Hyperpolarised NMR is a valuable technique for grading tumours and detecting treatment response through real-time, monitoring of bio-chemical reactions in vivo, which may also be resolved spatially. At present, however, the range of detectable reactions is limited, due to fast T1-dependent decay of the nuclear hyperpolarisation. Use of coupled spins-1/2 may improve this situation, since these may decay more slowly than T1 when the polarisation is trapped in the nuclear singlet (spin-0) state [1, 2]. Singlet order escapes many of the processes that result in signal loss, thereby preserving spin order over longer timescales [3], and potentially allowing detection of slower metabolic processes. Singlet order may also preserve hyperpolarization during transport to sites of interest in vivo, such as tumours, or allow more handling time of the sample before injection.

REFERENCES
1. Levitt, M. H. Singlet and other states with extended lifetimes, In Encyclopedia of Nuclear Magnetic Resonance (Wasylishen, R. K. H. a. R. E., Ed.), John Wiley, Chichester.
2. Levitt, M. H. (2012) Singlet nuclear magnetic resonance, Annu. Rev. Phys. Chem., 63, 1-17.
3. Tayler, M. C., Marco-Rius, I., Kettunen, M. I., Brindle, K. M., Levitt, M. H., and Pileio, G. (2012) Direct enhancement of nuclear singlet order by dynamic nuclear polarization, J. Am. Chem. Soc.