Full range complex ultrahigh sensitive optical microangiography

This Letter presents a useful method that combines the full range complex Fourier domain optical coherence tomography (OCT) with the ultrahigh sensitive optical microangiography (OMAG) to achieve full range complex imaging of blood flow within microcirculatory tissue beds in vivo. We propose to use the fast scanning axis to realize the full range complex imaging, while using the slow axis to achieve OMAG imaging of blood flow. We demonstrate the proposed method by using a high speed 1310?nm OCT/OMAG system running at 92?kHz line scan rate to image the flow phantoms in vitro, and the blood flows in tissue beds in vivo.     

Real Time and Full-range Complex Fourier Domain Optical Coherence Tomography

High speed complex full-range Fourier domain optical coherence tomography (FD-OCT) is demonstrated. This FD-OCT requires only a single A-scan for each single transversal position for full-range Fourier domain optical coherence tomography. The Fourier transform method is applied along the direction of the B-scan to reconstruct complex spectra, and the complex spectra compose a full-range OCT image.     

Real-time quadrature projection complex conjugate resolved Fourier domain optical coherence tomography

We present a novel algorithm for full-range imaging by suppression of the complex conjugate artifact in phase-shifting Fourier domain optical coherence tomography. This technique utilizes the projection of multiple phase-shifted interferograms onto an orthogonal basis set to reconstruct the complex interferogram. Full-range imaging with >30 dB suppression of the symmetric artifact is demonstrated using a 3 x 3 fiber coupler swept source OCT system, providing a depth range of 6.6mm with -8 dB roll-off in sensitivity at the depth boundaries relative to DC. Real-time display of full-range images of the anterior segment of the human eye acquired in vivo at a line rate of 6.67 kHz are presented.     

Rapid-scanning forward-imaging miniature endoscope for real-time optical coherence tomography

We developed a miniature endoscope that is capable of rapid lateral scanning and is suitable for real-time forward-imaging optical coherence tomography (OCT). The endoscope has an outer diameter of 2.4 mm, consisting of a miniature tubular lead zirconate titanate (PZT) actuator, a single-mode fiber-optic cantilever, and a graded-index lens. Rapid lateral scanning at 2.8 kHz is achieved when the fiber-optic cantilever is resonated with the PZT actuator. This allows OCT imaging to be performed by fast lateral beam scanning followed by slow depth scanning, which is different from the conventional OCT imaging sequence. Real-time OCT imaging with the endoscope operated in the new image acquisition sequence at 6 frames/s is demonstrated.     

Artifact removal in Fourier-domain optical coherence tomography with a piezoelectric fiber stretcher

We describe an artifact removal setup swept-source optical coherence tomography (OCT) system that enables high-speed full-range imaging. We implement a piezoelectric fiber stretcher to generate a periodic phase shift between successive A-scans, thus introducing a transverse modulation. The depth ambiguity is then resolved by performing a Fourier filtering in the transverse direction before processing the data in the axial direction. The dc artifact is also removed. The key factor is that the piezoelectric fiber stretcher can be used to generate discrete phase shifts with a high repetition rate. The proposed experimental setup is a much improved version of the previously reported B-M mode scanning for spectral-domain OCT in that it does not generate additional artifacts. It is a simple and low-cost solution for artifact removal that can easily be applied.     

复谱频域OCT成像的研究

采用频域技术的OCT系统，深度扫描信息由背向散射光谱的傅立叶反变换获得，简化了轴向扫描过程，从而使快速OCT成像成为可能．为了实现复杂生物组织的OCT快速成像，消除谱频域OCT的“混叠”现象、重建样品的真实层析结构，本文引入了相移干涉技术，构建了一套满量程复谱频域OCT实验系统，并为系统设计了特殊的分束镜和移相器，为最终实现复杂生物组织的OCT快速成像提供了条件．     

Imaging of subcutaneous blood vessels and flow velocity profiles by optical coherence tomography

We have applied a compact low power rapid scanning Doppler Optical Coherence Tomography system to monitor multi-dimensional velocity profiles within the complex vessels and simultaneous real-time non-invasive imaging of skin tissues morphology in vivo, in the wavelength range of 1.3–1.5 nm. Optical clearing of skin tissues has been utilized to achieve depth of OCT images up to 1.7 mm. Current approach enables applying low-power (0.4–0.5 mW) and low-noise broadband near-infrared light sources and obtaining OCT images with down to 12 μm spatial resolution. Two-dimensional time-domain OCT images of complex flow velocity profiles in blood vessel phantom and in vivo subcutaneous human skin tissues are presented. The effect of optical clearing on in vivo images is demonstrated and discussed.     

基于多级微反射镜的时空联合调制傅里叶变换成像光谱仪:原理及数据处理

介绍了一种基于多级阶梯微反射镜的时空联合调制傅里叶变换成像光谱仪的原理及数据处理方法.仪器利用一块多级阶梯微反射镜取代传统迈克尔逊干涉仪中的动镜以实现静态干涉,通过摆镜扫描使目标物体成像在不同的子阶梯反射面上从而获得目标物体不同光程差的干涉信息.某一时刻,目标物体经摆镜与前置成像系统后在平面镜与多级阶梯微反射镜上形成两个一次像点,两个一次像点被平面镜和多级阶梯微反射镜反射之后经后置成像系统最终成像在探测器焦平面上.平面镜与多级阶梯微反射镜之间的高度差会使到达探测器的两束光的光程差不同,因此探测器焦平面上可以获得目标物体的二维空间信息及一维干涉信息.根据多级阶梯微反射镜参数及光学系统设计参数计算得到摆镜步进角度为0.095°.利用实验获得的三维数据立方体进行了图像拼接与光谱复原.针对子阶梯反射镜存在宽度差异的问题,提出了一种基于极坐标霍夫变换的图像分割方法.为缓解拼接全景图中的间断线效应,将图像变换到HSI颜色空间并插值拟合其亮度分量后再变换回原空间.对拼接后的干涉图像进行了降维、去直流、寻址、切趾、相位校正、傅里叶变换及光谱分辨率增强等处理,完成了光谱复原工作.复原光谱分辨率为194 cm-1,优于设计指标(250 cm-1).     

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.     

High-speed complex conjugate resolved retinal spectral domain optical coherence tomography using sinusoidal phase modulation

We demonstrate high-speed complex conjugate artifact (CCA) resolved imaging of human retina in vivo using spectral domain optical coherence tomography. This technique utilizes sinusoidal reference mirror modulation to implement high-speed integrating buckets acquisition and a quadrature projection reconstruction algorithm in postprocessing. This method is illustrated experimentally using sets of four integrating bucket phase scans, acquired at 52 kHz, for DC suppression of 73 dB and complex conjugate suppression of 35 dB. Densely sampled (3000 A-scans/image, acquired at 4.3 images/s) full-depth in vivo images of optic nerve head show CCA suppression for most image reflections to the noise floor.     

Sample motion-insensitive, full-range, complex, spectral-domain optical-coherence tomography

We present a full-range, complex, spectral-domain optical-coherence-tomography (SD-OCT) system that is based on a double-beam scanning approach. The sample beams of two identical SD-OCT setups are combined collinearly by a bulk optic beam splitter before illuminating the object. The required phase shift for the complex signal reconstruction comes from the phase difference between both interferometers. Because of the double-beam scanning approach, our system is completely insensitive to sample motion. To demonstrate the performance of our setup, we present images of the human optic nerve head in vivo and of a human tooth.     

Integrated multimodal endomicroscopy platform for simultaneous en face optical coherence and two-photon fluorescence imaging

We report an all-fiber-optic scanning, multimodal endomicroscope capable of simultaneous optical coherence tomography (OCT) and two-photon fluorescence (TPF) imaging. Both imaging modalities share the same miniature fiber-optic scanning endomicroscope, which consists of a double-clad fiber with a core operating in single mode at both the OCT (1310 nm) and two-photon excitation (1550 nm) wavelengths, a piezoelectric two-dimensional fiber-optic beam scanner, and a miniature aspherical compound lens suitable for simultaneous acquisition of en face OCT and TPF images. A fiber-optic wavelength division multiplexer was employed in the integrated platform to combine the low coherence OCT light source and the femtosecond two-photon excitation laser into the same optical path. Preliminary imaging results of cell cultures and mouse tissue ex vivo demonstrate the feasibility of simultaneous real-time OCT and TPF imaging in a scanning endomicroscopy setting for the first time.     

基于快速扫描光学延迟线谐振扫描的相位调制方法

提出利用快速扫描光学延迟线(Rapid Scanning Optical Delay Line,RSOD)作为光学相干层析成像(Optical Coherence Tomography,OCT)系统的相位调制器,并采用正弦驱动方式(谐振扫描)来提高扫描频率,进而实现高频相位调制的方法.介绍了基于RSOD相位调制器的干涉信号包络解调方法,分析了大振镜低频率线性驱动、小振镜高频线性驱动和大振镜高速正弦驱动三种实施方案对OCT性能的影响,并针对谐振扫描方案中轴向扫描的非线性提出了图像畸变定量校正的方法.结果表明:RSOD大振镜谐振扫描的模式能够兼顾系统成像速度、成像范围以及系统信噪比的要求,是一种行之有效的相位调制方法.     

Path-length-resolved diffusive particle dynamics in spectral-domain optical coherence tomography

We describe a new method to measure the decorrelation rate of the optical coherence tomography (OCT) magnitude simultaneously in space and time. We measure the decorrelation rate of the OCT magnitude in a Fourier-domain OCT system for a large range of translational diffusion coefficients by varying the sphere diameter. The described method uses the sensitivity advantage of Fourier-domain OCT over time-domain OCT to increase the particle diffusion imaging speed by a factor of 200. By coherent gating, we reduce the contribution of multiple scattering to the detected signal, allowing a quantitative study of diffusive particle dynamics in high concentration samples. We demonstrate that this technique is well suited to image diffusive particle dynamics in samples with a complex geometry as we measure the morphology and diffusive particle dynamics simultaneously with both high spatial and high temporal resolution.     

扫描镜稳定度对TDI CCD测量精度的影响

利用TDI CCD成像数值仿真模型,研究了TDI CCD测量系统的测角精度随扫描镜速度稳定度的变化规律。首先根据TDI CCD推扫成像的物理过程,建立了数值仿真模型,设计了从光学像和扫描镜稳定度到数字图像的仿真链路;然后利用图像重心计算方法求取图像中心坐标并得到目标点的角位置坐标;通过蒙特卡诺法进行海量打靶试验,对结果进行统计得到扫描镜各稳定度水平上的测量精度值;最后将某工程样机的扫描镜速度稳定度带入仿真模型,仿真结果表明：测试误差增大5.67 μrad,达到了像元角分辨率的1/4。在光学测量系统的系统设计时,需要考虑像元分辨率及扫描镜稳定度的综合影响,选用合适的扫描镜稳定度要求,使测量角分辨率满足用户需求。     

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.     

Micromotor endoscope catheter for in vivo, ultrahigh-resolution optical coherence tomography

A distally actuated, rotational-scanning micromotor endoscope catheter probe is demonstrated for ultrahigh-resolution in vivo endoscopic optical coherence tomography (OCT) imaging. The probe permits focus adjustment for visualization of tissue morphology at varying depths with improved transverse resolution compared with standard OCT imaging probes. The distal actuation avoids nonuniform scanning motion artifacts that are present with other probe designs and can permit a wider range of imaging speeds. Ultrahigh-resolution endoscopic imaging is demonstrated in a rabbit with <4-microm axial resolution by use of a femtosecond Cr:forsterite laser light source. The micromotor endoscope catheter probe promises to improve OCT imaging performance in future endoscopic imaging applications.     

Interstitial Doppler optical coherence tomography

Doppler optical coherence tomography (OCT) can image tissue structure and blood flow at micrometer-scale resolution but has limited imaging depth. We report a novel, linear-scanning, needle-based Doppler OCT system using angle-polished gradient-index or ball-lensed fibers. A prototype system with a 19-guage (diameter of approximately 0.9 mm) echogenic needle is constructed and demonstrates in vivo imaging of bidirectional blood flow in rat leg and abdominal cavity. To our knowledge, this is the first demonstration of Doppler OCT through a needle probe in interstitial applications to visualize deeply situated microcirculation.     

Adaptive-optics ultrahigh-resolution optical coherence tomography

Merging of ultrahigh-resolution optical coherence tomography (UHR OCT) and adaptive optics (AO), resulting in high axial (3 microm) and improved transverse resolution (5-10 microm) is demonstrated for the first time to our knowledge in in vivo retinal imaging. A compact (300 mm x 300 mm) closed-loop AO system, based on a real-time Hartmann-Shack wave-front sensor operating at 30 Hz and a 37-actuator membrane deformable mirror, is interfaced to an UHR OCT system, based on a commercial OCT instrument, employing a compact Ti:sapphire laser with 130-nm bandwidth. Closed-loop correction of both ocular and system aberrations results in a residual uncorrected wave-front rms of 0.1 microm for a 3.68-mm pupil diameter. When this level of correction is achieved, OCT images are obtained under a static mirror configuration. By use of AO, an improvement of the transverse resolution of two to three times, compared with UHR OCT systems used so far, is obtained. A significant signal-to-noise ratio improvement of up to 9 dB in corrected compared with uncorrected OCT tomograms is also achieved.     

Holoscopy--holographic optical coherence tomography

Scanning optical coherence tomography (OCT) is limited in sensitivity and resolution by the restricted focal depth of the confocal detection scheme. Holoscopy, a combination of holography and Fourier-domain full-field OCT, is proposed as a way to detect photons from all depths of a sample volume simultaneously with uniform sensitivity and lateral resolution, even at high NAs. By using the scalar diffraction theory, as frequently applied in digital holographic imaging, we fully reconstruct the object field with depth-invariant imaging quality. In vivo imaging of human skin is demonstrated with an image quality comparable to conventionally scanned OCT.