Rotary mirror array for high-speed optical coherence tomography

We have developed a simple, high-speed, high-duty-cycle, linear optical delay line suitable for optical coherence tomography and optical Doppler tomography. Periodic longitudinal scanning is achieved by use of a tilted mirror array rotating at a constant speed. With a typical motor speed of 4000 rpm, our system has demonstrated a 2-mm axial scanning range, a 2400-Hz repetition rate, 94% duty cycle, and less than 0.1% nonlinear errors. Much higher repetition rates can be readily achieved by use of high-speed motors.     

Electrostatic forward-viewing scanning probe for Doppler optical coherence tomography using a dissipative polymer catheter

A novel flexible scanning optical probe is constructed with a finely etched optical fiber strung through a platinum coil in the lumen of a dissipative polymer. The packaged probe is 2.2 mm in diameter with a rigid length of 6mm when using a ball lens or 12 mm when scanning the fiber proximal to a gradient-index (GRIN) lens. Driven by constant high voltage (1-3 kV) at low current (< 5 microA), the probe oscillates to provide wide forward-viewing angle (13 degrees and 33 degrees with ball and GRIN lens designs, respectively) and high-frame-rate (10-140 fps) operation. Motion of the probe tip is observed with a high-speed camera and compared with theory. Optical coherence tomography (OCT) imaging with the probe is demonstrated with a wavelength-swept source laser. Images of an IR card as well as in vivo Doppler OCT images of a tadpole heart are presented. This optomechanical design offers a simple, inexpensive method to obtain a high-frame-rate forward-viewing scanning probe.     

Paired-angle-rotation scanning optical coherence tomography forward-imaging probe

We report a novel forward-imaging optical coherence tomography (OCT), needle-probe paired-angle-rotation scanning OCT (PARS-OCT) probe. The probe uses two rotating angled gradient-index lenses to scan the output OCT probe beam over a wide angular arc (approximately 19 degrees half-angle) of the region forward of the probe. Among other advantages, this probe design is readily amenable to miniaturization and is capable of a variety of scan modes, including volumetric scans. To demonstrate the advantages of the probe design, we have constructed a prototype probe with an outer diameter of 1.65 mm and employed it to acquire four OCT images, with a 45 degrees angle between adjacent images, of the gill structure of a Xenopus laevis tadpole. The system sensitivity was measured to be 93 dB by using the prototype probe with an illumination power of 450 microW on the sample. Moreover, the axial and the lateral resolutions of the probe are 9.3 and 10.3-12.5 microm, respectively.     

Fast scanning transmissive delay line for optical coherence tomography

A novel Fourier domain fast scanning optical delay line is proposed in which the walk-off is eliminated by only two passes through a diffraction grating. Working in transmission, the novel delay line is ideal for balanced optical coherence tomography configurations with recirculation of the reference beam. We evaluate theoretically and experimentally its walk-off and dispersion compensation capabilities.     

Rapid scanning all-reflective optical delay line for real-time optical coherence tomography

We describe a dispersion-free high-speed scanning optical delay line that is suitable for real-time optical coherence tomography, in particular, when an ultrabroadband light source is used. The delay line is based on all-reflective optics consisting of two flat and one curved mirrors. We achieve optical path-length scanning by oscillating one of the two flat mirrors with a resonant galvanometer. The delay line is compact and easy to implement. A total scanning depth of 1.50 mm with an 89% duty ratio, a maximal scanning speed of approximately 9.1 m/s, and a 4.1-kHz repetition rate has been demonstrated.     

Endoscopic optical coherence tomography based on a microelectromechanical mirror

An endoscopic optical coherence tomography (OCT) system based on a microelectromechanical mirror to facilitate lateral light scanning is described. The front-view OCT scope, adapted to the instrument channel of a commercial endoscopic sheath, allows real-time cross-sectional imaging of living biological tissue via direct endoscopic visual guidance. The transverse and axial resolutions of the OCT scope are roughly 20 and 10.2mum, respectively. Cross-sectional images of 500x1000 pixels covering an area of 2.9 mmx2.8 mm can be acquired at ~5 frames/s and with nearly 100-dB dynamic range. Applications in thickness measurement and bladder tissue imaging are demonstrated.     

Method for suppressing the mirror image in Fourier-domain optical coherence tomography

A method, novel to our knowledge, for effective mirror image suppression in Fourier-domain optical coherence tomography based on a phase shift between neighboring A-mode scans is demonstrated. By realizing that the phase shifts of the real and mirror images are mutually reversed and assuming that the real image intensities of the two successive A-mode scans are the same, we can solve a set of two coupled equations to obtain the real image signals. The images based on the scanning of a high-resolution spectral-domain optical coherence tomography system are processed to show effective mirror image suppression results. Compared with a similar method of broad application, our approach has the advantages of shorter process time and higher flexibility in selecting the concerned image portions for processing.     

Low-voltage polymer-based scanning cantilever for in vivo optical coherence tomography

Novel hand-held optical coherence tomography (OCT) probes with polymer cantilevers have been developed for clinical oral and skin imaging. An electroactive ionic polymer-metal composite cantilever was used to generate 3-mm transverse scanning movement of an optical fiber with applied 2-V linear alternating voltage at 1 Hz. Low driving voltage ensures safety. Two different optical designs achieve both forward and sidewise scanning and make it possible to image everywhere within the human oral cavity. In vivo OCT imaging of the human tongue is demonstrated.     

Retinal cone mosaic imaged with transverse scanning optical coherence tomography

We improved our recently reported retinal OCT system based on transverse priority scanning to achieve high resolution in both the transverse and the axial directions. The implementation of an additional SLO channel enables precise on-line focusing. The system enables imaging of the human retinal cone mosaic off the foveal center without adaptive optics. We demonstrate, for what is believed to be the first time, cone mosaic imaging simultaneously in the scanning laser ophthalmoscope and optical coherence tomography (OCT) channels. OCT B-scan images demonstrate that the cone mosaic is observable in two adjacent layers. Furthermore, we present what are believed to be the first C-scan OCT images of the cone mosaic and show that the major part of light backscattered from below the photoreceptor layer is not guided back toward the pupil by the photoreceptors.     

Complex ambiguity-free Fourier domain optical coherence tomography through transverse scanning

We introduce a simple and cheap method for phase-shifting Fourier domain optical coherence tomography (FDOCT) that does not need additional devices and can easily be implemented. A small beam offset at the fast beam-scanning mirror introduces a causal phase shift, which can be used for B-scan-based complex image reconstruction. We derive the conditions for optimal conjugate suppression and demonstrate the method on human skin in vivo for spectrometer-based FDOCT operating at 1300 nm employing a handheld scanner.     

Doppler optical coherence tomography with a micro-electro-mechanical membrane mirror for high-speed dynamic focus tracking

An elliptical microelectromechanical system (MEMS) membrane mirror is electrostatically actuated to dynamically adjust the optical beam focus and track the axial scanning of the coherence gate in a Doppler optical coherence tomography (DOCT) system at 8 kHz. The MEMS mirror is designed to maintain a constant numerical aperture of approximately 0.13 and a spot size of approximately 6.7 microm over an imaging depth of 1mm in water, which improves imaging performance in resolving microspheres in gel samples and Doppler shift estimation precision in a flow phantom. The mirror's small size (1.4 mm x 1 mm) will allow integration with endoscopic MEMS-DOCT for in vivo applications.     

Simultaneous dual-wavelength-band common-path swept-source optical coherence tomography with single polygon mirror scanner

We report a novel (to the best of our knowledge) simultaneous 1310/1550 two-wavelength band swept laser source and dual-band common-path swept-source optical coherence tomography (SS-OCT). Synchronized dual-wavelength tuning is performed by using two laser cavities and narrowband wavelength filters with a single dual-window polygonal scanner. Measured average output powers of 60 and 27 mW have been achieved for the 1310 and 1550 nm bands, respectively, while the two wavelengths were swept simultaneously from 1227 to 1387 nm for the 1310 nm band and from 1519 to 1581 nm for the 1550 nm band at an A-scan rate of 65 kHz. Broadband wavelength-division multiplexing is used for coupling two wavelengths into a common-path single-mode GRIN-lensed fiber probe to form dual-band common-path SS-OCT. Simultaneous OCT imaging at 1310 and 1550 nm is achieved. This technique allows for in vivo high-speed OCT imaging with potential application in functional (spectroscopic) investigations.     

Two-dimensional scanning probe driven by a solenoid-based single actuator for optical coherence tomography

We propose the two-dimensional scanning probe operating with a single actuator, which is thought useful as a sample probe for optical coherence tomography (OCT). The probe was designed to use a single-body lensed fiber cantilever loaded with an iron-bead and driven by a single-solenoid actuator. Elliptic spiral trace patterns were achieved using off-axis magnetic fields of the solenoid. A three-dimensional OCT image was obtained for a scanning area of 3.8 mm × 3.4 mm at an acquisition speed of 16.7 s/V. Up to 27 Hz B-scan rate, the proposed probe worked well, and 1000 A-scans were made per each B-scan.     

Double-reflection polygon mirror for high-speed optical coherence microscopy

We report on a high-speed, high-efficiency, high-duty-cycle, path-length-maintaining and linear beam scanner suitable for en face scanning optical coherence microscopy. Fast transverse beam scanning is achieved by use of a double-reflection polygon mirror (DRPM) rotating at a constant speed. With a motor speed of 18,000 rpm and a scanner diameter of 50 mm, the DRPM provides a line rate up to 3 kHz, +/-1.8 degrees scanning range, and 90% duty cycle. A much higher scanning speed and much larger scanning range can be readily achieved by increasing the scanner diameter.     

Multilayered scattering reference mirror for full field optical coherence tomography with application to cell profiling

A multilayered scattering structure is proposed and demonstrated as a reference mirror for use with full field optical coherence tomography (FF-OCT) to increase contrast of tissue imaging and provide compensation. Common-path FF-OCT systems were built demonstrating high resolution cell profiling. The use of this mirror with frequency domain FF-OCT allows 3D images in real time.     

Forward-imaging instruments for optical coherence tomography

We discuss the design and implementation of forward-imaging instruments for optical coherence tomography (OCT), which require the delivery, scanning, and collection of single-spatial-mode optical radiation. A hand-held surgical probe for use in open surgery can provide cross-sectional images of subsurface tissue before surgical incisions are made. A rigid laparoscope for minimally invasive surgical OCT imaging provides a simultaneous enface view of the area being imaged. OCT imaging is demonstrated on in vitro human specimens.     

Imaging needle for optical coherence tomography

We describe a miniature optical coherence tomography (OCT) imaging needle that can be inserted into solid tissues and organs to permit interstitial imaging of their internal microstructures with micrometer scale resolution and minimal trauma. A novel rotational coupler with a glass capillary tube is also presented that couples light from a rotating single-mode fiber to a stationary one. A prototype needle with a 27-gauge (~410-mum) outer diameter has been developed and is demonstrated for in vivo imaging. The OCT needle can be integrated with standard excisional biopsy devices and used for OCT-guided biopsy.     

Tracking optical coherence tomography

An experimental tracking optical coherence tomography (OCT) system has been clinically tested. The prototype instrument uses a secondary sensing beam and steering mirrors to compensate for eye motion with a closed-loop bandwidth of 1 kHz and tracking accuracy, to within less than the OCT beam diameter. The retinal tracker improved image registration accuracy to <1 transverse pixel (<60 microm). Composite OCT images averaged over multiple scans and visits show a sharp fine structure limited only by transverse pixel size. As the resolution of clinical OCT systems improves, the capability to reproducibly map complex structures in the living eye at high resolution will lead to improved understanding of disease processes and improved sensitivity and specificity of diagnostic procedures.     

Spectroscopic optical coherence tomography

Spectroscopic optical coherence tomography (OCT), an extension of conventional OCT, is demonstrated for performing cross-sectional tomographic and spectroscopic imaging. Information on the spectral content of backscattered light is obtained by detection and processing of the interferometric OCT signal. This method allows the spectrum of backscattered light to be measured over the entire available optical bandwidth simultaneously in a single measurement. Specific spectral features can be extracted by use of digital signal processing without changing the measurement apparatus. An ultrabroadband femtosecond Ti:Al(2)O(3) laser was used to achieve spectroscopic imaging over the wavelength range from 650 to 1000 nm in a simple model as well as in vivo in the Xenopus laevis (African frog) tadpole. Multidimensional spectroscopic data are displayed by use of a novel hue-saturation false-color mapping.     

Second-harmonic optical coherence tomography

Second-harmonic optical coherence tomography, which uses coherence gating of second-order nonlinear optical responses of biological tissues for imaging, is described and demonstrated. Femtosecond laser pulses were used to excite second-harmonic waves from collagen harvested from rat tail tendon and a reference non-linear crystal. Second-harmonic interference fringe signals were detected and used for image construction. Because of the strong dependence of second-harmonic generation on molecular and tissue structures, this technique imparts contrast and resolution enhancement to conventional optical coherence tomography.