Multislice tomographic imaging and analysis of human breast-equivalent phantoms and biological tissues

A laser transillumination tomographic system, consisting of electrical, optical, mechanical, and software components, to obtain multislice images of tissue-equivalent breast phantoms and biological tissues, is developed. The tissue-equivalent phantoms are prepared from paraffin wax mixed with wax color pigments by matching their surface backscattered profiles as measured by multiprobe laser reflectometer, with that of respective tissues. The optical parameters of these phantoms are determined by matching their reflectance profiles with that as obtained by Monte Carlo simulation of optical scattering. For multislice tomographic analysis conical breast phantoms of height 80.0 mm and 80.0 mm base diameter with inclusions of different optical properties and dimensions are developed. The resolution of the inclusions in the tomograms depends on their sizes and optical parameters. The minimum size of the inclusion as detected by this procedure in a slice of diameter 50.0 mm is 3.0 mm. The structural variation as observed in the tomograms of phantoms of combination of biological tissues indicates its possible applications in detecting the abnormalities developing in human healthy soft tissues.     

Wavelet representations for monitoring changes in teeth imaged withdigital imaging fiber-optic transillumination

Digital imaging fiber-optic transillumination (DIFOTI) is a novel method to detect and monitor dental caries, using light, a charge-coupled device (CCD) camera, and computer-controlled image acquisition. The advantages of DIFOTI over radiography include: no ionizing radiation, no film, real-time diagnosis, and higher sensitivity in detection of early lesions not apparent to X-ray, as demonstrated in vitro. Here, we present a method of processing DIFOTI images, acquired at different times, for monitoring changes. Of central importance to this application is pattern matching of image frames that is invariant to translation and rotation of a tooth, relative to the field of view of the imaging camera, and that is robust to changes in illumination source intensity. Our method employs: (1) wavelet modulus maxima representations for segmentation of teeth images; (2) first and second moments of gray level representations of DIFOTI images in the spatial domain, to estimate tooth location and orientation; and (3) multiresolution wavelet magnitude representations for quantitative monitoring. Even with illumination source intensity variation, it is demonstrated in vitro that such wavelet representations can facilitate detection of simulated clinical changes in light transmission that cannot be detected in the spatial domain     

Localized measurement of optical attenuation coefficients of atherosclerotic plaque constituents by quantitative optical coherence tomography

Optical coherence tomography (OCT) is a novel, high-resolution diagnostic tool that is capable of imaging the arterial wall and plaques. The differentiation between different types of atherosclerotic plaque is based on qualitative differences in gray levels and structural appearance. We hypothesize that a quantitative data analysis of the OCT signal allows measurement of light attenuation by the local tissue components, which can facilitate quantitative spatial discrimination between plaque constituents. High-resolution OCT images (at 800 nm) of human atherosclerotic arterial segments obtained at autopsy were histologically validated. Using a new, simple analysis algorithm, which incorporates the confocal properties of the OCT system, the light attenuation coefficients for these constituents were determined: for diffuse intimal thickening (5.5 +/- 1.2 mm(-1)) and lipid-rich regions (3.2 +/- 1.1 mm(-1)), the attenuation differed significantly from media (9.9 +/- 1.8 mm(-1)), calcifications (11.1 +/- 4.9 mm(-1) ) and thrombi (11.2 +/- 2.3 mm(-1)) (p < 0.01). These proof of principle studies show that simple quantitative analysis of the OCT signals allows spatial determination of the intrinsic optical attenuation coefficient of atherosclerotic tissue components within regions of interest. Combining morphological imaging by OCT with the observed differences in optical attenuation coefficients of the various regions may enhance discrimination between various plaque types.     

Terahertz Imaging of Three-Dimensional Dehydrated Breast Cancer Tumors

This work presents the application of terahertz imaging to three-dimensional formalin-fixed, paraffin-embedded human breast cancer tumors. The results demonstrate the capability of terahertz for in-depth scanning to produce cross section images without the need to slice the tumor. Samples of tumors excised from women diagnosed with infiltrating ductal carcinoma and lobular carcinoma are investigated using a pulsed terahertz time domain imaging system. A time of flight estimation is used to obtain vertical and horizontal cross section images of tumor tissues embedded in paraffin block. Strong agreement is shown comparing the terahertz images obtained by electronically scanning the tumor in-depth in comparison with histopathology images. The detection of cancer tissue inside the block is found to be accurate to depths over 1 mm. Image processing techniques are applied to provide improved contrast and automation of the obtained terahertz images. In particular, unsharp masking and edge detection methods are found to be most effective for three-dimensional block imaging.     

Three-dimensional reconstruction of transillumination tomographic images of human breast phantoms by red and infrared lasers

A laser transillumination tomographic system, using red and near infrared lasers, to obtain cross-sectional images of human breast phantoms and human hand is proposed. The scanning assembly is consisting of upward, downward, rotational and pitch movements. The phantoms, made of paraffin wax, agar gel, and milk placed in a glass model, are embedded with abnormalities like blood, water, solid objects, and tissues. By illuminating the phantoms at various heights by either red or infrared laser the projection data are collected. Based on 64 projections the tomogram of each section is constructed. By volume visualization procedure applied to the tomograms the objects of varying composition embedded within the phantoms are detected and their size, shape, and location depth are determined. The cross-sectional image of a human hand obtained by this procedure further shows the possibility of application of this technique for imaging of organs.     

Spatial harmonic imaging of X-ray scattering--initial results

Coherent X-ray scattering is related to the electron density distribution by a Fourier transform, and therefore a window into the microscopic structures of biological samples. Current techniques of scattering rely on small-angle measurements from highly collimated X-ray beams produced from synchrotron light sources. Imaging of the distribution of scattering provides a new contrast mechanism which is different from absorption radiography, but is a lengthy process of raster or line scans of the beam over the object. Here, we describe an imaging technique in the spatial frequency domain capable of acquiring both the scattering and absorption distributions in a single exposure. We present first results obtained with conventional X-ray equipment. This method interposes a grid between the X-ray source and the imaged object, so that the grid-modulated image contains a primary image and a grid harmonic image. The ratio between the harmonic and primary images is shown to be a pure scattering image. It is the auto-correlation of the electron density distribution at a specific distance. We tested a number of samples at 60-200 nm autocorrelation distance, and found the scattering images to be distinct from the absorption images and reveal new features. This technique is simple to implement, and should help broaden the imaging applications of X-ray scattering.     

Design of Large-aperture and Wide-band Optical Lens

The design of a large-aperture and wide-band optical lens for camera is presented. By utilizing the atmospheric window of infrared light, clear images can be achieved in the dark or poor visibility conditions. To use near-infrared and visible light to obtain images, the charge coupled device(CCD) is adopted as the image sensor of the lens with the center wavelength of 880 nm, which operates at the wavelength range from 400 nm to 1 000 nm. After calculating the parameters of optical lens, Sunnah type is selected as the initial structure. Through the optimization of optical design software ZEMAX, the lens obtains an excellent imaging performance. The modulation transfer function(MTF) can be more than 0.3 at the spatial frequency of 110 lp/mm, and the maximum distortion can be less than 0.1%.     

Optimized matching liquid with wide-slot antenna for microwave breast imaging

In this paper, we introduce an optimized matching liquid together with a wide-slot ultra-wideband antenna to be used in a breast microwave imaging system. The slot antenna is small with 13 mm × 14 mm × 0.625 mm dimensions so that many of them can be placed around a breast. The matching liquid is needed to effectively couple the microwave signal into breast tissues. Exhibiting a suitable permittivity and moderate loss, the matching liquid is a mixture of 83% sunflower oil with 17% distilled water. We build a phantom in order to investigate the penetration of microwave signal into the breast tissues. Experimental measurements and simulation results indicate that this matching liquid provides, nearly, the maximum scattering power from inside of breast tissues in interval [2.5, 7 GHz] that is an appropriate frequency range for breast imaging.     

Near field microwave brain imaging

A procedure for near field microwave imaging of biological tissues is presented. A two-port microstrip test fixture mounted on a 2D translation stage is employed to capture the transmission images of 1 mm thick slices of rat brain. Spatial resolution and contrast of such images are discussed in terms of insertion loss and extracted tissue permittivity     

A three-dimensional registration method for automated fusion of micro PET-CT-SPECT whole-body images

Micro positron emission tomography (PET) and micro single-photon emission computed tomography (SPECT), used for imaging small animals, have become essential tools in developing new pharmaceuticals and can be used, among other things, to test new therapeutic approaches in animal models of human disease, as well as to image gene expression. These imaging techniques can be used noninvasively in both detection and quantification. However, functional images provide little information on the structure of tissues and organs, which makes the localization of lesions difficult. Image fusion techniques can be exploited to map the functional images to structural images, such as X-ray computed tomography (CT), to support target identification and to facilitate the interpretation of PET or SPECT studies. Furthermore, the mapping of two functional images of SPECT and PET on a structural CT image can be beneficial for those in vivo studies that require two biological processes to be monitored simultaneously. This paper proposes an automated method for registering PET, CT, and SPECT images for small animals. A calibration phantom and a holder were used to determine the relationship among three-dimensional fields of view of various modalities. The holder was arranged in fixed positions on the couches of the scanners, and the spatial transformation matrix between the modalities was held unchanged. As long as objects were scanned together with the holder, the predetermined matrix could register the acquired tomograms from different modalities, independently of the imaged objects. In this work, the PET scan was performed by Concorde's microPET R4 scanner, and the SPECT and CT data were obtained using the Gamma Medica's X-SPECT/CT system. Fusion studies on phantoms and animals have been successfully performed using this method. For microPET-CT fusion, the maximum registration errors were 0.21 mm +/- 0.14 mm, 0.26 mm +/- 0.14 mm, and 0.45 mm +/- 0.34 mm in the X (right-left), Y (upper lower), and Z (rostral-caudal) directions, respectively; for the microPET-SPECT fusion, they were 0.24 mm +/- 0.14 mm, 0.28 mm +/- 0.15 mm, and 0.54 mm +/- 0.35 mm in the X, Y, and Z directions, respectively. The results indicate that this simple method can be used in routine fusion studies.     

Diffuser-aided diffuse optical imaging for breast tumor: a feasibility study based on time-resolved three-dimensional Monte Carlo modeling

This study proposed diffuser-aided diffuse optical imaging (DADOI) as a new approach to improve the performance of the conventional diffuse optical tomography (DOT) approach for breast imaging. The 3-D breast model for Monte Carlo simulation is remodeled from clinical MRI image. The modified Beer-Lambert's law is adopted with the DADOI approach to substitute the complex algorithms of inverse problem for mapping of spatial distribution, and the depth information is obtained based on the time-of-flight estimation. The simulation results demonstrate that the time-resolved Monte Carlo method can be capable of performing source-detector separations analysis. The dynamics of photon migration with various source-detector separations are analyzed for the characterization of breast tissue and estimation of optode arrangement. The source-detector separations should be less than 4 cm for breast imaging in DOT system. Meanwhile, the feasibility of DADOI was manifested in this study. In the results, DADOI approach can provide better imaging contrast and faster imaging than conventional DOT measurement. The DADOI approach possesses great potential to detect the breast tumor in early stage and chemotherapy monitoring that implies a good feasibility for clinical application.     

Performance of vibro-acoustography in detecting microcalcifications in excised human breast tissue: a study of 74 tissue samples

X-ray mammography is the principal modality used today for detection of breast microcalcifications and breast lesions associated with breast cancer. X-ray mammography, however, is ionizing and its sensitivity is greatly reduced in dense breasts. Hence, alternative noninvasive and nonionizing breast imaging tools that can aid physicians to better diagnose early-stage breast lesions are of great interest. Vibro-acoustography is a novel noninvasive imaging technique that uses ultrasound in a fundamentally new way. This method uses the radiation force of ultrasound to vibrate the tissue at low (kilohertz) frequency and records the resulting response to produce images that are related to the mechanical properties of the tissue. The goal of this study is to evaluate the performance of vibro-acoustography in detecting breast microcalcifications by conducting vibro-acoustography on 74 fixed breast tissue samples with known microcalcifications based on their radiographs. The results indicate that in most cases micro-calcifications can be detected by vibro-acoustography. Further development of vibro-acoustography may lead to a novel-imaging tool for in vivo detection of microcalcifications.     

Registered 3-D ultrasound and digital stereotactic mammography for breast biopsy guidance

Large core needle biopsy is a common procedure used to obtain histological samples when cancer is suspected in diagnostic breast images. The procedure is typically performed under image guidance, with freehand ultrasound and stereotactic mammography (SM) being the most common modalities used. To utilize the advantages of both modalities, a biopsy device combining three-dimensional ultrasound (3DUS) and digital SM imaging with computer-aided needle guidance was developed. An implementation of a stereo camera method was applied to SM calibration, providing a target localization error of 0.35 mm. The 3-D transformation between the two imaging modalities was then derived, with a target registration error of 0.52 mm. Finally, the needle guidance error of the device was evaluated using tissue-mimicking phantoms, showing a sample mean and standard deviation of 0.44 +/- 0.22 and 0.49 +/- 0.27 mm for targets planned from 3DUS and SM images, respectively. These results suggest that a biopsy procedure guided using this device would successfully sample breast lesions at a size greater than or equal to the smallest typically detected in mammographic screening (approximately 2 mm).     

基于光栅成像投影的微位移检测方法

提出了一种基于光栅成像投影的微位移检测方法，利用光学傅里叶变换原理给出了具体的理论分析。准直激光束照明的光栅通过一个4f系统成像投影在被测物体表面上，光栅投影经过被测物体表面反射后由另一个4f系统成像在探测光栅上。探测光栅由一个透镜组成像在光电探测器上，其中采用由起偏器、光弹调制器和检偏器组成的偏振调制单元对探测光强进行调制。通过在4f系统的频谱面上设置滤波光阑，在光电探测器上获得了与被测物体的微位移成正弦关系的光强变化，检测出光电探测器上的光强变化即可以获得被测物体的位移量。实验验证了该检测方法的可行性，其重复测量精度小于25nm(1σ)。     

采用空间分辨漫反射测定胃组织光学特性

研究了人正常胃黏膜及黏膜下层组织对488 nm,514.5 nm,532 nm,630 nm和632.8 nm的激光的光学特性及其差异,实验采用空间分辨反射光和CCD探测器以及非线性拟合确定组织光学特性。结果表明,人正常胃黏膜及黏膜下层组织对五个波长的激光的吸收系数、约化散射系数、光学穿透深度、漫射系数、漫反射率和漫反射率的位移都是随着激光波长的变化而变化的。其吸收系数的最大值在532 nm,其值为0.482 mm-1,最小值在632.8 nm,其值为0.224 mm-1,最大差异在532 nm和632.8 nm之间,其值为115%,最小差异在488 nm和532 nm之间,其值为1.90%。其约化散射系数的最大值在488 nm,其值为5.93 mm-1,最小值在632.8 nm,其值为3.87 mm-1,最大差异在488 nm和632.8 nm之间,其值为53.2%,最小差异在514.5 nm和532 nm之间,其值为3.25%。其光学穿透深度的最大值在632.8 nm,其值为0.612 mm,最小值在488 nm,其值为0.341 mm。其漫射系数的最大值在632.8 nm,其值为0.084 mm,最小值在488 nm,其值为0.055 mm。其漫反射率的最大值在630 nm,其值为0.356,最小值在532 nm,其值为0.271。其Δx的最大值在632.8 nm,其值为0.153 mm,最小值在488 nm,其值为0.100 mm。可见,人正常胃黏膜/黏膜下层组织对五个波长的激光的光学特性参数存在明显的差异。     

低照度背景下弱小目标的成像实验研究

无人机等弱小目标具有飞行高度低、反射截面小、热信息弱等特点,尤其在低照度背景下,单一成像方式难以实现对弱小目标的探测和识别。实验对比了可见光成像、微光夜视成像、长波红外成像、激光主动照明成像等对弱小目标的成像效果,目的是研究适用于不同照度背景下弱小目标的探测识别方法。外场实验中,被测目标为小型四旋翼无人机,尺寸为290 mm×290 mm×196 mm,实验环境照度在10?2~10?4 lx之间,作用距离范围0.5~2 km。成像实验结果表明:普通可见光系统无法在环境照度低于10?2 lx时成像;环境照度为10?3 lx时,微光夜视和长波红外热系统的识别距离仅为0.5 km;近红外激光（中心波长808 nm）主动照明与微光夜视结合的主动成像方式可增加对弱小目标的识别距离,同等条件下主动照明成像作用距离是被动成像的3倍。     

Transillumination imaging for blood oxygen saturation estimation of skin lesions

Detecting the early stages of melanoma can be greatly assisted by an accurate estimate of subsurface blood volume and blood oxygen saturation, indicative of angiogenesis. Visualization of this blood volume present beneath a skin lesion can be achieved through the transillumination of the skin. As the absorption of major chromophores in the skin is wavelength dependent, multispectral imaging can provide the needed information to separate out relative amounts of each chromophore. However, a critical challenge to this strategy is relating the pixel intensities observed in a given image to the wavelength-dependent total absorption existing at each spatial location. Consequently, in this paper, we develop an extension to Beer's law, estimated through a novel voxel-based, parallel processing Monte Carlo simulation of light propagation in skin which takes into account the specific geometry of our transillumination imaging apparatus. We then use this relation in a linear mixing model, solved using a multispectral image set, for chromophore separation and oxygen saturation estimation of an absorbing object located at a given depth within the medium. Validation is performed through the Monte Carlo simulation, as well as by imaging on a skin phantom. Results show that subsurface oxygen saturation can be reasonably estimated with good implications for the reconstruction of 3-D skin lesion volumes using transillumination toward early detection of malignancy.     

Amorphous carbon films as planarization layers deposited byplasma-enhanced chemical vapor deposition

A dry planarization process utilizing plasma-enhanced chemical vapor deposition (PECVD) of amorphous carbon (a-C:H) films has been developed. The degree of planarization obtained for these films is better than that of many conventional spun-on polymers. Carbon films 2.5 μm thick have been shown to planarize 1.5-μm-deep, 400-μm-wide trenches to within 0.2 μm. The deposition process can be carried out at room temperature with low ion bombardment energy (10 V) and fast deposition rate (300 nm/min). The planarization layers have been used in conjunction with both wet and dry deposited inorganic imaging layers in bilayer resist schemes to form submicrometer patterns     

高功率二极管激光器面阵四通抽运耦合系统

高功率二极管激光器面阵连续抽运1.1mmNd:YAG薄片,采用非球面柱透镜来准直二极管激光器线阵的快轴方向,然后用两个正交的柱透镜分别对快慢轴光进行成像,在薄片上形成10mm×7mm的抽运光斑。用球面反射镜将薄片未吸收的抽运光再一次通过Nd:YAG薄片,从而达到高的吸收效率,抽运光束在薄片上快慢轴方向上的束参数积分别为640mm·mrad和540mm·mrad。用CCD测得抽运光在薄片上的光强分布较均匀,面阵经非球面柱透镜和两个柱透镜后在10mm×7mm内的耦合效率为80.5%。     

Preparation and Holographic Recording of Diarylethene‐Doped Photochromie Films

This study investigated the photochromic properties and characterization of acetyl‐substituted diarylethene (DAMBTF6)‐doped fluoroacrylates media for holographic storage. For the rewritable holographic recording media, we prepared photochromic polymer films using an acrylate matrix by simple photocuring methods. Switching light sources from a visible (532 nm) to an ultraviolet (365 nm) produced transparent films that changed from pale yellow to red. Holographic recording was performed on the photochromic films by two interfering collimated plane wave beams. Excitation with a visible or ultraviolet light completely erased the records, and the film was rewritable either by 532 nm laser or by 325 nm laser within 2 seconds. Images were recorded onto a pixelated spatial light modulator with rectangular pixel apertures and reconstructed on the photochromic films to show recovery of the original images with high resolution.