振动声成像系统分辨率研究

本文从振动声成像的基本原理出发，通过引入点扩展函数PSF和定义轴向响应函数ARF，研究了由凹球面聚焦换能器分割而成的一种典型共焦换能器参数对振动声成像系统侧向分辨率和轴向分辨率的影响。计算研究表明：增大凹球面换能器的口径、减小几何焦距和提高中心频率均可以提高系统的侧向分辨率和轴向分辨率；但改变凹球面换能器的分割比例对两种分辨率影响不尽相同。综合考虑超声换能器激励、聚焦性能以及产生的辐射力效果等因素，则换能器应按等辐射面积原则分割为宜。文中还分析了介质的声衰减系数对实际轴向分辨率的影响。  

Vibro-acoustography and multifrequency image compounding

Vibro-acoustography is an ultrasound based imaging modality that can visualize normal and abnormal soft tissue through mapping the acoustic response of the object to a harmonic radiation force at frequency Δf induced by focused ultrasound. In this method, the ultrasound energy is converted from high ultrasound frequencies to a low acoustic frequency (acoustic emission) that is often two orders of magnitude smaller than the ultrasound frequency. The acoustic emission is normally detected by a hydrophone. Depending on the setup, this low frequency sound may reverberate by object boundaries or other structures present in the acoustic paths before it reaches the hydrophone. This effect produces an artifact in the image in the form of gradual variations in image intensity that may compromise image quality. The use of tonebursts with finite length yields acoustic emission at Δf and at sidebands centered about Δf. Multiple images are formed by selectively applying bandpass filters on the acoustic emission at Δf and the associated sidebands. The data at these multiple frequencies are compounded through both coherent and incoherent processes to reduce the acoustic emission reverberation artifacts. Experimental results from a urethane breast phantom are described. The coherent and incoherent compounding of multifrequency data show, both qualitatively and quantitatively, the efficacy of this reverberation reduction method. This paper presents theory describing the physical origin of this artifact and use of image data created using multifrequency vibro-acoustography for reducing reverberation artifacts.  

高分辨率扇形阵列超声激发振动声成像研究

对扇阵换能器的振动声成像进行了研究.在相关振动声成像和扇阵换能器的理论基础上，经过推导修正并得到了精确的速度势函数.进一步计算并仿真了系统点扩散函数（point spread function, PSF），构造了组织模型，进行了成像仿真.最后分析了影响扇阵换能器系统分辨率的因素.研究结果表明：用扇阵换能器进行振动声成像可以获得很高的图像分辨率及对比度，在高强度聚焦超声（HIFU）治疗的热损伤检测等方面有重要的应用价值.分析指出通过提高换能器工作频率，减小几何焦距，增大口径可以提高系统的分辨率. 关键词： 振动声成像 扇形阵 点扩散函数  

大张角共焦换能器对振动声成像的影响*

振动声成像是超声成像的一种重要形式,它可以得到包含共焦区组织的弹性信息和声衰减信息的信号,将接收到的信号用于成像即可获得反映组织特性的图像。该文对大张角共焦换能器作用下振动声成像中声辐射力和切变位移进行了理论计算和数值模拟,并通过改变张角变化及频率大小研究其对声辐射力和切变位移的影响。这项工作为大张角共焦换能器在振动声成像中的应用提供了理论支持。  

超声激发生物组织声发射的原理及应用

介绍一种利用双频共焦超声波获取组织内部特性信息的新方法一超声激发声发射(USAE)。本文着重说明了USAE的基本工作原理，然后介绍了USAE在医学成像和组织无损测温两方面的重要应用。最后指出了一些有待研究的问题。