An insight into the nuclear spins of hydrogen molecules could lead to sensitivity enhancement in magnetic resonance imaging (MRI).

Molecular hydrogen, H₂, exists in two forms termed para-hydrogen and ortho-hydrogen. These so-called spin isotopomers have slightly different physical properties, and different sets of nuclear spin and nuclear rotational states. In ortho-hydrogen the nuclear spins are parallel, while in para-hydrogen they are antiparallel. 

The exchange between the two forms of molecular hydrogen is usually caused by catalytic reactions or paramagnetic impurities. But Gerd Buntkowsky at Jena University, Germany, and colleagues have explained how the exchange between para-hydrogen and ortho-hydrogen can also result from interaction of a hydrogen molecule with a diamagnetic substance. 

Buntkowsky is an expert in solid-state nuclear magnetic resonance (NMR) and has been interested in para-hydrogen for several years, because it is important for sensitivity enhancements in NMR.

'The biggest challenge in the field is the development of biophysical and medical applications of these spin isotopomers. There, the extremely high spin polarization could be employed for sensitivity enhancements in MRI,' said Buntkowsky.

Water also exists in para and ortho forms, and Buntkowsky is keen to investigate this system too. '[Water] spin isotopomers are distinguishable by IR [infrared spectroscopy], and their concentration ratio is used in astronomy as a remote temperature sensor,' said Buntkowsky. 'In the future we want to analyze possible magnetic conversion pathways between these spin-isotopomers,' he said.

Philip J Earis