A novel magnetic material developed by British researchers may lead to dramatic improvements in the performance of Magnetic Resonance Imaging (MRI) systems.
Writing in today's Science, the researchers describe initial experiments confirming the exotic nature of the material produced.
Known as microstructured magnetic materials and dubbed "Swiss rolls" by Imperial College researcher John Pendry, they help obtain images by guiding radio-frequency magnetic flux from the body to the receiver coils of an MRI scanner with very little leakage.
The crucial feature of the material is that it consists of a periodic array of structures, each of which is much smaller than the wavelength of the radio-frequency fields it operates with.
The special properties of the flux-guiding device were formed by winding sheets of aluminized Mylar film, about 50 micrometers thick, around a cylindrical rod of Glass Reinforced Plastic. The aluminized Mylar film has an insulating backing which prevents any electrical contact between the layers of film. Nineteen of these bundles were arranged in a closely packed hexagonal array to form the bulk test material.
To demonstrate the potential of the new material, the team from Imperial College, the Medical Research Council and Marconi Caswell Ltd., placed their Swiss rolls between the object they were trying to image -- a researcher's thumb -- and a small receiver coil in a standard MRI device.
In control experiments in which the Swiss rolls were replaced by a piece of inert plastic, the thumb was not detected with the small coil. But with the Swiss rolls in place, helping to direct the radio-frequency magnetic flux from the thumb to the receiver coils, a clear image of the thumb's internal structure resulted.
The researchers claim that the new class of materials shows great potential to optimize existing MRI scanners, which are used extensively in hospitals around the world.
"Exploiting this class of materials could fundamentally change existing approaches to magnetic resonance imaging and spectroscopy," they write.
The idea of using microstructured magnetic materials in a Swiss roll structure came to the research team when they examined the potential of "photonic band gap" materials. Such materials can manipulate electromagnetic radiation of a certain frequency band and prevent it from escaping from the material in any direction.
Materials that can manipulate radio-frequency magnetic flux but do not disturb static or audio frequency fields are ideal for MRI systems, which require highly uniform static fields in order to produce undistorted images.
Conventional magnetic materials affect both static and radio-frequency fields, so that they cannot be used to manipulate radio-frequency flux without degrading image quality.
This research was the result of a collaboration between researchers in the department of physics at Imperial College, Marconi Caswell Ltd., and the Medical Research Council Clinical Sciences Centre, a division of Imperial College School of Medicine.
Authors include M.C.K. Wiltshire of Marconi Caswell Ltd.; J.B. Pendry and I.R. Young of the Department of Physics, Imperial College of Science, Technology and Medicine and D.J. Larkman, D.J. Gilderdale and J.V. Hajnal of the Robert Steiner MR Unit, Clinical Science Centre, Imperial College School of Medicine.
The research was jointly funded by Marconi Medical Systems and Marconi Caswell Ltd.
The Imperial College of Science, Technology and Medicine is an independent constituent part of the University of London. Founded in 1907, the College teaches a full range of science, engineering, medical and management disciplines at the highest level. The College is the largest applied science and technolgoy university institution in the UK.
The Medical Research Council (MRC) is a national organization funded by the UK taxpayer. Its business is medical research aimed at improving human health. The research it supports and the scientists it trains meet the needs of the health services, the pharmaceutical and other health-related industries and the academic world.
(Reference: Microstructured Magnetic Material for RF Flux Guides in Magnetic Resonance Imaging. Science Vol. 1291 No. 5505 - 2 February 2001.)
Medical Research Council
Marconi Caswell Ltd.