Imaging: Improving MRI tracers

A method that extends the lifetime of MRI-enhancing molecular tracers from seconds to hours is reported in Nature Communications. The new technique could allow the tracers to be prepared in bulk and transported to hospitals, rather than having to prepare them at the point of use, which is the current practice.

Through a process called dynamical nuclear polarization it is possible to prepare ‘hyperpolarized’ tracer molecules to which magnetic resonance imaging (MRI) machines are 10,000 times more sensitive than regular molecules. However, practical applications of hyperpolarized tracers have been limited by the short polarization lifetime (30-60 seconds), which means the complicated preparation procedure must be performed immediately before use.

With current methods, the tracer molecules must be mixed with a separate polarizing agent, which makes the process efficient but the close contact leads to interactions that cause the short polarization lifetime. Sami Jannin and colleagues demonstrate that by using a more indirect method hyperpolarization can be produced while keeping the tracer and polarizing agent microscopically separate. Their approach avoids the destructive interactions and allows them to demonstrate the preparation, storage and transport of hyperpolarized tracers with lifetimes that exceed five hours.

Currently, the polarization levels achieved by this method are lower than produced with existing techniques and the authors were unable to successfully demonstrate transport of the most common hyperpolarized tracer in clinical studies, sodium pyruvate. However, if developed successfully, the new approach means that hyperpolarized tracers could be prepared at a central facility and transported where needed, making scientific and clinical applications more practical.