March 26, 2009

Magnetic Spin MRI Could Improve Sensitivity 1000 Times

Shown here is an MRI image of a one-centimeter-wide tube containing smaller tubes covered with a molecule called pyridine

MIT Technology Review reports of a novel method of transferring magnetic spin can amplify the sensitivity of magnetic resonance imaging (MRI) a thousandfold, according to new research from the University of York in the United Kingdom. The new technique, Signal Amplification By Reversible Exchange (SABRE), achieves results without any chemical change being necessary. The SABRE method delivers a proven 1000-fold increase in sensitivity.

Professor Simon Duckett, from the University’s Department of Chemistry and Director of the Centre for Magnetic Resonance, said: "We have been able to increase sensitivity in NMR by over 1000 times so data that once took 90 days to record can now be obtained in just five seconds. Similarly, an MRI image can now be collected in a fraction of a second rather than over 100 hours for Nuclear Magnet Resonance [NMR].

Nuclear Magnetic Resonance (NMR) is what takes many hours and days. Replacing NMR with fast but sensitive spin MRI is where the speed gains are.

The new method, published today in the journal Science, enables the magnetization of a broad range of molecules--including drugs such as nicotine, and organic molecules such as antibodies designed to bind to tumors--so that they can be used as contrast agents.

Scientists first cool the molecule to create a form of molecular hydrogen, called parahydrogen, which has a highly ordered magnetic spin state. An iridium catalyst transfers the magnetic spin from the parahydrogen to other key elements, including oxygen, nitrogen, and carbon.

These polarized drugs or marker molecules are highly visible in MRI scans. "For example, you might use the technique to polarize the molecule that you know will stick to a brain tumor to see what's happening with an MRI scan. Currently MRI is not sensitive enough to do this," says York team member Gary Green, director of the York Neuroimaging Centre. Green notes that his team has already used the technique to polarize a range of key substances, including pyridine and nicotinic acid, which are present in many drugs.

Magnetic Resonance force microscopy has higher resolution but is not for scanning living bodies.

Green aims to begin animal tests of the technology this year, and clinical testing within five years. Extensive clinical testing needs to be done before this approach is approved for medical use.

This method isn't the first to prime molecules for use in MRI by boosting magnetic spin. Dynamic Nuclear Polarization (DNP), under development in the U.S., uses spin taken from electrons. DNP requires temperatures of 20 Kelvin and several hours for substances to be polarized for use in MRI, a disadvantage compared to the new technique. DNP polarization is 10 times higher than the magnetic spin MRI. The claim is that magnetic spin MRI can be improved to that level.

SABRE Method

Signal Amplification By Reversible Exchange: the SABRE method

Schematic representation of the SABRE method. The polarisation (represented by the orange colouring) is transferred from parahydrogen to a substrate which can then be seen by NMR and MRI.

MRI image of a SABRE-enhanced sample. Single average RAREst 1H image on a pyrazine sample on Bruker BioSpin 70/30 employing a 1350-fold signal gain. The data collected in 3 seconds that would otherwise take 42 days.

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