Those giant, claustrophobic, tunnel forming magnets used for magnetic resonance imaging (MRI) in labs and hospitals look so last century! They are pricey and heavy, making MRI systems immobile and demanding to install. Any alternative? Yes by implementing the pre-polarized MRI concept introduced some 15 years ago:

"Writing in the Journal of Magnetic Resonance, Vadim Zotev and colleagues report success in imaging a human brain using a different type of MRI system: lightweight, open, mobile and significantly cheaper.

By dividing the functions of these large-field magnets between two sets of magnets with different characteristics, Zotev et al. have produced the prototype of a machine that would be smaller and more open, as well as being capable of performing magnetic resonance imaging and magnetoencephalography at the same time.

Conventional MRI machines reconcile these different requirements by using magnets that are both powerful and homogeneous. But could the same effect be achieved by using two simpler magnets and switching between them? The first magnet, strong but relatively inhomogeneous, would polarize the sample, whereas the second, weak but highly homogeneous, would be optimized for collecting resonance signals. This concept, termed pre-polarized MRI, was originally introduced by Macovski and Conolly2 some 15 years ago, and has been pursued by several research teams since.

Zotev et al. now report obtaining images of a living human brain using pre-polarization at 30 millitesla (mT) and image data collection at just 46 microT, a similar strength to that of Earth's magnetic field and about 30,000 times weaker than that of typical clinical MRI machines. Using such small magnetic fields means that the frequencies of the signals produced by the oscillating nuclear spins are similarly reduced from the usual radiofrequency range to around 2 kilohertz — a frequency readily audible to the human ear (approximately three octaves above middle C)."