Major New Discoveries in the High-Frequency World of MRI
One of the main problems when it comes to ramping up the resolution of Magnetic Resonance Imagery (MRI) is that the extra blast of power required can have very undesirable results.
In short, a scanner capable of pumping out magnetic fields at higher energy levels can overexcite the atoms inside the body. Rather than helping to cure, it actually risks *cooking* the patient: “When you increase the magnetic field,” says Anna Hurshkainen, PhD studetn and researcher at Chair of Nano-Photonics and Metamaterials. “You also increase the specific absorption rate of the human body. This may lead to the heating of body parts. We need to make high-field MRI devices not only effective, but also safe.”
This potential outcome, one would imagine, could be rather tricky to explain to shocked relatives! But there is another issue: attempting to increase the quality of MRI images can, paradoxically, produce a *decrease* in clarity. MRI scanners work by agitating the hydrogen atoms in the body and then analysing the radio waves emitted – which create a kind of ‘echo’, somewhat in the manner of a more traditional radar or sonar – using them to build up a detailed picture of the internal architecture of the body. But increasing of the static magnetic field of MRI devices also increases both the ‘signal-to-noise ratio’ and what is called its ‘resonance frequency’ – useless white noise and counterproductive interference that can degrade and distort the ‘echo’ received.
In addition, the antennae used to pick up the signals are arranged in a grid, each working together and interacting to produce the finished image. But higher energy levels can result in electromagnetic coupling - jamming the signals and resulting in a decrease in the power efficiency of the antennae.
“This kind of MRI analysis results in an unclear image of the body,” explains Ms. Hurshkainen, “Despite the fact that resolution power can be increased, it will not improve quality of an image – some parts of it will be clear while others will be washed-out. Currently this is what researchers are trying to solve.”
To overcome these formidable difficulties, Ms. Hurshkainen employed an ingenious combination of new – and old - approaches. Some were dazzlingly simple. During an internship in the Netherlands, she was introduced to fellow-scientist Alexander Raymaykers and his work. Diapole Antennae, which consist of only two conductive elements, had been around since the beginning of radio communication, but only eight years ago were they first applied by Raymaykers and his team at UMC Utrecht to the field of MRI. The sheer, streamlined simplicity of their design served to overcome many of the issues encountered.
At the same time, Hurshkainen also began to utilize meta-materials developed by ITMO scientists at the International ‘Applied Radio Physics’ Research Center, headed by Irina Melchakova. Many of these were also previously well-known, but no-one had ever used them for developing MRI technologies Thanks to their specific makeup – which, on a molecular level, resemble two-dimensional mushrooms! – they decrease the electromagnetic cross-interference between antennae – and also address the problem of overheating human tissue.
“Now we know that it is possible to decrease specific absorption rate and also make pulse amplitude higher,” Anna Hurshkainen concludes, “So we have the opportunity to create high quality images and, at the same, ensure safe analysis.”
Ms. Hurshkainen has co-published an article in Journal of Magnetic Resonance, and met with a very positive reaction when she revealed her discoveries at the ISMRM Conference in Singapore. All of which is great news for doctors hoping to push the boundaries of the early diagnosis of common killer diseases. Their tools may soon be significantly sharper than before. And a great relief for patients too. No danger of emerging from your MRI scan medium-rare! Thanks to ITMO research, the future is looking a lot brighter – and safer – for magnetic resonance imagery.