A new ultrasonic transducer for improved contrast nonlinear imaging
A new ultrasonic transducer for improved contrast nonlinear imaging
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DOI：
10.1088/0031-9155/49/16/001
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发表时间：
2004-08-21
影响因子：
3.5
通讯作者：
de Jong, N
中科院分区：
文献类型：
--
作者：
Bouakaz, A;ten Cate, F;de Jong, N
二次谐波成像在对比度检测方面比基波成像有了显著的改进。这一改进是在二次谐波频率下可实现更高的对比度与组织比(CTR)的结果。然而，在许多情况下，在二次谐波下区分对比度和组织仍然是困难的，对比度检测仍然是当今的主要挑战之一，尤其是在毛细血管中。CTR的降低主要是由于组织中的非线性传播效应产生的二次谐波能量，从而掩盖了造影剂气泡的回声。在以前的研究中，我们从理论上证明了CTR随谐振数的增加而增加。因此，我们研究的目的是通过选择性地寻找更高的谐波频率来提高CTR。为了能够接收这些高频分量(三次至五次谐波)，构造了一种新型的超声相控阵换能器。新设计的主要优势是其较宽的频率带宽。新的阵列换能器包含以交错模式排列的两种不同类型的元素(奇数和偶数元素)。这种设计实现了独立的发送和接收模式。奇数单元的工作频率为2.8 MHz，带宽为80%，而偶数单元的中心频率为900 kHz，带宽为50%。探头连接到Vivid 5系统(GE-Vingmed)，并开发了适当的驱动软件。这种换能器的总带宽估计超过150%，与标准的医用阵列换能器相比，它可以在足够的灵敏度和信噪比下实现更高的谐波成像。本文介绍了阵列式换能器的设计和制作。此外，还对其声学特性进行了测量，并对其在体内外的非线性对比成像性能进行了评价。
Second harmonic imaging has provided significant improvement in contrast detection over fundamental imaging. This improvement is a result of a higher contrast-to-tissue ratio (CTR) achievable at the second harmonic frequency. Nevertheless, the differentiation between contrast and tissue at the second harmonic frequency is still in many situations cumbersome and contrast detection remains nowadays as one of the main challenges, especially in the capillaries. The reduced CTR is mainly caused by the generation of second harmonic energy from nonlinear propagation effects in tissue, which hence obscures the echoes from contrast bubbles. In a previous study, we demonstrated theoretically that the CTR increases with the harmonic number. Therefore the purpose of our study was to increase the CTR by selectively looking to the higher harmonic frequencies. In order to be able to receive these high frequency components (third up to the fifth harmonic), a new ultrasonic phased array transducer has been constructed. The main advantage of the new design is its wide frequency bandwidth. The new array transducer contains two different types of elements arranged in an interleaved pattern (odd and even elements). This design enables separate transmission and reception modes. The odd elements operate at 2.8 MHz and 80% bandwidth, whereas the even elements have a centre frequency of 900 kHz with a bandwidth of 50%. The probe is connected to a Vivid 5 system (GE-Vingmed) and proper software is developed for driving. The total bandwidth of such a transducer is estimated to be more than 150% which enables higher harmonic imaging at an adequate sensitivity and signal to noise ratio compared to standard medical array transducers. We describe in this paper the design and fabrication of the array transducer. Moreover its acoustic properties are measured and its performances for nonlinear contrast imaging are evaluated in vitro and in vivo.