Design and implementation of dynamic near-infrared optical tomographic imaging instrumentation for simultaneous dual-breast measurements

Dynamic near-infrared optical tomographic measurement instrumentation capable of simultaneous bilateral breast imaging, having a capability of four source wavelengths and 32 source-detector fibers for each breast, is described. The system records dynamic optical data simultaneously from both breasts, while verifying proper optical fiber contact with the tissue through implementation of automatic schemes for evaluating data integrity. Factors influencing system complexity and performance are discussed, and experimental measurements are provided to demonstrate the repeatability of the instrumentation. Considerations in experimental design are presented, as well as techniques for avoiding undesirable measurement artifacts, given the high sensitivity and dynamic range (1:10(9)) of the system. We present exemplary clinical results comparing the measured physiologic response of a healthy individual and of a subject with breast cancer to a Valsalva maneuver.     

Diffractive optical elements for simultaneous operation in reflection and transmission

It is advantageous for some diffractive optical element (DOE) applications to produce different output patterns in different circumstances. There has been considerable work on the design of wavelength multiplexing DOEs and in devices where the polarization of the incident light determines the output. One parameter that has not, to our knowledge, been exploited for pattern formation DOEs is the mode of operation, i.e., whether the element works in reflection or transmission. We present an approach for designing such devices and design an element with modeled efficiency, mean square error (MSE), and cross-talk of 65.9, 2.52, and 4.2% in transmission and 66.6, 2.50, and 3.5% in reflection. The element has been successfully fabricated and has measured efficiencies of 58.3% +/- 2 in reflection and 68.8% +/- 5 in transmission are reported.     

Compact optical imaging system for arrays of optical thyristors

A compact and modular optical system that employs gradient-refractive-index rod lenses to image arrays of Lambertian sources is characterized both experimentally and by ray-tracing simulations. A hybrid optical system that incorporates additional microlens arrays to reduce transmittance losses and aberrations is also modeled, and the two systems are compared.     

纳米声学及近场声成像技术

纳米声学是近年来迅速发展的新的学科领域,旨在亚微米和纳米尺度上来"听到"和"看到"我们尚未发现的物质世界。而近场声成像技术,像扫描探针声显微术(Scanning ProbeAcoustic Microscopy,SPAM)和压电响应力显微术(Piezoresponce Force Microscopy,PFM)等,不仅具有亚微米和纳米分辨力,而且能方便地对试样微区的表面形貌,材料的力学和电学等性质进行成像,是开展纳米声学研究的有效手段。文章结合实验结果,对SPAM和PFM等近场声成像技术作了简要介绍。     

Miniature endoscope for simultaneous optical coherence tomography and laser-induced fluorescence measurement

We have designed a multimodality system that combines optical coherence tomography (OCT) and laser-induced fluorescence (LIF) in a 2.0-mm-diameter endoscopic package. OCT provides approximately 18-microm resolution cross-sectional structural information over a 6-mm field. LIF spectra are collected sequentially at submillimeter resolution across the same field and provide histochemical information about the tissue. We present the use of a rod prism to reduce the asymmetry in the OCT beam caused by a cylindrical window. The endoscope has been applied to investigate mouse colon cancer in vivo.     

Application of optical and acoustic methods for estimation of fatigue damage

The results of the investigation of variations in the parameters of elastic wave propagation and microplastic characteristics of steels 12 (12GS) and (08Kh18N10T) during their fatigue damage are given. The characteristics of microplastic deformations (density of microzones subjected to plastic deformations and average value of microplastic deformations) are determined using an optical method with a help of a portable SPECTR-MET metallograpic complex. Attenuation and propagation velocities of bulk transverse and longitudinal elastic waves are shown to be sensitive to structural variations at an earlier stage of alloy damage. The degree of damage to the analyzed materials before formation of a macrocrack is estimated using a combination of an acoustic and an optical method of nondestructive testing.     

Numerical investigation of hyperspectral tomography for simultaneous temperature and concentration imaging

We investigate the simultaneous tomographic reconstruction of temperature and species concentration using hyperspectral absorption spectroscopy. Previous work on absorption tomography has relied on a small number of wavelengths, resulting in the requirement of a large number of projections and limited measurement capability. Here we develop a tomographic inversion method to exploit the increased spectral information content enabled by recent advancement in laser technologies. The simulation results clearly demonstrate that the use of hyperspectral absorption data significantly reduces the number of projections, enables simultaneous mapping of temperature and species concentration, and provides more stable reconstruction compared with traditional absorption tomographic techniques.     

Large-area, real-time imaging system for surface acoustic wavedevices

A system for imaging the particle displacement envelope of vibrational (transverse) modes of surface acoustic wave (SAW) devices is described. The modes are being imaged using a schlieren method for visualizing the acoustic power flow with a beam-expanded helium-neon (HeNe) laser. The optical arrangement uses internal reflection from within the quartz substrate to achieve high-efficiency acousto-optic diffraction of the laser light. The use of a CCD camera coupled with a frame grabber and a computer with image calculator software establishes an imaging system for large-area, real-time visualization, recording, accurate measurement, and analysis of vibrational modes of SAW devices. These methods are part of an effort to determine the relationship between acceleration sensitivity and transverse variations in the acoustic-mode shape in SAW resonators. Use of the system in imaging a 98 MHz SAW device is presented as an example     

Nonlinear optical and acoustic properties of thin films

The nonlinear optical and acoustic properties of thin films have been studied experimentally. The following nonlinear effects have been investigated: acoustic wave generation; stimulated light scattering due to acousto-optic interaction; and the influence of excitation conditions, film structure, and film composition on the above effects.     

Adaptive optical array receivers for detection of surface acoustic waves

Adaptive interferometric detection systems based on two-wave mixing in photorefractive crystals have been configured as distributed optical receivers. The spatial distribution of the detection laser power on the sample surface is controlled by use of phase gratings and amplitude masks. The responses of point, line, array, and chirped optical receivers to propagating surface acoustic waves (SAW's) are discussed theoretically and demonstrated experimentally. It is shown that by use of different object beam footprints it is possible to configure adaptive holographic SAW receivers that are either broadband or narrow band and that are preferentially sensitive to SAW's propagating in given directions. The receivers also allow for the distribution of laser power over the sample, eliminating the excessive heating or surface damage that can occur in some materials when high power, point-focused, detection lasers are used.     

Multichannel sampling schemes for optical imaging systems

We introduce a framework of focal-plane coding schemes for multichannel sampling in optical systems. A particular objective is to develop an ultrathin imager without compromising image resolution. We present a complete f/2.1 optical system with a thickness of 2.2 mm. The resolution is maintained in the thin optical system by an integrated design of the encoding scheme, the process of making the coding elements, and the decoding algorithms.     

Characterization of optical fiber imaging bundles for swept-source optical coherence tomography

Fiber imaging bundles have been investigated for use in endoscopic optical coherence tomography (OCT) systems, to obviate the requirement for scanning components within the endoscope probe section. Images have been acquired using several optical configurations, two of which are common path in design. Configurations have been selected as having potential for miniaturization and inclusion in endoscopic-type systems, since the advantages of employing imaging bundles are most clearly seen in this type of system. The various types of bundle available are described, and the properties of the leached bundles used here are discussed in detail, with reference to their effect upon the performance of OCT systems. Images are displayed from measurements made on a range of samples.     

Fluorophore-gold nanoparticle complex for sensitive optical biosensing and imaging

Fluorophores have been extensively used as the signal mediator in biosensing and bioimaging for a long time. Enhancement of fluorescence can amplify the signal, thus improving the sensitivity, enabling earlier and accurate disease detection and diagnosis. Some metal nanoparticles, such as gold and silver, can generate a strong electromagnetic field on their surface (surface plasmon field) upon receiving photonic energy. When a fluorophore is placed in the field, the field can affect the fluorophore electrons participating in fluorescence emission and change the fluorescence output. The change can be from complete quenching to significant enhancement, depending on the metal type, particle size and shape, excitation/emission wavelengths and quantum yield of the fluorophore, and the distance between the fluorophore and the particle surface. In this study, the effects of these parameters on the fluorescence enhancement of commonly used fluorophores by gold nanoparticles (GNPs) are theoretically analyzed. Experimentally, an NIR contrast agent with enhanced fluorescence was developed by carefully tailoring the distance between Cypate (ICG based fluorophore) and a GNP, via biocompatible spacer constructs. The effect of the GNP size (3.7-16.4 nm) and spacer length (3.2-4.6 nm) on fluorescence enhancement was studied, and the spacer length that provided the significant enhancement was determined. The spacer of 3.9 nm with 16.4 nm GNP provided the fluorescence of 360% of the control. The experimental data qualitatively agreed with the theoretical results and, thus, the theoretical analysis can be used as a guide for significantly improving the sensitivity of existing fluorescent contrast agents by properly utilizing GNPs and spacers.     

Integrated semiconductor optical sensors for cellular and neural imaging

We review integrated optical sensors for functional brain imaging, localized index-of-refraction sensing as part of a lab-on-a-chip, and in vivo continuous monitoring of tumor and cancer stem cells. We present semiconductor-based sensors and imaging systems for these applications. Measured intrinsic optical signals and tissue optics simulations indicate the need for high dynamic range and low dark-current neural sensors. Simulated and measured reflectance spectra from our guided resonance filter demonstrate the capability for index-of-refraction sensing on cellular scales, compatible with integrated biosensors. Finally, we characterized a thermally evaporated emission filter that can be used to improve sensitivity for in vivo fluorescence sensing.     

广义边缘CWD-Hough变换在宽带声成像中的应用

提出了一种基于广义边缘CWD—Hough（GMCWD—Hough）变换的宽带声成像方法。分析了基于时间伸缩-时延的宽带相关声成像的基本模型,介绍了广义边缘CWD—Hough变换。根据目标回波的时频分布特点,该方法基于时间一频率联合分析法,提取信号在时频域的分布特性参数进行时间伸缩时延的声成像。通过设计合理的广义边缘核函数,能有效避免常用的WVD方法产生的交叉项影响,检测性能优于常用的Wigner—ville分布方法。实验结果表明该声成像方法的有效性,不仅适合水声宽带成像,而且对于低信噪比条件下的其它成像方式也具有参考价值。     

Bubble-based acoustic radiation force elasticity imaging

Acoustic radiation force is applied to bubbles generated by laser-induced optical breakdown (LIOB) to study viscoelastic properties of the surrounding medium. In this investigation, femtosecond laser pulses are focused in the volume of gelatin phantoms of different concentrations to form bubbles. A two-element confocal ultrasonic transducer generates acoustic radiation force on individual bubbles while monitoring their displacement within a viscoelastic medium. Tone burst pushes of varying duration have been applied by the outer element at 1.5 MHz. The inner element receives pulse-echo recordings at 7.44 MHz before, during, and after the excitation bursts, and crosscorrelation processing is performed offline to monitor bubble position. Maximum bubble displacements are inversely related to the Young's moduli for different gel phantoms, with a maximum bubble displacement of over 200 microm in a gel phantom with a Young's modulus of 1.7 kPa. Bubble displacements scale with the applied acoustic radiation force and displacements can be normalized to correct for differences in bubble size. Exponential time constants for bubble displacement curves are independent of bubble radius and follow a decreasing trend with the Young's modulus of the surrounding medium. These results demonstrate the potential for bubble-based acoustic radiation force methods to measure tissue viscoelastic properties.     

Ultrasound-modulated optical tomography with intense acoustic bursts

Ultrasound-modulated optical tomography (UOT) detects ultrasonically modulated light to spatially localize multiply scattered photons in turbid media with the ultimate goal of imaging the optical properties in living subjects. A principal challenge of the technique is weak modulated signal strength. We discuss ways to push the limits of signal enhancement with intense acoustic bursts while conforming to optical and ultrasonic safety standards. A CCD-based speckle-contrast detection scheme is used to detect acoustically modulated light by measuring changes in speckle statistics between ultrasound-on and ultrasound-off states. The CCD image capture is synchronized with the ultrasound burst pulse sequence. Transient acoustic radiation force, a consequence of bursts, is seen to produce slight signal enhancement over pure ultrasonic-modulation mechanisms for bursts and CCD exposure times of the order of milliseconds. However, acoustic radiation-force-induced shear waves are launched away from the acoustic sample volume, which degrade UOT spatial resolution. By time gating the CCD camera to capture modulated light before radiation force has an opportunity to accumulate significant tissue displacement, we reduce the effects of shear-wave image degradation, while enabling very high signal-to-noise ratios. Additionally, we maintain high-resolution images representative of optical and not mechanical contrast. Signal-to-noise levels are sufficiently high so as to enable acquisition of 2D images of phantoms with one acoustic burst per pixel.     

基于图像处理器的传声器阵列实时声成像方法

为了解决传声器阵列用于声场分析时的精确且快速声成像的技术难题,提出了一种利用图像处理器(Graphics Processing Unit,GPU)的通用计算技术实现快速声成像算法。可控响应功率算法是广泛应用的一种声源定位算法,但计算量巨大,阻碍了它在实际场合中的应用。通过将可控响应功率算法进行任务分解及线程映射,实现了利用计算统一设备架构实现的基于GPU的可控响应功率声源成像定位算法,在特定阵元通道数和信号长度情况下,与基于CPU的声源定位计算方法相比,综合计算效率提高了约20倍,并将其成功地应用于平面螺旋阵的声成像应用中,实现了实时声成像定位。