【作者】 卢涛；

【导师】 王瑞康；

【作者基本信息】 天津大学 ， 物理电子学， 2007， 博士

【摘要】 光声成像(Photoacoustic Tomography/PAT)利用短脉冲激光照射生物组织所产生的超声波进行成像,反映生物组织对特定波长激光吸收特性的空间分布,可得到高分辨率和对比度的组织断层图像。本文首先对生物组织的光学和声学特性、光声信号的产生机理以及图像重建算法进行了总结。在此基础上,用数值模拟的方法研究了影响成像空间分辨率的若干因素。用数值模拟与实验相结合的方法研究了超声探头的频率响应特性对光声图像对比度的影响并提出了相应的信号处理方法。完成了基于线性阵列超声探头的光声成像系统,提高了光声成像的速度。完成了基于非聚焦针状超声探头的光声成像系统,得到了活体白鼠脑皮层血管和离体动物眼球的高对比度光声图像。主要内容包括:1.以点扩展函数(Point Spread Function/PSF)为依据,用数值模拟的方法计算了滤波器上限截止频率与带宽、探头探测面孔径大小以及探头的探测距离与光声成像空间分辨率的关系。结果表明:点扩展函数的半峰全宽(FWHM)随着滤波器带宽和上限截止频率的增加呈指数的关系减小;在相同的探头扫描半径情况下,点扩展函数的扩散范围随着探头有效探测面直径的增加而线性地扩大;在相同的探测面直径下,点扩展函数的扩散程度随着探头的扫描半径的减小而增加。模拟计算的结果为实验中成像空间分辨率的提高提供了理论依据。2.提出了基于维纳滤波的点源逆卷积的信号处理方法,避免了逆卷积过程中对宽带光声信号进行带通滤波时对滤波器带宽和截止频率的人为限制,宽带光声信号的幅频特性得到了很好地恢复,显著提高了光声图像的对比度。3.在国内率先对光声技术在眼科成像中的应用进行了试探性的研究,得到了高对比度的离体猪眼睛整体生理结构的光声图像。4.研究了探头的空间扫描位置对成像质量的影响,发现了图像中像素点空间位置坐标的累积误差是造成图像边缘变形的重要因素,可以通过适当增大探头的扫描半径来消除这一因素的影响。更多还原

【Abstract】 In photoacoustic tomography(PAT), a short-pulsed laser is used to irradiate biological tissue samples to generate acoustic wave. Photoacoustic image reconstructed from the photoacoustic(PA) signal reveals the spatial optical absorption distribution at a certain wave length and has the advantage of both high imaging resolution and contrast. In this dissertation, the optical and acoustic properties of biological tissue is firstly summarized. Then, several factors that influences the spatial resolution is researched by numerical simulation. The relationship between the transducer frequency response and imaging contrast is researched both by numerical simulation and experiment. The corresponding signal processing method is also proposed. A photoacoustic imaging system based on the linear acoustic transducer array is developed and the imaging speed had been improved. A photoacoustic imaging system based on unfocused needle acoustic transducer is developed and the photoacoustic image with high contrast and resolution of the blood vessel network inside mouse brain in-vivo and the porcine eyeball ex-vivo is acquired. The main contents in this dissertation is as follows:1. Taking the Point-Spread-Function(PSF) as the criteria, the relationship between the spatial resolution and the several influencing factors such as the band-width and upper cutoff frequency of the filter, the diameter of the transducer active detecting surface and the transducer detecting radius is researched numerically. The results shows that the full width at half maximum(FWHM) of PSF decreases exponentially with the increase of the band-width and the upper cutoff frequency of the filter. The PSF diffuses linerly with the increase of the active detecting diameter of the transducer. With the same active detecting diameter of the transducer, the PSF diffuses with the decrease of the transducer scanning radius. The numerical simulation provides the theoretical basis for the improvement of the spatial resolution of PA image.2. The deconvolution algorithm with wiener filter based on the transducer point source response is presented. The method had avoided the determination of the band-width and the cutt-off frequency of the band-pass filter manually during deconvolution. The frequency spectrum of the wide-band PA signal had been restored preferably and the imaging contrast had been improved. 3. The trial photoacoustic tomography for ophthalmology is performed. The two dimensional optical absorption image of the entire porcine eyeball was reconstructed with high imaging contrast.4. The relationship between the spatial position of the transducer and the PA image quality is researched. The accumulated spatial position error of pixels in PA image is founded to be the main factor that causes the distortion on the edge of the PA image. The distortion can be eliminated by the increase of transducer scanning radius.更多还原