编码孔径成像光谱仪光学系统设计

本文设计了一种以双Amici棱镜为分光元件的成像光谱系统,该系统主要包括前置望远物镜、编码板、双Amici棱镜、准直镜和成像镜.此类光学系统可以获得很高的衍射效率,相比于狭缝结构的成像光谱系统,该光谱仪为两维空间扩展的视场,无疑增加了设计难度.后期的数据反演算法对一次像面编码板的成像效果过于依赖,基于此,对光学系统的像差校正提出了更高的要求.本文设计、分析了基于双Amici棱镜的成像光谱仪的原理及特点,设计了一套完整的成像光谱系统.前置望远物镜的设计为像方远心,MTF在39线对处,达到0.8,成像质量良好.创新性的将前置望远物镜倒置用做准直系统.全系统各个波长在39线对处的MTF值均在0.65以上.对室外目标景物进行推扫成像,从获得的成像数据判断,本文设计的编码孔径成像光谱仪原理可行,衍射效率高,全视场成像质量良好,全谱段光谱数据可信.     

基于旋转扫描探头的OCT内窥成像系统设计*

为了同时获取样品的表面和深度信息,研究光学相干层析的成像原理,建立了基于光学相干层析技术的内窥系统,实现了旋转扫描成像,系统的工作波长为1 310 nm,工作带宽为80 nm.理论推导及计算机仿真得到了系统信噪比与干涉仪的分光比、反射率之间的关系并分析了理论分辨率和探测深度.提出外径为5 mm的内窥镜扫描探头,聚焦距离为12 mm,数值孔径NA为0.47,折射率分布常量A=0.218 7.利用微型电机驱动直角棱镜实现扫描,旋转速度为25 rpm,旋转一周得到640个采样点.采用多层盖玻片和洋葱表皮作为样品进行实验分析,得到了盖玻片和洋葱的图像,横向分辨率和纵向分辨率分别为10 μm和15 μm.结果表明,设计的光学相干层析内窥系统能够用于旋转扫描成像,获取更多的组织信息.     

基于旋转扫描探头的OCT内窥成像系统设计

为了同时获取样品的表面和深度信息,研究光学相干层析的成像原理,建立了基于光学相干层析技术的内窥系统,实现了旋转扫描成像,系统的工作波长为1 310 nm,工作带宽为80 nm.理论推导及计算机仿真得到了系统信噪比与干涉仪的分光比、反射率之间的关系并分析了理论分辨率和探测深度.提出外径为5 mm的内窥镜扫描探头,聚焦距离为12 mm,数值孔径NA为0.47,折射率分布常量A=0.218 7.利用微型电机驱动直角棱镜实现扫描,旋转速度为25 rpm,旋转一周得到640个采样点.采用多层盖玻片和洋葱表皮作为样品进行实验分析,得到了盖玻片和洋葱的图像,横向分辨率和纵向分辨率分别为10 μm和15 μm.结果表明,设计的光学相干层析内窥系统能够用于旋转扫描成像,获取更多的组织信息.     

基于合成孔径技术的内镜超声相控阵成像算法

利用孔径大小为2.32mm的16阵元换能器,搭建了一套16通道的内镜超声相控阵成像实验系统。在此基础上提出了一种适用于内镜成像的相控阵成像算法(PAI),该算法利用延时和叠加算法(DAS)取得扫描线数据,再利用合成孔径技术中的相干样点叠加,得到高分辨率图像。该相控阵成像算法实现了发射和接收的动态聚焦。经FieldII仿真和内镜探头超声成像实验验证,与延时和叠加算法以及动态接收聚焦算法(DRF)相比,图像的理论横向分辨率分别提高了93.68%和17.5%,实验获得的实际横向分辨率分别提高了92.78%和14.69%,验证了相控阵成像算法和实验系统的可行性。     

基于旋转相位编码与照明光束匹配的叠层衍射成像算法研究

在传统的叠层成像算法中引入一种旋转相位编码与照明光束相匹配.采用分块均匀分布的旋转相位调制器对衍射光进行调制,在探测面获得了相应的衍射图样.这种照明光束与相位匹配的方式有效地增加了解的约束条件,具有收敛速度快、抗噪声及抗位置偏差能力强等优点.与随机相位调制相比,本算法所引入的旋转相位调制器构造简单、使用便捷,因而在实时显微成像、超分辨成像等领域将具有更高的实用价值.     

超声内镜换能器的应用进展

超声内镜集结了超声检查与内镜检查双重功能,可以获得腹部和胸腔内器官的高质量图像,是一种先进的医疗设备。超声内镜探头的核心部分是超声换能器。超声内镜检查需经过狭窄的消化道或内窥镜的活检通道伸进体内,由于工作环境的限制,超声内镜用换能器与普通超声成像换能器相比,工作频率更高、尺寸更小、制作工艺更精密。本文从超声内镜所用换能器的外形结构、内部组成、工作模式及材料等角度,对目前国内外超声内镜换能器的应用进展情况进行了描述,并根据超声内镜换能器的现状对未来的发展趋势进行了分析。     

分时偏振成像系统中光束偏离的补偿方法研究

分时偏振成像系统需要通过旋转检偏器获取场景的偏振信息(I, Q, U), 检偏器的前后表面间不平行(也称为楔角)将导致成像光束发生偏离且随检偏器旋转而旋转, 这将降低偏振成像系统的空间分辨率和偏振测量精度. 本文提出调整检偏器相对于入射主光轴倾斜角的方法来补偿上述光束偏离. 以格兰棱镜作为检偏器, 根据几何光学理论, 推导了分时偏振成像系统光束偏离的一阶近似补偿模型, 获得倾斜角与格兰棱镜楔角之间的函数关系, 并通过仿真模拟验证了该补偿方法的可行性和有效性. 研究结果表明, 将格兰棱镜置于汇聚光路中, 光束偏离的一阶误差可以通过调节格兰棱镜的倾斜角有效补偿; 倾斜角大小与棱镜折射率、楔角及棱镜距电荷耦合元件靶面的距离成正比, 与棱镜厚度成反比. 该结果为研制高精度分时偏振成像系统提供了切实可行的理论依据.     

微小缺陷的非线性超声检测及其成像技术

采用通用超声检测设备并结合高通滤波技术获取了非线性超声的高次谐波信号,并将其用于薄板点焊焊核的微小缺陷检测及焊核的超声C扫描成像中。较之传统超声检测方法,采用非线性高次谐波检测薄板点焊焊核缺陷具有更高的时域分辨率及缺陷敏感度,能够更加准确的确定内部缺陷的位置及尺寸。此外,本研究还采用非线性高次谐波对薄板焊核进行超声成像分析,获得了清晰准确的焊核结构图像。非线性超声检测技术具有更高的检测效力,能够显著拓展检测系统的检测能力。      

基于柱弥散光源体内辐照的前列腺扫描光声成像仿体实验

光声成像技术是一种非常有前景的前列腺早期检测与成像的新技术. 在现有前列腺光声成像技术中, 通常采用的腺体外光源辐照方式由于受外围组织的影响, 容易减弱深部前列腺组织的光能量吸收, 导致辐照范围减小, 引起光声成像深度不足, 难以实现无损前列腺癌的检测. 本文基于前列腺组织的结构特征, 依据一种以柱状弥散光纤在尿道对前列腺实施光辐照、并利用外置于直肠内的长焦区聚焦式超声换能器检测光声信号的前列腺光声扫描成像技术, 构建了光声成像实验系统, 开展了仿体实验. 测试结果表明, 系统能够实现样品中吸收体的定位和成像, 结合柱弥散光源体内辐照可使成像深度提高, 同时侧向成像范围也较大. 初步结果表明, 借助柱弥散光源进行体内光辐照的光声信号新激发方式结合长焦区超声探头在前列腺癌早期无创诊断上具有潜在的应用前景.     

压电管式弯曲旋转超声电机激励模式研究

为了提高压电管式弯曲旋转超声电机输出特性,推导出定子一、二阶弯曲振动下力系数的计算公式。结果表明,利用定子二阶弯曲振动可获得更大的定子端面输出力。提出了一种将定子分为8个激振区的交叉组合激励模式,可实现定子的二阶弯曲振动激励。基于这种新的激励模式,研制了一台压电管式弯曲旋转超声电机的样机,该样机的定子外径10 mm、内径8 mm、长35 mm。在预压力1.0 N,激励电压峰峰值210 V,工作频率41.3 kHz时,实现了定子的二阶弯曲振动,样机的堵转转矩达到2.45 N·mm,空载转速为206 r/min。与将定子分为4个激振区的同尺寸的超声电机相比,堵转转矩和空载转速分别提高了17%和23%。      

数字式超声内窥成像系统(英文)

The development of a novel push-type ultrasonic endoscope is described in which probe rotation is accomplished by a small motor situated near the transducer. A digital FPGA-based ultrasound imaging system is implemented which uses coded excitation to increase the SNR and penetration depth, with probe rotation accomplished by a small motor situated near the transducer replacing the external motor and the long steel wire used in other ultrasonic endoscopes. The apparatus is tested continuously for 300 hours with no obvious problems. The coded excitation, digital quadrature demodulation imaging system can obtain ultrasonic images of higher quality and more information of the echo is preserved compared with the analog imaging system, because the analog digital conversion is moved to the first step of the signal processing.The digital imaging system possesses a higher SNR resulting in a sharp image. Locating the motor near the probe improves the consistency of rotational speed in comparison with external guide-wire rotation, and increases the image quality and life-span of these devices.     

Parameter optimization of pulse compression in ultrasound imaging systems with coded excitation

A linear array imaging system with coded excitation is considered, where the proposed excitation/compression scheme maximizes the signal-to-noise ratio (SNR) and minimizes sidelobes at the output of the compression filter. A pulse with linear frequency modulation (LFM) is used for coded excitation. The excitation/compression scheme is based on the fast digital mismatched filtering. The parameter optimization of the excitation/compression scheme includes (i) choice of an optimal filtering function for the mismatched filtering; (ii) choice of an optimal window function for tapering of the chirp amplitude; (iii) optimization of a chirp-to-transducer bandwidth ratio; (iv) choice of an appropriate n-bit quantizer. The simulation results show that the excitation/compression scheme can be implemented as a Dolph–Chebyshev filter including amplitude tapering of the chirp with a Lanczos window. An example of such an optimized system is given where the chirp bandwidth is chosen to be 2.5 times the transducer bandwidth and equals 6 MHz: The sidelobes are suppressed to −80 dB, for a central frequency of 4 MHz, and to −94 dB, for a central frequency of 8 MHz. The corresponding improvement of the SNR is 18 and 21 dB, respectively, when compared to a conventional short pulse imaging system. Simulation of B-mode images demonstrates the advantage of coded excitation systems of detecting regions with low contrast.     

Study on application of complementary Golay code into high frame rate ultrasonic imaging system

The high frame rate (HFR) ultrasonic imaging system, which is developed with limited diffraction beams, constructs images at a high frame rate. However the rectangular imaging area, to some extent, restricts the far field imaging information. At the same time, by virtue of one transmission event for constructing image, the system suffers from low SNR. In this paper we present a computationally efficient method to construct sector mode image and to increase the SNR in HFR system. The method uses orthogonal complementary Golay coded excitation to realize two transmit and receive events. Each emission simultaneously transmits two plane waves with different transmission angle. Then according to Golay code orthogonality, the received echo signals related to different angles are isolated and used to construct two images of different imaging area by HFR method. Finally the two images are synthesized to one frame of sector mode image.     

Potential of coded excitation in medical ultrasound imaging

Improvement in signal-to-noise ratio (SNR) and/or penetration depth can be achieved in medical ultrasound by using long coded waveforms, in a similar manner as in radars or sonars. However, the time-bandwidth product (TB) improvement, and thereby SNR improvement is considerably lower in medical ultrasound, due to the lower available bandwidth. There is still space for about 20 dB improvement in the SNR, which will yield a penetration depth up to 20 cm at 5 MHz [M. O'Donnell, IEEE Trans. Ultrason. Ferroelectr. Freq. Contr., 39(3) (1992) 341]. The limited TB additionally yields unacceptably high range sidelobes. However, the frequency weighting from the ultrasonic transducer's bandwidth, although suboptimal, can be beneficial in sidelobe reduction. The purpose of this study is an experimental evaluation of the above considerations in a coded excitation ultrasound system. A coded excitation system based on a modified commercial scanner is presented. A predistorted FM signal is proposed in order to keep the resulting range sidelobes at acceptably low levels. The effect of the transducer is taken into account in the design of the compression filter. Intensity levels have been considered and simulations on the expected improvement in SNR are also presented. Images of a wire phantom and clinical images have been taken with the coded system. The images show a significant improvement in penetration depth and they preserve both axial resolution and contrast.     

超声换能器对线性调频信号脉冲压缩性能的影响分析*

该文研究了不同编码带宽下超声换能器对编码信号脉冲压缩后信噪比与轴向分辨率的影响关系。将脉冲压缩后的时域峰值转化为频域积分的形式，得到考虑换能器影响的脉冲压缩信噪比公式。以线性调频信号为例，仿真与实验结果表明，编码激励相对于方波激励的信噪比增益随编码带宽的减小而增大，因为受换能器带宽限制，编码激励的轴向分辨率随编码带宽的增大先减小后趋于稳定。该研究为编码激励方法更有效地应用于超声检测的背景中提供了参考。     

In vivo three-dimensional photoacoustic tomography of a whole mouse head

An in vivo photoacoustic imaging system was designed and implemented to image the entire small animal head. A special scanning gantry was designed to enable in vivo imaging in coronal cross sections with high contrast and good spatial resolution for the first time to our knowledge. By use of a 2.25 MHz ultrasonic transducer with a 6 mm diameter active element, an in-plane radial resolution of approximately 312 microm was achieved. Deeply seated arterial and venous vessels in the head measuring up to 1.7 cm in diameter were simultaneously imaged in vivo with 804 nm wavelength laser excitation of photoacoustic waves.     

高分辨率快速数字化光声CT乳腺肿瘤成像

提出了一种基于聚焦线性阵列探测器的快速光声计算机断层成像技术（光声CT）.在光声二维图像重建中,根据阵列探测器机械扫描和电子扫描相结合的组合扫描模式,提出了改进的有限场滤波反投影重建算法.一方面该算法适合多元探测器旋转扫描模式,另一方面探测器的指向性函数作为反投影的权重因子提高了系统的横向分辨率.同时,该成像系统还利用柱面声透镜实现Z轴方向上的聚焦扫描以实现三维层析成像.实验中,这套成像系统空间分辨率达到0.2mm,Z轴方向分辨率为1.5mm,扫描一幅二维图像仅需150s,得到 关键词： 光声CT 有限场滤波反投影算法 声透镜聚焦 乳腺肿瘤检测     

基于聚焦换能器的超声透射CT技术*

超声透射CT技术能够重建物体横断面的图像,为了重建高质量图像,分别从换能器和图像重建算法两个方面展开研究。分析了弧形线聚焦换能器焦域处聚焦切片尺寸与换能器几何尺寸的关系及其对CT检测的影响。搭建了超声透射CT检测系统,以等角扇形束的扫描方式获取投影数据,并利用滤波反投影和最小二乘正交分解两种算法重建图像,对比发现最小二乘正交分解算法通用性更强,成像质量更佳。实验结果表明,利用聚焦换能器并结合最小二乘正交分解算法对物体进行CT检测,能够取得较好的成像结果,检测分辨力可达毫米量级。     

编码孔径光谱成像仪光学简化彗差对图谱反演误差分析

编码孔径光谱成像技术是近年来发展起来的一种新型光谱成像技术, 该技术在一次像面采用特定的编码模板对目标进行编码, 结合特殊的采样成像方式, 获得满足景物重构的采样数据量, 实现了空间信息和光谱信息的高精度重构, 具有高光通量、高信噪比等优势.但该技术实际的光学系统设计, 以及相应加工和装调过程中各种误差的存在, 将逐一传递反映到探测器精度与编码后图谱采样精度的不匹配, 这会引发最终重构图谱质量降低.本文侧重分析研究光学系统设计和研制装调中光学彗差相对设计值间存在的偏差, 通过几何光线追迹与波前像差联合计算的方法, 在成像面仿真出不同数值程度的彗差矩阵, 并以此来分析不同彗差下对重构图像质量的影响结果.并用其分析结论作为依据, 改进了编码孔径光谱成像仪的设计和研制, 提供了相应图像成像反演结果, 由此确保了编码孔径光谱成像仪的成像优势.     

The combined effect of spatial compounding and nonlinear filtering on the speckle reduction in ultrasound images

Recently, a spatial compounding ultrasound imaging method was presented that utilizes a conventional 64-element phased array transducer with two unfocused pistons, each placed at one of the sides of the phased array transducer. This method is augmented here by inclusion of nonlinear filtering of the compounded images. The combined effects of the specific spatial compounding and nonlinear filtering on speckle reduction in the generated ultrasound images are studied and evaluated in two stages: First, the image quality is studied when nonlinear filtering is used as part of the spatial compounding. The study is performed by simulations using the Field II program, by processing several B-mode images of a kidney. The second stage compares the results obtained by the simulations to those obtained by in vitro laboratory experiments. Five different compounding strategies and two nonlinear filters, Gaussian and anisotropic diffusion, are investigated and evaluated in terms of image quality parameters-contrast and signal-to-noise ratio. It is shown that the combination of "averaging+nonlinear Gaussian filtering" produces the greatest improvement of image quality. When compared to a conventional phased array imaging system, the spatial compounding method that includes the conventional 64-element phased array transducer with two unfocused pistons, and employs the "averaging+nonlinear Gaussian filtering" strategy, obtains improvement in SNR that has reached 334%. Thus, though this method necessitates a somewhat wider probe, it produces significantly improved images.