High resolution biomedical imaging using ultrasonic metamaterials

超声生物医学成像通常用于许多疾病的诊断。它能够显示软组织的详细结构，并且比其他成像方法（如CT或MRI成像）具有相对便宜和便携的优势。因此，它是许多诊断临床设置的好方法。目前人体超声成像的分辨率是由多种因素决定的，包括换能器的设计、操作频率和所需的穿透深度。然而，这种系统的成像性能有一个基本的限制，即衍射极限。即使在完美的传播介质中，这也设定了用传统方法聚焦光束所能达到的最小光斑尺寸。目前的建议旨在通过使用超材料来改善这一点，这将被纳入超声波换能器系统中。事实上，这些奇异的材料是由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。结果是，例如，它们可以具有负折射率，注意到传统材料的值总是正的。因此，如果设计正确，具有平行平边的板可以聚焦超声波。该研究将确定可用于生物医学超声频率的最佳设计，目前的情况是1-5兆赫兹。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，提出了新的设计，首先将在理论上建模，然后使用高分辨率增材制造（3D打印）技术构建。一旦建成，新结构将用生物医学超声换能器进行测试，并确定其在成像系统中的性能。通过这种方式，有望产生一种新的超声诊断方法，提高分辨率，可用于心血管疾病、前列腺癌和皮肤癌的诊断。

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.