Spectral-domain Optical Coherence Microscopy Research Articles

Complex master-slave enhanced optical coherence microscopy

We present an instrument designed to facilitate localization and high-resolution, optical coherence microscopy (OCM) imaging of small biological samples immersed in a medium several orders of magnitude greater in volume. A modified turret-equipped microscope stand was inserted into the sample arm of a spectral domain optical coherence microscopy (SD-OCM) system. The instrument enabled swift change of imaging objectives through the incorporation of complex master-slave interferometry (CMSI), providing tolerance to dispersion for any objective through the acquisition of a few (≥2) calibration spectra. We demonstrate the instrument’s ability to localize and image samples by providing examples of its application to optical phantoms and to a porcine oocyte immersed in a biological culture medium.

Imaging through a weakly scattering medium by spectral-domain optical coherence microscopy with a digital phase conjugation

A spectral-domain optical coherence microscope (SD-OCM) embedded by a digital phase conjugation is presented for high-resolution imaging of objects behind a weakly scattering medium. For high-resolution SD-OCM, keeping a narrow focusing spot even in a scattering medium is important. To compensate for the degradation of the focused spot due to the scattering, digital phase conjugation with a low-coherent light is introduced by measuring the distorted wavefront of coherent light and making wavelength conversion due to the difference between the coherent and low-coherent light beams. Experiments using a weakly scattering sheet with a scattering angle of 30 degrees showed us to improve the focused spot property and enhance the reflected intensity signal. We also demonstrate the feasibility of the system for the imaging of objects with periodic reflectance structures of 10 µm width.

Ultra-high-resolution SD-OCM imaging with a compact polarization-aligned 840 nm broadband combined-SLED source.

We analyze the influence of intrinsic polarization alignment on image quality and axial resolution employing a broadband 840 nm light source with an optical bandwidth of 160 nm and an output power of 12 mW tailored for spectral-domain optical coherence microscopy (SD-OCM) applications. Three superluminescent diodes (SLEDs) are integrated into a 14-pin butterfly module using a free-space micro-optical bench architecture, maintaining a constant polarization state across the full spectral output. We demonstrate superior imaging performance in comparison to traditionally coupled-SLED broadband light sources in a teleost model organism in-vivo.

High-spatial-resolution deep tissue imaging with spectral-domain optical coherence microscopy in the 1700-nm spectral band.

.We present three-dimensional (3-D) high-resolution spectral-domain optical coherence microscopy (SD-OCM) by using a supercontinuum (SC) fiber laser source with 300-nm spectral bandwidth (full-width at half-maximum) in the 1700-nm spectral band. By using low-coherence interferometry with SC light and a confocal detection scheme, we realized lateral and axial resolutions of 3.4 and in tissue (), respectively. This is, to the best of our knowledge, the highest 3-D spatial resolution reported among those of Fourier-domain optical coherence imaging techniques in the 1700-nm spectral band. In our SD-OCM, to enhance the imaging depth, a full-range method was implemented, which suppressed the formation of a coherent ghost image and allowed us to set the zero-delay position inside the samples. We demonstrated the 3-D high-resolution imaging capability of 1700-nm SD-OCM through the measurement of an interference signal from a mirror surface and imaging of a single 200-nm polystyrene bead and a pig thyroid gland. Deep tissue imaging at a depth of up to 1.8 mm was also demonstrated. This is the first demonstration of 3-D high-resolution SD-OCM in the 1700-nm spectral band.

Spectroscopic imaging with spectral domain visible light optical coherence microscopy in Alzheimer's disease brain samples.

A visible light spectral domain optical coherence microscopy system was developed. A high axial resolution of 0.88 μm in tissue was achieved using a broad visible light spectrum (425 – 685 nm). Healthy human brain tissue was imaged to quantify the difference between white (WM) and grey matter (GM) in intensity and attenuation. The high axial resolution enables the investigation of amyloid-beta plaques of various sizes in human brain tissue and animal models of Alzheimer’s disease (AD). By performing a spectroscopic analysis of the OCM data, differences in the characteristics for WM, GM, and neuritic amyloid-beta plaques were found. To gain additional contrast, Congo red stained AD brain tissue was investigated. A first effort was made to investigate optically cleared mouse brain tissue to increase the penetration depth and visualize hyperscattering structures in deeper cortical regions.

Ultrahigh speed spectral-domain optical coherence microscopy

We demonstrate a compact, ultrahigh speed spectral-domain optical coherence microscopy (SD-OCM) system for multiscale imaging of specimens at 840 nm. Using a high speed 512-pixel line scan camera, an imaging speed of 210,000 A-scans per second was demonstrated. Interchangeable water immersion objectives with magnifications of 10×, 20×, and 40× provided co-registered en face cellular-resolution imaging over several size scales. Volumetric OCM data sets and en face OCM images were demonstrated on both normal and pathological human colon and kidney specimens ex vivo with an axial resolution of ~4.2 µm, and transverse resolutions of ~2.9 µm (10×), ~1.7 µm (20×), and ~1.1 µm (40×) in tissue. In addition, en face OCM images acquired with high numerical aperture over an extended field-of-view (FOV) were demonstrated using image mosaicking. Comparison between en face OCM images among different transverse and axial resolutions was demonstrated, which promises to help the design and evaluation of imaging performance of Fourier domain OCM systems at different resolution regimes.

High-speed processing architecture for spectral-domain optical coherence microscopy

Optical coherence microscopy (OCM) is an interferometric technique that combines principles of confocal microscopy and optical coherence tomography (OCT) to obtain high-resolution en face images. Axial and lateral resolutions of several microns can be achieved using OCM depending on the numerical aperture (NA) of the objective and sample properties. We address the computational complexity that is inherent in spectral-domain OCM systems that limits its real-time capability as a microscope. An architecture that will improve the efficiency of the computation involved is presented. Currently, spectral-domain OCM images are obtained by individually taking the Fourier transform of each axial scan in cross-sectional frames and computationally slicing them to generate en face images. The real-time architecture presented here relies on the fact that only one Fourier domain point of a given axial scan needs to be computed rather than computing all the Fourier domain points, which can frequently require a significant amount of time to compute. This new realization has been shown to reduce the processing time to obtain the en face OCM images by a factor of 30.

Spectroscopic spectral-domain optical coherence microscopy

The spectroscopic content within optical coherence tomography (OCT) data can provide a wealth of information. Spectroscopic OCT methods are frequently limited by time-frequency trade-offs that limit high spectral and spatial resolution simultaneously. We present spectroscopic spectral-domain optical coherence microscopy performed with a multimodality microscope. Restricting the spatial extent of the signal by using high-numerical-aperture optics makes high-resolution spectroscopic information accessible, facilitated with spectral-domain detection. Simultaneous acquisition of multiphoton microscopy images is used to validate tissue structure and localization of nuclei within individual cells.

Integrated structural and functional optical imaging combining spectral-domain optical coherence and multiphoton microscopy

An integrated microscope that combines different optical techniques for simultaneous imaging is demonstrated. The microscope enables spectral-domain optical coherence microscopy based on optical backscatter, and multiphoton microscopy for the detection of two-photon fluorescence and second harmonic generation signals. The unique configuration of this integrated microscope allows for the simultaneous acquisition of both anatomical (structural) and functional imaging information with particular emphasis for applications in the fields of tissue engineering and cell biology. In addition, the contemporary analysis of the spectroscopic features can enhance contrast by differentiating among different tissue components.