Crystal Transducers for Ultrasound Harmonic Imaging

描述（由申请人提供）：对比剂的超声谐波成像是一种非常有用的方法，用于观察难以成像区域的血液灌注，如腹部器官的细毛细血管和通过肋骨的心脏成像。微泡对比剂的非线性声散射导致2次谐波和次谐波，比线性散射信号衰减更小，由于侧叶减少，表现出更高的横向分辨率。这些效果使得在更普遍的组织存在的情况下，检测到缓慢的、小体积的血流成为可能，这些组织的回声在基频上压倒了血液回波。然而，由于二次谐波发生在基频的2倍，次谐波发生在基频传输频率的1/2，用于谐波成像的换能器必须具有非常宽的带宽（通常为次谐波和二次谐波成像的150%或更高）。迄今为止，1-3个复合换能器，高阻抗声学背景，和/或多个匹配层不幸的是，所有这些方法也会降低传感器的灵敏度。单晶压电材料具有非常高的机电耦合系数，为产生固有大带宽的谐波成像换能器提供了一种方法。对于第一阶段的SBIR计划，将通过构建带宽为b> - 140%的设备并测试其对分散在水中的对比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该换能器将由1-3个晶体聚合物复合材料制成，具有中至高阻抗的衬底层和多个匹配层，这种结构已知具有比传统陶瓷换能器更大的带宽和同等或更好的灵敏度。该提议的努力将由TRS技术公司、布拉泰克公司、声学科学协会和托马斯杰斐逊大学合作。

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.