Acceleration of optical coherence tomography signal processing by multi-graphics processing units

A multi-GPU system designed for high-speed,real-time signal processing of optical coherencetomography(OCT)is described herein.For the OCT data sampled in linear wave numbers,themaximum procesing rates reached 2.95 MHz for 1024-OCT and 1.96 MHz for 2048-OCT.Data sampled using linear wavelengths were re-sampled using a time-domain interpolation method and zero-padding interpolation method to improve image quality.The maximum processing rates for1024-OCT reached 2.16 MHz for the time-domain method and 1.26 MHz for the zero-paddingmethod.The maximum processing rates for 2048-0CT reached_1.58 MHz,and 0.68 MHz,respectively.This method is capable of high-speed,real-time processing for O CT systems.

Investigation of changes in thickness and reflectivity from layered retinal structures of healthy and diabetic eyes with optical coherence tomography

OCT is usually employed for the measurement of retinal thickness. However, coherent reflected light carries more information characterizing the optical properties of tissue. Therefore, optical property changes may provide further information regarding cellular layers and early damage in ocular diseases. We investigated the possibility of OCT in detecting changes in the optical backscattered signal from layered retinal structures. OCT images were obtained from diabetic patients without retinopathy (DM, n = 38 eyes) or mild diabetic retinopathy (MDR, n = 43 eyes) and normal healthy subjects (n = 74 eyes). The thickness and reflectivity of various layered structures were assessed using a custom-built algorithm. In addition, we evaluated the usefulness of quantifying the reflectivity of layered structures in the detection of retinal damage. Generalized estimating equations considering within-subject inter-eye relations were used to test for differences between the groups. A modified p value of <0.001 was considered statistically significant. Receiver operating characteristic (ROC) curves were constructed to describe the ability of each parameter to discriminate between the eyes of DM, MDR and healthy eyes. Thickness values of the GCL + IPL and OPL showed a significant decrease in the MDR eyes compared to controls. Significant decreases of total reflectance average values were observed in all layers in the MDR eyes compared with controls. The highest AUROC values estimated for the total reflectance were observed for the GCL+IPL, OPL and OS when comparing MDR eyes with controls. Total reflectance showed a better discriminating power between the MDR eyes and healthy eyes compared to thickness values. Our results suggest that the optical properties of the intraretinal layers may provide useful information to differentiate pathological from healthy eyes. Further research is warranted to determine how this approach may be used to improve diagnosis of early retinal neurodegeneration.

WAVELENGTH PROBING OPTICAL COHERENCE TOMOGRAPHY

In swept-source optical coherence tomography(SSOCT),the swept-source stimulates system by a series of wavelengths in time sequence;a photo detector then collects all reflected/backscattered light from testing sample as the components of Fourier series.Due to the nature of the SSOCT,the processing in spectral domain can merge multiple swept-sources with different central wavelengths,which greatly increases the resolution of the OCT imaging.In the wavelength probing OCT,a standard broadband SSOCT system is used to extract the internal structure of the sample,and another narrow band light can be used to probe the spectral feature of the sample at the probing wavelength.

In-process monitoring in laser grooving with line-shaped femtosecond pulses using optical coherence tomography

A line-shaped beam is useful for increasing the processing speed in laser grooving and scribing.In laser grooving,depth control of the processed structure is important for performing precise processing.In this paper,in-process monitoring of the depth of a structure formed by femtosecond laser processing with a line-shaped beam using swept-source optical coherence tomography(SS-OCT)was demonstrated.In the evaluation of the SS-OCT system,the depth resolution,measurement accuracy,and axial measurable range were 15.8μm,±2.5μm and 5.3 mm,respectively.In laser grooving,the structural shape and the distribution of deposited debris were successfully monitored.The measured depth agreed well with the depth obtained using a laser confocal microscope.The proposed method will be effective for precise laser processing with feedback control of the laser parameters based on in-process monitoring of the processed structure.

光学PT扇束结构权重系数矩阵计算与实现

权重系数矩阵是光学过程层析成像(optical process tomography,简称光学PT)技术中非常重要的参数之一,它的传统计算是基于人工测算,其缺点是烦琐、且极其耗时。因此,本文利用Visual C++语言实现了光学过程层析成像系统扇束阵列传感器结构权重系数矩阵的即时计算。为光学敏感场灵敏度分布的计算、图像重建仿真以及光学PT系统的实现节省了时间,缩短了研究周期。

Swept source optical coherence tomography based on non-uniform discrete fourier transform

A high-speed high-sensitivity swept source optical coherence tomography （SSOCT） system using a high speed swept laser source is developed. Non-uniform discrete fourier transform （NDFT） method is introduced in the SSOCT system for data processing. Frequency calibration method based on a Mach-Zender interferometer （MZI） and conventional data interpolation method is also adopted in the system for comparison. Optical coherence tomography （OCT） images from SSOCT based on the NDFT method, the MZI method, and the interpolation method are illustrated. The axial resolution of the SSOCT based on the NDFT method is comparable to that of the SSOCT system using MZI calibration method and conventional data interpolation method. The SSOCT system based on the NDFT method can achieve higher signal intensity than that of the system based on the MZI calibration method and conventional data interpolation method because of the better utilization of the power of source.

TIME-DOMAIN INTERPOLATION ON GRAPHICS PROCESSING UNIT

The signal processing speed of spectral domain optical coherence tomography(SD-OCT)has become a bottleneck in a lot of medical applications.Recently,a time-domain interpolation method was proposed.This method can get better signal-to-noise ratio(SNR)but much-reduced signal processing time in SD-OCT data processing as compared with the commonly used zeropadding interpolation method.Additionally,the resampled data can be obtained by a few data and coefficients in the cutoff window.Thus,a lot of interpolations can be performed simultaneously.So,this interpolation method is suitable for parallel computing.By using graphics processing unit(GPU)and the compute unified device architecture(CUDA)program model,time-domain interpolation can be accelerated significantly.The computing capability can be achieved more than 250,000 A-lines,200,000 A-lines,and 160,000 A-lines in a second for 2,048 pixel OCT when the cutoff length is L=11,L=21,and L=31,respectively.A frame SD-OCT data(400A-lines×2,048 pixel per line)is acquired and processed on GPU in real time.The results show that signal processing time of SD-OCT can befinished in 6.223 ms when the cutoff length L=21,which is much faster than that on central processing unit(CPU).Real-time signal processing of acquired data can be realized.

Numerical Optimization of Sensitivity in Fourier Domain Optical Coherence Tomography

The details of crosssectional images based on Fourier domain optical coherence tomography play an important role that is limited to nonuniform sampling,spectral dispersion,inverse discrete Fourier transform(IDFT),and noise.In this section,we propose a method for emphasizing axial details to the greatest extent possible.After removing spectral dispersion,uniform discretization in the wavenumber domain is performed based on two interferograms via a specified offset in depth,with no spectrum calibration.The sampling number in IDFT is optimized to improve axial sensitivity up to 1.62 dB.The proposed process has the advantage of being based on numerical computation rather than hardware calibration,which benefits cost,accuracy,and efficiency.

Optimizing photoacoustic image reconstruction using cross-platform parallel computation

Three-dimensional(3D)image reconstruction involves the computations of an extensive amount of data that leads to tremendous processing time.Therefore,optimization is crucially needed to improve the performance and efficiency.With the widespread use of graphics processing units(GPU),parallel computing is transforming this arduous reconstruction process for numerous imaging modalities,and photoacoustic computed tomography(PACT)is not an exception.Existing works have investigated GPU-based optimization on photoacoustic microscopy(PAM)and PACT reconstruction using compute unified device architecture(CUDA)on either C++or MATLAB only.However,our study is the first that uses cross-platform GPU computation.It maintains the simplicity of MATLAB,while improves the speed through CUDA/C++−based MATLAB converted functions called MEXCUDA.Compared to a purely MATLAB with GPU approach,our cross-platform method improves the speed five times.Because MATLAB is widely used in PAM and PACT,this study will open up new avenues for photoacoustic image reconstruction and relevant real-time imaging applications.

Quantitative Schlieren Image-Noise Reduction Using Inverse Process and Multi-Path Integration

This report deals with introducing two new techniques based on a novel concept of complex brightness gradient in quantitative schlieren images, “inverse process” and “multi-path integration” for image-noise reduction. Noise in schlieren images affects the projections (density thickness) images of computerized tomography (CT). One spot noise in the schlieren image appears in a line shape in the density thickness image. Noise effect like an infectious disease spreads from a noisy pixel to the next pixel in the direction of single-path integration. On the one hand, the noise in the schlieren image reduces the quality of the image and quantitative analysis and is undesirable;on the other it is unavoidable. Therefore, the importance of proper noise reduction techniques seems essential and tangible. In the present report, a novel technique “multi-path integration” is proposed for noise reduction in projections images of CT. Multi-path integration is required the schlieren brightness gradient in two orthogonal directions. The 20-directional quantitative schlieren optical system presents only images of schlieren brightness in the horizontal gradient and another 20-directional optical system seems necessary to obtain vertical schlieren brightness gradient, simultaneously. Using the “inverse process”, a new technique enables us to obtain vertical schlieren brightness gradient from horizontal experimental data without the necessity of a new optical system and can be used for obtaining any optional directions of schlieren brightness gradient.

小波变换对OCT图像的降噪处理

通过分析光学相干层析成像系统中的噪音源以及不同噪音对成像质量的影响,利用小波变换的方法,结合软阈值滤波对图像去噪,消除噪音对图像的干扰,处理后图像变得清晰了,图像质量得以改善,表明该方法能达到减小图像噪音的目的·

基于ART的光学过程层析成像扇束图像重建

光学过程层析成像是近几年发展起来的一种新型的光学测量技术 ,它源于医学 CT的基本理论和方法 ,可认为是医学CT技术在工业过程监测领域的自然延伸和发展。然而 ,由于过程层析成像的被测对象为快速变化的工业过程 ,因此 ,其投影数据的数量比医学 CT少得多 ,而实时性则要求更高。利用一种扇束扫描制式的光学传感器有利于提高光学过程层析成像的空间分辨率及测量精度 ,但在这种扫描制式下 ,引用医学 CT的常见图像重建算法 (如数据重排方法、反投影法和滤波反投影法等 )却不适用或难以胜任工业检测的要求。为此提出了一种代数重建技术来提高光学过程层析成像的测量精度和速度。该算法不仅适用于少数投影数据的情况 ,也能使求解过程遍历几乎所有的图像像元 ,因此成像效果好和实时性较高 。

光学层析成像技术的研究动态

光学层析成像技术是利用光学的方法对流体或物体进行层析成像的一种新的技术 ,近年来发展很快。本文较系统地介绍了光学工业过程层析成像技术的基本原理、分类。

基于数字希尔伯特变换的OCT信号处理与系统实现

信号处理方法的选择是光学相干层析(OpticalCoherenceTomography,OCT)系统研制的重要环节,直接决定着OCT系统的硬件构建和实现。应用硬件实现OCT信号处理的方法虽然速度快,但存在硬件开销大,系统配置可调节性差等缺点。进而采用了基于数字希尔伯特变换的软件方法来处理OCT信号。该数字处理方法对探测得到的离散干涉实信号进行解析拓展,得到同时具有振幅信息和相位信息的复信号,其中的振幅信息被用于OCT的图像重建。介绍了研制的光纤OCT系统和各驱动单元的同步时序控制,最后给出了人体皮肤和洋葱的OCT高清晰层析图。

应用血管内超声/光学相干断层成像杂交技术研究冠状动脉钙化与斑块回缩的关系

目的:冠状动脉钙化是否与斑块回缩相关尚不清楚。本研究的目的是结合光学相干断层扫描(OCT)和血管内超声(IVUS)评估冠状动脉钙化和斑块回缩(PS)之间的关系。方法:15例患者,16支血管纳入本研究,术后即刻和术后5年联合应用OCT和IVUS评估钙化斑块面积变化和斑块回缩,及二者之间的关系。IVUS检测管腔面积(LA)、血管面积(VA)和斑块/中膜面积(PA)。将斑块/中层回缩(PS)定义为PA相对减少>5%。OCT检测钙化面积、钙化弧度和钙化长度。结果:术后即刻和5年随访时,共有72个OCT和IVUS完全匹配的横断面(共432个图)纳入该研究。72个横截面中,35个横截面在5年随访时显示为PS,37个横截面为非PS。斑块面积的变化分别与OCT测量的钙化面积变化呈负相关(r=-0.29,P=0.004),与OCT钙化弧度变化(r=-0.42,P<0.001),OCT钙化长度变化(r=-0.5,P<0.001)呈负相关,与IVUS测量的钙化弧度变化呈负相关(r=-0.31,P=0.024),而与管腔面积变化呈正相关(r=0.24,P=0.044)。结论:冠状动脉钙化斑块进展使得斑块回缩和管腔扩大。应用IVUS/OCT杂交技术能更好的评估钙化斑块进展和斑块回缩之间的相关性。

相衬光学相干层析在无损检测领域的应用

光学相干层析(Optical Coherence Tomography,OCT)作为一种具有微米级分辨率和毫米级量程的层析成像技术,可用于透明/半透明物体(如聚合物材料、陶瓷材料、复合材料等)内部微观结构信息的探测与成像。在结合了相衬方法后,该技术还可利用干涉信号的相位敏感特性,实现纳米级位移场与微应变级形变场的高灵敏度测量,用于材料内部全场力学行为的表征与测试。在近十余年发展中,相衬OCT已逐渐成为无损检测领域的研究热点,受到了国际相关学者的广泛关注。本文旨在介绍相衬OCT基本原理及其在检测领域典型应用(包括多层结构热变形场层析测量、聚合物内部固化过程可视化监测、材料内部微缺陷高灵敏辨识等)的基础上,对其未来发展进行探讨与展望。

激光扫描共焦检眼镜对黄斑囊样水肿成像的定量分析

背景黄斑囊样水肿（CME）可由多种眼底疾病导致，目前主要的无创临床诊断方法为彩色眼底照相和频域OCT（SD—OCT），OCT对于CME的断层形态和定量分析较好，但是对水肿的范围评价欠佳。基于激光扫描共焦检眼镜（cSLO）的视网膜成像技术对组织穿透性好，分辨率高，采集的眼底像清晰，对比度好，但是对于CME的检测价值尚不清楚。目的评价cSLO视网膜成像技术对CME定性和定量分析的临床价值。方法采用描述性研究方法，于2015年8—12月在北京同仁医院眼科中心确诊的CME患者24例24眼，采用cSLO视网膜成像技术对黄斑区进行放射状扫描和线扫（45°×45°，49个水平扫描），分别获得伪彩成像、绿光（532nm）反射成像和红外光（785nm）反射成像，应用EasyScan软件（1．2．2版）进行图像分析，并用传统彩色眼底照相技术和SD—OCT对患眼眼底进行成像，由专业的眼底病医师对每个图像的清晰度进行分级，并依CME图像和边界的清晰度进行评分。结果本组患者CME的原发病包括黄斑前膜（ERM）10例10眼、视网膜分支静脉阻塞（BRVO）6例6眼、视网膜中央静脉阻塞（CRVO）4例4眼、糖尿病视网膜病变（DR）3例3眼和CRVO合并BRVO1例1眼。传统彩色眼底照相可显示CME像，但边界不清；cSLO视网膜成像可见明显的CME范围，边界清晰。CME区cSLO视网膜成像的伪彩成像、IR反射像和绿光反射像清晰度平均评分分别为3．21±0．78、2．67±0．96和2．54±0．83，均明显高于传统彩色眼底照相的1．33±0．82，差异均有统计学意义（均P〈0．01）。结论cSLO视网膜成像技术对CME的成像质量明显优于传统彩色眼底照相，结合SD-OCT断层扫描图像可以为CME的诊断和病情监测提供更加全面的信息。

光学相干层析医学图像处理及其应用

由于人工分析光学相干层析(OCT)图像费时费力、主观及可重复性差,因而快速、精确与客观地检测与量化生物特征标记是OCT医学图像研究与疾病诊断的关键。本文综述了光学相干层析(OCT)医学图像处理技术与应用的研究进展。介绍了OCT成像技术的特点及其主要应用,OCT图像处理的难点、基本问题及主要研究内容;讨论了对时域OCT和频域OCT图像降噪、图像分类与图像分割的重要方法及应用,并分析了各种方法的优缺点及研究发展方向。此外,介绍了偏振敏感光学相干层析(PS-OCT)在医学图像分析中的应用。文中讨论的应用对象涉及到视网膜、角膜、冠脉、前列腺、牙齿、食道、结肠、膀胱、皮肤、乳腺等组织,可为人们综合了解OCT图像处理及其应用现状提供丰富的信息。

融合多种先验信息的光学层析图像重建

为克服光学层析成像的病态特性,将三种不同的先验信息模型引入到基于辐射传输方程的光学层析成像中,给出了对应于三种重建模型的重建算法,其中在线过程作为先验信息的重建算法中,提出一种神经网络优化算法。最后对这三种先验信息模型进行了综合比较和讨论,并在图像的平滑性、边缘保留特性、算法复杂性及重建效果方面对其进行定量比较,提出一种分析平滑性的算子和一种基于梯度的衡量边缘保留特性的算子。实验证明基于三种先验信息模型的重建算法均能提高重建图像质量,其中,平滑先验模型的平滑效果最好,马尔可夫随机场模型有较好的边缘保留特性,线过程模型在平滑图像的同时可以更好地保留图像边缘,并且重建精度较高。

宝石能谱CT在去金属体内植入物伪影中的应用

目的探讨宝石能谱CT在去金属体内植入物伪影中的应用。方法对28例有金属体内植入物的患者行能谱扫描,行容积再现(VR)、多平面重建技术(MPR)及最大密度投影(MIP)后处理。结果 VR、MPR、MIP后处理后所得图像均满足影像诊断的需要,影像质量优良率高达90%。结论宝石能谱CT能有效去除金属体内植入物伪影,在去金属体内植入物伪影中显示局部解剖结构起到不可替代的作用。