High Resolution Biomedical Imaging Using Ultrasonic Metamaterials

Lead Research Organisation: University of Leeds
Department Name: Electronic and Electrical Engineering

Abstract

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.

Publications

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Adams C (2018) HIFU Drive System Miniaturization Using Harmonic Reduced Pulsewidth Modulation. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

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Adams C (2017) An Adaptive Array Excitation Scheme for the Unidirectional Enhancement of Guided Waves. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

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Askari M (2020) An ultrasonic metallic Fabry-Pérot metamaterial for use in water in Additive Manufacturing

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Askari M (2020) Additive manufacturing of metamaterials: A review in Additive Manufacturing

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Astolfi L (2021) Holey-structured tungsten metamaterials for broadband ultrasonic sub-wavelength imaging in water. in The Journal of the Acoustical Society of America

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Nie L (2018) Combining Acoustic Trapping With Plane Wave Imaging for Localized Microbubble Accumulation in Large Vessels. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

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Nie L (2019) High-Frame-Rate Contrast-Enhanced Echocardiography Using Diverging Waves: 2-D Motion Estimation and Compensation. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

 
Description Acoustic metamaterials constructed from conventional base materials can exhibit exotic phenomena not commonly found in nature, achieved by combining geometrical and resonance effects. However, the use of polymer-based metamaterials that could operate in water is difficult, due to the low acoustic impedance mismatch between water and polymers. In this project we have developed the concept of "trapped air" metamaterial, fabricated via vat photopolymerization, which makes ultrasonic sub-wavelength imaging in water using polymeric metamaterials highly effective. This concept is demonstrated for a holey-structured acoustic metamaterial in water at 200-300 kHz, via both finite element modelling and experimental measurements, but it can be extended to other types of metamaterials. The new approach, which outperforms the usual designs of these structures, indicates a way forward for exploiting additive-manufacturing for realising polymer-based acoustic metamaterials in water at ultrasonic frequencies for sub-wavelength imaging.
Exploitation Route Experimental validation is still progressing but we have demonstrated the use of rapid prototype manufacture processes in the design of metamaterials for sub-wavelength imaging. Imaging with metamaterials in water is problematic and this research presents a solution applicable to biomedical imaging.
Sectors Aerospace, Defence and Marine,Electronics,Energy,Healthcare,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology

 
Description Responsive Mode
Amount £830,216 (GBP)
Funding ID EP/N034813/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2016 
End 11/2019
 
Description High Resolution Biomedical Imaging Using Ultrasonic Metamaterials 
Organisation University of Nottingham
Country United Kingdom 
Sector Academic/University 
PI Contribution Leeds provide experimental and simulation expertise.
Collaborator Contribution Our partners at Nottingham provide materials, materials manufacture and rapid prototyping of metamaterials for acoustic characterization by Leeds and Warwick
Impact Publications are reported elsewhere in this award.
Start Year 2016