Crystal Transducers for Ultrasound Harmonic Imaging

描述（申请人提供）：使用造影剂的超声谐波成像是一种非常有用的方法，用于观察难以成像的区域中的血液灌注，例如腹部器官中的细毛细血管和通过肋骨的心脏成像。来自微泡造影剂的非线性声散射导致比线性散射信号衰减更少的2和次谐波，由于旁瓣减少而表现出更高的横向分辨率，并且不易受诸如颜色模糊和声学阴影之类的伪影的影响。这些效应使得可以在更普遍的组织存在的情况下检测缓慢、小体积的血流，该组织的回波在基频处与血液回波重叠。然而，由于二次谐波发生在基波的2倍处，而次谐波发生在基波发射频率的1/2处，因此用于谐波成像的换能器必须具有非常宽的带宽（对于次谐波成像和二次谐波成像，通常为150%或更大）迄今为止，大约100%的带宽可以通过1-3个复合换能器，高阻抗声学背衬，和/或多个匹配层。不幸的是所有这些方法也导致换能器灵敏度降低。利用多层换能器可以获得具有良好灵敏度的更高带宽，但这对于阵列来说难以实现。表现出非常高的机电耦合系数的单晶压电体提供了一种产生具有固有大带宽的谐波成像换能器的手段。第一阶段SBIR计划，将通过构建带宽>140%的设备并测试其对分散在水中的造影剂产生的谐波信号的灵敏度来证明使用单晶换能器进行谐波成像的可行性。具有中等到高阻抗背衬层和多个匹配层的聚合物复合物。比传统的陶瓷基传感器灵敏度提出的努力将是TRS技术，Blatek公司，声学科学协会和托马斯杰斐逊大学之间的合作。

DESCRIPTION (provided by applicant): Ultrasound harmonic imaging with contrast agents is an extremely useful method for observing blood perfusion in hard to image areas such as fine capillaries in the organs of the abdomen and cardiac imaging through the ribs Nonlinear acoustic scattering from microbubble contrast agents leads to 2 and subharmonics that are less attenuated than linearly scattered signals, exhibit higher lateral resolution due to reduced side lobes, and are less susceptable to artifacts such as color blooming and acoustic shadowing These effects make it possible to detect slow, small volume blood flow in the presense of the much more prevalent tissue, whose echo overwhelms the blood echo at the fundamental frequency. However, since the 2nd harmonic occurs at 2 times the fundamental and the subharmonic at 1/2 the fundamental transmitted frequency, transducers used for harmonic imaging must have very broad bandwidths (typically 150% or greater for both sub and 2nd harmonic imaging) To date bandwidths of approximately 100% can be achieved with 1-3 composite transducers, high impedance acoustic backings, and/or multiple matching layers Unfortunately all these methods also cause reduced transducer sensitivity Higher bandwidths with good sensitivity can be obtained with multilayer transducers, but this is difficult to implement for arrays Single crystal piezoelectrics which exhibit very high electromechanical coupling coefficients offer a means of producing harmonic imaging transducers with inherently large bandwidths For this Phase I SBIR program the feasibility of using single crystal transducers for harmonic imaging will be demonstrated by constructing devices with bandwidths >140% and testing their sensitivity to harmonic signals generated by constrast agents dispersed in water The transducers will be fabricated from 1-3 crystal-polymer compoites with moderate to high impedance backing layers and multiple matching layers Such structures are known to have larger bandwidth with equivalent or better sensitivity than conventional ceramic based transducers The proposed effort will be a collaboration between TRS Technologies, Blatek, Inc, Acoustic Sciences Associates, and Thomas Jefferson University.