基于声透镜的三维光声成像技术

基于声透镜的光声成像系统中, 由样品的光声压分布等效样品的吸收分布, 进行光声像重建, 但之前的这种等效是一种近似, 理论上并不准确. 本文阐述了声透镜三维光声成像的基本原理, 揭示了声透镜像面上光声压信号的时间分布与样品轴向吸收分布之间的关系; 提出用积分法和希尔伯特变换提取光声信号瞬时值法, 解调样品吸收系数分布并重建光声像; 实验上, 对不同样品分别用积分法和希尔伯特变换法获取样品的吸收系数, 重建光声像的横向和轴向分辨率均约为1 mm, 实现了真正的三维快速光声成像.     

基于声学扫描振镜的超声/光声双模态成像技术

超声/光声双模态成像技术因其同时兼具超声的高分辨率结构成像和光声的高对比度功能成像优势,极大地推动了光声成像技术的临床应用推广.传统超声/光声双模态成像技术多基于超声成像所用阵列探头同时收集光声信号,系统结构紧凑且无需图像配准,操作便捷.但该类设备使用阵列探头和多通道数据采集,使得其成本较高;且成像结果易受通道一致性差异影响.本文提出了一种基于声学扫描振镜的超声/光声双模态成像技术,该技术采用单个超声换能器结合一维声学扫描振镜进行快速声束扫描,实现超声/光声双模态成像,是一种小型化、低成本的双模态快速成像技术.本文开展了系列仿体和活体成像研究,实验结果表明:系统有效成像范围为15.6 mm,超声和光声成像B扫描速度分别为1.0 s^–1和0.1 s^–1 (光声成像速度主要受制于脉冲激光器重复频率).基于本文所提技术研究,有助于进一步推动超声/光声双模态成像技术的临床转化和普及;也为基于超声信号检测的多模态成像技术提供了一种低成本、小型化和快速声信号检测的参考方案.     

基于长焦区聚焦换能器的扫描光声乳腺成像技术

报道了一种利用长焦区聚焦超声换能器检测光声信号的扫描光声乳腺成像系统.通过增加聚焦换能器焦区的长度,该技术可以快速实现对大块组织(如乳腺)的光声成像.测试结果表明,该实验系统能够对大块模拟样品中吸收体的位置、尺寸以及光能量吸收情况实现较为准确的成像.另外,实验中,该系统还可便捷地与传统的超声技术相结合,从而实现多模式复合的乳腺癌诊断.初步结果显示了该技术路线在乳腺癌早期诊断应用上的前景. 关键词： 乳腺癌诊断 光声成像 扫描光声层析术 脉冲回波法     

基于镂空阵列探头的反射式光声/热声双模态组织成像

光声和热声成像技术除激发源不同外,可共用一套数据采集和处理系统,具有天然的融合优势.本文提出了一种基于镂空阵列的反射式光声/热声双模态成像技术,该技术利用光纤与天线,通过镂空阵列的开孔进行光声/热声信号激发,使得激发光、微波和接收超声信号共轴,构成明场光声/热声双模态成像模式.通过对探头镂空部分晶元相位和幅值的补偿校准,成功实现了3 mm直径塑料管、人体手臂、手背和脚背的双模态成像.实验结果表明:系统空间分辨率为0.33 mm,双模态成像技术可同时提供组织的光学和微波吸收分布,有助于肿瘤、糖尿病足等疾病的精准检测,具有极广泛的临床应用前景.     

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     

基于声透镜成像系统的光声层析成像

光声成像是采用“光激发-超声波成像”的新型成像技术，它是检测强散射介质内部光吸收分布的一种有效医学影像技术.用短脉冲激光照射强散射介质(如生物组织)，强散射介质由于光声效应产生超声信号，使用具有成像能力的声透镜把声压分布成像于像面上，然后利用具有空间分辨能力的阵列光声传感器，把同一像面上的光声信号强度记录下来，最后根据光声信号强度的空间分布进行图像重组.根据成像系统物像共轭原理，同一物平面的光声信号到达像面的时延相等，而不同物面的光声信号到达同一个探测器平面的时延各不相同，因此，利用BOXCAR的门控积分 关键词： 光声层析成像 声透镜 光声信号     

光声信号的双谱分析方法研究

基于光声效应的光声光谱技术是光学与声学的有机结合, 可利用不同波长的入射光波, 产生不同的光声信号, 从而为组分识别、组织无损检测等提供高对比度图像, 是一种极具潜力的新型医学诊断技术.但光声光谱检测技术由于受检测方法的制约, 往往扫描时间较长, 而且信号的稳定性和图像识别的准确性也较差. 为了弥补单一光声光谱分析的局限性, 根据光声效应原理和振动理论, 提出了一种光声光谱与光声频谱相结合的双谱分析方法. 该方法通过光声频域信息的定量分析, 可以有效地提高不同组织的光声图像对比度, 从而提高光声成像的组分识别能力, 为光声频谱功能成像奠定理论基础. 实验结果显示, 光声光谱与光声频谱相结合的双谱分析方法可以较好地识别实验组织样品, 可实现高速、高分辨率的组分识别、组织探伤等, 具有广泛的应用前景和重要的临床诊断意义. 关键词： 光声成像 光声光谱分析 光声频谱分析     

生物医学光声成像

能够对组织体中的光学吸收体进行量化评估的光声成像(photoacoustic imaging)是一种有发展前景的医学成像模式.文章综述了处于快速发展阶段的光声成像技术.文章首先介绍光声成像的物理基础--光声效应.在此基础上,阐述光声成像技术的优势所在(与光学以及超声成像相比较).然后讨论目前该领域的主要技术路线,包括扫描层析术、计算机层析术以及原位探测成像技术.最后简要总结了光声成像技术在生物医学领域中的主要应用.     

自适应多光谱光声成像技术研究

光声成像技术是利用激光照射组织产生超声波成像的新型医学影像技术.在传统光声成像中,由于组织体内复杂的成分与环境会对入射光波产生较大的扰动而导致波前畸变、图像分辨率下降,从而降低诊断的准确性.为了克服这一影响,本文提出了一种自适应多光谱光声成像技术.该技术利用自适应光学技术可有效地降低组织对光波扰动的影响,提高系统成像分辨率与图像对比度.此外,该系统还融合了多光谱成像技术,可在多种波长下对目标成像,从而更好地进行组织结构识别、组分分析等.实验结果表明,该系统十分适用于复杂的生物组织光声成像,可极大地增强光声成像性能,在生物医学领域具有广阔的应用前景.     

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.     

基于多元线性阵列探测器的快速光声层析成像

报道了一种基于相控聚焦的多元线性阵列探测器进行快速光声层析成像的方法和装置,并实现了模拟组织的光声层析成像。实验中采用波长为532nm脉宽为7ns的倍频Q-YAG激光器作为激发光源。多元线性阵列探测器由320个振元组成,采用相控聚焦的方法成像,每次由11个振群的探测器接受信号并合并1路,一幅图像由64路这样的信号组成。实验结果能够正确反映样品中的光学吸收分布。与现有的方法比较,本系统具有快速方便的特点,它有望成为一种组织功能在体成像的新方法,发展成为一种低成本的实用的临床诊断装置。     

Photoacoustic Tomography of Biological Sample Using Phase-controlled Focus Algorithm

Photoacoustic (PA) imaging is a new imaging modality, which converts pressure signals received by a scanning detector to a local distribution of electromagnetic absorption density. In this paper an experiment result of a photoacoustic tomography to depths of ～7 mm for a real tissue is presented, using a 532-nm pulse YAG laser. The time-resolved stress detection technique was used for PA signal detection with a high temporal resolution. A phase-controlled focus algorithm was used for image reconstruction. Images of different depth profiles in tissue were obtained. The depth resolution was 30 μm and could be up to 10 μm using a wide-band tranducer.     

Photoacoustic Tomography of Biological Sample Using Phase-controlled Focus Algorithm

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Photoacoustic and ultrasonic coimage with a linear transducer array

A technique is developed to simultaneously acquire ultrasound and photoacoustic (PA) images based on a linear transducer array. The system uses conventional ultrasound for rapid identification of potential targets. After a target is identified, the ultrasound echo and PA signals can be simultaneously obtained with optimized excitation and a signal collection sequence. The corresponding ultrasound impedance and optical absorption images are reconstructed with a phase-controlled algorithm. The approach can effectively reduce the artifacts associated with a conventional filter backprojection algorithm used in PA imaging by linear scanning. The technique provides a new approach for practical applications.     

多模态光声分子成像进展*

现代的各种医学影像术,如射线成像、CT、正电子发射(PET)、磁共振(MR)、超声(US)、荧光(FL)等都各具特色,并成功地应用于多种疾病的诊疗。但每种影像术都不能对生物组织做出完整的描述。由若干个成像技术组成的多模态成像技术,是获得组织更多信息的有效途径。光声(PA)成像是能提供组织的成分和功能信息的新成像技术。它不仅灵敏,可以对较深层的组织进行实时、快速、安全的成像,而且可以利用光声光热造影剂实施非侵入的光热靶向治疗。因此,与光声成像相结合的多模态分子成像是实现精准诊疗的重要技术途径。该文以手持US-PA探头的双模态成像系统,直径为1 mm的血管內窥镜US-PA成像系统,可同时用于术前和术中的US-PA-FL三模态成像系统,以及采用外磁场可操控的磁共振-光声光热分子造影剂、进行MR-PA成像引导的光热治疗技术为例,对多模态光声分子成像系统在医学诊断、手术和光热治疗方面的进展做简单介绍。     

High-contrast imaging based on wavefront shaping to improve low signal-to-noise ratio photoacoustic signals using superpixel method

Photoacoustic(PA) imaging has drawn tremendous research interest for various applications in biomedicine and experienced exponential growth over the past decade. Since the scattering effect of biological tissue on ultrasound is two-to three-orders magnitude weaker than that of light, photoacoustic imaging can effectively improve the imaging depth.However, as the depth of imaging further increases, the incident light is seriously affected by scattering that the generated photoacoustic signal is very weak and the signal-to-noise ratio(SNR) is quite low. Low SNR signals can reduce imaging quality and even cause imaging failure. In this paper, we proposed a new wavefront shaping and imaging method of low SNR photoacoustic signal using digital micromirror device(DMD) based superpixel method. We combined the superpixel method with DMD to modulate the phase and amplitude of the incident light, and the genetic algorithm(GA) was used as the wavefront shaping algorithm. The enhancement of the photoacoustic signal reached 10.46. Then we performed scanning imaging by moving the absorber with the translation stage. A clear image with contrast of 8.57 was obtained while imaging with original photoacoustic signals could not be achieved. The proposed method opens new perspectives for imaging with weak photoacoustic signals.     

Method of bimodal photoacoustic and ultrasound microscopy for simultaneous structural and functional diagnostics of biotissues

The excitation of external electrode of focused photoacoustic (PA) detector by the backscattered laser radiation can ensure a cost-effective upgrade from single-modality PA microscopy to dual-modality PA/US imaging. In this work we approbated thermoelastic generation of probing ultrasonic pulses for bimodal photoacoustic (PA) and optically mediated Ultrasound (US) microscopy in vivo, using single optical pulse delivered from tunable laser to form both PA and US A-scans. The presented results of bimodal in vivo visualization of rat brain provide with the experimental evidence, that the proposed approach can be used for both functional and structural bioimaging simultaneously.     

Lensless high-resolution photoacoustic imaging scanner for in vivo skin imaging

We previously launched a high-resolution photoacoustic (PA) imaging scanner based on a unique lensless design for in vivo skin imaging. The design, imaging algorithm and characteristics of the system are described in this paper. Neither an optical lens nor an acoustic lens is used in the system. In the imaging head, four sensor elements are arranged quadrilaterally, and by checking the phase differences for PA waves detected with these four sensors, a set of PA signals only originating from a chromophore located on the sensor center axis is extracted for constructing an image. A phantom study using a carbon fiber showed a depth-independent horizontal resolution of 84.0 ± 3.5 µm, and the scan direction-dependent variation of PA signals was about ± 20%. We then performed imaging of vasculature phantoms: patterns of red ink lines with widths of 100 or 200 μm formed in an acrylic block co-polymer. The patterns were visualized with high contrast, showing the capability for imaging arterioles and venues in the skin. Vasculatures in rat burn models and healthy human skin were also clearly visualized in vivo.     

Design and characteristics of a differential Helmholtz resonant photoacoustic cell for infrared gas detection

The Helmholtz resonant photoacoustic (PA) cell is a very convenient design of PA system for air pollution monitoring based on infrared molecular absorption. A simple differential Helmholtz resonator designed for flow measurements is presented in this work. The investigation of the PA systems characteristics based on this design includes experimental study of the responsitivity both of the separate photoacoustic cell and the whole photoacoustic system applied to trace gases detection. The experimental observations are compared to the theoretical predictions. A simple arrangement to enhance the photoacoustic signal of the whole system by a factor of 2 is presented.     

Viscoelasticity imaging of biological tissues with phase-resolved photoacoustic measurement

A method for noninvasive viscoelasticity imaging of biological tissues using phase-resolved photoacoustic measurement is presented. We deduced the process of photoacoustic effect on the basis of thermal viscoelasticity theory, and established the relationship between the photoacoustic phase delay and the viscosity-elasticity ratio for soft solids. Agar phantoms with different densities and different absorption coefficients were used to verify the dependence of photoacoustic phase-resolved viscoelasticity measurements. Moreover, viscoelasticity imaging of tissues was obtained with a photoacoustic point scanning system. The photoacoustic phase-resolved method provides a basis for viscoelasticity imaging, which can potentially be used for detection of viscoelastic properties and lesions of biological tissues.