316 results about "Fourier domain" patented technology

The invention describes several embodiments of an adapter which can make use of the devices in any commercially available digital cameras to accomplish different functions, such as a fundus camera, as a microscope or as an en-face optical coherence tomography (OCT) to produce constant depth OCT images or as a Fourier domain (channelled spectrum) optical coherence tomography to produce a reflectivity profile in the depth of an object or cross section OCT images, or depth resolved volumes. The invention admits addition of confocal detection and provides simultaneous measurements or imaging in at least two channels, confocal and OCT, where the confocal channel provides an en-face image simultaneous with the acquisition of OCT cross sections, to guide the acquisition as well as to be used subsequently in the visualisation of OCT images. Different technical solutions are provided for the assembly of one or two digital cameras which together with such adapters lead to modular and portable high resolution imaging systems which can accomplish various functions with a minimum of extra components while adapting the elements in the digital camera. The cost of such adapters is comparable with that of commercial digital cameras, i.e. the total cost of such assemblies of commercially digital cameras and dedicated adapters to accomplish high resolution imaging are at a fraction of the cost of dedicated stand alone instruments. Embodiments and methods are presented to employ colour cameras and their associated optical sources to deliver simultaneous signals using their colour sensor parts to provide spectroscopic information, phase shifting inferometry in one step, depth range extension, polarisation, angular measurements and spectroscopic Fourier domain (channelled spectrum) optical coherence tomography in as many spectral bands simultaneously as the number of colour parts of the photodetector sensor in the digital camera. In conjunction with simultaneous acquistion of a confocal image, at least 4 channels can simultaneously be provided using the three color parts of conventional color cameras to deliver three OCT images in addition to the confocal image.

Fourier domain a/LCI (faLCI) system and method which enables in vivo data acquisition at rapid rates using a single scan. Angle-resolved and depth-resolved spectra information is obtained with one scan. The reference arm can remain fixed with respect to the sample due to only one scan required. A reference signal and a reflected sample signal are cross-correlated and dispersed at a multitude of reflected angles off of the sample, thereby representing reflections from a multitude of points on the sample at the same time in parallel. Information about all depths of the sample at each of the multitude of different points on the sample can be obtained with one scan on the order of approximately 40 milliseconds. From the spatial, cross-correlated reference signal, structural (size) information can also be obtained using techniques that allow size information of scatterers to be obtained from angle-resolved data.

The present invention relates to a method of measuring motion of an object such as a heart by magnetic resonance imaging. A pulse sequence is applied to spatially modulate a region of interest of the object and at least one first spectral peak is acquired from the Fourier domain of the spatially modulated object. The inverse Fourier transform information of the acquired first spectral-peaks is computed and a computed first harmonic phase image is determined from each spectral peak. The process is repeated to create a second harmonic phase image from each second spectral peak and the strain is determined from the first and second harmonic phase images. In a preferred embodiment, the method is employed to determine strain within the myocardium and to determine change in position of a point at two different times which may result in an increased distance or reduced distance. The method may be employed to determine the path of motion of a point through a sequence of tag images depicting movement of the heart. The method may be employed to determine circumferential strain and radial strain.

An optical interference apparatus for carrying out Fourier domain optical coherence tomography including means to provide multiple beams whereby interferograms are recorded simultaneously for a plurality of different focal depths within a substance to be examined, each interferogram being provided by one of the multiple beams. Means are provided for combining images derived from said interferograms for a plurality of different focal depths, whereby a single image may be constructed with an increased depth of field. The axial spacing of the foci is calculated to take into account the Rayleigh range of the focal waist in the substance to be examined.

An image forming method uses an optical coherence tomography as to an optical axis direction of plural pieces of image information of an object. First image information of an object is obtained at a first focus with respect to an optical axis direction to then object. A focusing position is changed by dynamic focusing from the first focus to a second focus along the optical axis. The second image information of the object is obtained at the second focus. A third image information, tomography image information of the object and including a tomography image of the first focus or the second focus, is obtained by Fourier domain optical coherence tomography. A tomography image or a three-dimensional image of the object is formed in positional relation, in the optical axis direction, between the first image information and the second image information using the third image information.

A system and method for projection number and radiation dose reduction in tomographic imaging that creates a three dimensional cross sectional image of an object by the reconstruction of its projections. Images of a superior quality can be obtained with a fewer number projections than seen with conventional methods by reconstruction of projections that have been pre-processed and preferably placed in the Fourier domain with a Fractional Fourier Transform (FrFT) or forward Pseudo-polar Fast Fourier transform (PPFFT). The projections are iteratively refined through formulation of a constrained optimization problem with constraints in object space and Fourier space preferably solved with a gradient descent algorithm incorporating a Bregman iterative regularization or a continuative regularization. By using an exact Fourier-based iterative algorithm as well as physical and mathematical constraints, convergence to a lowest-possible noise state that is also strictly consistent with the measured data can be obtained.

This invention permits retinal images to be acquired at high speed and with unprecedented resolution in three dimensions (4×4×6 μm). The instrument achieves high lateral resolution by using adaptive optics to correct optical aberrations of the human eye in real time. High axial resolution and high speed are made possible by the use of Fourier-domain optical coherence tomography. Using this system, we have demonstrated the ability to image microscopic blood vessels and the cone photoreceptor mosaic.

A methodology is described to reduce the complexity of filters for face recognition by reducing the memory requirement to, for example, 2 bits/pixel in the frequency domain. Reduced-complexity correlations are achieved by having quantized MACE, UMACE, OTSDF, UOTSDF, MACH, and other filters, in conjunction with a quantized Fourier transform of the input image. This reduces complexity in comparison to the advanced correlation filters using full-phase correlation. However, the verification performance of the reduced complexity filters is comparable to that of full-complexity filters. A special case of using 4-phases to represent both the filter and training/test images in the Fourier domain leads to further reductions in the computational formulations. This also enables the storage and synthesis of filters in limited-memory and limited-computational power platforms such as PDAs, cell phones, etc. An online training algorithm implemented on a face verification system is described for synthesizing correlation filters to handle pose/scale variations. A way to perform efficient face localization is also discussed. Because of the rules governing abstracts, this abstract should not be used to construe the claims.

Methods, fourier domain optical coherence tomography (FDOCT) interferometers and computer program products are provided for removing undesired artifacts in FDOCT systems using continuous phase modulation. A variable phase delay is introduced between a reference arm and a sample arm of an FDOCT interferometer using continuous phase modulation. Two or more spectral interferograms having different phase delay integration times are generated. The spectral interferograms are combined using signal processing to remove the undesired artifacts. Systems and methods for switching between stepped and continuous phase shifting Fourier domain optical coherence tomography (FDOCT) and polarization-sensitive optical coherence tomography (PSOCT) are also provided herein.

Methods, systems, and apparatuses are provided for measuring one or more sinusoidal Fourier components of an object. A structured second radiation is generated by spatially modulating a first radiation. The structured second radiation illuminates the object, The structured second radiation is scaled and oriented relative to the object. The object produces a third radiation in response to the illuminating. A single-element detector detects a portion of the third radiation from multiple locations on the object substantially simultaneously for each spatial modulation of the first radiation and for each orientation of the second radiation. A time-varying signal is produced based on said detected portion of the third radiations. One or more characteristics of the one or more sinusoidal Fourier components of the object are estimated based on the time-varying signal.

Methods and systems are disclosed of sensing an object. A first radiation is spatially modulated to generate a structured second radiation. The object is illuminated with the structured second radiation such that the object produces a third radiation in response. Apart from any spatially dependent delay, a time variation of the third radiation is spatially independent. With a single-element detector, a portion of the third radiation is detected from locations on the object simultaneously. At least one characteristic of a sinusoidal spatial Fourier-transform component of the object is estimated from a time-varying signal from the detected portion of the third radiation.

The present invention is directed to an ophthalmologic measurement method which can depict three-dimensional structures of the interfaces of an eye by short-coherence interferometry based on reference points. For this purpose, the pupil is illuminated at a plurality of points by a short-coherence illumination source. The measurement beam reflected at these points by the interfaces and surfaces of the eye is superimposed with a reference beam. The measurement data which are generated in this way are spectrally split by a diffraction grating, imaged on a two-dimensional detector array and conveyed to a control unit which determines a three-dimensional structure of all intraocular interfaces and surfaces of the eye. In the suggested Fourier domain OCT method, the depiction of three-dimensional structures is preferably carried out by spline surfaces or polygon surfaces. In doing so, it is possible to determine the depth positions of the measurement beams in many points of the pupil with a single recording of the array camera in that the pupils are illuminated by a diaphragm grid and the reference mirror contains a periodic phase grid.

An optical measurement system and apparatus for carrying out cataract diagnostics in an eye of a patient includes a Corneal Topography Subsystem, a wavefront aberrometer subsystem, and an eye structure imaging subsystem, wherein the subsystems have a shared optical axis, and each subsystem is operatively coupled to the others via a controller. The eye structure imaging subsystem is preferably a fourierdomain optical coherence tomographer, and more preferably, a swept source OCT.

Arrangements, apparatus and methods are provided according to exemplary embodiments of the present invention. In particular, at least one first electro-magnetic radiation may be received and at least one second electro-magnetic radiation within a solid angle may be forwarded to a sample. The second electro-magnetic radiation may be associated with the first electro-magnetic radiation. A plurality of third electro-magnetic radiations can be received from the sample which is associated with the second electro-magnetic radiation, and at least one portion of the third electro-magnetic radiation is provided outside a periphery of the solid angle. Signals associated with each of the third electro-magnetic radiations can be simultaneously detected, with the signals being associated with information for the sample at a plurality of depths thereof. The depths can be determined using at least one of the third electro-magnetic radiations without a need to utilize another one of the third electro-magnetic radiations.

The invention discloses a high-dynamic weak-signal rapid capture method for a direct sequence spread spectrum system, belonging to the field of radio communication. Because a spread spectrum carrier has a chirp signal characteristic under the condition of high-dynamic motion (high-speed and high-acceleration), the high-dynamic weak-signal rapid capture method comprises the steps of: firstly, carrying out carrier Doppler frequency compensation by using a time frequency focusing characteristic of fractional order Fourier transform; secondly, carrying out incoherent accumulation on a spread frequency signal by using an order resolving capacity of the fractional order Fourier transform; and finally, carrying out capture judgment on the signal in an order Fourier domain by using a constant false alarm rate detection technology. According to the invention, the difficulty of incapability of long-time coherent accumulation under the high-dynamic condition in the traditional Fourier transform based rapid capture method is solved; and under the condition of high dynamicity and low signal to noise ratio, the signal to noise ratio is effectively increased and the signal capture time is shortened. In addition, a rapid algorithm exists in the invention and is easy to realize on the engineering in real time.

The invention relates to a non coherent demodulation method, which belongs to the signal processing field, is used in Chirp spread spectrum technology demodulation, can reduce phase shift error, multipath time delay error and Doppler shift effect, and achieves better performance over multipath fading channels and IEEE802.15.4a S-V standard channels. The fundamental principle of the invention is: utilizing a Chirp signal as an impulse function in a proper fractional Fourier domain, i.e. fractional Fourier transformation achieves an excellent focusing ability to the Chirp signal sent by the CCS system. For the advantage of Chirp signal processing in fractional Fourier transformation, the fractional Fourier transformation can be used in CSS spread spectrum technology to demodulate Chirp signals with different modulation frequencies. The demodulation to CCS system is realized by implementing fractional Fourier transformation to the received base band data, and judging the code element by detecting the peak value of the focusing order. The method reduces the demand to frequency synchronization, needs no phase synchronization, and achieves better performance over multipath frequency selectively fading channels.