Current medical imaging technologies allow visualization of tissue anatomy in the human body at resolutions ranging from 100 micrometers to 1 millimeter. These technologies are generally not sensitive enough to detect early-stage tissue abnormalities associated with diseases such as cancer and atherosclerosis, which require micrometer-scale resolution. Here, optical coherence tomography was adapted to allow high-speed visualization of tissue in a living animal with a catheter-endoscope 1 millimeter in diameter. This method, referred to as "optical biopsy," was used to obtain cross-sectional images of the rabbit gastrointestinal and respiratory tracts at 10-micrometer resolution.

In Vivo Endoscopic Optical Biopsy with Optical Coherence Tomography

The diffraction tomography theorem is adapted to one-dimensional length measurement. The resulting spectral interferometry technique is described and the first length measurements using this technique on a model eye and on a human eye in vivo are presented.

Measurement of intraocular distances by backscattering spectral interferometry

Apparatus and method for increasing the sensitivity in the detection of optical coherence tomography and low coherence interferometry (“LCI”) signals by detecting a parallel set of spectral bands, each band being a unique combination of optical frequencies. The LCI broad bandwidth source is split into N spectral bands. The N spectral bands are individually detected and processed to provide an increase in the signal-to-noise ratio by a factor of N. Each spectral band is detected by a separate photo detector and amplified. For each spectral band the signal is band pass filtered around the signal band by analog electronics and digitized, or, alternatively, the signal may be digitized and band pass filtered in software. As a consequence, the shot noise contribution to the signal is reduced by a factor equal to the number of spectral bands. The signal remains the same. The reduction of the shot noise increases the dynamic range and sensitivity of the system.

Apparatus and method for ranging and noise reduction of low coherence interferometry LCI and optical coherence tomography OCT signals by parallel detection of spectral bands

An apparatus and method are provided. In particular, at least one first electro-magnetic radiation may be provided to a sample and at least one second electro-magnetic radiation can be provided to a non-reflective reference. A frequency of the first and/or second radiations varies over time. An interference is detected between at least one third radiation associated with the first radiation and at least one fourth radiation associated with the second radiation. Alternatively, the first electro-magnetic radiation and/or second electro-magnetic radiation have a spectrum which changes over time. The spectrum may contain multiple frequencies at a particular time. In addition, it is possible to detect the interference signal between the third radiation and the fourth radiation in a first polarization state. Further, it may be preferable to detect a further interference signal between the third and fourth radiations in a second polarization state which is different from the first polarization state. The first and/or second electro-magnetic radiations may have a spectrum whose mean frequency changes substantially continuously over time at a tuning speed that is greater than 100 Tera Hertz per millisecond.

Method and apparatus for performing optical imaging using frequency-domain interferometry

A system and method for imaging of a sample, e.g., biological sample, are provided. In particular, at least one source electro-magnetic radiation forwarded to the sample and a reference may be generated. A plurality of detectors may be used, at least one of the detectors capable of detecting a signal associated with a combination of at least one first electro-magnetic radiation received from the sample and at least one second electro-magnetic radiation received from the reference. At least one particular detector may have a particular electrical integration time, and can receive at least a portion of the signal for a time duration which has a first portion with a first power level greater than a predetermined threshold and a second portion immediately preceding or following the first portion. The second portion may have a second power level that is less than the predetermined threshold, and extends for a time period which may be, e.g., approximately more than 10% of the particular electrical integration time.

System and method for optical coherence imaging

A Michelson-type spectral interferometer that uses a common beam path for the reference and the sample arms is described. This optical arrangement is more compact and stable than the more commonly used dual-arm interferometer and is well suited for frequency-domain optical coherence tomography of biological samples. With a 16-bit CCD camera, the instrument has sufficient dynamic range and resolution for imaging to depths of 2 mm in scattering biological materials. Images obtained with this spectral interferometer are presented, including cross-sectional images in a Xenopus laevis tadpole.

http://www.swsciences.com/research/papers/Vakhtin_2003_ApplOpt_CommonPathInterferometer.pdf

Common-path interferometer for frequency-domain optical coherence tomography.

Differential spectral interferometry (DSI), a novel method of biomedical imaging that combines the high dynamic range of optical coherence tomography (OCT) with inherently parallel low-bandwidth image acquisition of spectral interferometry (SI), is described. DSI efficiently removes the deleterious dc background inherent in SI measurements while maintaining the parallel nature of SI. We demonstrate DSI on both synthetic and biological samples. Because DSI preserves the low-bandwidth, parallel nature of SI, it is competitive with OCT for biomedical applications in terms of image quality and acquisition rate.

/pdf/differential-spectral-interferometry-an-imaging-technique-3k9x130q0a.pdf

Differential spectral interferometry: an imaging technique for biomedical applications.

A method of resolving the complex conjugate ambiguity in Fourier-domain OCT is described. The complex differential spectral interferogram is obtained by simultaneous acquisition of the first and second harmonics of the ac component of the phase-modulated interferogram. The harmonics represent the imaginary and real parts of the interferogram, respectively. The complex conjugate rejection ratio is found to be at least 45 dB and is limited by background noise.

Resolving the complex conjugate ambiguity in Fourier-domain OCT by harmonic lock-in detection of the spectral interferogram

A new method of resolving the complex conjugate ambiguity in FD-OCT, where the quadrature components of the interferogram are obtained by simultaneous acquisition of the first and second harmonics of the phase-modulated interferogram, is presented.

Resolving the Complex Conjugate Ambiguity in FD-OCT by Harmonic Lock-In Detection of the Spectral Interferogram

A method for evaluating the condition of a ceramic coating deposited on a substrate comprising illuminating the ceramic coating with light, measuring the intensity of light returned from the ceramic coating as function of depth in the coating and transverse position on the coating, and analyzing the measured light intensities to obtain one or more of intensity of the light returned from the exposed coating surface relative to the intensity of light returned from the coating/substrate interface, intensity of the light returned from the coating/substrate interface relative to the intensity of light returned from the bulk of the ceramic coating, determination of roughness at the exposed surface of the ceramic coating, and determination of roughness of the interface between the ceramic coating and underlying bond coat or substrate.

Kristen A. Peterson

Papers

Common-path interferometer for frequency-domain optical coherence tomography.

Differential spectral interferometry: an imaging technique for biomedical applications.

Resolving the complex conjugate ambiguity in Fourier-domain OCT by harmonic lock-in detection of the spectral interferogram

Resolving the Complex Conjugate Ambiguity in FD-OCT by Harmonic Lock-In Detection of the Spectral Interferogram

Method for non-destructive evaluation of ceramic coatings