Application of Reconstruction and Optimization Algorithms in Optical Tomography

Optical tomography is a non-invasive technique that uses visible or near infrared radiation to analyze biological tissues. Researchers take immense attention towards advancement in optical tomography because of its low cost and an advantage of providing anatomical information. Based on the information of optical characteristics, forward and inverse problem of tomography are solved. In this research, finite element method is employed for forward problem and gradient-based optimization algorithm is developed for inverse problem of optical tomography. It is found from simulations that information about imaging is processed more distinctly and in less computational time. Normal and abnormal conditions in imaging are readily distinguished.?Simulations are carried out in Matlab. Different scenarios are developed and are simulated to validate the performance of reconstruction and optimization algorithms in optical tomography.

Reconstructions for Continuous-Wave Diffuse Optical Tomography by a Globally Convergent Method

In this paper, a novel reconstruction method is presented for Near Infrared (NIR) 2-D imaging to recover optical absorption coefficients from laboratory phantom data. The main body of this work validates a new generation of highly efficient reconstruction algorithms called “Globally Convergent Method” (GCM) based upon actual measurements taken from brain-shape phantoms. It has been demonstrated in earlier studies using computer-simulated data that this type of reconstructions is stable for imaging complex distributions of optical absorption. The results in this paper demonstrate the excellent capability of GCM in working with experimental data measured from optical phantoms mimicking a rat brain with stroke.

Imaging of arterial plaque by quadrature swept-source optical coherence tomography with signal to noise ratio enhancements

Arterial plaque from a myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbit is visualized and characterized using a signal to noise ratio enhanced swept-source optical coherence tomography system with a quadrature interferometer (QSS-OCT). A semiconductor optical amplifier is used in the sample arm to amplify the weak signal scattered from arterial plague. Signal to noise ratio improvement are demonstrated in our QSS-OCT system. This finding results into an increase of the penetration depth possible in OCT images, from 1 mm to 2 mm. Preliminary results show that vulnerable plaque with fibrous cap, macrophage accumulations and calcification in the arterial tissue are measurable with our QSS-OCT system.

Experimental validation for time-domain fluorescence diffuse optical tomography of linear scheme

We present a full three-dimensional, featured-data algorithm for time-domain fluorescence diffuse optical tomography that inverts the Laplace-transformed time-domain coupled diffusion equations and employs a pair of appropriate transform-factors to effectively separate the fluorescent yield and lifetime parameters. By use of a time-correlation single-photon counting system and the normalized Born formulation, we experimentally validate that the proposed scheme can achieve simultaneous reconstruction of the fluorescent yield and lifetime distributions with a reasonable accuracy.

Improving depth resolution of diffuse optical tomography with an exponential adjustment method based on maximum singular value of layered sensitivity

The sensitivity of diffuse optical tomography （DOT） imaging exponentially decreases with the increase of photon penetration depth, which leads to a poor depth resolution for DOT. In this letter, an exponential adjustment method （EAM） based on maximum singular value of layered sensitivity is proposed. Optimal depth resolution can be achieved by compensating the reduced sensitivity in the deep medium. Simulations are performed using a semi-infinite model and the simulation results show that the EAM method can substantially improve the depth resolution of deeply embedded objects in the medium. Consequently, the image quality and the reconstruction accuracy for these objects have been largely improved.

In vivo evaluation of laser-induced choroidal neovascularization in rats simultaneously using optical coherence tomography and photoacoustic microscopy

Determination of the precise location and the degree of the Choroidal neovascularization(CNV)lesion is essential for diagnosation Neovascular age-related macular degeneration(AMD)and evaluation the efficacy of treatment.Noninvasive imaging techniques with specific contrast for CNV evaluation are demanded.In this paper,two noninvasive imaging techniques,namely Optical coherence tomography(OCT)and Photoacoustic microscopy(PAM),are combined to provide specific detection of CNV for their complimentary contrast mechanisms.In vivo time-serial evaluation of Laser-induced CNV in rats is present at days 1,3,5,7,14,21 after laser photocoagulation is applied to the rat fundus.Both OCT and PAM show that the CNV increases to its maximum at day 7 and decreases at day 14.Quantification of CNV area and CNV thickness is given.The dual-modal information of CNV is consistent with the histologic evaluation by hematoxylin and eosin(H&E)staining.

Fiber lenses for ultra-small probes used in optical coherent tomography

We present a design, construction and characterization of different variations of GRIN and ball fiber lenses, which were recently proposed for ultra-small biomedical imaging probes. Those fiber lens modules are made of a single mode fiber and a GRIN or ball fiber lens with or without a fiber spacer between them. The lens diameters are smaller than 0.3 mm. We discuss design methods, fabrication techniques, and measuring performance of the fiber lenses. The experimental results are compared to their modeling results. The fabrication of a high quality beam director for both lens types is presented as well. These fiber integrated beam directors could be added on the tips of the fiber lenses for side-view probes. A needle probe made by these fiber lenses is demonstrated as a sample of the ultra-small probe for biomedical imaging application. In vivo human finger images acquired by a swept source optical coherence tomography using the fiber lenses with different beam profiles were shown, which indicates the important impact of

PRELIMINARY STUDY ON SKIN CANCER DETECTION IN SENCAR MICE USING MUELLER OPTICAL COHERENCE TOMOGRAPHY

We report on the use of a fiber-based Mueller-matrix optical coherence tomography(OCT)system with continuous source-polarization modulation for in vivo imaging of early stages of skin cancer in SENCAR mice.A homemade hand-held probe with integrated optical scanning and beam delivering optics was coupled in the sample arm.The OCT images show the morphological changes in skin resulting from pre-cancerous papilloma formations that are consistent with histology,thus demonstrating the system’s potential for early skin cancer detection.

Adaptive optics optical coherence tomography for retina imaging

When optical coherence tomography （OCT） is used for human retina imaging, its transverse resolution is limited by the aberrations of human eyes. To overcome this disadvantage, a high resolution imaging system for living human retina, which consists of a time domain OCT system and a 37-elements adaptive optics （AO） system, has been developed. The AO closed loop rate is 20 flames per second, and the OCT has a 6.7-μm axial resolution. In this paper, this system is introduced and the high resolution imaging results for retina are presented.

In vitro birefringence imaging with spectral domain polarization-sensitive optical coherence tomography

Spectral domain polarization-sensitive optical coherence tomography （SDPS-OCT） is a depth-resolved polarization-sensitive interferometry which integrates polarization optics into spectral domain optical co- herence tomography （SD-OCT）. This configuration can obtain birefringence information of samples and improve the imaging speed. In this paper, horizontally polarized light is used to replace natural light of the source. Then, right-rotated circularly polarized light is the incident sample light. To obtain two orthogonal components of the polarized interferogram, the reflected light of the reference arm is set to be 45° linearly polarized light. These two components are acquired by two spectrometers synchronously. The system was employed to achieve 12.8μm axial resolution and 4.36μm transverse resolution. We have imaged in vitro chicken tendon and muscle tissues with these svstem.

Spectral calibration in spectral domain optical coherence tomography

A novel spectral calibration method is developed for spectral domain optical coherence tomography system. The method is based on two measurements of interference spectra from two reference mirror positions. It removes the influence of dispersion mismatch, and hence accurately determines the spectral distribution on the line-scan charge-coupled device （CCD） for sequent precise interpolation. High quality imaging can be realized with this method. Elimination of the degradation effect caused by dispersion mismatch is verified experimentally, and improved two-dimensional （2D） imaging of fresh orange pulp based on the proposed spectral calibration method is demonstrated.

Measurement of crater geometries after laser ablation of bone tissue with optical coherence tomography

The feasibility of measuring crater geometries by use of optical coherence tomography （OCT） is examined. Bovine shank bone on a motorized translation stage with a motion velocity of 3 mm/s is ablated with a pulsed CO2 laser in vitro. The laser pulse repetition rate is 60 Hz and the spot size on the tissue surface is 0.5 mm. Crater geometries are evaluated immediately by both OCT and histology methods after laser irradiation. The results reveal that OCT is capable of measuring crater geometries rapidly and noninvasively as compared to histology. There are good correlation and agreement between crater depth estimates obtained by two techniques, whereas there exists distinct difference between crater width estimates when the carbonization at the sides of craters is not removed.

OCT图像多教师知识蒸馏超分辨率重建

光学相干断层成像(OCT)广泛应用于眼科诊断与辅助治疗,但其成像质量不可避免地受到散斑噪声和运动伪影影响。本文提出了一种针对OCT超分辨率任务的多教师知识蒸馏网络MK-OCT,使用不同优势的教师网络训练平衡、轻量级和高效的学生网络。MK-OCT中高效通道蒸馏方法ECD的使用也使得模型能够更好地保留视网膜图像的纹理信息,满足临床需要。实验结果表明,与经典超分辨率网络相比,本文所提模型在重建精度和感知质量两个方面均表现优异,模型尺寸更小,计算量更少。

Spatial Fourier-decomposition optical fluorescence tomography-theoretical investigation

A new three-dimensional （3D） optical fluorescent tomographic imaging scheme is proposed with structured illumination and spatial Fourier-domain decomposition methods for the first time. In this spatial Fourierdecomposition optical fluorescence tomography （SF-OFT）, the intensity of focused excitation light from an objective lens is modulated to be a cosine function along the optical axis of the system. For a given position in a two-dimensional （2D） raster scanning process, the spatial frequency of the cosine function along the optical axis sweeps in a proper range while a series of fluorescence intensity are detected accordingly. By making an inverse discrete cosine transformation of these recorded intensity profiles, the distribution of fluorescent markers along the optical axis of a focused laser beam is obtained. A 3D optical fluorescent tomography can be achieved with this proposed SF-OFT technique with a simple 2D raster scanning process.

Effects of age on ocular anterior segment dimensions measured by optical coherence tomography

Background Older subjects tend to have smaller ocular anterior segment. The present study aimed to measure anterior segment dimensions with optical coherence tomography （OCT） and quantitatively assess the effect of age and other factors. Methods Anterior segment OCT images were obtained in normal subjects residing in the greater Los Angeles area. Four line scans were acquired at the 90%, 45%, 0% and 135% meridians of each eye. Computer calipers acquired anterior segment dimensions of corneal diameter, anterior chamber width, corneal vault and anterior chamber depth on OCT images. Measurements from 4 meridians were averaged. Axial length and corneal power were measured by partial coherence interferometry. Univariate and multivariate analyses were performed to assess correlations. Results Sixty-six eyes of 33 normal subjects （aged 22-65 years, 19 Asians, 14 Caucasians） were enrolled. For every 1 year of age, corneal diameter was 0.03：3 mm narrower （P 〈0.01）, anterior chamber width was 0.031 mm narrower （P 〈0.01）, corneal vault was 0.016 mm lower （P 〈0.01）, and anterior chamber depth was 0.025 mm lower （P 〈0.01）. Asian eyes had smaller corneal diameter （P=-0.035） and anterior chamber width （P=0.015） compared with those of Caucasian eyes. Body height showed positive correlation with corneal diameter （0.039 mm per centimeter of height, P 〈0.01） and corneal vault （0.024 mm per centimetre of height, P 〈0.01）. Gender did not have an independent effect on anterior segment dimensions. Conclusions Anterior segment dimensions were smaller in older subjects. Age-related changes may affect the tolerability of long-term implants such as phakic intraocular lens.

继发性牙根纵裂诊断的研究进展

牙根纵裂是一种源自牙根的纵向裂纹,可发生在活髓牙和根管治疗后牙齿,是病因复杂、预后较差的牙体硬组织疾病。发生于牙髓治疗后的牙根纵裂称为继发性牙根纵裂(secondary vertical root fracture,SVRF),对SVRF的诊断,应结合临床体征(如疼痛、肿胀、牙齿松动、位于牙龈边缘附近的窦道和深而窄的孤立牙周袋)和根尖片(如牙周膜增宽、垂直骨丧失和根周骨丧失、根周“晕圈状”或“J”形的透射影)进行综合判断。对疑似牙根纵裂的牙齿,应通过锥形束CT(cone⁃beam computed tomography,CBCT)等三维影像学辅助诊断,如CBCT显示牙根上的折裂线以及颊侧或舌侧骨板缺损;优化设置CBCT参数,如选用小视野CBCT、增强染料辅助的应用、使用金属伪影还原工具(metal artifact reduction,MAR)等方法提高CBCT诊断SVRF的精确度。使用多种影像技术可对不同宽度的裂纹进行检测,如核磁共振成像(magnetic resonance imaging,MRI)中表现为异常的高强度信号;使用数字减影技术(digital subtraction radiography,DSR)进行图像处理后出现的黑色线状区域;不同宽度的裂纹在光学相干断层扫描(optical coherence tomography,OCT)可表现为高亮度线或暗区。人工智能(artificial intelligence,AI)诊断技术和预测模型也是SVRF诊断的辅助手段。通过各种无创手段仍然无法确诊的SVRF病例,可通过根管内直视和翻瓣手术中直视发现SVRF。

Fast Monte Carlo inversion for extracting the optical properties of tubular tissues

Reconstruction of absorption coefficient μa and scattering coefficient μs is very important for applications of diffuse optical tomography and near infrared spectroscopy. Aiming at the early cancer detection of cervix and stomach, we present a fast inverse Monte-Carlo scheme for extracting μa and μs of a tubular tissue from the measurement on frequency domain. Results show that the computation time for reconstructing one set of μa and μs is less than 1 min and the relative errors in reconstruction are less than ±10% for the optical properties of normal cervical tissue and precancerous lesions.

光声成像及其在生物医学中的应用

光声成像是一种新近迅速发展起来、基于生物组织内部光学吸收差异、以超声作媒介的无损生物光子成像方法,它结合了纯光学成像的高对比度特性和纯超声成像的高穿透深度特性的优点,以超声探测器探测光声波代替光学成像中的光子检测,从原理上避开了光学散射的影响,可以提供高对比度和高分辨率的组织影像,为研究生物组织的结构形态、生理特征、代谢功能、病理特征等提供了重要手段,在生物医学临床诊断以及在体组织结构和功能成像领域具有广泛的应用前景.对光声成像技术的机理、光声成像技术和方法、光声图像重建算法以及光声成像在生物医学上的应用情况作一个简单介绍,希望有助于推动我国在该领域的科研和开发应用工作的迅速发展.

近红外漫射光层析成像实验研究

实验验证了所建立的时间分辨光学层析成像测量系统的光学参量预测能力、多个测量通道的一致性,表明了本测量系统具有层析成像的潜力.研究了采用特征数据量(平均飞行时间、广义脉冲谱技术为基础的用数据类型R)及全时间分辨数据的图像重建算法在光学参量重建准确度、重建出的对象尺寸、空间分辨率等方面的各自优势.

20MHzB型超声与频域光学相干断层扫描在黄斑病变诊断中的对比观察

背景黄斑区病变的形态学检查在疾病的早期诊断中发挥着重要作用。频域光学相干断层扫描（OCT）在屈光间质混浊眼的检查受到限制，传统的10MHzB型超声检查对黄斑病变的分辨率较低，20MHzB型超声检查在黄斑区疾病中的应用是一种新的方法。目的应用频域OCT和20MHzB型超声对黄斑病变进行形态学对比观察，探讨20MHzB型超声对黄斑疾病的临床诊断价值。方法收集在天津医科大学眼科中心确诊的黄斑病变患者51例51眼，患眼均行频域OCT扫描，然后行20MHzB型超声检查。黄斑病变按频域OCT检查的形态学改变进行分类，分析20MHzB型超声的声像学特征，探讨病因。结果根据频域OCT检查检出黄斑裂孔10眼，B型超声显示黄斑区实性圆顶状回声表浅隆起，病变中央呈孔状凹陷。频域OCT检出的黄斑水肿16眼、神经上皮层脱离6眼和视网膜劈裂4眼，B型超声均显示黄斑区球壁表面的局限性带状表浅隆起，其下见液性无回声间隙。频域OCT检出的视网膜色素上皮（RPE）层脱离15眼，B型超声检查显示黄斑区球壁表面局限带状强回声表浅隆起，光带较厚，其下见液性无回声间隙。结论20MHzB型超声能对几种常见的黄斑病变进行初步鉴别，与频域OCT相比，黄斑病变B型超声表现的识别能力稍欠，但在屈光问质混浊的情况下，B型超声的诊断作用优于频域OCT。