Fourier Domain Detection Research Articles

Light scattering methods for tissue diagnosis.

Light scattering has become a common biomedical research tool, enabling diagnostic sensitivity to myriad tissue alterations associated with disease. Light-tissue interactions are particularly attractive for diagnostics due to the variety of contrast mechanisms that can be used, including spectral, angle-resolved, and Fourier-domain detection. Photonic diagnostic tools offer further benefit in that they are non-ionizing, non-invasive, and give real-time feedback. In this review, we summarize recent innovations in light scattering technologies, with a focus on clinical achievements over the previous ten years.

Biomedical Imaging and Optical Biopsy using Optical Coherence Tomography

Optical coherence tomography (OCT) is an emerging imaging modality which can generate high resolution, cross-sectional and three dimensional images of microstructure in biological systems. OCT is analogous to ultrasound B mode imaging, except that it uses light instead of sound. Imaging is performed by measuring the echo time delay of backscattering in the tissue as a function of transverse position. The penetration depth of OCT imaging is limited by attenuation from scattering to ~2 to 3 mm in most tissues, however image resolutions of 1–15 um may be achieved. OCT functions as a type of optical biopsy enabling in situ visualization of tissue microstructure with resolutions approaching that of conventional histopathology. Imaging can be performed in real time without the need to remove and process a specimen as in conventional biopsy. OCT technology utilizes advances in photonics and fiber optics such as femtosecond broadband lasers, high speed wavelength swept lasers and line scan camera technologies. Recent developments using Fourier domain detection achieve dramatic improvements in resolution and imaging speed. Three dimensional, volumetric imaging with extremely high voxel density is now possible, enabling microstructure and pathology to be visualized and rendered in a manner analogous to MR imaging. OCT has become a standard clinical diagnostic in ophthalmology, where it can image retinal pathology with unprecedented resolutions. OCT is also being developed for other applications ranging from cancer detection in endoscopy, to intravascular imaging in cardiology. This presentation will discuss OCT technology and its applications.

Fourier domain multispectral multiple scattering low coherence interferometry

We have implemented multispectral multiple scattering low coherence interferometry (ms2/LCI) with Fourier domain data collection. The ms2/LCI system is designed to localize features with spectroscopic contrast with millimeter resolution up to 1cm deep in scattering samples by using photons that have undergone multiple low-angle (forward) scattering events. Fourier domain detection both increases the data acquisition speed of the system and gives access to rich spectroscopic information, compared to the previous single channel, time-domain implementation. Separate delivery and detection angular apertures reduce collection of the diffuse background signal in order to isolate localized spectral features from deeper in scattering samples than would be possible with traditional spectroscopic optical coherence tomography. Light from a supercontinuum source is used to acquire absorption spectra of chromophores in the visible range within a tissue-like scattering phantom. An intensity modulation and digital lock-in detection scheme is implemented to mitigate relative intensity and spectral noise inherent in supercontinuum sources. The technical parameters of the system and comparative analysis are presented.

High-speed interferometric spectrally encoded flow cytometry

Spectrally encoded flow cytometry (SEFC) is a promising technique for noninvasive in vivo microscopy of blood cells. Here, we introduce a novel SEFC system for label-free confocal imaging of blood cells flowing at velocities of up to 10 mm/s within 65μm-diameter vessels. The new system employs interferometric Fourier-domain detection and a high-speed wavelength-swept source, allowing 100kHz line rate, sufficient for sampling the rapidly flowing cells 80μm below the tissue surface. The large data sets obtained by this technique would improve diagnosis accuracy, reduce imaging time, and open new possibilities for noninvasive monitoring of blood in patients.

Numerical reconstruction of 3D image in Fourier domain confocal optical coherence microscopy

Along with high longitudinal resolution of optical coherence tomography, confocal optical coherence microscopy (OCM) provides high transversal resolution due to relatively high numerical apertures. However, the presence of relatively high numerical apertures leads to limited depth of field, which reduces the speed of OCM and decreases the advantage of Fourier domain detection. In this paper we propose a numerical processing technique for three-dimensional image reconstruction in Fourier domain OCM. It takes into account not only the defocus of different parts of imaged volumetric sample, but also the effects of upper layers’ refractive index on imaging the sample inner structure. Besides providing sharp coherence gated imaging, this technique also allows for determining both the geometrical thickness and refractive index of the sample layers.

Use of optical coherence tomography in the diagnosis and management of uveitis.

Regatieri, Caio V. MD, PhD; Alwassia, Ahmad MD; Zhang, Jason Y. MD; Vora, Robin MD; Duker, Jay S. MD Author Information

High-speed optical coherence tomography: basics and applications

In the past decade we have observed a rapid development of ultrahigh-speed optical coherence tomography (OCT) instruments, which currently enable performing cross-sectional in vivo imaging of biological samples with speeds of more than 100,000 A-scans/s. This progress in OCT technology has been achieved by the development of Fourier-domain detection techniques. Introduction of high-speed imaging capabilities lifts the primary limitation of early OCT technology by giving access to in vivo three-dimensional volumetric reconstructions on large scales within reasonable time constraints. As result, novel tools can be created that add new perspective for existing OCT applications and open new fields of research in biomedical imaging. Especially promising is the capability of performing functional imaging, which shows a potential to enable the differentiation of tissue pathologies via metabolic properties or functional responses. In this contribution the fundamental limitations and advantages of time-domain and Fourier-domain interferometric detection methods are discussed. Additionally the progress of high-speed OCT instruments and their impact on imaging applications is reviewed. Finally new perspectives on functional imaging with the use of state-of-the-art high-speed OCT technology are demonstrated.

Three-dimensional ultrahigh resolution optical coherence tomography imaging of age-related macular degeneration

Ultrahigh resolution optical coherence tomography (OCT) enhances the ability to visualize different intra retinal layers. In age-related macular degeneration (AMD), pathological changes in individual retinal layers, including photoreceptor inner and outer segments and retinal pigment epithelium, can be detected. OCT using spectral / Fourier domain detection enables high speed, volumetric imaging of the macula, which provides comprehensive three-dimensional tomographic and morphologic information. We present a case series of AMD patients, from mild drusen to more advanced geographic atrophy and exudative AMD. Patients were imaged with a research prototype, ultrahigh resolution spectral / Fourier domain OCT instrument with 3.5 microm axial image resolution operating at 25,000 axial scans per second. These cases provide representative volumetric datasets of well-documented AMD pathologies which could be used for the development of visualization and imaging processing methods and algorithms.

Spectral Optical Coherence Tomography in Video-Rate and 3D Imaging of Contact Lens Wear

To present the applicability of spectral optical coherence tomography (SOCT) for video-rate and three-dimensional imaging of a contact lens on the eye surface. The SOCT prototype instrument constructed at Nicolaus Copernicus University (Torun, Poland) is based on Fourier domain detection, which enables high sensitivity (96 dB) and increases the speed of imaging 60 times compared with conventional optical coherence tomography techniques. Consequently, video-rate imaging and three-dimensional reconstructions can be achieved, preserving the high quality of the image. The instrument operates under clinical conditions in the Ophthalmology Department (Collegium Medicum Nicolaus Copernicus University, Bydgoszcz, Poland). A total of three eyes fitted with different contact lenses were examined with the aid of the instrument. Before SOCT measurements, slit lamp examinations were performed. Data, which are representative for each imaging mode, are presented. The instrument provided high-resolution (4 microm axial x 10 microm transverse) tomograms with an acquisition time of 40 micros per A-scan. Video-rate imaging allowed the simultaneous quantitative evaluation of the movement of the contact lens and assessment of the fitting relationship between the lens and the ocular surface. Three-dimensional scanning protocols further improved lens visualization and fit evaluation. SOCT allows video-rate and three-dimensional cross-sectional imaging of the eye fitted with a contact lens. The analysis of both imaging modes suggests the future applicability of this technology to the contact lens field.

Three‐dimensional high‐speed optical coherence tomography for the investigation of the cornea and anterior eye‐segments

Abstract Purpose: Optical coherence tomography (OCT) has a history of more than a decade for posterior eye investigations. This posterior OCT has been optimized for retinal investigation and is not suitable for anterior eye examinations, although interest for the application of OCT to the anterior eye exist. Recently, anterior‐segment OCT has been introduced and its application fields are rapidly extending. However, these anterior OCT systems are based on a time‐domain OCT configuration, which has relatively slow measurement speed; hence, it is difficult to have a full three‐dimensional (3‐D) tomographic dataset. Methods: Our group recently demonstrated ultra‐high‐speed corneal & anterior eye segment OCT (CAS‐OCT). This OCT system is based on Fourier domain detection and provides 20,000 A‐lines/sec. This fast measurement speed enables a full 3‐D dataset of the anterior eye within 2 sec. This 3‐D dataset provides several useful applications : e.g. visualisation of the internal structure of the bleb of glaucoma surgery. An en‐face projection or en‐face OCT slices are available from the 3‐D dataset, which enables en‐face assessment of corneal diseases whose extension directly relates to the patient's visual acuity. Results: Using this 3‐D CAS‐OCT, we have examined 46 eyes with several types of pathologies including granular, Avellino and lattice corneal dystrophy, post LASIK corneal changes, keratoplasty, keratoconus, iris nodules, anterior synechiae, angle recession, ciliary body detachment, scleritis, and several types of glaucoma surgery; trabeculectomy, trabeculotomy, and laser iridotomy. Conclusions: In the presentation, we introduce our CAS‐OCT and show clinical outcomes form the above‐mentioned examinations.

Ultrahigh-resolution, high-speed, Fourier domain optical coherence tomography and methods for dispersion compensation

Ultrahigh-resolution optical coherence tomography uses broadband light sources to achieve axial image resolutions on the few micron scale. Fourier domain detection methods enable more than an order of magnitude increase in imaging speed and sensitivity, thus overcoming the sensitivity limitations inherent in ultrahigh-resolution OCT using standard time domain detection. Fourier domain methods also provide direct access to the spectrum of the optical signal. This enables automatic numerical dispersion compensation, a key factor in achieving ultrahigh image resolutions. We present ultrahigh-resolution, high-speed Fourier domain OCT imaging with an axial resolution of 2.1 ìm in tissue and 16,000 axial scans per second at 1024 pixels per axial scan. Ultrahigh-resolution spectral domain OCT is shown to provide a ~100x increase in imaging speed when compared to ultrahigh-resolution time domain OCT. In vivo imaging of the human retina is demonstrated. We also present a general technique for automatic numerical dispersion compensation, which is applicable to spectral domain as well as swept source embodiments of Fourier domain OCT.