Superior scans

22 February 2009


Scientists have found a way to dramatically increase the power of MRI scans, and at the same time accommodate more portly-patients.

MRI machineWriting in this week's Nature, Zurich-based researchers David Brunner and his colleagues present a new way to capture consistent body scans at superior resolution.  Traditional MRI works by placing a patient in a powerful 1-3 Tesla magnetic field.  This causes the protons in the patient's body to line up with the field.  A short burst of radio waves is then used to perturb the orientation of the protons which then snap back into line, producing their own radio signals in the process.  These emitted radio signals are picked up by coils surrounding the scanner bore (the tube into which a patient is inserted), and used to build up a three dimensional picture of the person's body.

But to boost the resolution of a scanner's images requires a more powerful magnet, which in turn requires higher frequency radio signals to be used.  Eventually a point is reached whereby the radio signals form a chain of waves along the scanner called a standing wave, and this results in scanning 'dead-spots', a bit like the under-cooked areas in food heated in a microwave lacking a turntable.

The breakthrough pioneered by the Zurich team has been to substitute a 'travelling radio wave' which originates outside the scanner and passes in pulses along a cylindrical tube called a wave-guide surrounding the scanner, exposing the patient to a very uniform radio field, something that was very tricky to achieve before.  This same wave-guide is then also used to pick up the signals from the patient's body and convey them to an antenna at the end of the scanner, which feeds them into a computer for assembling into an image.

So far the researchers have scanned team member Klaas Pruessmann's leg.

'I didn't want to risk scanning my head the first time we tried this,' said Pruessmann, 'so we decided to start with my leg!' The result is very high quality images with no dark patches caused by dead spots.  Another major bonus of the approach is that it can easily be retrofitted to existing scanners, offering an immediate improvement to the quality of the images they can produce, even with less powerful magnets.


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