Chengming Wang

Compressed sensing with linear-in-wavenumber sampling in spectral-domain optical coherence tomography

We propose a novel method called compressed sensing with linear-in-wavenumber sampling (k-linear CS) to retrieve an image for spectral-domain optical coherence tomography (SD-OCT). An array of points that is evenly spaced in wavenumber domain is sampled from an original interferogram by a preset k-linear mask. Then the compressed sensing based on l1 norm minimization is applied on these points to reconstruct an A-scan data. To get an OCT image, this method uses less than 20% of the total data as required in the typical process and gets rid of the spectral calibration with numerical interpolation in traditional CS-OCT. Therefore k-linear CS is favorable for high speed imaging. It is demonstrated that the k-linear CS has the same axial resolution performance with ~30 dB higher signal-to-noise ratio (SNR) as compared with the numerical interpolation. Imaging of bio-tissue by SD-OCT with k-linear CS is also demonstrated.

Tiny endoscopic optical coherence tomography probe driven by a miniaturized hollow ultrasonic motor

Abstract. We present an endoscopic probe for optical coherence tomography (OCT) equipped with a miniaturized hollow ultrasonic motor that rotates the objective lens and provides an internal channel for the fiber to pass through, enabling 360 deg unobstructed circumferential scanning. This probe has an outer diameter of 1.5 mm, which is ultra-small for motorized probes with an unobstructed view in distal scanning endoscopic OCT. Instead of a mirror or prism, a customized aspheric right-angle lens is utilized, leading to an enlargement of the numerical aperture and thus high transverse resolution. Spectral-domain OCT imaging of bio-tissue and a phantom are demonstrated with resolution of 7.5  μm(axial)×6.6  μm(lateral) and sensitivity of 96 dB.

Label-free subcellular 3D live imaging of preimplantation mouse embryos with full-field optical coherence tomography

Early patterning and polarity is of fundamental interest in preimplantation embryonic development. Label-free subcellular 3D live imaging is very helpful to its related studies. We have developed a novel system of full-field optical coherence tomography (FF-OCT) for noninvasive 3D subcellular live imaging of preimplantation mouse embryos with no need of dye labeling. 3D digitized embryos can be obtained by image processing. Label-free 3D live imaging is demonstrated for the mouse embryos at various typical preimplantation stages with a spatial resolution of 0.7 [micro sign]m and imaging rate of 24 fps. Factors that relate to early patterning and polarity, such as pronuclei in zygote, shapes of zona pellucida, location of second polar body, cleavage planes, and the blastocyst axis, can be quantitatively measured. The angle between the two second cleavage planes is accurately measured to be 87 deg. It is shown that FF-OCT provides a potential breakthrough for early patterning, polarity formation, and many other preimplantation-related studies in mammalian developmental biology.

Spectral-domain optical coherence tomography with a Fresnel spectrometer

We propose a novel spectral-domain optical coherence tomography (SD-OCT) equipped with a Fresnel spectrometer, which utilizes a Fresnel zone plate (FZP) as both dispersion and focusing optics and thus spreads the spectral interferogram evenly in wavenumber domain because of the proportional relation between the focal length of the FZP and the wavenumber. With no need of the conversion calculation from wavelength to wavenumber in conventional SD-OCT, this new design is favorable for fast imaging with high resolution. As only a FZP and CCD are used, the Fresnel spectrometer is simple and compact. It is experimentally shown that its performance is as good as that of numerical interpolation in conventional SD-OCT. Imaging of bio-tissue by Fresnel SD-OCT is also demonstrated.

Ultrahigh-speed optical coherence tomography utilizing all-optical 40 MHz swept-source

We present an ultrahigh-speed optical coherence tomography (OCT) based on an all-optical swept-source with an A-scan rate of 40 MHz. The inertia-free swept-source, which has its output power of 41.2 mW and tuning range of 40 nm and high scan linearity in wavenumber with Pearsons correlation coefficients r of 0.9996, consists of a supercontinuum laser, an optical band-pass filter, a linearly chirped fiber Bragg grating, an erbium-doped fiber amplifier, and two buffer stages. With sensitivity of 87 dB, high-speed OCT imaging of biological tissue in vivo is also demonstrated.

Linear-in-wavenumber swept laser with an acousto-optic deflector for optical coherence tomography

We report a novel linear-in-wavenumber (k-linear) swept laser source based on an acousto-optic deflector (AOD). The AOD-based optical filter includes an acousto-optic deflector and a reflection grating. The laser may tune k linearly in wavenumber over time due to its appropriate configuration and is favorable for fast imaging because it avoids data resampling and recalibration, as are required in conventional swept source optical coherence tomography (SS-OCT). We achieved k-linearity with Pearsons r correlation coefficients of 0.99995 without and 0.99997 with optimization. The laser has a tuning range of 50 nm, a 3 dB swept range of 42 nm (FWHM), output power of 2.56 mW, 6 dB sensitivity roll-off depth of 0.941 mm, and central wavelength of 1064 nm at a scanning rate of ∼20 kHz. Scanning rate as high as ∼400 kHz is also achieved for this laser with the tuning range 49 nm, swept linearity of 0.99990, output power of 2.30 mW, and a 6 dB sensitivity roll-off depth 0.550 mm. SS-OCT imaging with linear-in-wavenumber swept laser is also demonstrated.

Understanding three-dimensional spatial relationship between the mouse second polar body and first cleavage plane with full-field optical coherence tomography

Abstract. The morphogenetic relationship between early patterning and polarity formation is of fundamental interest and remains a controversial issue in preimplantation embryonic development. We use a label-free three-dimensional (3-D) imaging technique of full-field optical coherence tomography (FF-OCT) successfully for the first time to study the dynamics of developmental processes in mouse preimplantation lives. Label-free 3-D subcellular time-lapse images are demonstrated to investigate 3-D spatial relationship between the second polar body (2PB) and the first cleavage plane. By using FF-OCT together with quantitative study, we show that only 25% of the predicted first cleavage planes, defined by the apposing plane of two pronuclei, pass through the 2PB. Also only 27% of the real cleavage planes pass through the 2PB. These results suggest that the 2PB is not a convincing spatial cue for the event of the first cleavage. Our studies demonstrate the feasibility of FF-OCT in providing new insights and potential breakthroughs to the controversial issues of early patterning and polarity in mammalian developmental biology.

Characterization of automotive paint by optical coherence tomography.

Automotive paint is common trace evidence that plays a significant role in many vehicle-related criminal cases. However, the conventional methods of obtaining tomographic images tend to damage the samples. Optical coherence tomography (OCT) is a novel method to obtain high-resolution and cross-sectional images of the automotive paints in a non-destructive, and high-speed manner. In this study, OCT was applied to image and analyze the automotive paint, using scanning electron microscope (SEM) as reference. Eight automotive paint samples of different brands were examined. The images of multi-layer structures provided by OCT system with 5μm depth resolution were consistent with those by SEM. To distinguish different paints with similar visual appearance, we extracted internal structural features from the images using peak analysis and optical attenuation fit. Six characterized parameters were found to distinguish the samples including the optical path length (OPL) of base coat, the optical attenuation coefficient (OAC) of base coat, the OPL of clear coat, the back-scattering ratio (BSR) of clear coat and base coat, the OPL of primer surfacer, and the BSR of base coat and primer. Statistical differences were evaluated by an independent t-test with p<0.05. OCT was applied to analyze repainted paint as well. Three-dimensional OCT reconstruction of the paints was also implemented to create en face (transverse section) images for morphology examination and comparison. These results suggest that OCT imaging can provide additional new features for analyzing the automotive paints and thereby may be a promising supplement to traditional methods. Meanwhile, the OCT system is favorable for achieving in-situ and real-time examination at the scene of crime.

Noninvasive three-dimensional live imaging methodology for the spindles at meiosis and mitosis

Abstract. The spindle plays a crucial role in normal chromosome alignment and segregation during meiosis and mitosis. Studying spindles in living cells noninvasively is of great value in assisted reproduction technology (ART). Here, we present a novel spindle imaging methodology, full-field optical coherence tomography (FF-OCT). Without any dye labeling and fixation, we demonstrate the first successful application of FF-OCT to noninvasive three-dimensional (3-D) live imaging of the meiotic spindles within the mouse living oocytes at metaphase II as well as the mitotic spindles in the living zygotes at metaphase and telophase. By post-processing of the 3-D dataset obtained with FF-OCT, the important morphological and spatial parameters of the spindles, such as short and long axes, spatial localization, and the angle of meiotic spindle deviation from the first polar body in the oocyte were precisely measured with the spatial resolution of 0.7 μm. Our results reveal the potential of FF-OCT as an imaging tool capable of noninvasive 3-D live morphological analysis for spindles, which might be useful to ART related procedures and many other spindle related studies.

Optical computing for optical coherence tomography

We propose an all-optical Fourier transformation system for real-time massive data processing in high speed optical coherence tomography (OCT). In the so-called optical computing OCT, fast Fourier transformation (FFT) of A-scan signal is optically processed in real time before being detected by photoelectric detector. Therefore, the processing time for interpolation and FFT in traditional Fourier domain OCT can be dramatically eliminated. A processing rate of 10 mega-A-scans/second was experimentally achieved, which is, to our knowledge, the highest speed for OCT imaging. Due to its fiber based all-optical configuration, this optical computing OCT system is ideal for ultrahigh speed volumetric OCT imaging in clinical application.