基于温度不敏感源-探测器距离的测量方法的模拟研究

温度变化是影响近红外无创血糖测量精度的主要因素之一。为降低温度变化对近红外漫反射光谱的影响,提出了一种基于温度不敏感源-探测器距离的测量方法,即在漫反射光强对人体组织温度变化不敏感的源-探测器距离处进行光谱测量。利用Monte Carlo方法模拟了温度为30～40 ℃、葡萄糖浓度为0～300 mmol·L-1的皮肤组织在多个源-探测器距离处的漫反射光强。根据模拟结果,分析了人体皮肤组织模型中温度不敏感源-探测器距离的存在性及其受葡萄糖浓度变化的影响;比较了1 000 nm处温度恒定和温度变动时,不同源-探测器距离处漫反射光强与葡萄糖浓度的相关性;进一步地,利用六个波长(1 000,1 050,1 100,1 150,1 350和1 410 nm)下的温度不敏感源-探测器距离及其他距离处的漫反射光强,建立了葡萄糖的偏最小二乘(PLS)模型,并比较了这些模型在温度恒定和温度变动时的预测精度。结果表明,在1 000～1 440 nm范围内,人体存在温度不敏感源-探测器距离,且葡萄糖浓度变化对该距离的影响可以忽略不计;当组织温度变化时,温度不敏感源-探测器距离处的漫反射光强与葡萄糖浓度的相关性及建模效果均明显优于其他源-探测器距离,基本接近样品温度恒定时的情况。研究表明,基于温度不敏感源-探测器距离的测量方法能有效降低温度变化对漫反射光强的影响,有望提高近红外漫反射无创血糖测量的精度。     

银纳米链状材料的制备及近红外吸收性质

报道了利用水/油相界面反应,采用湿化学法合成银纳米链状材料的方法,并对这种材料的近红外吸收性质和光热转换性质进行了研究。TEM分析表明,银纳米材料为链状结构,直径约为50nm,长度分布范围较宽,从几十纳米至几百纳米。这种材料具有强的近红外吸收特性,随着还原剂加入量的增加,吸收带逐渐展宽(800～1300nm),而且平坦。这种材料具有优异光热转换性质,一经808nm激光照射,温度迅速提高。该材料优异的近红外吸收和光热转换性质,使其在红外断层成像和近红外热疗等领域具有广阔的应用前景。     

Time-resolved reflectance at null source-detector separation: improving contrast and resolution in diffuse optical imaging

We propose a novel approach to imaging in diffusive media based on time-resolved reflectance measurements at null source-detector separation. This approach yields better spatial resolution and contrast as compared to the classical approach, which typically employs a separation of 20-40 mm. Results are obtained by an analytical perturbation approach to diffusion theory and on Monte Carlo simulations. Practical implementation with state-of-the-art technology and performance of a complementary approach based on the use of small but not null source-detector separation are also discussed.     

Near-infrared dyes as contrast-enhancing agents for spectroscopic optical coherence tomography

Optical coherence tomography (OCT) images of biological tissues often have low contrast. Spectroscopic optical coherence tomography (SOCT) methods have been developed to enhance contrast but remain limited because most tissues are not spectrally active in the frequency bands of laser sources commonly used in OCT. Near-infrared (NIR) dyes with absorption spectra features within the OCT source spectrum can be used for enhancing contrast in this situation. We introduce and demonstrate the use of NIR dyes as contrast agents for SOCT. Contrast-enhanced images are compared with fluorescence microscopy, demonstrating a link between SOCT and fluorescence imaging.     

High-resolution near-infrared tomographic imaging simulations of the rat cranium by use of a priori magnetic resonance imaging structural information

Near-infrared (NIR) optical image reconstruction that incorporates magnetic resonance image (MRI) structural data was tested in a series of simulated reconstructions. NIR diffuse tomography generally suffers from comparatively low spatial resolution. By using the fine structural detail that is available with MRI, combined with the functional information of NIR spectroscopy, it is possible to design a new image-reconstruction methodology that provides high-resolution images that are correlated with hemoglobin concentration and oxygen saturation. To test this concept a MRI spin-echo image of a rat cranium was used to obtain an outline of the bone, brain, and muscle tissues, and this information was incorporated into an iterative-based diffuse tomography reconstruction. These simulations represent what is believed to be the first attempt at evaluating a spatially constrained iterative-reconstruction MRI-NIR imaging modality for brain tissue.     

Rapid Clearance of IR783 and Methyl-β-cyclodextrin Complex for Improved Tumor Imaging

Near-infrared (NIR) fluorescence cancer imaging with targeted NIR fluorophores holds considerable promise for accurate detection and cancer diagnosis. Among the various NIR heptamethine cyanine dyes reported previously, IR783 as a single small molecule has been widely used for tumor-targeted imaging without the additional conjugation of targeting moieties. Despite the potential advantages of IR783, the major problems, such as its non-specific uptake in normal tissues/organs and slow clearance, remain to be solved. A key determinant of sensitivity and detectability in tumor imaging is the improvement of the tumor-to-background ratio (TBR). Herein, a simple and effective supramolecular complex self-assembled from IR783 and methyl-β-cyclodextrin is developed to improve tumor imaging accompanied by rapid clearance from the body. The IR783-cyclodextrin complex allowed for rapid whole body biodistribution, which remarkably reduced non-specific background uptake, and thus increased the TBR value within 24 h post-injection. Therefore, this strategy is applicable in combination with many different types of carbocyanine dyes for improved tumor imaging.     

Video-rate near-infrared optical tomography using spectrally encoded parallel light delivery

A novel parallel source implementation approach to near-infrared tomography is demonstrated through spectral encoding of the light delivery. This new technique allows many sources to be input into the tissue at the same time, and a high-resolution spectrometer is used to spatially spread out the signals from each spectrally encoded source. The parallel sampling of all sources at all detection locations renders rapid imaging. Acquisition of complete tomographic data sets at a video rate of 35 frames/s is achieved for imaging of a 6.35 mm diameter inclusion with an absorption coefficient of 0.01 mm(-1) and a reduced scattering coefficient of 1.5 mm(-1) that is moving along a circular path inside a 1% Intralipid solution.     

空间分辨光谱和可见/近红外光谱的番茄颜色等级判别

比较分析空间分辨光谱和单点可见/近红外光谱（可见/短波近红外光谱和中波近红外光谱）对番茄颜色的识别能力。根据番茄表面和内部颜色将600个样品分为6个等级（green, breaker, turning, pink, light red和red）。分别利用新型空间分辨光谱系统（550~1 650 nm）,可见/短波近红外光谱仪（400~1 100 nm）和中波近红外光谱仪（900~1 700 nm）采集番茄的空间分辨（spatially-resolved, SR）光谱和单点可见/近红外（SP Vis/NIR）光谱,建立番茄等级的偏最小二乘判别（PLSDA）模型,比较其对番茄颜色等级的预测效果。结果表明, SR光谱组合可在最佳单一SR光谱基础上进一步提高番茄颜色的识别能力,对番茄表面颜色和内部颜色的识别率可分别达到98.8%和84.6%。光源-检测器距离较近的SR光谱对番茄表面颜色的识别有帮助,而光源-检测器距离较远的SR光谱能较好的判别番茄内部颜色。SP NIR光谱在对番茄表面颜色判别中与SR光谱具有一定可比性,其分类准确率可达到95%,但SP Vis/NIR光谱在对番茄内部颜色识别中具有较低的分类准确率,分类结果远不如SR光谱,说明SR光谱比SP Vis/NIR光谱对番茄颜色的判别更具潜力。     

Near-Infrared Imaging Using a High-Speed Monitoring Near Infrared Hyperspectral Camera(Compovision)

This review paper reports near-infrared (NIR) imaging studies using a newly-developed NIR camera, Compovision. Compovision can measure a significantly wide area of 150 mm×250 mm at high speed of between 2 and 5 s. It enables a wide spectral region measurement in the 1 000～2 350 nm range at 6 nm intervals. We investigated the potential of Compovision in the applications to industrial problems such as the evaluation of pharmaceutical tablets and polymers. Our studies have demonstrated that NIR imaging based on Compovision can solve several issues such as long acquisition times and relatively low sensitivity of detection. NIR imaging with Compovision is strongly expected to be applied not only to pharmaceutical tablet monitoring and polymer characterization but also to various applications such as those to food products, biomedical substances and organic and inorganic materials.     

Transport-based image reconstruction in turbid media with small source-detector separations

We demonstrate a new method for imaging through several millimeters of a turbid sample with a resolution of approximately 100 mum by combining aspects of confocal reflectance microscopy and diffuse optical tomography. By laterally displacing the pinhole aperture of a confocal microscope we can achieve small source-detector separations and detect minimally scattered light. A reconstruction algorithm based on the first Born approximation to the radiative transport equation is then used to reconstruct an image of a 100-mum absorbing object located 2 mm beneath the surface.     

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.     

Depth-adaptive regularized reconstruction for reflection diffuse optical tomography

We study reflection diffuse optical tomography using two-dimensional (2D) continuous-wave source-detector arrays on the surface of semi-infinite medium, aiming at imaging the perfusion and the hemoglobin oxygen saturation variation of human cerebral cortex with brain activation. We had previously formulated the inverse problem with Moore-Penrose inversion. When we use simple regularization in this inverse problem, the reconstruction sensitivity decreases markedly with the depth so that the signal in the deep range may be masked by an unwanted signal in the shallow range. In this paper, we propose a depth-adaptive regularized reconstruction, in which we assign a smaller regularization parameter with the depth. We demonstrate improvement of the three-dimensional (3D) reconstruction uniformity using the proposed scheme.     

Analysis of Light Propagation in a Three-Dimensional Realistic Head Model for Topographic Imaging by Finite Difference Method

Near infrared topographic imaging is a novel non-invasive technique to obtain the activated region in the brain cortex. The light propagation in the head is strongly scattered and this causes results in poor spatial resolution and contrast in the topographic images. Adequate modelling of light propagation in the head in order to deduce the volume of tissue interrogated by a source-detector pair for topographic imaging is very important to improve the quality of image of brain activity. In this study, the light propagation in a three-dimensional realistic head model is calculated by the finite difference method. The geometry of the model is generated from axial slices of an MRI scan. The topographic image is obtained from the change in intensity detected by source-detector pairs caused by the brain activity. The images obtained by two types of source-detector arrangement are compared to evaluate the efficiency of source-detector arrangement. The results show that the double-density arrangement improves the quality of the topographic image of the brain activity.     

Rapid magnetic resonance-guided near-infrared mapping to image pulsatile hemoglobin in the breast

A near-IR (NIR) tomography system with spectral-encoded sources was built to quantify the temporal contrast in human breast tissue using guidance from magnetic resonance imaging. The systems were integrated with a custom breast coil interface to provide simultaneous acquisition. The NIR signal was synchronized to simultaneous finger pulse oximeter plethysmogram, which offered a frequency reference. A 0.1 s temporal delay of the absorption pulse within adipose tissue relative to fibroglandular tissue was found, in an initial human study, showing the potential for novel contrast imaging of fast flow signals in deep tissue.     

Forward imaging OCT endoscopic catheter based on MEMS lens scanning

This Letter reports a fully packaged microelectromechanical system (MEMS) endoscopic catheter for forward imaging optical coherence tomography (OCT). Two-dimensional optical scanning of Lissajous patterns was realized by the orthogonal movement of two commercial aspherical glass lenses laterally mounted on two resonating electrostatic MEMS microstages at low operating voltages. The MEMS lens scanner was integrated on a printed circuit board and packaged with an aluminum housing, a gradient index fiber collimator, and an objective lens. A home-built spectral-domain OCT system with 60 kHz A-line acquisition rate was combined with the endoscopic MEMS catheter. Three-dimensional images of 256×256×995 voxels were directly reconstructed by mapping the A-line datasets along the Lissajous patterns. The endoscopic catheter can provide a new direction for forward endoscopic OCT imaging.     

Near-infrared laser scanning confocal microscopy and its application in bioimaging

Near-infrared (NIR) fluorescence imaging is an important imaging technology in deep-tissue biomedical imaging and related researches, due to the low absorption and scattering of NIR excitation and/or emission in biological tissues. Laser scanning confocal microscopy (LSCM) plays a significant role in the family of fluorescence microscopy. Due to the introduction of pinhole, it can provide images with optical sectioning, high signal-to-noise ratio and better spatial resolution. In this study, in order to combine the advantages of these two techniques, we set up a fluorescence microscopic imaging system, which can be named as NIR-LSCM. The system was based on a commercially available confocal microscope, utilizing a NIR laser for excitation and a NIR sensitive detector for signal collection. In addition, NIR fluorescent nanoparticles (NPs) were prepared, and utilized for fluorescence imaging of the ear and brain of living mice based on the NIR-LSCM system. The structure of blood vessels at certain depth could be visualized clearly, because of the high-resolution and large-depth imaging capability of NIR-LSCM.     

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.     

Applying LED in full-field optical coherence tomography for gastrointestinal endoscopy

Optical coherence tomography (OCT) has become an important medical imaging technology due to its non-invasiveness and high resolution. Full-field optical coherence tomography (FF-OCT) is a scanning scheme especially suitable for en face imaging as it employs a CMOS/CCD device for parallel pixels processing. FF-OCT can also be applied to high-speed endoscopic imaging. Applying cylindrical scanning and a right-angle prism, we successfully obtained a 360° tomography of the inner wall of an intestinal cavity through an FF-OCT system with an LED source. The 10-μm scale resolution enables the early detection of gastrointestinal lesions, which can increase detection rates for esophageal, stomach, or vaginal cancer. All devices used in this system can be integrated by MOEMS technology to contribute to the studies of gastrointestinal medicine and advanced endoscopy technology.     

Diffuse optical tomography: Present status and its future

Diffuse optical tomography (DOT) is one of the emerging modalities for the non-invasive imaging of thick biological tissues using near-infrared (NIR) light. This article reviews the fundamentals and development of DOT technology since its advent in the early 1990s, including the modeling of light propagation in biological tissues which strongly scatter and weakly absorb NIR light, the optical properties of biological tissues in the NIR wavelength range, three typical measurement methods, image reconstruction algorithms, and so forth. Then various studies are referred to for improvement of the DOT images, which are essentially low in quality due to the ill-conditioned and underdetermined problem. Studies and clinical applications presently attracting much attention are discussed in some detail. Finally, the expected future developments are summarized.     

Fiber-optic-bundle-based optical coherence tomography

A fiber-optic-bundle-based optical coherence tomography (OCT) probe method is presented. The experimental results demonstrate this multimode optical fiber-bundle-based OCT system can achieve a lateral resolution of 12 microm and an axial resolution of 10 microm with a superluminescent diode source. This novel OCT imaging approach eliminates any moving parts in the probe and has a primary advantage for use in extremely compact and safe OCT endoscopes for imaging internal organs and great potential to be combined with confocal endoscopic microscopy.