New low-power MRI machine

As reported in January's issue of the IEEE Spectrum, what is essentially a very low power MRI (magnetic resonance imaging) machine has produced its first images of a human brain. Whereas a standard MRI machine produces magnetic fields of around 1.5 tesla, this new version produces only around 46 microtesla - an over thirty thousand-fold reduction, and a field apparently comparable in strength to the earths' magnetic field. This reduction in power results in a slightly different method for producing the images.

In a standard MRI machine, a strong magnetic field is used to align the proton in each of the hydrogen atoms before using an RF pulse to knock them out of alignment. As they snap back into alignment with the magnetic field, they emit a signal which can be detected and used to create a 3D image. In the new version, the very small magnetic field isn't enough to align the protons, so a short duration (1 second) magnetic pulse of slightly higher magnitude (30 millitesla). The resulting signals are very small, so an array of highly sensitive magnetometers are used (so-called superconducting quantum interference devices, or SQUIDS). A hugely important additional advantage of using these SQUIDS is that they are also used in the MEG (magnetoencephalography) imaging technique. This potential for MRI and MEG using the same machine raises the intriguing possibility of producing simultaneous structural images (using the MRI) and brain activation maps (using the MEG).

One other major advantage of using this low-power MRI technique is its potential to image tumors. Due to the subtle differences between cancerous and non-cancerous tissue, the differences are not readily captured by standard MRI pictures - whereas the low-power version can. Furthermore, the possibility arises of using this type of imaging during operations themselves, as the very low magnetic fields used would not interfere with the use of metal surgical implements. As with any newly developed technology though, it will be a fair few years before it will be in full use - although this situation will be helped due to comparatively low cost of the new device: due to the absent need for high magnetic fields, the new machines may cost as little as one tenth of its high-powered counterpart.

UPDATE 29/01: Vaughan at MindHacks has pointed out the downsides of using SQUIDs, which I didn't mention.