功能近红外光谱在大脑成像中的研究及应用

近红外光谱的650~1000 nm是大脑成像的"光学窗口",功能近红外光谱技术对大脑成像具有非侵入、无需注射造影剂、成本低和方便等优点,被应用于脑成像。概述了近红外光谱在大脑成像中的原理、方法及发展,总结分析了功能近红外光谱技术对大脑探测在提高系统分辨率方法的3个主要阶段,提出了存在的问题和发展前景。     

光学成像帮助监控新生婴儿

近红外辐射能够对软组织和血液进行成像，并用于临床研究和癌症检测。Paula Gould解释这项技术在不久的将来是如何用于监 控早产儿的大脑。伦敦大家的科学家们正在准备在一个高度复杂和精密的系统——人类婴儿上测试的新型光学成像仪。伦敦大学由David Delpy领导的生物光学研究小组已经设计了一台高技术的成像仪，专门用于早产的和临危的新生婴儿。使用近红外辐射，他们希望将在忍受强烈的焦虑情绪时婴儿大脑组织的氧化和活动进行成像。因为光学成像是无创伤性的，且没有电离辐射，所以它非常适合于对虚弱病人的持续监控。这项技术依赖在…     

近红外光学膜厚监控系统的研制

在光学真空镀膜膜厚监控过程中,近红外波段信号弱、外界干扰大、信噪比低,难于检测监控.运用相干检测、锁相放大原理,在光学真空镀膜机可见光波段监控系统的基础上,研制了锁相放大器和改装近红外探头组成的近红外光学膜厚监控系统,成功实现近红外膜厚监控信号的压噪、放大、滤波和检测监控.     

红外硒基硫系玻璃光学非均匀性及影响因素分析

针对Ge-Sb-Se硫系玻璃光学非均匀性(内部条纹、裂纹、气泡、均匀性等)检测与表征的困难,提出了一种利用样品的近红外透射图像、及中红外线扩散函数和调制传递函数(MTF)并举表征其光学非均匀性的新方法,并建立了相应的检测装置。在此基础上,对自制的Ge28Sb12Se60(mol%)硫系玻璃样品进行了内部缺陷和光学均匀性测试,并比较分析了样品平面度与平行度对实验结果的影响。结果表明,近红外透射成像能清晰地检测到样品内部的条纹分布和缺陷;中红外线扩散函数和MTF可半定量地表征样品的光学非均匀特性;当表面光圈小于1时,均匀Ge-Sb-Se硫系玻璃样片的线扩散函数呈高斯分布,MTF实验值与理论值相近且平均值相差小于10%。     

矿井瓦斯光学遥测新技术

介绍了一种遥测低浓度甲烷气体的完全光学方法。遥测系统的实验装置由1.33μm 高辐射 InGaAsP LED、气体吸收室以及2km 长的低损耗石英光纤网络组成。实验结果表明空气中甲烷的检测极限约为2 000ppm,即甲烷爆炸下限(LEL)的4%。这个结果证明由近红外 LED 或 LD 和超低损耗石英光纤网络组成的完全光学甲烷遥测系统完全适用于煤矿井下的瓦斯检测。     

光学医学成像实验技术综述：I——直接成像法

近红外光辐射医学成像研究已经愈来愈受到重视。光学成像法与现有的辐射成像方法相比具有辐射是非电离的；可以区分软组织；能够得到组织体功能信息等优点，因此光学医学成像法可作为连续成像的检测仪器应用在乳癌诊断、新生儿脑部含氧或缺氧分析、成人组织功能的检测等医学领域。本文综述了近红外光辐射医学成像研究的实验技术之一 直接成像法     

近红外光谱(NIRS)技术的大鼠胶质瘤活体在位检测研究

采用一套专门设计的由微创光纤探头组成的光纤光谱仪生物组织光学参数测试系统,实时在位地获取C6胶质瘤大鼠脑组织的近红外光学参数,探讨以此为指标判别肿瘤基本信息、辅助临床诊断的可能性.利用该测试系统对患有C6胶质瘤的大鼠脑部肿瘤侧和正常侧进行近红外光谱检测.实验结果表明:优化散射系数和血氧饱和度可反映肿瘤位置及病理分化程度信息.证实近红外微探针技术对胶质瘤定性诊断是可行的,为近红外光谱技术临床应用打下基础.     

简讯

用于检测胸腔癌的便携式近红外漫射光成像仪据美国《JournalofBiomedicalOptics》报道,美国康涅狄格大学的研究人员研制了一种频域近红外光学断层扫描系统。这种断层扫描系统是设计用来与常规的超声方法一同进行胸腔癌检测的。其特点是,光学     

磁共振辅助的近红外扩散光学断层成像

将大脑磁共振T1加权像分割为头皮、头骨、脑脊液、灰质和白质,并生成分层体网格.利用具有大脑解剖结构信息的分层体网格建立近红外扩散光学断层成像前向光学模型和实现功能重建,可以避免目前所使用的半球头模或图谱头模空间定位不准的问题,解决图像重建过程中所解方程的欠定性和病态性.在棋盘格旋转视觉刺激及扩张视觉刺激实验中,基于磁共振图像的扩散光学断层成像重建的含氧血红蛋白图像具有更高的空间分辨率及定位精度.     

光学瞄具宽光谱透射率检测及误差影响因素分析

透射率参数是评价光学瞄具成像亮度和清晰程度的重要参数,介绍了一种高精度的光学瞄具宽光谱透射率的检测系统。针对检测过程中影响检测精度的因素包括偏振的敏感性、光束偏移、系统的杂散光、探测器的非线性和空间均匀性,结合验证实验和光学模拟软件(tracepro)给出定量的分析以及仪器的合成不确定度。对于探测器非线性误差利用最小二乘法原理予以修正。标定实验表明,可见光波段的透射率测量误差小于0.35%,近红外波段透射率测量误差小于0.65%。     

Noninvasive measurement of regional cerebral blood flow change with H(2)(15)O and positron emission tomography using a mechanical injector and a standard arterial input function

To estimate changes in regional cerebral blood flow (rCBF) without arterial sampling in the study of functional-anatomical correlations in the human brain, using (15)O-labeled water and PET, a standard arterial input function was generated from the input function in 10 normal volunteers with dose calibration and peak time normalization. The speed and volume of injection were precisely controlled with a mechanical injector. After global normalization of each tissue activity image, the standard arterial input function was applied to obtain estimated CBF images. Relative changes in estimated rCBF to whole brain mean CBF(DeltaFest) and those in regional tissue activity (DeltaC) were compared with true relative rCBF changes (DeltaF) in 40 pairs of images obtained from 6 normal volunteers. DeltaFest correlated well with DeltaF, whereas DeltaC consistently underestimated DeltaF. This noninvasive method simplifies the activation studies and provides the accurate estimation of relative flow changes.     

Mathematical model for the hemodynamic response to venous occlusion measured with near-infrared spectroscopy in the human forearm

We propose a mathematical model to describe the hemodynamic changes induced by a venous occlusion in a human limb. These hemodynamic changes, which include an increase in blood volume, a reduction in blood flow, and modifications to the oxygen saturation of hemoglobin, can all be measured noninvasively with near-infrared spectroscopy (NIRS). To test the model, we have performed NIRS measurements on the human forearm, specifically on the brachioradialis muscle, during venous occlusion induced by a pneumatic cuff inflated around the upper arm to pressures within the range 10-60 mmHg. We have found a good agreement between parameters measured by NIRS (total hemoglobin concentration and hemoglobin saturation) and the corresponding model parameters (capacitor voltage and arterial/capillary branch current). In particular, model and experiment indicate that the time constant for blood accumulation during venous occlusion (approximately 73-79 s) is much slower than the time constant for blood drainage following cuff release (approximately 5 s). These results indicate that this mathematical model can be a valuable analytical tool to characterize, optimize, and further develop diagnostic measurement schemes that use venous occlusion approaches.     

Optimal design of a thermistor probe for surface measurement ofcerebral blood flow

Microthermistors are put on the surface of cerebral cortex to monitor local cerebral blood flow (CBF) continuously with minimal tissue damage and disturbance to the normal physiological state. Using a distributed, dynamic model of the measurement system, we simulated the effects of this flow measurement method under isothermal and adiabatic boundary conditions. Numerical results show that the adiabatic boundary condition can provide maximal sensitivity to perfusion changes at physiological perfusion levels. The constant power and constant temperature operating modes are compared in terms of output relation, sensitivity, and frequency response through analytical and numerical solutions. While the steady-state relations between thermistor measurements and perfusion for the two modes do not differ significantly, the constant temperature mode has better frequency response. Analytical results show that the relative sensitivity is the same for the two modes and is approximately proportional to the radius of thermistor. If there is an unperfused layer surrounding the thermistor, the sensitivity will decrease as the thickness of the layer increases. Simulations predict that the thermal measurement has a low-pass frequency response and the cutoff frequency is inversely proportional to the probe surface area. The results provide a theoretical foundation to the optimal design of thermistor probe for continuous CBF measurement from tissue surface.     

Effect of 805 nm on reliability of 735/805/850-nm LED involved near-infrared spectroscopy biomedical device

Near-infrared spectroscopy (NIRS) has been widely used in biomedicine due to its capability of noninvasively detecting hemodynamic variations in relative deep tissue. Most NIRS devices utilized multiple-wavelengths integrated LED as the sources, of which the 735/805/850-nm LED was mostly employed. As we known, the 735/850-nm combination is enough for quantifying the changes of oxy-hemoglobin (∆ HbO₂) and deoxy-hemoglobin (∆ Hb). Then how is the effect of the wavelength 805 nm of 735/805/850-nm LED on the measurement reliability? Here we performed blood model experiments with 57 human blood samples and recorded optical density variations at above 3 wavelengths. Both of the least squares method and multi-variable linear regression analysis were used to quantify ∆ HbO₂ and ∆ Hb with three-wavelength combination (735/805/850-nm) and two-wavelength combination (735/850-nm) respectively. By comparing the quantified values with the real values, we found that the results obtained from 735/850-nm combination are more close to reality than the 735/805/850-nm combination. This study reported, for the first time, that 805 nm actually took a negative effect on measurement reliability of NIRS. It indicates to get rid of 805 nm from such LED design to reduce the LED cost and get higher reliability for NIRS instrumentation.     

用多层Monte—Carlo模型研究脑部光学无损的问题

利用近红外光对人脑进行无损检测有良好的应用前景。然后脑部客观存在的多层结构使人位对从较深部位提取有用信息产生疑问。本文利用Ｍｏｎｔｅ－Ｃａｒｌｏ方法对人头部建立了光传播的多层模型,对光在头部的传播模式和脑部结构对提取深部信息的影响得出了一些结果,本文结果表明,由于脑脊液透明层的存在,使近红光在头部能够探测较深部位珠生理参数变化但难于获得较好的空间分辨能力。     

Characterization of dynamic 3-D PET imaging for functional brainmapping

Methods for optimizing the acquisition, reconstruction and analysis of positron emission tomography (PET) images for functional brain mapping have been investigated. The scatter fraction and noise-equivalent count rate characteristics were measured for the ECAT 951/31R PET scanner operating in septa-extended two-dimensional (2-D) and septa-retracted three-dimensional (3-D) modes. The 3-D mode is shown to provide higher signal-to-noise images than the 2-D mode at specific activities less than 30 kBq/ml. To enable increased temporal resolution in dynamic 3-D PET activation studies, a parallel version of the 3-D reconstruction algorithm was developed. Implementation of the reprojection algorithm on an 88 processor i860 supercomputer resulted in a more than tenfold increase in reconstruction speed compared to a single i860 processor system. An investigation of the optimal duration for imaging brain activations was undertaken in 12 normal subjects using repeated H₂¹⁵O slow infusions and a visually presented lexical decision task. The significance of change in regional cerebral blood flow (CBF) was determined using statistical parametric maps for images acquired during stimulation, immediately after stimulation, and commencing 1 min after cessation of the stimulus. Regions of CBF change were detected in all three images. Dynamic 3-D, or four-dimensional (4-D), PET activation scanning is shown to be practical and likely to further improve the sensitivity of PET for detection of subtle regional CBF changes in functional brain mapping research     

A mathematical model of cerebral blood flow chemical regulation. I.Diffusion processes

This paper proposes a mathematical model which describes the production and diffusion of vasoactive chemical factors involved in oxygen-dependent cerebral blood flow (CBF) regulation in the rat. Partial differential equations describing the relations between input and output variables have been replaced with simpler ordinary differential equations by using mathematical approximations of the hyperbolic functions in the Laplace transform domain. This model is composed of two submodels. In the first, oxygen transport from capillary blood to cerebral tissue is analyzed to link changes in mean tissue oxygen pressure with CBF and arterial oxygen concentration changes. The second submodel presents equations describing the production of vasoactive metabolites by cerebral parenchyma, due to a lack of oxygen, and their diffusion towards pial perivascular space. These equations have been used to simulate the time dynamics of mean tissue PO2, perivascular adenosine concentration, and perivascular pH to changes in CBF. The present simulation points out that the time delay introduced by diffusion processes is negligible if compared with the other time constants of the system under study. In a subsequent work the same equations will be included in a model of the cerebral vascular bed to clarify the metabolite role in CBF regulation.     

Imaging the Cerebral Blood Flow With Enhanced Laser Speckle Contrast Analysis (eLASCA) by Monotonic Point Transformation

Laser speckle contrast analysis (LASCA) has been demonstrated as a full-field method for imaging the cerebral blood flow (CBF). However, conventional LASCA is limited to extremely low dynamic range because of the ambient background field, dark current, and other anomalies in the circuits of a charge-coupled device camera, which makes it difficult to analyze the spatiotemporal variabilities in CBF. In this study, we proposed an enhanced LASCA (eLASCA) method to improve the dynamic range of LASCA based on monotonic point transformation. In investigating the influence of moderate hypothermia ($hbox{32}pm hbox{0.5};^circ$ C) on capillary CBF change, eLASCA presented much more significant decrease of relative CBF than LASCA (hypothermia: 189% versus 137%, postrewarming: 151% versus 119%). Statistically, eLASCA resulted in a higher confidence degree ( $p=0.009$) of CBF change after the rewarming than LASCA ( $p=0.013$). In addition, eLASCA greatly improves the CBF visualization, which is very helpful in demonstrating the details of CBF change.      

A reliable integrative autocorrelator device for particle fluctuation rate monitoring

The monitoring of particle fluctuation rate is of great importance in the biomedical field, especially in applications concerning the near-infrared spectroscopy (NIRS) monitoring of blood flow. Blood flow is one of the most important indexes to estimate the body functional status, while the existing technologies for its measurements have some limitations. NIRS is non-invasive, continuous real-time, applicable to blood flow monitoring of a variety of vessel sizes and deeper depths. Autocorrelation module, which is capable of processing optical signals and getting blood flow data with the upper computer module, is an important part of near-infrared monitoring blood flow method. In this study, we integrated the upper computer module into the autocorrelator device, reduced man-made errors caused by multiple modules, and made the device more convenient and reliable. We also tested its performance and reliability. The result showed that the device has great potentiality in measuring the particle fluctuation rate conveniently, accurately and reliably. In future, the device will be tested in noninvasive clinic trials to verify its monitoring effects.     

A mathematical model of cerebral blood flow chemical regulation.II. Reactivity of cerebral vascular bed

In the present paper an original mathematical model of the chemical oxygen-dependent cerebral blood flow (CBF) regulation in the rat is proposed. Taking into account recent experimental works, the model assumes that oxygen acts on cerebral vessels through an indirect mechanism, mediated by the release of two metabolic substances (adenosine and H+) from tissue, and that any change in perivascular concentration of these substances affects the diameter of both the medium and small pial arteries as well as of intracerebral arterioles. The model is composed of several submodels, each closely related to a different physiological event. mathematical equations, which describe the reaction of the vasoactive portion of the cerebral vascular bed, are reported in detail and justified. The model permits the simulation of the role played by chemical factors in the control of CBF under many different physiological and pathological conditions in an attempt to clarify their relevance. Several events associated with an alteration in oxygen supply to tissue (auto-regulation to changes in arterial and venous pressure, reactive hyperemia following on cerebral ischemia, arterial hypoxia) have been simulated with the model. The results suggest that chemical factors, adenosine and H+, play a significant but not exclusive role in the regulation of the cerebral vascular bed. The action of other mechanisms (which are probably neurogenic) must be hypothesized to explain completely the CBF changes occurring in vivo.