Time-gated Fourier-domain optical coherence tomography

A novel optical coherence tomography (OCT) system is presented that combines Fourier-domain OCT with incoherent nonlinear time gating. By processing backscattered light in the optical domain, the user can select a restricted depth field of view for improved contrast and acquisition speed. This technique has the additional advantage that imaging is done in the infrared (approximately 1280 nm) but is detected in the visible(approximately 504 nm).     

基于受激辐射信号的谱域光学相干层析分子成像方法

鉴于不同生理病理状态下组织复折射率实部的变化不大,传统光学相干层析(OCT)成像技术在分子特异性识别上存在先天不足.为此,本文提出了基于受激辐射信号的OCT成像方法,可在实现传统散射成像的同时,实现基于受激辐射信号的分子成像.在超高分辨率谱域OCT系统的基础上,通过增设光谱分光与调制抽运光支路,建立了基于单宽谱光源的抽运探测谱域OCT系统,详细推导了调制抽运下受激辐射信号的获取与成像公式.利用搭建的抽运探测谱域OCT系统,实现了瞬态受激辐射信号的相干探测.基于同时获取的受激辐射OCT信号和传统OCT信号,成功重构了氮化物粉末构建样品的基于受激辐射信号的分子对比OCT图像.     

光纤型光学相干层析成像系统的研制

光学相干层析(OCT)成像技术是一新近发展的高分辨力生物医学成像手段,能非侵入性地对活体内部的结构与生理功能进行可视化观察。采用宽带近红外光源,基于迈克耳孙干涉原理和外差探测方法,建立了单模光纤型光学相干层析成像系统,相干地提取从生物体内部返回的深度分辨的弹性散射光信息,并依此构筑了自然状态下活体组织的二维光学相干层析成像图像和三维光学相干层析成像图像。光纤化设计的光学相干层析成像系统紧凑、灵活,便于与光纤导管、内窥镜和其它成像装置的有机结合,以拓展其观察范围和应用领域。     

Molecular contrast in optical coherence tomography by use of a pump-probe technique

We describe a novel technique for contrast enhancement in optical coherence tomography (OCT) that makes possible molecular-specific imaging for what is believed to be the first time. A pump-probe technique is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample-arm light acting as probe light. A signal processing technique for three-dimensional localization of the transient absorption signal is described, and preliminary results exhibiting OCT contrast from methylene blue dye in multilayer and scattering phantoms are presented.     

Fourier domain optical coherence tomography using optical demultiplexers imaging at 60,000,000 lines/s

We describe high-speed Fourier domain optical coherence tomography (OCT) using optical demultiplexers (ODs) for spectral dispersion. The OD enables separation of a narrow spectral band of 14 GHz (0.11 nm) from a broadband incident light at 256 different frequencies in 25.0 GHz intervals centered at 192.2 THz (1559.8 nm). OCT imaging of 60,000,000 axial scans per second was achieved through parallel signal acquisition using 256 balanced photoreceivers to simultaneously detect all the output signals from the ODs in a Fourier domain OCT system. OCT imaging at a 16 kHz frame rate, 1100 A-lines per frame, 3 mm depth range, and 23 microm resolution was demonstrated using a resonant scanner for lateral scanning.     

Full range complex spectral optical coherence tomography technique in eye imaging

We demonstrate a new implementation of complex spectral optical coherence tomography (OCT) in biomedical imaging. By reconstruction of both amplitude and phase we are able to use the negative and positive optical path differences to get images of objects of considerable thickness. An accompanying reduction of coherent noise improves the quality of the images. The property of the complex spectral OCT that permits the measurement range to be increased and permits the simultaneous use of phase and amplitude in spectral systems was not described previously. To show the potential of this technique we measured an anterior chamber of a porcine eye in vitro.     

Spectral domain second-harmonic optical coherence tomography

Optical coherence tomography (OCT) provides micrometer-scale structural imaging by coherent detection of backscattered light. Molecular contrast in OCT has been demonstrated using transient absorption, coherent anti-Stokes Raman scattering, and second-harmonic (SH) generation. The sensitivity of molecular contrast signals can be enhanced by use of Fourier domain techniques. We have constructed a spectrometer-based Fourier domain SH-OCT system for simultaneous acquisition of the fundamental and SH signals. We report a >30 dB increase in SH sensitivity over a similar time domain SH-OCT system and demonstrate contrast between cartilage and bone using collagen as the contrast agent.     

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.     

提高布里渊光时域反射应变仪测量空间分辨力的等效脉冲光拟合法

由于探测光脉冲宽度受到限制,布里渊光时域反射仪(BOTDR)在对光纤上的应变进行分布式测量时,空间分辨力只能达到1 m。针对布里渊光时域反射仪单次采样接收背向布里渊散射信号(BBS)需要一定的时间,提出了基于等效脉冲光的多洛仑兹拟合法以提高其应变测量的空间分辨力。该方法将探测光脉冲在布里渊光时域反射仪完成单次采样所需的时间上进行积分,将积分函数作为等效脉冲光的表达式,再根据等效脉冲光的形状将布里渊光时域反射仪接收到的背向布里渊散射谱(BBS)细分,并对它进行多洛仑兹迭代拟合,准确求得每个细分布里渊散射谱的中心频率,进而利用光纤中布里渊频移与应变的对应关系,得到光纤中与细分布里渊散射谱对应的细分光纤单元上的应变情况。实验结果表明,利用这种方法,可使布里渊光时域反射仪应变测量的空间分辨力提高至0.05 m。     

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.     

Molecularly sensitive optical coherence tomography

Molecular contrast in optical coherence tomography (OCT) is demonstrated by use of coherent anti-Stokes Raman scattering (CARS) for molecular sensitivity. Femtosecond laser pulses are focused into a sample by use of a low-numerical-aperture lens to generate CARS photons, and the backreflected CARS signal is interferometrically measured. With the chemical selectivity provided by CARS and the advanced imaging capabilities of OCT, this technique may be useful for molecular contrast imaging in biological tissues. CARS can be generated and interferometrically measured over at least 600 microm of the depth of field of a low-numerical-aperture objective.     

Spectral heterodyne tomography

A novel method of optical coherent tomography—spectral heterodyne tomography—is proposed. Spectral heterodyne tomography is based on parallel heterodyne detection of a multitude of frequencies of the light backscattered by an object under study. The result of this detection is a spectral distribution of the amplitude and phase of the scattered radiation. Subsequent numerical processing allows one to find the distribution of scattering centers over the depth corresponding to the point of entrance of the incident light. The proposed method is potentially characterized by a higher efficiency as compared with the most successful approach to optical coherence tomography, based on heterodyne scanning interferometry.     

Measurement of the hemoglobin oxygen saturation level with spectroscopic spectral-domain optical coherence tomography

We report the measurement of the hemoglobin (Hb) oxygen saturation level in human blood with a spectroscopic spectral-domain optical coherence tomography (SSD-OCT) system based on the crossover behavior of Hb and oxyhemoglobin (HbO(2)) absorption coefficients around 800 nm. By calculating the ratio of the exponential decay constant of A-mode scan signal in the long-wavelength range (>800 nm) over that in the short-wavelength range (<800 nm), the relative oxygen saturation level of Hb can be calibrated. Such a relative level can be used for practical diagnosis application after a golden standard is built by comparing the variation of the OCT result with that of a conventional method, such as the use of a blood gas analyzer. In our experiment, the variation curve based on the SSD-OCT measurement, which has the advantages of noninvasive, real-time, and high-resolution measurements, is coincident with that of using a commercial blood gas analyzer.     

Optical coherence tomography

Optical Coherence Tomography (OCT) is a new technology for performing high-resolution cross sectional imaging. OCT is analogous to ultrasound imaging, except that it uses light instead of sound. OCT can provide cross sectional images of tissue structure on the micron scale in situ and in real time. OCT functions as a type of optical biopsy and is a powerful imaging technology for medical diagnostics because unlike conventional histopathology which requires removal of a tissue specimen and processing for microscopic examination, OCT can provide images of tissue in situ and in real time. OCT can be used where standard excisional biopsy is hazardous or impossible, to reduce sampling errors associated with excisional biopsy, and to guide interventional procedures.     

Linear optical coherence tomography system with extended measurement range

Optical coherence tomography (OCT) sensors traditionally use scanning optical delay lines with moving parts and a single detector. OCT systems with a linear detector array (linear OCT or L-OCT) are simple and robust, but a detector with approximately 10,000 pixels is needed for an imaging depth of 2mm, which is necessary for most biomedical applications. We present a new optical setup for L-OCT with an increased measurement range. An additional grating performs a reduction of the spatial frequencies of the fringe pattern on the detector without loss in the signal-to-noise ratio, so the signal can be sampled with a minimal number of pixels. The theory for this approach is addressed and the first measurements are presented.     

被动差分光学吸收光谱法监测污染源排放总量研究

研究了一种测量污染源污染气体(如SO2、NO2)排放总量的光学遥测方法,即采用被动差分光学吸收光谱(DOAS)系统在移动平台(如汽车)上对污染源排放烟羽进行扫描测量,利用被动差分光学吸收光谱处理方法对系统采集的天顶太阳散射光谱进行处理获取柱密度,在结合测量时段的气象(风场)信息后获得污染气体的排放通量,最终得到排放总量。着重描述了获得烟羽垂直柱密度的差分光学吸收光谱方法以及污染气体排放通量的计算方法,并利用车载被动差分光学吸收光谱系统对某一热电厂SO2排放进行了外场测量,实验结果与在线设备的对比表明:这种基于被动差分光学吸收光谱光学遥测方法能够用于污染源排放总量的快速测量。     

OCT技术在发育生物学中的应用

基于光学低相干反射测量而发展起来的光学相干层析技术（ Optica1 Coherence Tomography,OCT）是一种新型的成像技术，它可以对强散射介质如生物组织实施非侵入性的快速活体成像。与传统的组织切片相比,OTC可以大大减少对发育形态成像所需的时间、复杂程度及成本。非接触和非侵入式的成像方式有助于研究个体发育中由基因变异所引起的形态和功能变化，因而在发育生物学的研究当中有着广阔的应用前景。概述了OCT技术在发育生物学当中诸方面的应用情况。     

Parallel frequency-domain optical coherence tomography scatter-mode imaging of the hamster cheek pouch using a thermal light source

We use a parallel frequency-domain optical coherence tomography (FDOCT) system to generate a scatter-mode image of the hamster cheek pouch epithelium. To our knowledge, this is the first optical coherence tomography (OCT) image of a biological sample obtained using a thermal light source in the frequency domain. The system employs an imaging spectrometer to acquire depth-resolved profiles from adjacent spatial points without the need for any scanning. To enable this imaging modality, we have considered that signals originating from multiple depths combine in a different manner in FDOCT compared to time-domain optical coherence tomography (TDOCT). Because a multicomponent FDOCT signal is a coherent sum, it is necessary to limit the number of modes that contribute to the detected signal. Conversely, multicomponent TDOCT signals can be represented as incoherent sums, where increasing the number of modes improves the signal.     

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．     

光源对相干层析系统特性的影响

在分析相干层析系统成像机理的基础上，从理论上研究了光源对系统成像特性的影响，在考虑干涉条纹的强度用概率函数处理的条件下，由分析得出相干层析成像系统相当于一个复振幅的线性空间不变系统，从而给出相干函数和光源的功率谱密度之间的关系。通过对使用不同光源的系统相干传递函数比较，得出了采用具有较大线宽的低相干光源，系统的空间分辨率更好，可使测量更精确的结论。本文的工作为光学相干层析成像系统的优化设计提供了理论依据。