School of
Information Technology and Electrical Engineering

Speaker: Haiwei Chen
Seminar Date: Wed, 21/02/2018 - 14:00
Venue: 78-421
Host: Prof Stephen Wilson

Seminar Type:  MPhil Confirmation Seminar


Magnetic resonance imaging (MRI) has become a preferred and indispensable modality for a wide range of scientific and clinical applications because of its superior imaging quality for soft tissues. MRI systems with ultra-high main magnetic field (7 Tesla and above) offer many advantages such as higher signal-to-noise ratio (SNR), improved spatial resolution and enhanced susceptibility contrast. However, various challenges and issues are emerging associated with the increased magnetic field strength. Among these challenges, radio frequency (RF) relevant problems such as  inhomogeneity and excessive RF heating, are the main bottlenecks which prevent the ultra-high field MRI system from clinical applications. The solutions which can thoroughly solve those RF related problems have been seeking in recent years. The perfect approaches, however, have not been discovered.

A RF shield is essential to prevent the RF fields interfering with other system components, especially gradient coils during image acquisition. Without RF shield, the RF coils and the gradient coils will interference with each other, leading to artefacts and noises in the acquired images. Therefore, RF shield takes an important role in magnetic resonance imaging quality. Conventional RF shields utilise slotted copper sheets or copper sheets with the thickness less than three skin depths to reduce the eddy current induced on the shield. However, the induced current on the RF shield, which is out-of-phase compared with the current on the RF coils, weaken the  field strength and increase the SAR. Therefore, new structure of RF shield is in great demand to improve the efficiency with reduced SAR.

In this project, a novel RF shield using metamaterial absorber was designed for 9.4 T MRI. The metamaterial absorber is composed with layered unit cell and lumped capacitors which are used to reduce the structure size. This new design focuses on improving the magnetic excitation field  efficiency and reducing the specific absorption rate (SAR) in the subject. Full-wave simulation results were presented and compared with a conventional copper RF shield. The results indicated that the proposed structure can achieve improved efficiency and reduced global maximum SAR. The future experimentally validation will be conducted on a 9.4 T MRI scanner (Bruker Biospin, Ettlingen, Germany) located at the University of Queensland.


Haiwei Chen received his Bachelor Degree from Northeastern University, China in 2016. He joined the UQ MRI group in 2017 as a MPhil candidate under the supervision of Prof. Feng Liu, Prof. Stuart Crozier, Dr. Lei Guo and Dr. Mingyan Li. His research interests include the metamaterial design and application in ultra-high field MRI.