Cellview Imaging Inc.

Optos Plc

Aker Subsea Inc.

Oti Ophthalmic Technologies Inc.

L&r Medical Inc.

Mark Hathaway

Rishard Weitz

John Rogers

Richard Hope Carter

John A Rogers

John Rodgers

Channel separation in ophthalmologic systems is achieved by introducing a small angle between each beam incident on the scanner. The multiple channels are emitted from multiple emitters positioned such that their respective beams reach an X-Y scanner with small angular separations between the beams. This removes the need for dichroic components to combine the multiple channels into a single beam. This also allows the emitters to use the same wavelength if desired, such as in a combined SLO and OCT system in which it may be desirable to use the same light source in order to reduce the cost and complexity of the system.

Angular separation of scan channels

A method is provided for determining the thickness of a retina. A single beam is used to illuminate the retina of a patient. Interference between reflections off different layers within the retina cause autocorrelation in the returned signal. An FFT applied to the autocorrelation signal reveals the strongest autocorrelation, which indicates the distance between the nerve fiber layer (NFL) and the layers between the inner segment/outer segment (IS/OS) and the retinal pigment epithelium (RPE), the dominant scatterers. By analyzing autocorrelation, a single beam can be used. This avoids the problem of movement of the patient, arising in the use of a standard OCT interferometer, resulting in a simpler and less expensive technique of measuring retinal thickness.

Retinal Thickness

A method is provided for determining the thickness of a retina. A single beam is used to illuminate the retina of a patient. Interference between reflections off different layers within the retina cause autocorrelation in the returned signal. A spectrometer produces a frequency spectrum of the beam reflected by the retina, and an FFT applied to the frequency spectrum produces a spatial domain signal (SDS). Autocorrelation within the reflected beam results in edges within the spatial domain signal, and the spatial coordinate of the SDS at which the power of the SDS drops precipitously indicates the distance between the nerve fiber layer (NFL) and the layers between the inner segment/outer segment (IS/OS) and the retinal pigment epithelium (RPE), the dominant scatterers. By analyzing autocorrelation, a single beam can be used. This avoids the problem of movement of the patient, arising in the use of a standard OCT interferometer, resulting in a simpler and less expensive technique of measuring retinal thickness.

Retinal thickness

In line-scan scanning laser ophthalmoscopy (SLO) a narrowband of wavelengths is required. For greater flexibility the frequencies of this narrowband should be selectable. This is possible using a broadband tunable single mode source, but such a solution is expensive. A system is provided in which an extended broadband source is used. Light from the extended source passes to a diffraction grating, which introduces a wavelength dependent angular separation when reflecting the light. By rotating the diffraction grating, only light of a selectable narrowband passes through a fixed output slit for use by the line-scan SLO system. Alternatively, the diffraction grating can be fixed and a rotatable mirror lying between the diffraction grating and the output slit can be used to select the wavelengths reaching the line-scan SLO system.

Diffraction grating for wavelength selection in line-scan SLO

In a OCT interferometer it is necessary to balance dispersion within the reference arm with dispersion within the object arm. This is normally done by replicating within the reference arm the components found in the object arm. This adds to the complexity and cost of the OCT interferometer. A method is provided for determining the design of and designing a simplified OCT interferometer, in which the reference arm contains only a single piece of glass of a single glass type. This reduces the cost and complexity of the OCT interferometer, and reduces power loss and undesired reflections within the reference arm.

Dispersion compensation

In an OCT system, the autocorrelation signal depends only on the strength of the signal in the object arm scattered back from a patient's retina and is a result of different reflections from different layers of the retina interfering with each other. The strength of the autocorrelation signal depends on how well focused the system is. Normally the autocorrelation signal is treated as noise. However by removing the reference path signal, the autocorrelation signal is easily measured and analyzed. The optimal focus can the then be found by adjusting the focus value until the autocorrelation signal is maximized.

Focusing algorithm in OCT-only systems

A method of transmitting on a transmission line a set of carrier signals of which at least one component represents a respective data value and the carrier signals are of different frequencies ranging from a lowest frequency to a highest frequency, in which the respective component of each carrier above the lowest frequency is adjusted on transmission in accordance with a selected relationship between that respective component and the corresponding component of the next lower frequency so as to compensate for the frequency-dependent effect of the transmission line on those components. The components may be amplitudes. The relationship may be a ratio of the respective and corresponding components. Alternatively each respective component may be adjusted in accordance with a scaling factor dependent on the previous data value presented by the corresponding component of next lower carrier frequency, the scaling factor being a ratio between a predetermined value and the said corresponding component, the predetermined value depending on the said previous data value. The components may be phases and the phase of each carrier after the first may be set from the phase of the previous lower frequency carrier augmented by the ratio of the data value in bits and the number of bits that can be carried by the respective component.

Signal encoding for frequency division multiplexing on transmission lines

A modem for use with a subsea transmission line comprises a digital signal processor responsive to a succession of segments of a data signal to produce a respective set of orthogonal frequency division multiplexed signals and to transmit those signals as a burst on the transmission line, and to prepend the burst with a start signal comprising a cyclically time-varying signal envelope-modulated with a Gaussian waveform. The modem is also arranged to convert signals received from the transmission line into a succession of digital samples and to process those samples to obtain an indication of the peak of the Gaussian waveform whereby to provide a datum for decoding a received burst of OFDM signals.

Indicating and detecting the start of signal transmission employing frequency division multiplexing

A method of performing spectral OCT imaging on a target involves repeatedly scanning said target along a transverse scanning line with an object beam derived from an OCT interferometer having a narrowband source. The wavelength of the narrowband source is modulated over a range of wavelengths at a rate that is slow relative to the rate of scanning the target. The object beam returned from the target is detected to produce a set of data obtained from multiple scans along said scanning line over the entire range of wavelengths. The data is then processed to extract an OCT image (typically a B-scan) of the target containing depth information.

Swept source OCT apparatus

In an OCT apparatus, an object light beam is returned from a target and interferes with a reference light beam. Image information is obtained from a depth Z in the target that depends on the optical path difference between the object and reference beams with a resolution that depends on the coherence length of the light. A scanner transversely scans the target with the object beam over a plurality of image points defined by the resolution of the apparatus. Interface optics directs the reference and object beams onto an array of detector elements such that the optical path difference between the reference beam and the object beam varies across the array. The reference beam and the object beam interfere with each other over the array of detector elements for individual image points on the target during each transverse scan. A memory stores a subset of data points corresponding to each individual image point obtained from each detector elements of the array. A processor processes one or more of the subsets of data points to derive image information extending over a range of depths in the target for each individual image point. The obtained image information is displayed on a displace device.

En-face OCT with parallel detector array

Apparatus for obtaining depth profile information from a transparent object, includes a confocal scanner for producing an en-face image of the object in an x-y plane, a spectral optical coherence tomography (OCT) apparatus for producing an OCT scan along at least one line in the z direction passing through a point in the x-y plane, and a display device. A processing unit displays on the display device the en-face image and an indication of the position of the point so as to permit the location of the OCT scan to be determined on the en-face image. The position point can be adjusted by the user when viewing the image. In other embodiments, SLO and OCT images are produced from a common aperture, and spectral OCT images are produced simultaneously with fluorescence images.

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Canterbury, United Kingdom

Mark Hathaway