Sonophoretic Delivery for Contrast and Depth Improvement in Skin Optical Coherence Tomography

Our previous studies demonstrated the feasibility of using a sonophoretic delivery method to enhance skin light transmittance with topical application of optical clearing agents using spectroscopy. In this study, we examined the effect of ultrasound [surgeon-performed (SP)] on optical coherence tomography (OCT) imaging depth and contrast of in vitro and in vivo skin. Sixty percent glycerol (G) and SP with a frequency of 1 MHz and a power of 0.75 W over a 3 cm probe was simultaneously applied for 15 min. We find that 60% G/SP results in a twofold increase in achievable OCT imaging depth for in vitro porcine skin and induces 11% shrinkage of the skin. For in vivo human skin, OCT imaging depth and contrast is significantly improved within 30 min of treatment. Imaging depth is increased from 1.4 to 2 mm, and dermal vasculature is clearly visualized in the deeper tissue. OCT imaging of the skin treated with 60% glycerol shows little enhancement in contrast or imaging depth over 60 min. We first demonstrate the superb ability of sonophoretic delivery for in vivo human skin optical clearing, particularly in accelerating the clearing rate. The greater clearing efficiency of glycerol implemented with ultrasound may be attributed to more effective dehydration.     

The effect of light losses in double integrating spheres on opticalproperties estimation

The double integrating sphere setup (DIS) measures diffuse reflectance, diffuse transmittance and collimated transmittance, from which the optical properties of tissue (the absorption coefficient μ _a, the scattering coefficient μ_s and the anisotropy of scattering g) are estimated. The effect of light losses in the DIS and optical thickness on optical properties estimation by the inverse adding doubling algorithm (IAD) and uniqueness of measurement have been investigated using a Monte Carlo method. Results were obtained for optical properties in turbid tissues (0.80⩽albedo⩽0.99, 0.80⩽anisotropy⩽ 0.99, 1.5⩽optical thickness⩽7.5) sandwiched between glass slides. At optical thickness=6.0 the loss of light through the glass slides is ranging from 13%±0.5% (at albedo=0.80) to 15%±0.5% (at albedo=0.98) of the incident power. The loss of light at the exit port in the transmittance sphere is increasing up to 50% of the incident power at highly forward scattering. These losses result in a dependency on optical thickness of the optical properties estimation by the IAD algorithm. Furthermore, because of these losses, the DIS setup measurement is found to be fundamentally nonunique, when simultaneously measuring the diffuse reflectance, diffuse transmittance and collimated transmittance     

Effects of compression on soft tissue optical properties

Tissue optical properties are necessary parameters for prescribing light dosimetry in photomedicine. In many diagnostic or therapeutic applications where optical fiber probes are used, pressure is often applied to the tissue to reduce index mismatch and increase light transmittance. In this paper, we have measured in vitro optical properties as a function of pressure with a visible-IR spectrophotometer. A spectral range of 400-1800 mm with a spectral resolution of 5 nm was used for all measurements. Skin specimens of a Hispanic donor and two Caucasian donors were obtained from the tissue bank. Bovine aorta and sclera, and porcine sclera came from a local slaughter house. Each specimen, sandwiched between microscope slides, was compressed by a spring-loaded apparatus. Then diffuse reflectance and transmittance of each sample were measured at no load and at approximately 0.1, 1, and 2 kgf/cm². Under compression, tissue thicknesses were reduced up to 78%. Generally speaking, the reflectance decreased while the overall transmittance increased under compression. The absorption and reduced scattering coefficients were calculated using the inverse adding doubling method. Compared with the no-load controls, there was an increase in absorption and scattering coefficients among most of the compressed specimens     

Determination of epithelial tissue scattering coefficient using confocal microscopy

Most models of light propagation through tissue assume the scattering properties of the various tissue layers are the same. The authors present evidence that the scattering coefficient of normal cervical epithelium is significantly lower than values previously reported for bulk epithelial tissue. They estimated the scattering coefficient of normal and precancerous cervical epithelium using measurements of the reflectance as a function of depth from confocal images. Reflectance measurements were taken from ex vivo cervical biopsies and fit to an exponential function based upon Beer's law attenuation. The mean scattering coefficients derived were 22 cm/sup -1/ for normal tissue and 69 cm/sup -1/ for precancerous tissue. These values are significantly lower than previously reported for bulk epithelial tissues and suggest that scattering of bulk tissue is dominated by the stroma. They also suggest that computational models to describe light propagation in epithelial tissue must incorporate different scattering coefficients for the epithelium and stroma. Further, the lower scattering of the epithelium suggests greater probing depths for fiber optic probes used by optical diagnostic devices which measure reflectance and fluorescence in epithelial tissue. The difference in scattering between normal and precancerous tissue is attributed to increased nuclear size, optical density, and chromatin texture. The scattering coefficients measured here are consistent with predictions of numerical solutions to Maxwell's equations for epithelial cell scattering.     

Accurate measurement of total attenuation coefficient of thin tissue with optical coherence tomography

Noninvasive accurate measurements of tissue optical properties are needed for many diagnostic and therapeutic applications. Optical coherence tomography (OCT) recently proposed for high-resolution imaging in tissue can potentially be applied for accurate, noninvasive, and high-resolution measurement of tissue total attenuation coefficient. However, confocal function (dependence of OCT sensitivity on the distance of probed site from the focal plane of the objective lens) and multiple scattering substantially limit the accuracy of the measurement with the OCT technique. We studied the influence of the confocal function and multiple scattering on the accuracy of the measurement and proposed methods that provide measurement of the total attenuation coefficient with a significantly reduced systematic error. Experiments were performed in tissue phantoms and porcine and human skin in vitro and in vivo. Our data indicate that the tissue total attenuation coefficient can noninvasively be measured in vivo with the accuracy of 5%-10% in the range from 0.5 to 17 mm/sup -1/ and about 20% in the range up to 40 mm/sup -1/. These results suggest that the proper correction of the OCT-based measurement for the confocal function and multiple scattering provides absolute values of tissue total attenuation coefficient with high accuracy and resolution that may not be achievable by other optical techniques in vivo.     

Optical and electrical properties of ZnO thin film containing nano-sized Ag particles

Low-temperature crystallized ZnO thin film was achieved by sol–gel process using zinc acetate dihydrate and 2-methoxyethanol as starting precursor and solvent, respectively. Ag nanoparticles were prepared with uniform size at 4.4 nm by spontaneous reduction method of Ag 2-ethylhexanoate in dimethyl sulfoxide (DMSO). The optical and electrical properties of ZnO thin films containing various contents of Ag-nanoparticles were monitored. Light scattering and charge emission and scattering behaviors of Ag nanoparticles in ZnO film were found. The incorporation of Ag nanoparticles into Al-doped ZnO film was also investigated. The optical transmittance was not degraded but the increase of electrical sheet resistance was found. The effect of Al-dopant on the transmittance and electrical sheet resistance of ZnO film was found too great to distinguish the positive effect of the incorporation of Ag nanoparticles into Al-doped ZnO thin films.     

Optical coherence tomography for ophthalmic imaging: new techniquedelivers micron-scale resolution

The authors have developed a new technique for micron scale resolution cross-sectional imaging of ocular and other biological tissue, called optical coherence tomography (OCT). OCT is similar to B-scan ultrasonic imaging, except that image contrast relies on differences in optical rather than acoustic backscattering characteristics of tissue. In contrast to ultrasound and nonlinear optical gating techniques, low-coherence interferometry is used to resolve the position of reflective or optical backscattering sites within a sample. Two-dimensional tomographic images of a thin, optical slice of tissue may be obtained with 10 μm longitudinal and lateral resolution. Optical heterodyne detection and the application of noise-reduction techniques originally developed for optical communication achieve sensitivity to reflected light as small as 10^-10 of the incident optical power. OCT is non-contact, non-invasive, and has superior resolution to conventional clinical ultrasound. Unlike scanning laser ophthalmoscopy and scanning laser tomography, the optical sectioning capability of OCT is not limited by the pupil aperture and ocular aberrations. OCT may be implemented in a compact, low-cost, fiber-optic based interferometer that is easily coupled to existing ophthalmic instrumentation. Here, the authors demonstrate high-speed in vivo OCT imaging in both the anterior and posterior eye, and highlight the system's potential usefulness for the early diagnosis and quantitative monitoring of a variety of ocular diseases and treatments     

比较式光学电流互感器的分析设计与试验研究

缺乏长期稳定性是光学电流互感器走向实用化、实现大面积推广的主要阻碍,针对这一问题,提出一种新补偿方案--比较式光学电流互感器。它将光学测量法与比较测量法相结合,巧妙地实现了对线性双折射和Verdet常数这两个稳定性影响因子的同时补偿。设计了双输入双输出的解调方法及相应的传感头结构和信号处理单元。这种解调方法可以更好地克服光路及电路的不一致对测量结果的影响,提升互感器的整体性能。试验结果表明：比较式光学电流互感器的线性度可达到IEC 0.2级要求;在光学电流互感器适用的220 kV以上电压等级应用场合,比较式光学电流互感器具有较好的抗干扰性能;在50 ℃温度变化范围内,普通光学电流互感器的误差变化量高达16%,而比较式光学电流互感器的误差变化仅有1%,证实了基于比较法的补偿方案的有效性。     

Frequency-domain optical detection of subsurface blood vessels:experimental and computational studies using a scattering phantom

A simple method to localize blood vessels beneath the surface of tissue could be very useful during laparoscopic and endoscopic procedures. However, the detection of blood vessels deep within tissue using light is limited by tissue scattering. In the study, frequency-domain photon migration methods were used to detect blood vessels within a scattering medium. The depth at which blood vessels could be detected was greater than 10 mm. The experimental measurements agree well with predictions obtained from the diffusion approximation to the radiative transport equation. These studies demonstrate the potential of frequency-domain optical methods to detect subsurface blood vessels     

Sized-fiber reflectometry for measuring local optical properties

Sized-fiber spectroscopy describes a device and method for measuring absorption and reduced scattering properties of tissue using optical fibers with different diameters. The device used in this paper consists of two fibers with diameters of 200 and 600 μm. Each fiber emits and collects its own backscattered light. Backscattered light measurements for solutions with absorption coefficients of 0.1-2.0 cm ^-1 and reduced scattering coefficients of 5-50 cm^-1 demonstrate that the device is most sensitive for the highest scattering materials. Monte Carlo simulations suggest the device is insensitive to the fiber illumination characteristics and that the light returning to the fiber is nearly uniform over all directions. Finally, experiments and Monte Carlo simulations of the sized-fiber device indicate that 50% of the signal arises from roughly 1.2 and 1.9 reduced mean-free paths for the 200- and 600-μm fibers, respectively     

A Clear Vision for Laser Diagnostics (Review)

Fundamentals and advances of tissue optical properties control as a novel approach for the improvement of linear and nonlinear biomedical spectroscopy and imaging are discussed. The optical immersion method for the use of exogenous optical clearing agents is described and overviewed.     

Three‐dimensional analysis of light transmittance characteristics in many index ellipsoids connected in series

The three‐dimensional optical technique has been applied to analysis of the experimental results related to magnetic wave scattering phenomena. Recently, we have developed an ideal equation for analyzing the three‐dimensional transmittance character of light scattered due to many index ellipsoids. The index ellipsoids are arranged directly along the light axis in series. In this case, the index ellipsoid size and the gap distance between each index ellipsoid and neighbor one are considered as a calculation condition. By using an analysis equation devised by us, we have sought to determine the condition under which the light can be passed through many transparent mediums with high efficiency. From the numerical calculations, the condition for maximum transmittance of light 100% is obtained when a spherical and elliptic index ellipsoids are alternately arranged with respect to each other. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 12–18, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20311     

传像光纤束透过率测量方法研究

光学纤维的传光特性不同于一般的成像光学系统,透过率的测量方法也不同。区别在于,测量传像光纤束透过率时不能采用平行光束,而测量成像光学系统透过率时,即可以采用会聚光束,又可以采用平行光束,只要不拦光即可。光在光纤束中遵循全反射的传光原理,而光在成像光学系统中遵循折、反射传光原理。通过对细小口径传像光纤束透过率的测量方法进行了实验、检测研究,得到一个新的测量光纤束透过率的方法。此方法完全不同于目前国标中光纤束透过率测量方法,又区别于成像光学系统透过率的测量方法。测量传像光纤束透过率时,要求光在光纤束中既要避免拦光现象又要满足全反射条件。我们根据光纤束传光原理研制了一个测量连接装置加到光谱仪的测量光路里,构成一个光纤束透过率测量光路系统。该测量法的重心在测量连接装置上。用该测量法成功地完成了细小口径成像光纤束透过率参数的测量,测量结果与设计预期值接近,测量准确度满足用户使用要求。     

镀膜玻璃在线质量检测系统的研究和实现

基于光学的色散原理,本文研制了一种可以在线检测镀膜玻璃光学性质的仪器。该仪器采用光纤作为传光载体,利用线阵CCD与光栅的配合完成对玻璃透射和反射光谱测量。光纤对光的发射和接收避免了杂散光的干扰噪声;光栅和高灵敏度的线阵CCD可实现高精确度的光谱采集。通过计算机强大的计算能力,可以实现透射率、反射率、各种色差测量和显示,如CIE1931色坐标（x,y）以及CIE1976色坐标（U,V,W）等,并且能够反馈给生产线,实现对镀膜玻璃光学特性的在线检测及生产线的自动控制。     

Optical properties effects upon the collection efficiency of optical fibers in different probe configurations

When optical fibers are used for delivery and collection of light, two major factors affect the measurement of collected light: 1) light transport in the medium from the source to the detection fiber and 2) light coupling to the optical fiber (which depends on the angular distribution of photons entering the fiber). This paper studies the latter factor, describing how the efficiency of the coupling depends on the optical properties of the sample. The coupling dependence on optical properties is verified by comparing experimental data to a simple diffusion model and to a Monte Carlo (MC)-corrected diffusion model. Mean square errors were 7.9% and 1.4% between experiments and the diffusion, and experiments and the MC-corrected models, respectively. The efficiency of coupling was shown to be highly dependent on the numerical aperture (NA) of the optical fiber. However, for lower scattering, such as in soft tissues, the efficiency of coupling could vary two- and threefold from that predicted by fiber NA. The collection efficiency can be used as a practical guide for choosing optical fiber-based systems for biomedical applications.     

An Optical Imaging Technique Using Deep Illumination in the Angular Domain

This paper describes a novel optical imaging method, deep illumination angular domain imaging (ADI), for detecting micron-scale objects within highly scattering media. The new optical imaging is a much simpler and less expensive solution as compared to other available optical imaging techniques. In principle, deep illumination ADI uses collimation detection capabilities of small acceptance angle devices to extract photons emitted from the scattered light created by a laser source, aimed deep beneath the turbid medium surface. The laser source forms an illumination ball within the medium that emits scattered light in all directions and illuminates objects near the surface from behind. Consequently, when photons from this illumination ball pass an object and reach the angular filter, light that is not subsequently scattered passes through to a camera detector, whereas scattered photons are rejected by the filter. Image results obtained are recorded for different phantom locations, phantom sizes, and medium scattering levels. Our images clearly display sub-204 m phantoms when placed 3 mm deep within a test scattering medium with total effective attenuation coefficient (mu'_eff) up to 5.8^-1 cm or 2.5 mm deep in chicken tissue tests. Preliminary digital image processing shows the image contrast enhancement and the definition improvement.     

应用微结构配光材料的格栅灯光学性能研究

运用挤出压印成型制备了表面添加微结构的PS漫反射板和PMMA扩散板,测试了漫反射板的反射率和漫反射率及扩散板的透光率和雾度。基于前期制备的微结构配光材料,将其应用在格栅灯上,测试了格栅灯的光学性能。微结构配光材料提高了格栅灯的光效,同时保障了光线均匀性。     

Intraoperative application of optical spectroscopy in the presenceof blood

A simple but effective method of spectral processing was developed to minimize or remove the effects of the presence of superficial blood on tissue optical spectra and, hence, enhance the performance of optical-spectroscopic-based in vivo tissue diagnosis and surgical guidance. This spectral-processing algorithm was developed using the principles of absorption-induced light attenuation wherein the ratio of fluorescence intensity (F) and the hth power of diffuse reflectance intensity (Rd) at a given emission wavelength λ_m is immune to spectral distortions induced by the presence of blood on the tissue surface. Here, the exponent h is determined by the absorption coefficients of whole blood at the excitation and emission wavelengths. The theoretical basis of this spectral processing was verified using simulations and was experimentally validated. Furthermore, the optical spectra of brain tissues collected in vivo was processed using this algorithm to evaluate its impact on brain tissue differentiation using combined fluorescence and diffuse reflectance spectroscopy. Based on the simulation, as well as experimental results, it was observed that using F/Rd^h h can effectively reduce or remove spectral distortions induced by superficial blood contamination on tissue optical spectra. Thus, optical spectroscopy can also be used intraoperatively for applications such as surgical guidance of tumor resection     

多光路光散射扬尘检测方法研究

针对传统扬尘传感器在测量方法中测量精度低、长期户外测量精度保持性差的不足,在Mie光散射原理基础上,研究了一种多光路扬尘检测方法,设计了一套面向建筑工地扬尘检测的光学扬尘浓度测量系统。介绍了扬尘监测系统的光学测量原理,研究了新方法中光通量和离子浓度计算方法,并对检测系统参数进行了优化分析。设计了多光路激光扬尘检测系统,分析了光透过率与粉尘层厚度之间关系。对所设计系统以国控点数据为基础进行了对比实验,实验结果表明新方法相对国控点数值最大偏差8.5%,较PPD4NS检测精度明显提高。     

基于光学散射原理的气溶胶光度计开发

为应对高效准确的气溶胶质量浓度测量问题,本文使用光散射法测量气溶胶质量浓度原理开发了一套气溶胶光度计。设计了恒流量控制模块,利用待测气溶胶在激光照射下产生的前向散射光与质量浓度成正比原理,使用光电倍增管将光信号转换成电信号,根据相同测量条件下高精度对比仪器结果进行线性系数计算。经实验证明,本文开发气溶胶光度计系统示值误差在能在±5%以内,重复性偏差在3%以内,符合气溶胶光度计校准规范的要求,实现了气溶胶质量浓度测量,具有较好的应用价值。