Merks Egon J W, van Neer Paul, Bom Nicolaas, van der Steen Antonius F W, de Jong Nico
Department Biomedical Engineering, Erasmus MC, Rotterdam, The Netherlands.
Ultrasound Med Biol. 2009 Oct;35(10):1690-9. doi: 10.1016/j.ultrasmedbio.2009.05.010. Epub 2009 Aug 3.
Catheterization remains the gold standard for bladder volume assessment, but it is invasive, uncomfortable to the patient and introduces the risk of infections and traumas. Acoustic measurement of the bladder volume reduces the need for a urinary catheter. Recently, a new method to non-invasively measure the volume of liquid filled cavities in vivo on the basis of nonlinear wave propagation has been introduced. To implement this method, two different multilayer ultrasound transducers were developed. Both transducers consisted of a first piezo-electric layer of lead zirconate titanate (PZT) to transmit waves at a fundamental frequency (2 MHz) and a second piezo-electric layer (copolymer) to receive a wide range of frequencies including harmonics. To suppress the inherent susceptibility of the film to electromagnetic waves, one of the two transducers, i.e., an "inverted" multilayer transducer, had the copolymer layer located inside the structure. The other multilayer transducer, i.e., a "normal" multilayer transducer, had the copolymer film located on the outside. Both transducers were compared with a commercially available broadband piezo-composite transducer, with respect to their transmit and receive transfer functions, their pulse-echo responses and their electromagnetic susceptibility (EMS) in reception. It was concluded that to measure up to at least the third harmonic frequency component with good sensitivity in combination with high transmit sensitivity at the fundamental frequency, a multilayer structure is preferred. To optimize for the EMS in reception, and hence also the signal-to-noise ratio, an inverted geometry, as proposed in this paper, was proven to be most effective.
导尿术仍是膀胱容量评估的金标准，但它具有侵入性，会让患者感到不适，还存在感染和创伤风险。膀胱容量的声学测量减少了对导尿管的需求。最近，一种基于非线性波传播在体内非侵入性测量液体填充腔体积的新方法被提出。为了实现该方法，开发了两种不同的多层超声换能器。两种换能器均由一层锆钛酸铅（PZT）压电层以基频（2MHz）发射波和一层共聚物压电层接收包括谐波在内的宽频率范围的波组成。为抑制薄膜对电磁波的固有敏感性，两种换能器中的一种，即“倒置”多层换能器，将共聚物层置于结构内部。另一种多层换能器，即“常规”多层换能器，将共聚物薄膜置于外部。将两种换能器与市售宽带压电复合换能器在发射和接收传递函数、脉冲回波响应以及接收时的电磁敏感性（EMS）方面进行了比较。得出的结论是，为了在基频具有高发射灵敏度的同时，以良好的灵敏度测量至少到三次谐波频率分量，多层结构是优选的。为了优化接收时的EMS，进而优化信噪比，本文提出的倒置几何结构被证明是最有效的。
