence tomography

Full-field optical coherence tomography (FF-OCT) capable of in vivo cellular-level imaging is demonstrated for nonscanning horizontal cross-sectional imaging. The system is based on a white light interference microscope illuminated by a thermal light source. A dual-channel two-dimensional (2-D) detection technique incorporated with a pair of CCD cameras has been developed, where a pair of interferometric images with phase difference of pi/2 are simultaneously captured using an achromatic phase shifter. By acquiring an additional pair of images with a conventional phase shift method, a horizontal cross section is derived from every two consecutive CCD frames, enabling OCT imaging at the video rate. Using an ultrabroad bandwidth illumination incorporated with relatively high NA (0.8 NA) water immersion objectives, an axial resolution of 0.8 microm and a transverse resolution of 0.7 microm are experimentally confirmed. A field of view of 215 microm x 215 microm is covered by the 500 x 500 pixel CCD cameras. We demonstrate, for what is believed to be the first time, in vivo cellular-level blood flow imaging of a Xenopus laevis tadpole by FF-OCT.

An efficient algorithm used for full-field optical coherence tomography

An efficient algorithm for computing optical coherence tomography is presented, which is based on the discrete differences of a time/depth sequence of interferograms. The existing multiple-step phase-shift algorithms, including those solved from Carré and Hariharan equations as well as circular-step algorithm proposed by Dubois et al., are analyzed and compared with the proposed algorithm. The analytical and experimental results show the computational efficiency of the new algorithm outperforms others. The simulations also demonstrate that the algorithm based on derivatives of four phase-shifted images is less sensitive to the phase-shift noise comparing to traditional 4-step phase-shift-based algorithm.