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.

The International Space Station (ISS) employs a suite of portable and permanently located gas monitors to insure crew health and safety. These sensors are tasked with functions ranging from fixed mass spectrometer based major constituents analysis to portable electrochemical sensor based combustion product monitoring. An all optical multigas sensor is being developed that can provide the specificity of a mass spectrometer with the portability of an electrochemical cell. The technology, developed under the Small Business Innovation Research program, allows for an architecture that is rugged, compact and low power. A four gas version called the Multi-Gas Monitor was launched to ISS in November 2013 aboard Soyuz and activated in February 2014. The portable instrument is comprised of a major constituents analyzer (water vapor, carbon dioxide, oxygen) and high dynamic range real-time ammonia sensor. All species are sensed inside the same enhanced path length optical cell with a separate vertical cavity surface emitting laser (VCSEL) targeted at each species. The prototype is controlled digitally with a field-programmable gate array/microcontroller architecture. The optical and electronic approaches are designed for scalability and future versions could add three important acid gases and carbon monoxide combustion product gases to the four species already sensed. Results obtained to date from the technology demonstration on ISS are presented and discussed.

/pdf/optical-multi-gas-monitor-technology-demonstration-on-the-1lufvrbf8n.pdf

Optical Multi-Gas Monitor Technology Demonstration on the International Space Station

High-Performance Optical Contaminant Monitor for Spacecraft and Habitats

Tunable diode laser spectroscopy (TDLS) is an advanced trace and major gas monitoring technology with unmatched selectivity, range and stability. The technology demonstration of the TDLS based Multi-Gas Monitor (MGM), initially reported at the 2014 ICES conference, has been operating continuously on the International Space Station (ISS) for over 15 months as of this writing. The MGM is designed to measure oxygen, carbon dioxide, ammonia and water vapor in ambient cabin air in a low power, relatively compact device. While on board, the MGM experienced a number of challenges, planned and unplanned, including a test of the ammonia channel using a commercial medical ammonia inhalant and carbon dioxide spikes from thruster firings from another payload. Data from the unit was downlinked once per week and compared with other analytical resources on board, notably the Major Constituent Analyzer (MCA), a magnetic sector mass spectrometer. MGM spent the majority of the time installed in the Nanoracks Frame 2 payload facility in front breathing mode, sampling the ambient environment of the Japanese Experiment Module (JEM), but was also used to analyze recirculated rack cooling air. MGM can be operated in portable mode (via internal rechargeable lithium ion polymer batteries or by plugging into any Express Rack 28VDC connector). Results show excellent stability and agreement with MCA data for oxygen and carbon dioxide. The ammonia challenge (~ 75 ppm) was successful as well, showing very rapid response time in both directions. Water vapor results showed weekly spikes corresponding to dry out cycling of JEM condensing heat exchangers and good agreement with dew point measurements in Columbus module. None of the 4 sensor channels has degraded perceptibly to date. Work on expanding the capability in next generation devices has just begun. Target gases include combustion products, formaldehyde and hydrazine. Various hand-held and integrated laser spectroscopy based monitors are envisioned for use on ISS, Orion and Exploration missions.

/pdf/laser-spectroscopy-multi-gas-monitor-results-of-a-year-long-3k7rq8azhx.pdf

William R. Wood

Papers

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

Differential spectral interferometry: an imaging technique for biomedical applications.

Optical Multi-Gas Monitor Technology Demonstration on the International Space Station

High-Performance Optical Contaminant Monitor for Spacecraft and Habitats

Laser Spectroscopy Multi-Gas Monitor: Results of a Year Long Technology Demonstration on ISS