High resolution biomedical imaging using ultrasonic metamaterials

超声生物医学成像被常规用于许多疾病的诊断。它能够显示软组织的详细结构，与CT或MRI成像等其他成像方法相比，具有相对便宜和便携的优势。因此，它是一种很好的方法，适用于许多诊断临床环境。目前超声成像在体内的分辨率由各种因素决定，包括换能器设计、操作频率和所需的穿透深度。然而，这类系统的成像性能有一个基本的限制--即衍射限制。这设置了聚焦光束可以通过传统方法实现的最小光斑尺寸，即使在理想的传播介质中也是如此。目前的提议旨在通过使用超材料来改善这一点，这种材料将被并入超声波换能器系统。事实上，这些奇异的物质是由一个复杂的几何结构组成的，其内部结构包含许多亚波长特征。它们可以共同作用，使材料的行为方式与正常结构完全不同。其结果是，例如，它们可以有负的折射率，注意到对于传统材料来说，该值总是正值。因此，只要设计正确，具有平坦平行边的平板就可以聚焦超声波。研究将确定可以用于生物医学超声频率的最佳设计，在目前的情况下，该频率将为1-5 MHz。到目前为止，声学超材料通常被设计为低得多的频率，并用于空气中。在这个项目中，提出了新颖的新设计，首先将从理论上建模，然后使用高分辨率加法制造(3D打印)技术来构建。一旦建成，新的结构将用生物医学超声换能器进行测试，并确定它们在成像系统中的性能。通过这种方式，它有望产生一种新的超声诊断方法，分辨率提高，可能对心血管疾病、前列腺癌和皮肤癌的诊断有用。

Ultrasound biomedical imaging is used routinely for the diagnosis of many diseases. It has the ability show detailed structures of soft tissues, and has the advantage over other imaging methods, such as CT or MRI imaging, of being relatively cheap and portable. It is thus a good method for many diagnostic clinical settings. The current resolution of ultrasonic imaging in the body is determined by various factors, including transducer design, frequency of operation, and depth of penetration required. However, there is a fundamental limit to the imaging performance of such systems - namely the diffraction limit. This sets the minimum spot size that a focused beam can achieve by conventional means, even in a perfect propagation medium. The present proposal aims to improve this by the use of metamaterials, which will be incorporated within an ultrasonic transducer system. These exotic materials are, in fact, made up of a complicated geometry, where the internal structure contains many sub-wavelength features. These can act together to make the material behave in a way that is totally different from normal structures. The result is that they can, for example, have a negative refractive index, noting that for conventional materials the value is always positive. Thus, a plate with flat parallel sides can focus ultrasound, provided it is designed correctly.The research will identify the best designs that can be used at biomedical ultrasound frequencies, which in the present case will be 1-5 MHz. To date, acoustic metamaterials have been designed typically for much lower frequency, and for use in air. In this project, novel new designs are proposed, which will first be modelled theoretically, and then constructed using high-resolution additive manufacturing (3D printing) techniques. Once built, the new structures will be tested with biomedical ultrasound transducers, and their performance in imaging systems determined. In this way, it is hoped to produce a new approach to diagnostic ultrasound, with resolution enhancement that could be useful for cardiovascular disease, prostate and skin cancer diagnosis.