A novel approach to the aperture windowing in medical imaging

A new technique is proposed to improve the lateral resolution in the conventional B-mode imaging systems, which enables a simple array aperture windowing in the transmitting mode. Amplitude shaping is performed without modifying the transmitting voltage of the array elements, but only varying the excitation pulse length from one element to another. This method presents some attractive practical advantages, and the reduction of the sidelobe energy is comparable to that attainable with a conventional aperture windowing. Parametric plots are given, which transform an amplitude apodization into a 'time apodization' for any type of transducer array.     

Ultrasonic guided wave focusing by a generalized phased array

Ultrasonic guided wave focusing by a generalized phased array is studied based on dispersion curves in a multi-layered medium. The different phase of the guided waves with different frequency is added on the excitation signal on each element of the transducer array for focusing. This can be realized by designing a proper excitation pulse based on the dispersion curves of the guided waves for each of the transducer array elements. The numerical simulation results show that the guided waves with different modes, different frequency components, and from different elements of the transducer array can all be focused at the target and focusing is achieved.     

基于超声相控阵的环焊缝缺陷检测方法研究

针对传统超声探头焦距固定,检测位置的改变就要更换相应焦距的探头而影响检测效率的问题,提出一种基于超声相控阵换能器的环焊缝缺陷检测方法。而超声相控阵具有电子偏转和电子聚焦特性,能在不移动的情况下发射偏转聚焦超声束,有效地解决了上述问题。首先基于超声相控线阵换能器的声场特点,采用数值分析方法,研究了影响声束偏转聚焦性能的几个主要参数。然后给出了与超声相控阵换能器相连接的多通道数据采集系统结构。介绍了单通道声信号的硬件结构及相应的信号处理方法,实现了对换能器中单个阵元的精确延时的控制。实验结果表明,优化设计的超声相控线阵换能器具有较高的检测精度和检测效率。     

超声阵列的多频脉冲压缩方法研究

脉冲压缩方法通过采用编码信号激励与脉冲压缩接收来提高超声检测的时间分辨率和信噪比。然而,受换能器带宽的限制,编码信号的时间带宽积往往有限,影响脉冲压缩效果。开展了基于超声阵列的多频脉冲压缩方法研究,超声阵列是由具有不同中心频率和带宽的多个阵元组成,从而使得整个阵列具有比单个换能器更宽的带宽。提出了压缩后叠加取包络的脉冲压缩方法,并研究了这种方法在提高时间分辨率和主副瓣比上的技术方案,对多频脉冲压缩的超声阵列进行了设计与优化,发现多频脉冲压缩方法能很大程度地提高时间分辨率,并能有效地抑制各阵元信号叠加产生的周期副瓣。理论和实验结果表明,这种压缩后叠加取包络的方法得到的时间分辨率在性能上受阵元带内不平整度的影响很小,能使阵元压缩包络中的主副瓣比得到明显改善。     

楔块中脉冲声场及相控阵成像自检研究

相控阵横波检测必须在换能器前方加上楔块,对于楔块中的声场进行研究具有重要意义。本文通过数值计算和物理实验研究了超声相控阵楔块中的脉冲声场,分析并解释了超声相控阵系统自检成像过程中各种波形的产生机理和转换过程。首先从固体中超声传播理论出发,采用时域有限差分方法对相控阵楔块中各阵元独立发射条件下的脉冲声场进行仿真计算,给出了超声脉冲在楔块中的传播过程;然后开展了对应边界条件下相控阵楔块的B模式成像实验。数值模拟和物理实验的结果基本一致。本文的研究初步展示了楔块中的脉冲声场,其结果可为超声相控阵系统自检和楔块设计提供参考。     

Piezoelectrically actuated flextensional micromachined ultrasound transducers

This paper presents novel micromachined two-dimensional array piezoelectrically actuated flextensional transducers that can be used to generate sound in air or water. Micromachining techniques to fabricate these devices are also presented. Individual unimorph array elements consist of a thin piezoelectric annular disk and a thin, fully clamped, circular plate. We manufacture the transducer in two-dimensional arrays using planar silicon micromachining and demonstrate ultrasound transmission in air at 2.85 MHz with 0.15 microm/V peak displacement. The devices have a range of operating resonance frequencies starting from 450 kHz up to 4.5 MHz. Such an array could be combined with on-board driving and addressing circuitry for different applications.     

多通道超声相控阵驱动控制系统设计

低强度经颅聚焦超声是一种利用脉冲聚焦超声调控脑神经元的治疗技术。为抑制人颅骨的非均质性和个体结构差异影响,须对多阵元相控阵聚焦换能器的各阵元进行参数调控实现经颅精准定位聚焦,各阵元参数调控需通过相位控制和驱动电路系统来实现。该文设计并搭建了一种基于直接数字式频率合成技术的多通道相位、幅值独立可调的相控驱动系统。实测结果表明,可实现正弦波和方波高精度相控输出,输出信号电压峰峰值在0~37.5 V可调,相位分辨率为0.1°,延时误差小于1 ns,可满足多阵元相控阵聚焦换能器驱动及其所需相位分辨率的需要。     

Proposal of the nano-sensing device and system using a nano-waveguide transducer for distributed sensors

We propose a new concept of a distributed sensing system using a nano-waveguide and an array waveguide. The small change in physical quantity affects the change in device parameters such as refractive index or length, which is relatively absorbed and observed by the resonant wavelength. In principle, the dense wavelength separation is generated by using a soliton pulse propagating within a ring resonator system, whereas a resonant signal can be stored within the nano-waveguide, i.e. a transducer, which is formed by the sensing device. Induced change in the resonant signal at each wavelength occurs, and can be detected by using the optical spectrum analyzer. Such a proposed device is suitable to perform the measurements in the nano-scale regime such as force, stress and temperature. Moreover, the distributed or multiplexed sensing applications are also available using the nano-waveguide sensing device incorporating the array waveguide, which is discussed in details. Quantum measurement using the same system is also described.     

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。     

Feasibility of 3D harmonic contrast imaging

Improved endocardial border delineation with the application of contrast agents should allow for less complex and faster tracing algorithms for left ventricular volume analysis. We developed a fast rotating phased array transducer for 3D imaging of the heart with harmonic capabilities making it suitable for contrast imaging. In this study the feasibility of 3D harmonic contrast imaging is evaluated in vitro. A commercially available tissue mimicking flow phantom was used in combination with Sonovue. Backscatter power spectra from a tissue and contrast region of interest were calculated from recorded radio frequency data. The spectra and the extracted contrast to tissue ratio from these spectra were used to optimize the excitation frequency, the pulse length and the receive filter settings of the transducer. Frequencies ranging from 1.66 to 2.35 MHz and pulse lengths of 1.5, 2 and 2.5 cycles were explored. An increase of more than 15 dB in the contrast to tissue ratio was found around the second harmonic compared with the fundamental level at an optimal excitation frequency of 1.74 MHz and a pulse length of 2.5 cycles. Using the optimal settings for 3D harmonic contrast recordings volume measurements of a left ventricular shaped agar phantom were performed. Without contrast the extracted volume data resulted in a volume error of 1.5%, with contrast an accuracy of 3.8% was achieved. The results show the feasibility of accurate volume measurements from 3D harmonic contrast images. Further investigations will include the clinical evaluation of the presented technique for improved assessment of the heart.     

基于FPGA的高强度聚焦超声相位控制系统设计*

多阵元相控阵换能器具有焦距可调和可实现经颅聚焦等优势,近来受到众多研究者的关注,其相位控制系统是决定多阵元相控换能器能否应用于临床的关键技术之一。在输出信号稳定的同时提高高强度聚焦超声相位控制系统精度是设计过程中的重点与难点。本文基于现场可编程门阵列设计了一种高强度聚焦超声相位控制系统。实测结果表明,多通道延时分辨率为1 ns,延时误差小于1 ns,可满足多阵元高强度聚焦超声治疗相控聚焦换能器延时精度的需要。     

A new-style phased array transducer for HIFU

Considering the complexity of common phased array, and relatively slow mechanical scanning of the single transducer, a new-style transducer that has a changeable focus and a simple control system is needed. The sector phased array transducer, which has many advantages including easy fabrication, movable focus, and a simple control system, can reach the desired requirements. This paper has demonstrated its feasibility by the computation of acoustic field in (y, z) plane. The 24-element phased array, of which the length of the focal region is about 10 mm, and the maximum lateral diameter is about 1.5 mm, can accomplish the adjustment of the focus position. The maximum lateral displacement is 1.5 mm, and the treatment area is about 9 multiples of the single transducer, and only six power amplifiers are needed.     

基于时间反转法的相控换能器声场的仿真研究

相控换能器具有焦距可调的优势。本文以82阵元相控换能器建立的3D数值仿真模型为例,基于时间反转法提取阵元的激励信号,利用时域有限差分(FDTD)法对Westervelt声波非线性传播方程进行声场数值仿真,研究不同阵元分布、偏离声轴的距离、设定焦距大小对形成声场的影响,可调控范围及其消除旁瓣方法。研究结果表明,随机分布相控阵可明显降低声场中的旁瓣;随着偏离声轴距离的增加,主瓣声压幅值逐渐减小,旁瓣与主瓣的最大声强比值r逐渐增大,且沿声轴的可调控范围逐渐减小;随声轴方向上设定焦距的增加,主瓣声压幅值先增大后减小,r值先减小后增大;基于时间反转法的高声压旁瓣消除法可在一定程度上扩大相控阵声场的可调控范围。     

用于光声层析成像的虚拟阵列探测及逆拉东变换

提出用固定孔径的换能器虚拟阵列探测器进行数据采集,该换能器只需对样品进行180扫描。实验中,使用调Q Nd: YAG激光器作为光源,激光器输出激光波长为532 nm,重复频率为10 Hz,脉宽为7 ns;使用非聚焦换能器进行光声信号探测,其接收面直径为6 mm,中心频率为2.25 MHz,接收到光声信号用逆拉东变换进行图像重建。以小白鼠的离体爪子作为成像对象,换能器由旋转电机控制并以2作为旋转步长进行180旋转扫描获取实验数据,运用逆拉东变换进行了图像重建。所重建的图像比较清晰地反映了爪子内部的骨骼分布。由此表明,逆拉东变换可以用于光声成像,并且实现了有限角度的光声成像。     

用于光声层析成像的虚拟阵列探测及逆拉东变换

提出用固定孔径的换能器虚拟阵列探测器进行数据采集,该换能器只需对样品进行180扫描。实验中,使用调Q Nd: YAG激光器作为光源,激光器输出激光波长为532 nm,重复频率为10 Hz,脉宽为7 ns;使用非聚焦换能器进行光声信号探测,其接收面直径为6 mm,中心频率为2.25 MHz,接收到光声信号用逆拉东变换进行图像重建。以小白鼠的离体爪子作为成像对象,换能器由旋转电机控制并以2作为旋转步长进行180旋转扫描获取实验数据,运用逆拉东变换进行了图像重建。所重建的图像比较清晰地反映了爪子内部的骨骼分布。由此表明,逆拉东变换可以用于光声成像,并且实现了有限角度的光声成像。     

水平管道段塞流特征参数的压差波动分析

分析了压力波动信号互相关求液塞速度存在的不足，引入了压差波动分析法；明确了液塞到达和离开上、下游测压点的时刻与压差波动信号起峰点与落峰点位置的关系；指出了压差信弓脉冲宽度为液塞义到达上游测压点和液塞尾离开下游测压点的时间间隔，脉冲宽度与液塞速度的乘积为液塞长度与差压传感器间距之和．把空气－水、柴油和机械油的试验结果与文献中经验关系式进行了对比，验证了该测量方法的正确性．     

Acoustic power measurement of high intensity focused ultrasound in medicine based on radiation force

How to measure the acoustic power of HIFU is one of the most important tasks in its medical application. In the paper a whole series of formula for calculating the radiation force related to the acoustic power radiated by a single element focusing transducer and by the focusing transducer array were given. Various system of radiation force balance (RFB) to measure the acoustic power of HIFU in medicine were designed and applied in China. In high power experiments, the dependence of radiation force acting the absorbing target on the target position at the beam axis of focusing transducer was fined. There is a peak value of "radiation force" acting the absorbing target in the focal region when the acoustic power through the focal plane exceeds some threshold. In order to avoid this big measurement error caused by the 'peak effect' in focal region, the distance between the absorbing target of RFB and the focusing transducer or transducer array was defined to be equal to or less than 0.7 times of the focal length in the National Standard of China for the measurements of acoustic power and field characteristics of HIFU. More than six different therapeutic equipments of HIFU have been examined by RFB for measuring the acoustic power since 1998. These results show that RFB with the absorbing target is valid in the acoustic power range up to 500W with good linearity for the drive voltage squared of focusing transducer or array. The uncertainty of measurement is within +/-15%.     

大电流恒功率放电技术在大功率DPL中的应用

针对大功率激光二极管泵浦固体激光器(DPL)对大功率驱动电源的特殊要求,设计了一种大电流恒功率放电及驱动控制电路。将该电路与现有的充电和过流保护电路组成一套完整的激光二极管阵列驱动电源,并应用于基于大功率激光二极管阵列的DPL系统中。该驱动电源可为DPL系统提供频率为20 Hz,脉冲宽度为230 s,200 A以上的驱动电流,这将对多种以DPL为基础的激光武器系统产生重要的实际应用价值。     

主动相位偏置折叠型萨尼亚克光纤传感阵列时分复用技术

针对折叠结构萨尼亚克(Sagnac)光纤传感阵列存在噪声光与信号光混叠的问题,提出了一种主动相位偏置时分复用方案.在传统梯形结构传感阵列的基础上,通过调整总线光纤的长度关系和附加延迟光纤的方法,使噪声光和信号光依次交替返回而不会发生混叠.进一步分析表明,通过调整延迟光纤环的长度,可以使输入光脉冲的重复频率达到标准时分复用系统重复频率的二分之一.整个阵列的相位偏置由一个与输入光脉冲同步的相位调制信号驱动集成光学芯片实现.实验演示了一个两基元的传感阵列,最小时间间隔为331.25 ns,输入光脉冲重复频率可达754.727 kHz,在5 kHz处相位灵敏度为7.3μrad√(Hz),探头间串扰约为-51.75 dB.     

Ultrasonic focusing and scanning with multiple waves

This paper presents a new focusing and scanning method which focuses multiple waves on a target. The key of the method is to control excitation pulses for each element of the transducer array. The excitation pulse on each array element is obtained by time reversing the signal received by the same element, which is generated by an imaginary source at the target. The excitation pulses from all array elements are transmitted and arrive at the target simultaneously, and focusing is achieved. The performance of the two methods is compared in numerical examples, and it is demonstrated that the proposed method achieves a satisfactory focusing and a good signal-to-noise ratio no matter where the target location is.